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Abstract: Electrical resistances of roots and stems of hydroponically raised willows (Salix schwerinii) were studied and related to root morphology. Willow cuttings with and without roots were set in a constant electric field (effective voltage of 0.1 V, sine-AC, 128 Hz) in a hydroponic solution. The electrical resistance of different components in the measurement system was measured and analysed in relation to root surface area in contact with the cultivation solution. Axial resistivities of single root segments and of stems were measured. The results showed that the resistance decreased in relation to an increase in the contact surface area of the roots with the solution. The resistance depended strongly on the contact area of the stem with the solution, however, thus causing bias in the evaluation of root surface area. This work is a new contribution for the understanding of current pathways in the root system as exposed to an external electric field and for developing a non-destructive method to study plant roots accordingly. It may be concluded that the electrical resistance method is a useful non-destructive method to study roots and their physiological properties. Electrical analogues for roots and stem comprising resistors are discussed in relation to in situ measurements.
Abstract: Information on plant roots is increasingly needed for understanding and managing plants under various environmental conditions, including climate change. Several methods have been developed to study fine roots but they are either destructive or cumbersome, or may not be suitable for studies of fine root functionality. Electrical impedance, resistance, and capacitance have been proposed as possible non-destructive measures for studying roots. Their use is limited by a lack of knowledge concerning the electrical circuit of the system. Electrical impedance spectroscopy (EIS) was used for hydroponically raised willows (Salix schwerinii) to estimate the root system size. The impedance spectra were investigated in three experimental set-ups and the corresponding appropriate lumped models were formulated. The fit of the proposed lumped models with the measured impedance spectra data was good. The model parameters were correlated with the contact area of the roots and/or stems raised in the hydroponic solution. The EIS method proved a useful non-destructive method for assessing root surface area. This work may be considered to be a new methodological contribution to understanding root systems and their functions in a non-destructive manner.
Abstract: This review critically examines the role of boron (B) in forests in view of recent findings on B nutrition and the continuing occurrence of B deficiency. Many perceptions about the role of B in plants and its uptake and mobility have been altered since the last review on B in forest trees in 1990. Now there is evidence for a fundamental role of B in the formation of the pectic structure in primary cell walls in plants, and further roles in membrane function are being explored. In plants, channel-mediated B uptake, active B uptake and B uptake by mycorrhizas have been shown, B transporters have been identified, and B retranslocation has been shown. We explore these findings and their consequences on forest trees and on ecosystems that they dominate. Particular emphasis is placed on B retranslocation and B in mycorrhizal symbiosis, given their importance in trees. Following from impaired development of the primary cell wall in B-deficient trees, disorders in the structural development of organs and whole plants are manifested. This has consequences for tree form, affecting wood quality and productivity. At a stand level, at least part of the value of wood production is lost by the time the deficiency symptoms appear. As symptoms identifying deficiency in many tree species are too easily confused with many other effects, greater use should be made of foliar analysis but this requires establishing robust prognostic values for the trees of interest. There is still no explanation as to why root tip and mycorrhiza development are among the first phenomena to be affected as the B supply decreases. Whether B is required by, or whether it is useful for fungi, is still an open question. Boron remobilisation within trees may be a key factor in the occurrence of forests in areas with very low B availability, as most of the B in the whole stand can be in the standing biomass. The ability to remobilise B varies considerably between species, but we suggest that there is a continuum rather than a strict division to B-retranslocating and non-retranslocating species. Boron output from forest ecosystems with potential for leaching is controlled by adsorption in the soil, which is still poorly understood particularly in soils with abundant organic matter. Increased concentrations of phenolic compounds in B-deficient plants and possibly altered lignin concentration can affect plant defence systems to herbivory and pathogens, and nutrient and carbon release through decomposition. Hence, B nutrition and fertilisation of low-B stands can have implications both to the resistance of trees to biotic stress, as well as influence the cycles of other nutrients and carbon in forests.
Abstract: Abstract Inadequate boron (B) nutrition can affect the structural integrity and chemical composition of plant tissues. The changes in mass and element concentrations were studied using silver birch (Betula pendula Roth) leaf litter from seedlings grown with or without added B (Blitter+ or Blitter−). The litter was produced in a growth room, and it was incubated in either B fertilised or control forest plots (Bsoil+ or Bsoil−) between the moss and humus layers in two Norway spruce stands for 13 months. Additionally, the field decomposition experiment included long-term N and P application treatments (Nsoil and Psoil). Blitter+ somewhat reduced the remaining litter mass. In contrast, Bsoil+ increased it, possibly because of lower soil pH. The +Nsoil treatment reduced the remaining mass. Blitter+ increased the remaining P, S, Cu, Cd, Ni and Zn but reduced Pb. Remaining B was high in the Blitter– which also accumulated B from soil. Bsoil increased remaining Ca, Cd, Mg, Na, Pb, and slightly reduced N (in N fertilised plots). These changes in decomposition and element release have a potential to affect nutrient, carbon, and heavy-metal cycles in areas where B deficiencies are common, and where B fertilisation is practised.
Abstract: Fungi are usually thought not to have a boron (B) requirement. It is not known if mycorrhizas take up B from low concentrations that are common in forest soils, as fungi might also immobilise B. Here, we studied the B concentrations in sporophores of 49 ectomycorrhizal and 10 saprotrophic fungi to assess whether B is translocated in mycelium or not. Additionally, P and metal concentrations were measured for comparison.
Variability both within species and between species was very large, as the lowest measured B concentration was 0.01 mg kg-1 in Amanita muscaria, and the highest was 280 mg kg-1 in Paxillus involutus. No categorical difference was found between saprotrophic and mycorrhizal fungi. The majority of species did not accumulate B at more than 0.01-3 mg kg-1, but there were some species that consistently had median concentration values higher than 5-6 mg kg-1 and much higher maximum values, particularly Paxillus involutus, Lactarius necator and several Russula species. Most species increased their B concentration in B fertilised plots, but there were exceptions, particularly Rozites caperatus and Lactarius camphoratus. Boron concentrations did not correlate with those of other elements.
In conclusion, B is translocated in the mycelia of most of the studied species. The differences between species may be due to differences in their water use, or carbohydrates used in translocation. It remains to be studied, if B concentrations in mycorrhizas or mycelia in soil are in the same order of magnitude as the larger ones found here, and if this has any effects on the host plants.
Abstract: Abstract Adequate boron (B) nutrition may decrease concentrations of phenolic compounds and enhance structural integrity and lignification in plants, compared with suboptimal B. This could affect decomposition in areas where B deficiencies are common. The mass loss and changes in element concentrations in Norway spruce needle litter were studied with combinations of litter from high-B and low-B trees, incubated for 29 months, in either B fertilised or control plots without B addition. The litter originated from the same Norway spruce field experiments. Additionally, the field experiments included long-term N and P treatments. Initially, lowest lignin concentrations were found in Norway spruce litter from the treatment P and particularly in the combination B + P, and highest in the B + N fertilised plots. The mass loss of Norway spruce litter was not affected by the treatments. However, Blitter increased Cu accumulation. The litter from the B + P fertilised plots accumulated considerably more Al, Ca, S and Zn than the other treatments, whereas B together with N reduced the remaining amounts of these elements. Reduced nutrient release from litter may have far-reaching consequences on nutrient cycles in forests.
Abstract: <b><i>Background:</i></b> High nutrient supply has been frequently used in ultraviolet-B (UV-B) research, although it is unnatural for many species. <br /><br /><b><i>Aims:</i></b> To study the effect of increased irradiance of UV-B on the photosynthetic capability of silver birch (<i>Betula pendula</i> Roth.) seedlings. <br /><br /><b><i>Methods:</i></b> The seedlings were grown in a greenhouse in a substrate composed of birch forest top soil and sand, without additional supply of mineral nutrients. The increased daily integrated irradiance of UV-B (GPAS) was equivalent to 25% stratospheric ozone depletion under clear sky, and the treatment was started at seedling emergence. Leaf gas exchange was measured under saturating light conditions, and CO<sub>2</sub>-assimilation rate, stomatal conductance and intercellular CO<sub>2</sub> concentration were computed. Initial and total activity of RuBisCO and the concentrations of RuBisCO, chlorophylls, and soluble protein were measured in the same leaf. Total nitrogen concentration was also measured, as well as carbon isotope discrimination. <br /><br /><b><i>Results:</i></b> None of the variables measured were affected by UV-B at either of the two sampling dates (58 d and 76 d after the beginning of the treatment) except for stomatal conductance (interaction with time only). <br /><br /><b><i>Conclusions:</i></b> Consequently, it is unlikely that significant damage to photosynthesis of silver birch seedlings will occur in a natural setting under current and projected changes in solar UV-B.
Abstract: We examined the quality and decomposition of naturally abscised leaves of silver birch (<i>Betula pendula</i>) seedlings subjected to three different levels of fertilization under ambient and elevated levels of temperature and CO<sub>2</sub>. At the end of the second growing season, the chemical composition of the litter collected from the seedlings was analyzed. Whole-leaf samples from pooled litter from each of the four replicates from each treatment were put in mesh bags and transferred to ambient climate in the field. The remaining mass of litter was measured by sampling bags in May and October throughout the four-year incubation period. Fertilization with all nutrients decreased the initial carbon and tannin contents of litter, and increased the proportion of the fast-decomposing fraction, but still fertilization slowed down the decomposition of this fraction. Initially, the estimated proportion of the fast-decomposing fraction was smallest in elevated CO<sub>2</sub>Â +Â temperature, and largest in ambient climate. During decomposition, elevated growth-temperature slowed down decomposition of the fast fraction under ambient CO<sub>2</sub> but increased it under elevated CO<sub>2</sub>. The changes in litter decomposition rates found over four years were not very large. However, we conclude that the interactions of different factors lead to different results than if the factors had been studied separately, and future studies should take interactions into account.
Abstract: Boron deficiency, manifested as shoot dieback, is a problem in conifer stands growing on soils with high nitrogen availability in Fennoscandia. Earlier observations on Norway spruce (Picea abies L. Karst.) suggest that freezing tolerance is decreased by boron deficiency. Here, the effect of boron fertilization on cold acclimation of Norway spruce was studied in a young stand with initially low boron status two years after fertilization. Buds, stems, needles and roots were collected at five sampling times during cold acclimation and subsequently exposed to series of freezing temperatures. Lethal temperatures of organs were assessed by electrolyte leakage method (EL) and visual scoring of damage (VS). Freezing tolerance of buds was measured also by differential thermal analysis (DTA).
The mean boron (B) concentration in needles was 4 mg kg–1 in unfertilized and 21 mg kg–1 in B-fertilized trees while critical level of B deficiency is considered to be 5 mg kg–1. The risk for increased freezing injuries in the low-B trees was not evident since all trees achieved cold hardiness that would be sufficient in central Finland. At two sampling times out of five, shoots or stem of B-fertilized trees were slightly more freezing tolerant than non-fertilized trees. However, the present study does not give strong evidence for the hypothesis that decreased freezing tolerance in B deficiency would be a triggering factor for leader dieback in Norway spruce at the B levels studied.
Abstract: In boreal regions, soil can remain frozen after the start of the growing season. We compared relationships between root characteristics and water relations in Scots pine (Pinus sylvestris L.) saplings subjected to soil frost treatments before and during the first week of the growing period in a controlled environment experiment. Delayed soil thawing delayed the onset of sap flow or totally blocked it if soil thawing lagged the start of the growing period by 7 days. This effect was reflected in the electrical impedance of needles and trunks and in the relative electrolyte leakage of needles. Prolonged soil frost reduced or completely inhibited root growth. In unfrozen soil, limited trunk sap flow was observed despite unfavorable aboveground growing conditions (low temperature, low irradiance, short photoperiod). Following the earliest soil thaw, sap flow varied during the growing season, depending on light and temperature conditions, phenological stage of the plant and the amount of live needles in the canopy. The results suggest that delayed soil thawing can reduce tree growth, and if prolonged, it can be lethal.
Abstract: The ability to survive freezing and thawing is a key factor for the existence of life forms in large parts of the world. However, little is known about the freezing tolerance of mycorrhizal fungi and their role in the freezing tolerance of mycorrhizas. Threshold temperatures for the survival of these fungi have not been assessed experimentally. We grew isolates of Suillus luteus, Suillus variegatus, Laccaria laccata, and Hebeloma sp. in liquid culture at room temperature. Subsequently, we exposed samples to a series of temperatures between +5 degrees C and -48 degrees C. Relative electrolyte leakage (REL) and re-growth measurements were used to assess the damage. The REL test indicated that the lethal temperature for 50% of samples (LT(50)) was between -8.3 degrees C and -13.5 degrees C. However, in the re-growth experiment, all isolates resumed growth after exposure to -8 degrees C and higher temperatures. As many as 64% of L. laccata samples but only 11% in S. variegatus survived -48 degrees C. There was no growth of Hebeloma and S. luteus after exposure to -48 degrees C, but part of their samples survived -30 degrees C. The fungi tolerated lower temperatures than was expected on the basis of earlier studies on fine roots of ectomycorrhizal trees. The most likely freezing tolerance mechanism here is tolerance to apoplastic freezing and the concomitant intracellular dehydration with consequent concentrating of cryoprotectant substances in cells. Studying the properties of fungi in isolation promotes the understanding of the role of the different partners of the mycorrhizal symbiosis in the freezing tolerance.
Abstract: Abstract The increase in concentrations of phenolic compounds in boron (B) deficiency has been demonstrated in many herbaceous plant species, but information on woody plants is scarce. It has been suggested that accumulation of phenolic compounds plays a role in the development of cold hardiness in herbaceous plants but also that B deficiency decreases winter hardiness. Here we study the effects of B nutrition on phenolic compounds in Norway spruce (Picea abies L.) in the course of cold acclimation. Phenolic compounds were analysed in Norway spruce seedlings from three different B-fertilisation treatments in two harvests: non-acclimated and cold-acclimated seedlings. Norway spruce phenolic compounds consisted mainly of condensed tannins. During B deficiency, condensed tannins and monocoumaroyl–astragalin der. 1 increased in non-acclimated seedlings. The increase in tannins was 21%, which was nearly significant. However, the effect of B on phenolic compounds was almost absent in cold-acclimated seedlings. The condensed tannin concentration increased much more with time in the simulated autumn than due to B deficiency, and we conclude that the B effect was probably not large enough to be important for the hardening of the seedlings. The total phenolic concentrations more than doubled during the course of cold hardening suggesting that phenolics have a role in the winter hardiness in Norway spruce.
Abstract: Abstract Susceptibility of trees to freezing injury has been suggested to increase in boron (B) deficiency but there is no experimental evidence to support this proposition. In this study, Norway spruce (Picea abies L. Karst.) seedlings were cultivated for two growing seasons in deficient, intermediate and ‘optimal’ B levels. Cold hardening of the seedlings was measured after the second growing season. Freezing tolerance in tips of shoots, needles, stems and roots was determined by controlled freezing tests and electrolyte leakage method, and that of buds, in addition, by differential thermal analysis (DTA). Electrical impedance was used to monitor changes in the apoplastic space during cold acclimation. Root dry weight and shoot height growth were lower in B deficiency. Cold acclimation of buds and stems was reduced by B deficiency. When hardened seedlings were subjected to subzero temperatures for 3 weeks, extracellular electrical resistance of stems became the highest at the lowest B supply which was probably due to decreased desiccation tolerance. As a conclusion, susceptibility to freezing damage may be increased by B deficiency in Norway spruce trees.
Abstract: Loss of apical dominance is a well-known boron (B) deficiency symptom in trees. Recent field studies indicate that B deficiency may cause irreversible damage in emerging leader buds leading to bushy growth, and changes in developing needles in mature Norway spruce trees. We experimentally studied if timing of B application affects needles and buds of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings with low initial B levels. The treatments were: no B (B0); B supply from the beginning of the simulated summer (B1); starting soon after bud burst (B2) and starting at the occurrence of first needle primordia in new spruce buds (B3). At the end of the experiment, B concentration in B1 was 23 mg kg−1 (pine) or 17 mg kg−1 (spruce) and lower in the later applications. In B0 it was at deficiency limit. In B0, B2 and B3, there were fewer sclerenchyma cells, and cavities occurred in vascular cylinders in pine needles, and in spruce buds there were more tanniferous cells in the primordial shoots compared to B1. Furthermore, in all but B1 there was cell collapse in the bud apex of some spruce seedlings. The experimentally induced changes were the same as earlier reported in B deficient conifers in the field, and indicate, similarly as in the field that adequate B is necessary throughout the growing season for healthy growth, particularly for spruce. The differences between spruce and pines are due, at least partly, to the differences in time frame of needle development and in the differences in development of conducting tissues in the buds.
Abstract: Two-year-old silver birch (Betula pendula) saplings were grown for a third growing season in controlled-environment rooms (dasotrons) at three soil temperatures (5, 10, and 20 °C). All trees grew the first flush of leaves, but the growth of the second flush was almost completely inhibited at the two lower temperatures. The dry weight of the second-flush leaves was 50 times larger at 20 °C than at 5 and 10 °C, with about 100 times more nitrogen. Root growth was less affected than shoot growth. Chlorophyll content, net assimilation rate and stomatal conductance were lower at low soil temperatures. The value of the cytoplasm resistance estimated from the electric impedance spectra was lower at 5 °C than at 10 or 20 °C. Leaf water potential was highest at the lowest soil temperature, and intercellular carbon dioxide concentration was only slightly lower in saplings growing in cooler soil. We conclude that the effect of long-term exposure to cold soil on net assimilation and growth was not caused by stomatal closure alone. It is likely to be additionally mediated by the limited nitrogen acquisition at the low soil temperatures, and perhaps additionally by some other factor. As the growth depression of aboveground parts in response to low soil temperature was more significant in silver birch than what has earlier been found in conifers, the relative changes in air and soil temperature may eventually determine whether birch will become more dominant in boreal forests with climate change.
Abstract: * Background Effects of cooling rates on bud frost hardiness have been studied but there is little information on bud responses to thawing. Since the cell wall pore size has been found to increase with boron (B) deficiency, B deficiency may affect the supercooling ability of buds in winter. * Methods The effects of duration of thawing time and rate of cooling on bud frost hardiness of Norway spruce (Picea abies) were studied in a B fertilization trial in February 2003 and March 2005. Frost hardiness of apical buds was determined by differential thermal analysis (DTA) and visual scoring of damage. * Key Results In 2003, the freezing point of primordial shoots of buds (Tf), i.e. the low-temperature exotherm (LTE), was, on average, -39 degreesC when buds were thawed for less than 3 h and the Tf increased to -21 degreesC after 18 h of thawing. During the first 4 h of thawing, the rate of dehardening was 6 degreesC h-1. In 2005, buds dehardened linearly from -39 degreesC to -35 degreesC at a rate of 0middle dot7 degreesC h-1. In 2003, different cooling rates of 1-5 degreesC h-1 had a minor effect on Tf but in 2005 with slow cooling rates Tf decreased. In both samplings, at cooling rates of 2 and 1 degreesC h-1, Tf was slightly higher in B-fertilized than in non-fertilized trees. By contrast, at very short thawing times in 2003, Tf was somewhat lower in B-fertilized trees. * Conclusions There was little evidence of reduced frost hardiness in trees with low B status. This study showed that buds deharden rapidly when exposed to above-freezing temperatures in winter, but if cooled again they reharden more slowly. According to this study, rapid dehardening of buds has to be taken into account in assessments of frost hardiness.
Abstract: Abstract Loss of apical dominance in boron-deficient trees has been suggested to be due to frost damage of terminal buds and leaders. Excessive nitrogen (N) supply can exacerbate boron (B) deficiency by the dilution-effect. N may also have direct effects on winter hardiness. We studied frost hardening of buds of Norway spruce (Picea abies L. Karst.) in healthy-looking trees and in trees with growth disturbances. The effect of B and N on frost hardiness was studied in a factorial fertilisation experiment during cold acclimation. Frost hardiness was determined by differential temperature analysis (DTA) and scoring of visual damage. In a DTA profile of apical buds with a piece of stem, low-temperature exotherm (LTE) predicted bud injury, while two of the observed high-temperature exotherms and two of the observed intermediate-temperature exotherms were non injurious. Appearance of LTE followed changes in air temperature. The risk of frost damage was not affected by fertilisation treatments or previously observed growth disturbances. However, when the bud structure was deformed by severe B deficiency, the supercooling ability disappeared. Such buds are probably killed by freezing in nature and therefore, frost damage may play a secondary role in the development of growth disturbances.
Abstract: Effects of the timing of soil thawing in the spring on Scots pine (Pinus sylvestris L.) were studied under controlled laboratory conditions. Sixteen 6-year-old saplings were lifted from the field, replanted in containers and placed in four treatments in controlled environment (CE) chambers with four replicate saplings per chamber. The saplings were held in the CE chambers during one simulated winter and one simulated growing season. The soil was frozen to -2 degrees C during a second simulated winter in the CE chambers, and the soil thawing treatments began at the end of the second simulated winter. Soil thawing began at various times before (no delay in thawing) and after (delay in thawing) chamber air conditions were changed from simulated winter to simulated summer. Delayed soil thawing subjected saplings to stress, with the severity of stress depending on the length of the delay in thawing. If there was no delay or only a short delay in soil thawing, stress was minor and reversible. A 2-week delay in soil thawing led to death of the saplings. Stress was apparent as decreases in the variable to maximal chlorophyll fluorescence ratio (Fv/Fm), chlorophyll a/b ratio and needle water potential. In needles of stressed saplings, apoplastic electrical resistance first decreased and then increased and there were anomalies in the electrical impedance spectra of the stems. Stress from the soil thawing treatments affected both root and shoot growth.
Abstract: The effects of two boron (B) levels on growth, shoot water potential, gas exchange and nutrient accumulation in Norway spruce [Picea abies (L.) Karst.] seedlings were studied in a growth room experiment lasting 22 weeks which included well-watered control seedlings and seedlings exposed to one (8 days) or two (6+8 days) periods of drought and a rewatering period (8 days) at the end of the experiment. The effects of B and drought were monitored during drought and recovery. Needle B concentrations were 6 mg kg(-1) (-B treatment) and 34 mg kg(-1) (+B treatment) at the end of the experiment. The -B seedlings showed visible symptoms of damage in the upper shoot after repeated drought and had reduced height growth, root dry mass, allocation of biomass to roots and formation of root tips and mycorrhizas and reduced needle P, Ca, and Mg concentrations and contents. In contrast, N-15 uptake, shoot water potential and gas exchange were not markedly affected by B. It can be concluded that the visible symptoms of damage at low B were probably related to reduced B transport due to repeated drought. In contrast, the effects of low B on growth, particularly of the roots, and on nutrient uptake can be regarded as early effects which occur before any influence on shoot water potential or gas exchange. The positive effects of B on root biomass and nutrient accumulation are of particular importance regarding the establishment of young seedlings in the field.
Abstract: Soil temperature is a main factor limiting root growth in the boreal forest. To simulate the possible soil-warming effect of future climate change, 5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment rooms. The seedlings were acclimated to a soil temperature of 16 degreesC during the first (GSI) and third growing seasons (GSIII), but were assigned to random soil-temperature treatments of 9, 13, 18 and 21 degreesC during the second growing season (GSII). In GSII, shoot diameter growth was lowest in the 21 degreesC treatment and root growth was lowest in the 9 degreesC treatment. In GSIII, shoot height and root length growth improved in seedlings that had been kept at 9 degreesC during GSII, indicating compensatory growth in response to increased soil temperature. The temporary decrease in soil temperature had no long-lasting significant effect on seedling biomass or total nutrient uptake. At the end of GSIII, fine roots of seedlings exposed to a soil temperature of 21 degreesC in GSII were distributed more evenly between the organic and mineral soil layers than roots of seedlings in the other treatments. During GSII and GSIII, root growth started earlier than shoot growth, decreased during the rapid shoot elongation phase and increased again as shoot growth decreased.
Abstract: Boron (B) is an essential micronutrient for plants but it is thought not to be essential for fungi. We studied whether the extraradical mycelia of Paxillus involutus in symbiosis with silver birch (Betula pendula) take up B and transport it to the host plant. We grew mycorrhizal plants in flat microcosms with a partitioning wall, below which there was only extraradical mycelium. A boric acid solution enriched in B-10 was applied to these mycelia. Increased B-10/B-11 isotope ratios were subsequently measured in birch leaves, stems, and roots plus mycorrhizas in the upper compartment. Boron was therefore taken up by the mycorrhizal mycelia and transported to the host plant in this species combination.
Abstract: Boron (B) has been found to be phloem mobile in species that translocate polyols, whereas it is almost immobile in other species. The objectives of the present study were to survey B mobility in deciduous trees, and to relate it to the presence of polyols. The stable isotope B-10 was applied as a tracer to mature leaves of seedlings, and growing leaves were subsequently harvested for B isotope analysis. Extensive B mobility was found in Sorbus aucuparia and Prunus padus, species with high sorbitol content, but also in Ulmus glabra, with only trace amounts of B-complexing polyols. Alnus incana, Fraxinus excelsior, Betula pubescens and Larix sibirica also translocated B-10 into new leaves. Mannitol in Fraxinus and pinitol in Larix probably explain this. A. glutinosa did not remobilize B, although the polyol concentrations were almost identical to A. incana, a closely related species. B mobility was not as closely related to the presence of polyols as expected, and it appears that to some degree remobilization occurs in many plant species. (C) New Phytologist (2004).
Abstract: We previously traced B-10-enriched boric acid from shoots to roots to demonstrate the translocation of boron (B) in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings. To gain a more detailed understanding of B translocation, we sought: (1) to demonstrate B retranslocation directly, by showing that foliar-applied B-10 is located in the new growth after dormancy; and (2) to assess whether shoot-applied B affects growth in the long term. We applied B-10-enriched boric acid to needles of Scots pine and Norway spruce seedlings. After a dormancy period and 9 weeks of growth, small but significant increases in the B-10 isotope were found in the new stem and needles of both species. In Scots pine, the total B concentration of the new stem was also increased. Both species contained polyols, particularly pinitol and inositol. Boron-polyol complexes may provide a mechanism for mobilizing B in these species. To determine the long-term effects of applied B, seedlings were grown for two growing seasons after the application of B-10 to shoots. In Norway spruce, the proportion of B-10 in the root systems and current needles of the harvest year was slightly higher than in the controls, and in Scots pine root systems, marginally so. The B treatment had no effect on growth of Norway spruce seedlings. In Scots pine seedlings, the B treatment caused a 33% increase in total dry mass and significantly increased the number of side branches.
Abstract: The effects of boron (13) fertilizer applied 10 growing seasons earlier were studied in mature Norway spruce (Picea abies (L.) Karst.) trees in long-term factorial fertilization experiments at two field sites. Needle nutrient status, above-ground and below-ground growth and delta(13)C and carbon concentrations in the annual rings were measured. Needle B concentrations varied between 4 and 19 mg kg(-1) on the plots that had not received B fertilization. On the B-fertilized plots they varied between 15 and 39 mg kg(-1). The lowest B concentrations were on the plots that had received N or NCa fertilization. Needle Mn and Zn concentrations were lower on the B plots than on the plots that had not received B fertilization, although not significantly. Mean annual volume growth was slightly higher on the B plots at the more fertile site, but not at the less fertile one. The living:dead fine root mass ratio and living fine root length were also higher on the B-fertilized plots than on the unfertilized plots, but delta(13)C was not significantly affected, suggesting that the water status of the trees was not markedly altered by the increase in root growth. The carbon concentration in the annual rings was higher in the B-fertilized trees than in the unfertilized ones, suggesting the importance of B for wood formation. (C) 2003 Elsevier Science B.V. All rights reserved.
Abstract: The effects of increased ultraviolet-B (UV-B) radiation on the growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings were studied in greenhouse conditions. Seedlings-planted in a birch-forest top soil and sand substrate-were grown without additional nutrient supply. Ultraviolet treatment started immediately after the seedlings emerged and the daily integrated biologically effective UV-B irradiance on the UV-B-treated plants was equivalent to a 25% depletion of stratospheric ozone under clear sky conditions. Visible symptoms of UV-B damage or nutrient deficiency were not observed throughout the experiment. Seedling height and dry weight (DW) (measured after 58 days and 76 days of treatment) were not affected by increased UV-B. However, a significant shift in DW allocation toward roots resulted in a lower shoot/root ratio and leaf area ratio in UV-B-treated plants compared to control plants. At the first harvest (after 58 days of treatment), the percentage of various mycorrhizal morphotypes and the number of short roots per unit of root length or weight were not affected by increased UV-B despite significantly increased DW allocation toward roots. Subtle reduction in the allocation of nitrogen (N) to leaves and increased allocation of phosphorus (P) to roots may suggest cumulative effects that could affect the plant performance over the long-term.
Abstract: Five-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment chambers. Plants were acclimated to a soil temperature of 16 degreesC during the first and third growing seasons, but were allocated at random to soil temperature treatments of 9, 13, 18 and 21 degreesC during the second growing season. Low soil temperature during the second growing season depressed stomatal conductance and photosynthetic rate (A) per unit of projected leaf area, although intercellular CO2 concentrations did not differ significantly between treatments. At all soil temperatures, total chlorophyll concentration first decreased and then increased, although the rate of increase and the final concentration increased with soil temperature, which may explain the effect of soil temperature on A. Neither chlorophyll a/b ratio nor leaf nitrogen concentration was significantly affected by soil temperature. Treatment differences disappeared during the third simulated growing season when plants were again acclimated to a soil temperature of 16 degreesC.
Abstract: We studied the effect of soil temperature on nutrient allocation and mycorrhizal development in seedlings of Scots pine (Pinus sylvestris L.) during the first 9 weeks of the growing season. One-year-old seedlings were grown in Carex-peat from a drained and forested peatland at soil temperatures of 5, 9, 13 and 17 °C under controlled environmental conditions. Fourteen seedlings from each temperature treatment were harvested at intervals of three weeks and the current and previous year’s parts of the roots, stems and needles were separated. Mineral nutrient and Al contents in all plant parts were determined and the tips and mycorrhizas of the new roots were counted. Microbial biomass C and N in the growth medium were determined at the end of the experiment. None of the elements studied, except Fe, were taken up from the soil by the seedlings during the first three weeks. Thereafter, the contents of all the elements increased at all soil temperatures except 5 °C. Element concentrations in needles, stems and roots increased with soil temperature. Higher soil temperature greatly increased the number of root tips and mycorrhizas, and the numbers of mycorrhizas increased more than did the length of new roots. Cenococcum geophilum was relatively more abundant at lower soil temperatures (5 and 9 °C) than at higher ones (13 and 17 °C). A trend was observed for decreased microbial biomass C and N in the peat soil at higher soil temperatures at the end of the experiment.
Abstract: The effects of sustained low soil temperature on growth and allocation of biomass and carbohydrates in Scots pine (Pinus sylvestris L.) were studied by exposing 1-year-old seedlings to soil temperatures of 5 °C for 0, 3, 6 or 9 weeks and subsequently for 9 weeks at 13 °C. Growth at 5 °C soil temperature at the beginning of the growing season reduced the height of new shoots but the length of the cold soil period did not affect the final height. Some new root tips emerged during the 5 °C soil temperature period. Prolific root growth did not start until the soil temperature was increased from 5 to 13 °C, but new root growth was scarce during the first 3 weeks even at 13 °C, a clearly more favourable soil temperature than 5 °C. Seedlings exposed to a temperature exceeding 5 °C over any 3-week period during the first 9 weeks had above- and below-ground biomasses that were equivalent, whereas continual exposure to 5 °C reduced shoot and root growth. The above-ground biomass of the seedlings did not increase any more after Week 12, nor did the below-ground biomass after Week 15. Biomass allocation among the different parts of the seedlings was not greatly affected by the length of the cold soil period. Our results indicate that the accumulation of above-ground biomass is mainly dependent on the air temperature and not soil temperature. Element allocation followed the pattern of biomass allocation, except for N, which increased in the above-ground parts throughout the experiment, and Fe, which had already accumulated during the first 3 weeks. The seedlings grown for a longer time at low soil temperatures contained lower amounts of starch but similar amounts of soluble sugars throughout the experiment.
Abstract: Nutrient conservation is considered important for the adaptation of plants to infertile environments. The importance of leaf life spans in controlling mean residence time of nutrients in plants has usually been analyzed in relation to nutrients that can be retranslocated within the plant. Longer leaf life spans increase the mean residence time of all mineral nutrients, but for non-mobile nutrients long leaf life spans concurrently cause concentrations in tissues to increase with leaf age, and consequently may reduce non-mobile nutrient use efficiency. Here we analyze how the role of leaf life span is related to the mobility of nutrients within the plant. We use optimality concepts to derive testable hypotheses, and preliminarily test them for boron (B), a nutrient for which mobility varies among plant species. We review published and unpublished data and use a simple model to assess the quantitative importance of B retranslocation for the B budget of mature conifer forests and as a mechanism for avoiding toxicity.
Abstract: Changes in secondary metabolites in silver birch (Betula pendula) seedlings are presented in response to ultraviolet-B radiation (UV-B) and nutrient addition. Concentrations of individual secondary metabolites and nutrients were measured in leaves of greenhouse-grown silver birch seedlings exposed to five time-integrated irradiances of biologically effective UV-B (I-BE(UV-B)) and fertilized with two relative nutrient addition rates. Several phenolics were not only induced by UV-B, but their concentration was dependent on UV-B daily time-integrated irradiance. Relative nutrient addition rate also affected the concentration of phenolics but had little effect on the UV-B daily time-integrated irradiance-responses. The mineral nutrient concentration of leaves was affected by nutrient addition but not by increasing I-BE(UV-B). Possible threshold-exposures for the accumulation of secondary metabolites or nutrients were not detected. UV-B and relative nutrient addition rate have mainly an additive (rather than synergistic) effect in silver birch, and leaves respond to increasing UV-B by synthesizing metabolites (e.g. flavonols), which are important UV-B filters. This study reports the first UV-B-exposure-response curves for individual secondary metabolites and nutrients in leaves of a woody tree species.
Abstract: The effects of lateral far-red light (FR) and nutrient supply on the growth and nitrogen accumulation of silver birch (Betula pendula) seedlings were studied with the objective of testing the following hypotheses: (1) silver birch seedlings grow taller in response to increased FR irradiance received from the side; (2) this response is modulated by the nutritional status of the seedlings; and (3) an increase in lateral FR irradiance, and concomitant decrease in red to far-red photon ratio, affects the carbon and nitrogen economies of the seedlings. Two factorial experiments, each with two levels of mineral nutrient availability and two light treatments (background ’white’ light with and without additional lateral FR simulating light reflected by neighbours in a sparse canopy) were done with small seedlings. The two experiments differed in PAR irradiance. The results of these experiments were that (1) stem elongation rate was increased by lateral FR addition, (2) there was no interaction between this effect and the nutritional status of the seedlings, and (3) neither whole plant accumulation of nitrogen nor dry weight increment was affected by lateral FR under either mineral nutrient supply regime.
Abstract: Norway spruce (Picea abies (L.) Karst.) seedlings fertilized with boron (B) at three rates were grown in a 3:7 mix of forest humus and quartz sand for 18 weeks. Half of the seedlings were not watered during the last 9 days of the experiment (drought treatment). The role of B in drought resistance was assessed by comparing the effects of seedling internal B concentration on the water relations, photosynthesis, growth and nutrition of well-watered and drought-treated seedlings. At the end of the drought treatment, needle B concentrations were 7.0 mg kg(-1) at the lowest B supply rate and 17.5 and 23.5 mg kg(-1), respectively, at the higher supply rates. Seedlings at the lowest B supply rate had fewer root tips and mycorrhizas than seedlings at the higher B supply rates. Drought treatment had a more pronounced effect on the water relations and net photosynthetic rate of seedlings than B treatment. Although seedlings at the higher B supply rates lost water more rapidly than seedlings at the low B supply rate-leading to faster stomatal closure and decreased photosynthesis-drought did not affect their final height, whereas drought reduced height growth of seedlings at the low B supply rate.
Abstract: The effects of three boron levels on the growth dynamics and ectomycorrhizas of seedlings of Norway spruce [Picea abies (L.) Karst.] were studied in a growth room experiment. The seedlings were grown in forest humus mixed with quartz sand for 16 weeks. The B treatment was applied in the nutrient solution. Stem height, dry weight, number of root tips, mycorrhizas as well as B and N concentrations in the seedlings were monitored in sequential harvests. By the last harvest, in week 16, needle B concentrations were 6.6 mg kg(-1) at the lowest B level and 17.5 mg kg(-1) and 26.5 mg kg(-1) at the two higher levels. Boron slightly increased the stem hei-ht and the total dry weight, but did not affect N content of the seedlings. Low internal B reduced the number of root tips and mycorrhizas as well as mycorrhizal percentage and root dry weight, which indicates the importance of B for root growth in Norway spruce seedlings. The seedlings crown with adequate internal B had more root tips than those receiving the two lower B treatments as early as week 9, when needle B concentrations at the lowest B supply were 16.0-17.3 mg kg(-1), which has previously been considered a sufficient B level. Therefore, the critical needle B concentrations should perhaps be re-examined.
Abstract: We studied effects of soil temperature on shoot and root extension growth and biomass and carbohydrate allocation in Scots pine (Pinus sylvestris L.) seedlings at the beginning of the growing season. One-year-old Scots pine seedlings were grown for 9 weeks at soil temperatures of 5, 9, 13 and 17 degrees C and an air temperature of 17 degrees C. Date of bud burst, and the elongation of shoots and roots were monitored. Biomass of current and previous season roots, stem and needles was determined at 3-week intervals. Starch, sucrose, glucose, fructose, sorbitol and inositol concentrations were determined in all plant parts except new roots. The timing of both bud burst and the onset of root elongation were unaffected by soil temperature. At Week 9, height growth was reduced and root extension growth was much less at a soil temperature of 5 degrees C than at higher soil temperatures. Total seedling biomass was lowest in the 5 degrees C soil temperature treatment and highest in the 13 degrees C treatment, but there was no statistically significant difference in total biomass between seedlings grown at 13 and 17 degrees C. In response to increasing soil temperature, below-ground biomass increased markedly, resulting in a slightly higher allocation of biomass to below-ground parts. Among treatments, root length was greatest at a soil temperature of 17 degrees C. The sugar content of old roots was unaffected by soil temperature, but the sugar content of new needles increased with increasing soil temperature. The starch content of all seedling parts was lowest in seedlings grown at 17 degrees C. Otherwise, soil temperature had no effect on seedling starch content.
Abstract: In contrast to earlier beliefs, it is now known that baron (B) can be retranslocated complexed with sugar alcohols in some plant species. Conifers had been thought not to translocate sugar alcohols in the phloem. However, 1 d after applying B-10 enriched boric acid to shoots of Scots pine and Norway spruce seedlings, we found increases in both the amount and proportion of B-10 in the root systems in both species. We conclude that B is translocated in the phloem from shoots to roots in spruce and pine, and therefore it is possible that these species retranslocate B. (C) 2000 Annals of Botany Company.
Abstract: We studied the response of Scots pine (Pinus sylvestris L.) to supplementary far-red sidelight in seedlings grown in a forest soil substrate without additional nutrient supply. Our aim was to determine possible changes in the accumulation and allocation of dry weight and mineral nutrients and the presence of mycorrhizas. Half of the seedlings were grown in light conditions simulating reflected far-red light (FR) from neighbouring plants and the other half were controls not receiving additional FR. PAR irradiance was kept constant in both treatments. At the first harvest (41 d of treatment), FR+ had no effect on stem height, biomass accumulation or allocation. However, at the end of the experiment (93 d of treatment), an increase in stem extension rate and stem dry weight was observed in FR+ seedlings when compared to controls. Both control and treated plants had several morphological types of ectomycorrhizas, but no effect of FR+ on the frequency of these morphotypes was observed. Nor was the concentration of ergosterol or estimated mycorrhizal fungal biomass affected. Nutrients were more responsive to the light quality treatment: P concentration in roots and N and P contents in stems and roots were higher in FR+ plants than in control seedlings. These results are in contrast to those of a previous study in which the root system of pine seedlings, which were fertilised and had less developed mycorrhizas, was reduced by FR+.
Abstract: The effects of supplementary far-red sidelight on the formation of mycorrhizas and on the accumulation and allocation of dry weight and mineral nutrients were studied in Scots pine (Pinus sylvestris L.) seedlings. Starting one week after germination the seedlings were subjected to two different light quality regimes: control and simulated sparse-canopy conditions (FR+). In the FR+ regime, light reflected by neighbouring plants was simulated by means of supplementary far-red light sources, which reduced the horizontal red/far-red photon ratio (R:FR) without affecting PAR. Seedlings were harvested after three months of treatment. FR+ increased stem height and decreased the total dry weight of seedlings. Dry weight allocation to needles was not affected, whereas dry weight allocation to roots was reduced and that to stems was increased in FR+ treated seedlings. The total number of short root tips and developing mycorrhizas per seedling were lower in FR+ than in control plants. Most short roots were developing mycorrhizas, while non-mycorrhizal short roots and mycorrhizas with mantle or external mycelium were very scarce. Changes in the allocation of nutrients in general followed the changes in dry weight allocation, and changes in nutrient content followed those in total dry weight. However, mismatches among these changes resulted in significant changes in nutrient concentrations in some organs: the concentrations of nitrogen and potassium in needles and the concentration of nitrogen in stems were higher in FR+ than in control seedlings. Changes in biomass and nutrient allocation under low R:FR may promote rapid height growth during early development in stands of Scots pine seedlings, but concomitant reductions in growth of the root system and mycorrhizas may negatively affect tree performance over the long term. [References: 42]
Abstract: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) seedlings were grown in a greenhouse for four months in three different soils. The soils were from a field afforestation site on former agricultural land: soil from a pine site, soil from a spruce site and soil from a birch site. Pots without seedlings were included. The aim was to discover, independent of the effects of the different quality of aboveground litter and microclimate under the tree species, whether the roots change the microbial activities and chemical characteristics of the soil, whether the changes are dependent on the tree species, and whether the changes vary in different soils.
Abstract: We studied the effects of light quality and nutrient supply on growth and nitrogen accumulation in silver birch (Betula pendula Roth) seedlings to test three hypotheses: (1) growth Of birch seedlings is sensitive to changes in light quality; (2) the response of birch seedling growth to light quality depends on nutrient supply; and (3) assimilation and allocation of nitrogen by birch seedlings are affected by light quality. The two light regimes simulated the spectral quality of sunlight and shadelight, but did not differ in photosynthetic photon flux density, and the two nutrient supply regimes differed in the rate of supply, but not in the composition, of mineral nutrients. + Accumulation and allocation of dry weight and nitrogen were strongly affected by nutrient supply regime, but light quality had little effect. During the first 15 days of the experiment, the largest effect of light quality was on height growth, which was greater in seedlings in simulated shadelight than in seedlings in simulated sunlight. Light quality had little effect on dry weight and nitrogen allocation to the stem during this period. However, at the end of the experiment (Day 29), there was an increase in N concentration per unit dry weight in leaves and stems of seedlings in the simulated shadelight plus high nutrient supply treatment. [References: 37]
Abstract: Birch (Betula pendula Roth) seedlings were grown under enhanced u.v.-B radiation and simulated forest-soil conditions, after which individual secondary metabolites were determined in the leaves. It was found that not all of the u.v.-absorbing secondary metabolites of the seedlings responded to supplementary u.v.-B radiation. Under increased u.v.-B radiation, significant increases in concentration were observed only for the major flavonoid, quercitrin, the minor flavonoid, myricetin-3-galactoside, and for chlorogenic acid. On the other hand, 3,4’dihydroxypropiophenone-3-beta-D-glucopyranoside decreased under u.v.-B irradiation. The concentration of phenolic compounds in the leaves changed during the growing season (between two harvests) but this change was not related to u.v.-B enhancement. A low availability of mineral nutrients did not impair the capacity of the seedlings to accumulate u.v.-protecting phenolic compounds under increased u.v.-B radiation. The growth conditions used might have affected the intracellular concentrations of secondary metabolites, and thus furnished the birch seedlings with an increased tolerance of u.v.-B radiation. These findings point to the significance of certain phenolic components in the protection of deciduous trees against u.v.-B radiation.
Abstract: Boron (B) retention was studied in the mor humus of podzolic soil from boreal Norway spruce (Picea abies (L.) Karst.) forests. In a long-term liming experiment, ground limestone had been applied 30 years earlier and again 12 years before sampling. Additionally a short-term field experiment was done to separate the effect of increased pH from calcium (Ca) addition. In the short-term experiment the treatments were control and two doses of CaCO3, CaSO4 and sodium + potassium (Na + K) carbonate mixture. These treatments were applied in the year before sampling. The B retention data conformed to a Freundlich model better than to a Langmuir model. Considerable B adsorption occurred, probably mostly due to the large organic matter content of mor. Liming significantly increased the quantity of adsorbed B in both experiments. Incubation with added B for 8 weeks considerably increased B retention and reduced the difference between limed and unlimed soil. CaSO4 had no effect on B retention characteristics, whereas Na + K treatment caused changes similar to those of lime. Therefore Ca probably has little influence on B adsorption in this pH range (3.0-5.9). [References: 28]
Abstract: Seedlings of contrasting tropical tree species were grown at two levels of photon flux, and two levels of nutrient supply. The CO2 exchanges of plant organs were measured, in an attempt to account for the overall carbon balance of the plants in terms of the photosynthesis and respiration of their constituent parts (buds, stems, roots and leaves that were recently fully expanded, mature and senescing). On a per plant basis the buds and leaves dominated the carbon balance. High photon flux and high nutrient supply increased the respiration rate. The relative importance of leaves of different age in whole plant photosynthetic production and respiration was different in the two species and was affected by the light regime. Maintenance respiration of both species was about the same (0.036-0.050 g CO2 g-1 d-1) but the pioneer species Trema displayed a much higher rate of growth respiration than did Milicia.
Abstract: The effects of lime, increased soil pH and increased soil Ca concentration on the mycorrhizas of Norway spruce. [Picea abies (L.) Karst.] were studied independently of each other to elucidate the different mechanisms through which lime may influence mycorrhizas in acidic soil. In a field experiment (mature Norway spruce in podzol), lime was applied as CaCO3; increased Ca concentration without an increase in pH was achieved with CaSO4; and soil pH was increased without calcium by means of Na2CO3 and K2CO3 (Na+K treatment). Treatments were done in October, and mycorrhizas were counted from samples collected in the following June and September. All treatments increased the percentage of dead short root tips compared to controls in September, and Na+K already in June. Cenococcum geophilum Fr. increased in proportion in plots treated with Na+K. In a sand culture experiment, Norway spruce seedlings were grown from seed and inoculated with Cenococcum geophilum, or root inoculum, or left uninoculated. When mycorrhizas were beginning to form, CaCO3 and CaSO4 treatments were applied. Six weeks later, the percent of dead short root tips in both salt treatments was significantly increased from control, but formation of mycorrhizas was not inhibited by treatments. As all the treatments increased the proportion of dead short root tips, it is concluded that lime directly and adversely affected mycorrhizas of Norway spruce in sand culture and in mor humus. Both increased ionic strength and increased pH may be reasons for this rather than Ca2+ specifically.
Abstract: Effects of liming and B fertilization on Norway spruce [Picea abies (L.) Karst.] mycorrhizas were studied in factorial field experiments. The lime was applied twice, about 30 years and 12 years before sampling (2000 and 4000 kg ha-1 dolomite). B was applied at the rate of 1.5 kg B ha-1 two years before sampling. Boron fertilization doubled the number of root tips in the top 10 mm of the humus layer. The proportion of dead short root tips was increased from 10 % in control plots to 29 % in the limed plots. Numbers of dead root tips were increased when both lime and B were applied. The % of mycorrhizas with external mycelium was slightly increased and the % of Piloderma croceum Erikss. and Hjortst. was decreased by lime. In conclusion, adverse effects of lime on mycorrhizas were found, which were ameliorated by B fertilization, but lime-induced B deficiency alone was not the only reason for the effects of lime on root mortality.
Abstract: The effects of liming on concentrations of boron and other elements in Norway spruce [Picea abies (L) Karst.] needles and in the mor humus layer were studied in long-term field experiments with and without B fertilizer on podzolic soils in Finland. Liming (2000+4000 kg ha-1 last applied 12 years before sampling) decreased needle B concentrations in the four youngest needle age classes from 6–10 mg kg-1 to 5 mg kg-1. In boron fertilized plots the corresponding concentrations were 23–35 mg kg-1 in control plots and 21–29 mg kg-1 in limed plots. Both liming and B fertilizer decreased the Mn concentrations of needles. In the humus layer, total B concentration was increased by both lime and B fertilizer, and Ca and Mg concentrations and pH were still considerably higher in the limed plots than controls. Liming decreased the organic matter concentration in humus layer, whilst B fertilizer increased it. The results about B uptake were confirmed in a pot experiment, in which additionally the roles of increased soil pH and increased soil Ca concentration were separated by means of comparing the effects of CaCO3 and CaSO4. Two-year-old bare-rooted Norway spruce seedlings were grown in mor humus during the extension growth of the new shoot. The two doses of lime increased the pH of soil from 4.1 to 5.6 to 6.1, and correspondingly decreased the B concentrations in new needles from 22 to 12 to 9 mg kg-1. However, CaSO4 did not affect the pH of the soil or needle B concentrations. Hence the liming effect on boron availability in these soils appeared to be caused by the increased pH rather than increased calcium concentration.
Abstract: Mycorrhizal [Paxillus involutus (Batsch) Fr.] and non–mycorrhizal Sitka spruce [Picea sitchensis (Bong.) Carr.] seedlings were grown to comparable size and with comparable shoot N, P and K concentrations in a perlite nutrient solution culture. Shoot water potentials of mycorrhizal and non–mycorrhizal seedlings were related to the moisture content of the substrate during a drying cycle. At any given substrate moisture content, mycorrhizal plants had significantly lower water potentials than non–mycorrhizal plants, the difference being about O.l MPa. In a factorial experiment there was no effect of mycorrhizal infection on stomatal conductance or net photosynthetic rate in either well–watered or droughted seedlings.
Abstract: The photosynthetic performances of two tropical tree species, a pioneer Nauclea diderrichii (De Wilde.) Merrill, and a climax species Entandrophragma angolense (Welw.) C. DC., both from West Africa, were compared. Young plants were grown in controlled environments where photon flux density and nutrient supply were varied. A/C1 curves of the two species were very similar, both showing an increased initial slope and maximal rate of photosynthesis when the leaves had been grown at high photon flux density. Nutrient supply had a similar, but smaller, influence. However, the pioneer Nauclea showed a greater increase in initial slope in relation to both light and nutrient supply. It also showed greater anatomical response to light, developing a second layer of palisade mesophyll when grown at high photon flux density. Light response curves of photosynthesis were also determined. The apparent quantum efficiency was insensitive to growing conditions, but the carboxylation rate, dark respiration and tight-saturated photosynthetic rate were sensitive to the light climate of growth. The pioneer Nauclea displayed an increase in assimilation rate as the photosynthetic photon flux density was increased beyond 300 ?mol m-2s-1, but Entandrophragma did not, and often showed a decline.
Abstract: Containerised, mycorrhizal (Image) and nonmycorrhizal Sitka spruce (Image) seedlings were grown to comparable size and nutrient contents. The effects of drought were assessed by (1) following the decline of total shoot water potentials in relation to soil moisture content, and (2) measuring net photosynthesis, leaf conductances and plant water potentials after droughting seedlings. Most parameters measured did not show a mycorrhizal effect, whether plants were subjected to drought or not.
