Water and plant litter inputs as key factors controlling soil microbial biomass and carbon source utilization in a Mediterranean and semi-arid region

Background/Question/Methods Global climate models demonstrate alterations in rain temporal and spatial distribution. Such alterations might have a most pronounced effect on water availability in Mediterranean and semi-arid regions due to their characteristically high evaporation intensities. Understanding the consequences of altering water availability in Mediterranean and semi-arid regions for soil microbial communities is essential considering the crucial functions that soil microorganisms perform for soil fertility. The aim of this study was to evaluate water as a regulator of soil microbial biomass and activity, and to assess the effect of plant canopy presence on microbial functional diversity. Water manipulation treatments aimed to reflect potential changes in precipitation regimens, including: 1) supplemented winter rainfall; 2) simulated winter drought; and 3) a control. Soil samples were collected seasonally both under plant canopies (Sarcopoterium spinosum) and between shrubs (control). Soil abiotic parameters (moisture, organic carbon, dissolved organic carbon and total soluble nitrogen contents) as well as biotic parameters (microbial CO₂ evolution, biomass, substrate utilization profile and functional diversity) were determined.

Results/Conclusions Preliminary results showed higher soil moisture and organic carbon contents in the Mediterranean compared to the semi-arid location, as well as under plant canopies compared to the open spaces. On the other hand, total soluble nitrogen content was found to be higher in the semi-arid location and in the open-space samples. Microbial functional diversity showed higher values in soil samples collected under plant canopies compared to control samples at both the Mediterranean and semi-arid sites. However, the various water manipulation treatments were not found to have a positive effect on microbial community values. We believe that   microbial functional data collected along a spatial and temporal scale will contribute to our ability to predict functional changes in terrestrial ecosystems.