Dpto. de Cristalografía, Mineralogía y Química Agrícola Facultad de Química (Universidad de Sevilla) C/Profesor García González, 1, 41012, Sevilla, Spain
Graduate in Biological Sciences (2004) PhD in Biology (2010)
Gema Bárcenas Moreno was born in Úbeda (Jaen, Spain). When she was 8 years old, she moved to Granada (Spain) where studied Biology degree at Granada University. She has developed her PhD studies related to soil quality in Mediterranean area at Agrochemitry and Environment Department of Miguel Hernandez University in Alicante (Spain). During this period se has moved twice to Lund University (Sweden) for short-term stays at Microbial Ecology Department under supervision of Dr. Erland Bååth. Actually, Gema Bárcenas is member of MedSoil Research Group and is teaching at Seville University (Spain).
Research lines: Soil microbiology, microbial ecology, forest fire, fire-affected soils Reviewer for the following SCI journals: Biology and Fertility of Soils, Soil and Tillage Research Memberships: Sociedad Española de la Ciencia del Suelo, International Union of Soil Sciences
Abstract: A field experiment was carried out in a semiarid agricultural Mediterranean area located at the " El Teularet" experimental field in the Enguera Sierra (Valencia, southeast Spain) to assess the influence of different agricultural management systems on indicators of soil biological quality and activity (microbial biomass C, basal respiration, C mineralization coefficients, metabolic quotient (qCO2), respiratory quotient (RQ: moles CO2 evolved/moles O2 consumed), soluble C and dehydrogenase, urease, protease-BAA, phosphatase and β-glucosidase activities), one year after treatment establishment. The management practices assayed were as follows: application of the herbicides paraquat, glyphosate or oxyfluorfen, addition of olive tree pruning residues, ploughing, sowing of oats+addition of crop residues+ploughing, sowing of Medicago sativa, sowing of oats and vetch+addition of crop residues and addition of oat straw. A non-treated plot was used as control soil and a plot under natural vegetation was used as a standard of local, high quality soil. The plots with addition of oat straw had higher values of enzymatic activity, microbial biomass and respiration, reaching similar values to soil under native vegetation. The lowest levels of soil biological quality indicators were observed in the plots with application of some type of herbicide. Low RQ values were observed in these plots as consequence of the scarce-null inputs of organic matter, suggesting an increase in organic matter recalcitrance. The addition of oat straw to soil can be considered an effective technology, due to the rapid improvement of soil quality, for carrying out sustainable agriculture in semiarid Mediterranean agroecosystems.
Abstract: Soil water repellency is usually modified after wildfires by the combustion of soil organic matter and plant residues, and is considered to be the cause of important changes in the hydrological response of burned soils. In this research, the interactions between burning temperature, soil water content, water repellency and stability of aggregates have been studied. Samples collected from soils under eucalyptus forest in Spain, Mexico, and Australia were treated at 100-150, 200-250, and 400-450 ºC under dry and moist conditions in the laboratory, and temperature profiles and changes in water repellency were analyzed using the water drop penetration time test and the contact angle method. In order to study the effects of burning temperature on aggregate stability, undisturbed top soil samples (0-5 cm depth) were collected at five soil plots at Sierra de Aracena Natural Park (SW Spain) and treated at different temperatures ranging between 50 and 400 ºC. The results showed that soil water repellency did not change significantly with respect to unheated control samples at temperatures between 100-150 oC, but decreased considerably between 250-300 ºC and practically disappeared after heating to 400-450 oC. Soil moisture induced a decrease of water repellency in samples treated at 100-150 oC and 250-300 ºC, but its effect was negligible at higher temperatures. Laboratory heat treatments reduced soil aggregate stability, especially after exposure to temperatures above 200 ºC.
Abstract: Temperature not only has direct effects on microbial activity, but can also affect activity indirectly by changing the temperature dependency of the community. This would result in communities performing better over time in response to increased temperatures. We have for the first time studied the effect of soil temperature (5-50 °C) on the community adaptation of both bacterial (leucine incorporation) and fungal growth (acetate-in-ergosterol incorporation). Growth at different temperatures was estimated after about a month using a short-term assay to avoid confounding the effects of temperature on substrate availability. Before the experiment started, fungal and bacterial growth was optimal around 30 °C. Increasing soil temperature above this resulted in an increase in the optimum for bacterial growth, correlated to soil temperature, with parallel shifts in the total response curve. Below the optimum, soil temperature had only minor effects, although lower temperatures selected for communities growing better at the lowest temperature. Fungi were affected in the same way as bacteria, with large shifts in temperature tolerance at soil temperatures above that of optimum for growth. A simplified technique, only comparing growth at two contrasting temperatures, gave similar results as using a complete temperature curve, allowing for large scale measurements also in field situations with small differences in temperature.
Abstract: The intensity of a fire is an important factor determining the recovery of soil microorganisms after a forest fire, since it can alter the quality and quantity of carbon sources. Recovery of the microbial community was studied in a Mediterranean pine forest soil subjected to different temperatures to simulate the short-term effects of fire intensity on bacterial and fungal growth, estimated using leucine incorporation for bacteria and acetate incorporation into ergosterol for fungi. Soil samples were heated for 15 min at 50, 80, 120, 200, 300, 400 and 500 °C. After inoculation with fresh soil, and adding water to achieve 60% WHC, the soils were incubated at 20 °C for 21 days. Bacterial growth was initially inhibited in the samples heated above 50 °C (totally inhibited ⥠200 °C), but recovered within days to levels much higher than the control, except for the samples heated at 500 °C, where growth remained low throughout the incubation period due to the destruction of most of the organic matter. After the first week of incubation, the bacterial response decreased to values close to, but still above, that of the control. Samples heated at 200 °C showed the highest cumulative bacterial growth. Fungal growth was initially lower than in the control in all the heated samples (totally inhibited ⥠200 °C). Fungal growth recovered slowly during incubation in soils heated at ⤠300 °C, but the cumulative growth in heated soils did not exceed that in the control. No fungal growth was observed in samples heated at the two highest temperatures. Soil respiration was initially totally inhibited in soil heated at ⥠200 °C, but recovered rapidly in all soils; the highest respiration being observed already 1 day after inoculation. This is the first time both fungal and bacterial growth has been directly estimated in heated soils. High soil pH favouring bacteria can explain these results, but the differences in fungal and bacterial responses suggest a competitive interaction between these groups.
Abstract: Many authors have reported increased water repellency in fire-affected areas [1, 2]. Research
on post-fire soil erosion shows a range of results. Many authors have found increased soil
erosion and runoff rates after fire, due to factors as loss of vegetation canopy, low structural
stability of soils and enhanced runoff flow on soil surfaces affected by fire-induced
hydrophobicity. Fingered wetting fronts in water repellent soils have been reported by
different authors [3, 4, 5] while a uniform and broadly horizontal wetting front developed in
wettable soils. However, the heterogeneity of results, the influence of vegetation, and the
diversity of responses after burning makes necessary the study and characterization of these
processes with special interest in recurrently burned Mediterranean areas.
The objectives of this research are to study the effect of burning in water repellency (WR) in
Mediterranean soils under oaks and pines, to study the relationship of fire-induced WR and
other soil parameters, and to study the effect of fire-induced WR in hydrological and erosional
responses of soils under oaks and pines in the study area.
Abstract: Forest fires are one of the main disturbances in Mediterranean ecosystems and their number,
size and intensity have increased over the last few decades [1, 2]. Although fire effects on soil
depend on many factors, one of the main factors that control these effects is fire intensity,
which depends on two components: temperatures reached and time of residence of the heat [3,
4].
Different temperatures cause different effects on soil properties. Giovannini [5] summarized
the effects of heating on the soil quality in these distinct sections: heating up to 220ºC:
complete dehydration of the soil, including the gel forms; heating from 220º to 460ºC:
combustion of the soil organic matter, most of the nutritional elements are mineralized;
heating from 460º to 700ºC: produces the loss of the OH groups from the clays; heating
beyond 700ºC: produces the disruption of the carbonates.
However, the rate at which energy can be transmitted through the soil is also limited by the
thermal properties of the soil. Consequently, the duration of burning (fire residence time) is a
key factor controlling the effects on soils properties [6, 7]. Thus, the time the heating remains
can be considered the most damaging component of fire intensity to soil [8].
Despite the general agreement about the importance of determining fire residence time, this
parameter is not available in studies of fire affected soils; therefore, obtaining this data can be
very useful to assess fire effects on soil.
Near infrared reflectance (NIR) spectroscopy has been used to develop predictive models of
the Maximum Temperature Reached (MTR) in burned soils [9, 10]. NIR spectroscopy obtains
the reflectance spectra of a sample in the range of the NIR region (780-2500 nm). In this
region, different chemical bonds of organic molecules absorb the radiation. The radiation is
absorbed in accordance with the concentration of these compounds. Therefore, NIR spectra
contain information about the organic composition of the soil, which is modified by the effect
of fire [9].
The main objective is to study the use of NIR to developed models that will be able to
estimate how long a burned soil remained over a temperature (Time Over Temperature -
TOT).
Abstract: Dada la dificultad de aislar el efecto la intensidad del fuego en los trabajos de campo, este
experimento se centró en la aplicación de un rango de temperaturas bajo condiciones
controladas de laboratorio para estudiar la respuesta microbiana en un suelo quemado con
diferente intensidad. Para ello, el suelo de un área forestal madura de la provincia de
Alicante, fue incubado al 60% de su capacidad de campo durante 4 dÃas y se sometió a
quemas de 15 minutos a diferentes temperaturas (control, 120, 200, 300 y 400ºC). Una vez
realizadas las quemas, las muestras se inocularon con suelo control para simular un
proceso acelerado de recolonización microbiana. El crecimiento bacteriano (incorporación
de 3H-leucina), crecimiento fúngico (incorporación de 14C-Acetato) y la respiración
edáfica, fueron analizados, y la evolución de la mineralización del carbono fue estudiada
en los valores acumulados de CO2 desprendido durante la incubación (21 dÃas), ajustando
los valores acumulados a una función doble exponencial que nos estima la presencia de dos
pool de carbono con diferente velocidad de mineralización.
Los resultados relativos al crecimiento bacteriano (incorporación de leucina) mostraron la
gran capacidad de las bacterias para crecer en el suelo quemado, especialmente en las
muestras expuestas a 200-300ºC. Los picos de máximo crecimiento bacteriano se dieron
entre el segundo y cuarto dÃa de incubación y mantuvieron valores superiores al control
hasta el final del experimento, exceptuando aquellas muestras quemadas a 400ºC.
Los hongos, al contrario que las bacterias, se vieron afectados negativamente con la quema
permaneciendo bajo los niveles del control durante todo el experimento.
La tasa de respiración fue máxima inmediatamente tras las quemas coincidiendo con un
marcado incremento del carbono soluble. Sin embargo, ambos parámetros comenzaron a
disminuir rápidamente hasta niveles próximos al control en la primera semana de
incubación.
Los valores acumulados de respiración fueron mayores al control en todos los tratamientos,
siendo las muestras quemadas a 300ºC las que mostraron los valores acumulados más
altos. La mineralización del pool lábil y el recalcitrante mostraron valores superiores o
similares al control en las muestras expuestas entre 120 y 300ºC. Sin embargo, las
muestras expuestas a 400ºC se caracterizaron por una elevada mineralización del pool lábil
(equiparable a las muestras quemadas a 300ºC) pero una marcada disminución de la
mineralización del pool recalcitrante con respecto al control.
Con los resultados obtenidos se puede apreciar la marcada influencia de las
transformaciones del carbono en la respuesta microbiana y el patrón de mineralización,
revelando un proceso de sucesión entre microorganismos estrategas de la ârâ que
consumirÃan rápidamente el carbono lábil al inicio de la incubación y los microorganismos
estrategas de la âkâ que crecerÃan más lentamente degradando sustratos más complejos
durante todo el experimento.
Abstract: Plant species can affect fire intensity and severity causing different immediate and postfire
responses of the microbial community. This was studied in a laboratory heating
experiment (300ºC during 20 min) using soil collected under Pinus hallepensis (PIN) and
Quercus coccifera (KER). Dried plant material was added (1g per 20g soil) before heating
resulting in six different treatments: non-heated control samples amended with the
original plant material (PIN0 and KER0); PIN samples heated with pine (PINp) or kermes
oak litter (PINc); KER samples heated with kermes oak (KERc) or pine litter (KERp).
Heated soils were inoculated with the original soil (1g per 20g soil) and water to achieve
60% WHC was added. Bacterial and fungal abundance (plate count) and biomass index
(phospholipid fatty acid analysis) were measured 3 and 28 days after inoculation.
Bacterial numbers were higher in heated than in control samples at both measurement
occasions. Added litter only affected KER samples immediately after heating, where soil
amended with kermes oak had more bacteria than those amended with pine litter.
Fungal abundance decreased below control values immediately after heating. After 28
days KER showed significant higher fungal abundance than PIN samples in both heated
and control samples. Plant material was important in PIN samples, where PINp had lower
fungal abundance than PINc.
Contrary to the plate count data, both fungal and bacterial biomasses indices decreased
due to heat treatments. Plant litter only affected to a minor degree. Fungal and bacterial
biomasses were higher in KER than PIN heated samples. Soils amended with kermes oak
had higher fungal biomass than those amended with pine litter.
Thus, plant species was shown as a significant factor determining the microbial response
after heating, most likely due to different fuel nature and possible presence of different
soil microbial communities associated with each plant species.
Abstract: Fire intensity is one of the most important factors determining fire severity and the
subsequent effect on soil microorganisms, since it can alter the quality and quantity of
carbon sources or induce the appearance of toxic compounds. Fire intensity will thus
influence both short and long-term response of the soil microbial communities.
In this work a Mediterranean pine forest soil was subjected to different heating
temperatures to study the short-term effect of fire intensity on bacterial and fungal
growth, estimated using leucine incorporation for bacteria and acetate incorporation
into ergosterol for fungi. Soil samples were heated during 15 minutes at each
temperature (non-heated control, 50, 80, 120, 200, 300, 400, and 500 ºC). After heating
the soil samples were inoculated with fresh soil (1g per 100g heated soil), and distilled
water to achieve 60% WHC was added. The total incubation period at 20ºC was 21 days.
Bacterial growth was initially inhibited by heating above 50 ºC, but recovered within days
to levels much higher than the control, except for the 500 ºC treatment, where bacterial
growth remained low all the time. The bacterial response decreased after the first week
to values close to the control. Samples heated at 200ºC showed the highest cumulative
bacterial growth and it was still higher than the control values at the end of the
experiment. Fungal growth was initially lower than the control in all high temperature
treatments. Although fungal growth recovered slowly during the experiment, it never
became much higher than the control in the three highest heating treatments.
That bacteria are favoured compared to fungi in heated soil has earlier been reported in
other studies, but this is the first time growth has directly been estimated. Usually
increased pH after fire due to ash deposition has been suggested as the reason for
bacteria being favoured. High soil pH can also explain our result, although pH in heated
soil did not change due to initial high soil pH. However, fungal and bacterial activities
showed opposite behaviour in the experiment, indicating possible competitive
interaction between these microorganism groups.
Abstract: The main objective of this work is the study of the effect of wildfire on soil microbial
abundance in three different plant communities associated with different altitudes
in âSierra Nevadaâ (Granada, Spain). The abundance of 2 microbial groups (aerobic
bacteria and filamentous fungi) was measured by dilution plate count technique using
selective media and Fungi/Bacteria ratio was calculated. Samples were collected in
three areas located on the Sierra Nevada Mountain between 1300 and 2000 m over sea
level which were affected by a large wildfire in 2005. Two samplings were carried out
8 and 13 months after fire and samples were collected in both burned and unburned
(control) zones in each plant community area. Area A is located at 2000 m altitude
and is composed of alpine vegetation formed by creeping bearing shrubs. Area B is
located at 1800m and it is formed by Quercus rotundifolia forest. Area C, at 1300
m altitude, is an area with tall grass and shrubs which was also affected by another
wildfire 25 years ago.
Microbial abundance showed significantly higher values in burned over unburned areas
in both groups, Fungi and Bacterial, and in each sampling and plant community.
We observed significantly different responses to fire incidence among plant community
areas. Bacterial abundance in first sampling showed a general increase with fire
but this increase was significantly higher in B than in A or C. Nevertheless, fungal
abundance shows a slighter increment than bacterial. In the second sampling, bacterial
abundance increases in burned areas with regard to the controls but this increment
was significantly higher in B than in the other areas. Fungal abundance variation between
burned and control areas in second sampling did not show significant differences
among plant communities although the increase in C was much more marked
than in A or B. Statistically significant differences were found in Fungi/Bacteria ratio
response to fire among different plant communities in both samplings. Area A did not
show variation between burned and unburned samples in 1st sampling and showed an
important decrease in 2nd sampling; area B showed an important decrease in the ratio
in both samplings; area C increased the ratio values in 1st sampling and kept similar
values in the 2nd one.
It is probable that fire intensity and severity were different in the 3 plant communities
and this caused different immediate and post-fire responses in microbial populations
among the plant communities studied. But also, the variations in the response of microbial
abundance and the Fungi/Bacteria ratio after the presence of fire could be
influenced by the possible presence of the different microbial communities associated
with each plant community which is determined by altitude distribution. Nutrients input
via ash deposition could explain the generalized increase in microbial abundance
months after fire and the higher increment in bacterial over fungal abundance could
also be mainly due to the increment of pH as a consequence of the incorporation of
ash into the soil.
Abstract: Fire intensity and severity depends on different parameters that are decisive for the effects on soil.
Important factors affecting fire intensities are microrelief, wind speed and direction, soil and fuel
moisture content, and the type and spatial distribution of fuel. Water content is a major factor
affecting heat transfer in soils and the effectiveness of the heat for lysing microbial cells. In this
work we have studied the immediate effects of two different wildfires on microbial populations.
Four groups of soil microbial populations were assessed (filamentous Fungi, aerobic Bacteria,
Spore formers and Actinomycetes). The study sites are located in a Mediterranean ecosystem
dominated by Pinus halepensis Miller in southeast Spain (Alicante). Burned areas were located in
the Sierra Grana and in the Sierra Mariola Natural Park. The wildfire episodes were in August and
November, 2005, respectively. Twenty soil samples per site were collected immediately after a fire
(10 from burned zones and 10 from unburned zones). Soil samples were taken under Pinus
halepensis Miller and under different Mediterranean shrubs. Regarding the Sierra Grana fire, the
most affected population was filamentous fungi that were severely reduced (99.5% less) and the
Spore formers were the least affected population (91.8% less), both regarding unburned samples. In
the Sierra Mariola fire in contrast, Spore formers were the most reduced group (65% less) whereas
aerobic Bacteria and Actinomycetes populations were 3-fold and 2-fold higher than the control
values, respectively. It is speculated that different fire severity is responsible for the differences
found between the sites.
Abstract: A long-term experiment was designed to study the relationship between soil losses
and soil quality conditions analyzing different physical, chemical and biological soil
properties. Different treatments were carried out in an agricultural terrace in âEl Teularet
experimental stationâ in the Sierra of Enguera (Valencia, southeast Spain), getting 13
different plots. In this paper we show the results of the state of available fungi and bacteria
populations one year after the application of the treatments, due to the close relationship of
structural stability and the resistance of the soil to erosive processes. The major growth for
both populations was observed in the plots with the addition of rest of vegetal material. Less
growth was observed in the plots with some type of herbicide and the plot with geo-text.
