Effects of management on plant litter traits and consequences for litter mass loss and Collembola functional diversity in a Mediterranean agro-forest system

Abstract

Plant litter decomposition depends on the nutrient content and the amount of recalcitrant materials such as lignin and phenolic compounds. These traits are inherent to the plant species providing the litter. In agro-ecosystems, the type of land management may also shape litter traits and then influence the litter decomposition process. However, the effects of management practice/intensity on litter traits have not been addressed in previous studies, particularly in Mediterranean systems. Our aim was to test the effect of management practices on litter traits associated to nutritional quality and recalcitrance and the resulting effects on fungal biomass, Collembola communities and decomposition parameters in cork-oak agro-forest systems. A litterbag experiment was conducted using litter of dominant plant species, Quercus suber L. and Agrostis pouretii L., collected in an organic agro-forest system and in its neighbor conventional farm. We also tested the effects of litter mixtures using these two contrasting litter types, and the subsequent effects on Collembola communities and decomposition parameters. Land management influenced initial litter traits, mostly in terms of phenolics concentration, higher on the conventional site, and P concentrations, that were higher on the organic farm. After the decomposition experiment, fungal biomass was significantly higher on Quercus litters from the conventional management, while %P and %phenolics were significantly higher in litters from organic compared to conventional management. Collembola richness was significantly higher in Quercus treatments and in litter mixtures compared to single Agrostis litters. These recorded more epigeous species and collembolans with bigger body size, which apparently found more suitable habitat or resource availability in mixtures than in single Agrostis litters. Mixed litters also favored higher fungal biomass, and P and phenolics concentrations, in relation to single litters. Yet, land management and litter mixtures did not explain litter mass loss. Decay rates were higher in Agrostis than in Quercus litter, due to the differences in the initial litter traits (lignin, phenolics and P contents). Particularly, litter mass loss was positively related to P concentration and negatively associated to the concentration of phenolics.