Direct and indirect plant-soil interactions in a semi-arid Mediterranean shrubland (NE Spain)

Dynamics between plants and soil control important processes such as community succession, nutrient cycling or resilience to environmental change. Until now, most research on plant-soil interactions has focused on uni-directional and species-specific effects of plants on soil and vice-versa, under controlled-conditions experiments, but little is known about the direct and indirect interactions between the plant community and the underlying soil under field conditions. We investigated these interactions in a semi-arid shrubland from NE Spain. We sampled plant biomass, nitrogen availability in soil, soil microbial biomass C, soil water infiltration capacity, soil bulk density and quality of plant tissue. These parameters were related to each other to build a statistical plant soil interaction model that was analyzed through regression and Structural Equation Modeling analyses. This statistical model was hypothesized to reveal important mechanisms for community regulation. Plant biomass was fundamentally dependent on water infiltration capacity and microbial biomass C was fundamentally dependent on nitrogen availability. Plant biomass interacted indirectly with microbial biomass C by directly affecting nitrogen stock and quality of plant tissue. Similarly, plant biomass modulated the soil bulk density. We demonstrated that vegetation has a preeminent role in the regulation of biological processes in this ecosystem through control on nutrient status, microbial biomass and mechanical soil conditions. Conclusions extracted from this study can be valuable in restoring and conserving similar ecosystems at risk of disappearing due to desertification.