Mediterranean coastal conditions and litter type drive litter microbial responses to drought stress

Abstract

AbstractWarming and disturbance of precipitation dynamics are expected in the Mediterranean basin, resulting in longer, more intense drought and heat waves. Here we investigated how litter microbial functioning and responses to stress may be shaped by coastal environmental conditions, and whether this depends on litter type (Pinus halepensis, Pistacia lentiscus and their admixture). Mesocosms of monospecific and mixed litters collected from both inland and coastal areas were subjected to either control (25°C, 60% water holding capacity [WHC]) or stress conditions (five drying‐rewetting [D/rW] cycles: 1 week of drying at 35°C, 1 week at 25°C, 60% WHC). Litters were characterised using chemical analyses (C/N ratio and solid‐state 13C nuclear magnetic resonance [NMR] spectroscopy) and indicators of microbial activity (lignocellulolytic activities, basal respiration [BR], active microbial biomass [MB], fungal and bacterial catabolic profiles). Litter type controlled cellulases and basal respiration in litters from the inland area (e.g. positive correlations between these microbial indicators and di‐O‐alkyl C + O‐alkyl C and %N), whereas the litter‐type effect was smoothed for the coastal area. Fungal and bacterial catabolic profiles were mainly shaped by the coastal conditions and litter type, respectively, indicating that fungi were more sensitive to coast‐specific conditions and bacteria more sensitive to their immediate surrounding (i.e. litter type). After D/rW cycles, microbial catabolic profiles showed: (a) a stronger stress impact on microbial communities from the inland area and (b) pre‐exposure to coastal constraints limited the drought effect on decomposers from the coastal area. Our findings reveal that coastal environmental conditions and litter type are major drivers of microbial functioning and responses to drought stress.Highlights Poorly documented litter functioning in Mediterranean coastal environments is here investigated Coastal conditions smoothed litter type effect on certain microbial markers Pre‐exposure to stress (coastal conditions) limited drought effect on microbial catabolic profiles Coastal areas should be considered when evaluating microbial functioning and responses to drought