Adaptation of soil microbial communities to temperature: comparison of fungi and bacteria in a laboratory experiment

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

Functional implications of the pH-trait distribution of the microbial community in a re-inoculation experiment across a pH gradient

We compared the influence of the microbial community composition and the environmental conditions for the functioning - microbial growth and respiration - and trait distribution - bacterial pH tolerance - of soil microorganisms across a pH gradient. Sterilised soil microcosms, including pH 4.1, 5.2, 6.7 and 8.3, with added plant litter were inoculated with unsterilized soil in a factorial design and monitored during two months. The trait distribution - pH-tolerance - of bacterial communities converged with the pH of the soil environment. Still, the different inoculum communities could result in suboptimal pH-tolerance in all soil pH environments; inoculum communities derived from low pHs had lower than optimal pH-tolerance in high soil pH environments, and vice versa. The functioning of bacterial communities with trait distributions mismatched to the soil pH environment was impaired. The legacy of the initial bacterial trait distribution on bacterial pH tolerance and functioning was detected within one week and remained for two months in all soil pH environments. Fungal inoculum communities derived from low compared to high pHs resulted in higher fungal functioning. Thus, in contrast with bacteria there was no evidence that variation in pH-tolerance influenced fungal performance. Instead the fungal inoculum size appeared to explain these results. Bacteria dominated respiration in high pH while fungi dominated at low pH environments. Consequently, respiration was affected by how well-matched the bacterial trait distribution was to the pH of the soil environment at higher pHs. At low pH, the inoculum size of fungi appeared to determine the respiration

Relationships between soil water repellency and microbial community composition under different plant species in a Mediterranean semiarid forest

Soil water repellency (SWR) can influence many hydrological soil properties, including water infiltration, uneven moisture distribution or water retention. In the current study we investigated how variable SWR persistence in the field is related to the soil microbial community under different plant species (P. halepensis, Q. rotundifolia, C. albidus and R. officinalis) in a Mediterranean forest. The soil microbial community was determined through phospholipid fatty acids (PLFA). The relationships between microbiological community structure and the soil properties pH, Glomalin Related Soil Protein (GRSP) and soil organic matter (SOM) content were also studied. Different statistical analyses were used: Principal Component Analysis (PCA), ANOVA, Redundancy Analysis and Pearson correlations. The highest concentrations of PLFA were found in the most water repellent samples. PCA showed that microorganism composition was more dependent of the severity of SWR than the type of plant species. In the Redundancy Analysis, SWR was the only significant factor (p<0.05) to explain PLFA distributions. The only PLFA biomarkers directly related to SWR were associated with Actinobacteria (10Me16:0, 10Me17:0 and 10Me18:0). All the results suggest that a strong dependence between SWR and microbial community composition

El papel de las cenizas en la hidrofobicidad del suelo en un área mediterránea afectada por un incendio forestal: estudio en condiciones de campo

Ministerio de Ciencia e Innovación de España- Proyecto HYDFIRE-CGL2010-21670-C02-0