Complex effects of habitat fragmentation on plant‐soil microbial interactions in Mediterranean Holmoak forests

Abstract

The adverse effects of habitat fragmentation on biodiversity have been widely explored; however, little research has been conducted to understand its effects on ecosystem functioning. Effects of forest fragmentation are tightly linked to the surrounding matrix in terms of nutrient inputs and spatial constraints, leading to complex edge effects. Soil ecosystem processes related to carbon cycling are particularly important since soils are the largest carbon pool in terrestrial ecosystems, and habitat fragmentation affects their sink capacity and their vulnerability to global change. Soil organic matter (SOM) decomposition is affected directly by the canopy cover. Thus, the effects of an agricultural matrix could be overridden by the direct effects of canopy rather than by habitat fragmentation itself. In order to evaluate which key factors could be driving SOM decomposition in fragmented landscapes, we analyzed potential enzymatic activities (β-glucosidase, chitinase and phosphatase acid) and field soil respiration in fragmented Mediterranean Holm oak forests. We evaluated if the impact of fragmentation on soil microbial functioning could be explained through its effect on microhabitat characteristics by using structural equation models. Variables measured included biotic (microbial biomass), abiotic (soil moisture, temperature, organic matter, pH, nutrients) and tree structural (stem diameter, canopy projection, leaf area index) characteristics. Tree effects on soil functioning (enzymatic activities) were potentiated by the influence of the agricultural matrix. As expected, trees created a microenvironment where the increment of SOM modified the pH, increasing soil moisture and decreasing temperature, rising the amount of microbial biomass and, therefore, improving the functioning of soil microbial community. Agricultural matrix influence on SOM decomposition was mainly indirect, through its positive effect on tree size. Mediterranean fragmented forests with high influence of agricultural matrix could increase SOM decomposition rates, decreasing soil carbon sink capacity.