Environmental Drivers of Microbial Functioning in Mediterranean Forest Soils

Abstract

Mediterranean forests own distinct characteristics resulting from climate, soil, and vegetation that affect soil microbial communities' assembly and their associated functions. We initiated a multiscalar analysis of environmental drivers of soil functioning to (1) identify pertinent factorial scales and (2) determine the relative importance of soil, vegetation, and geoclimate relative influences in shaping soil microbial functions across the French Mediterranean forests. Soil samples (0-15 cm) were collected from 60 forest sites and soil physico-chemical and microbiological properties were assessed across different factorial scales i.e., bioclimates, slope exposures, and forest stands. Patterns in microbial catabolic potential (i.e., extracellular enzymes and microbial respiration) and carbon (C) source utilisation (i.e., catabolic-level physiological profiling) were partitioned between vegetation cover, soil characteristics and geoclimate components. Our results reveal that the catabolic potential of soil microbes was strongly influenced by the forest stands, and mainly relied on ammonium and nitrate contents. In contrast, variation in C-source utilisation was mainly explained by vegetation cover. Soil metabolic capacities of microorganisms and resulting C dynamics were largely constrained by climate parameters, which suggests potentially important consequences for soil C storage. Our study revealed diverse structuration patterns between the catabolic potential and the carbon-source utilisation of soil microbial communities, and gives insights into the underlying mechanisms of soil microbial functioning in Mediterranean forests.

Bacterial and fungal community composition and community-level physiological profiles in forest soils

“…Similarly, Klimek et al reported that the bacterial CLPP was influenced by nutrient status in the O horizon, but such an effect was not observed in the A horizon in temperate forest soils [ 41 ]. In contrast, significant effects of nutrient status on the bacterial CLPP were observed in pine forest soil [ 5 ] and Mediterranean forest soils [ 42 ]. Hence, the contribution of nutrient status to the CLPP is likely to vary between sites, and factor(s) influencing the CLPP might be site-specific.…”

Fire Damage to the Soil Bacterial Structure and Function Depends on Burn Severity: Experimental Burnings at a Lysimetric Facility (MedForECOtron)

“…The changes that took place after fire in the C substrate utilization profiles were almost negligible and ascribed to changes in SOM [54], but they returned to the prefire state in the short term. Both low vulnerability and high resilience have been related to the recovery of vegetation cover and plant composition [65]. The changes detected in the CLPPs were related to time after fire due to the increases in charcoal and ash that promoted soil functionality, changes in phenolic compounds and polymers, and plant recovery [18,66,67], affected by seasonal dynamics [21,68].…”

Ectomycorrhizal fungal diversity decreases in Mediterranean pine forests adapted to recurrent fires

“…Edaphic conditions (mainly pH and P) were the main factors explaining differences in enzymatic profiles among populations of both pine species. Similarly, Brunel, Silva, and Gros (2020) observed that edaphic parameters, and not climate and vegetation, significantly explained microbial functioning patterns in Mediterranean soils. Among their multiple functions, an outstanding feature of ECM fungi is their ability to mobilize nutrients from the soil (Smith & Read, 2008).…”