Decomposers’ activity along a spatial gradient in a Mediterranean agroforestry system
Résumé
Litter decomposition is an important process involved in nutrient cycling and soil fertility in ecosystems. In alley-cropping agroforestry systems, contrasted litters from the intercropped annual and perennial plants are more or less mixed and decomposed depending on the distance from the tree lines. Our aim was to unravel the determinants of C, N and P mineralization in such a heterogeneous agroecosystem. We hypothesized that there is a spatial gradient of functional capacity of decomposers perpendicular to the tree line. Decomposers would rather be K-strategists close to the tree line and r-strategists in the middle of crop alley. We also aimed at testing the Home Field Advantage hypothesis in our system. We thus conducted an in situ experiment for 7 months at Restinclières (France) with walnut trees intercropped with peas/cereals. We placed litterbags made of a mixture of pea and walnut leaves, or each of the two separately, on the tree line, at 1.5 and 5.25 meters from it. After 2, 4 and 7 months, we measured soil microbial activity, nematode abundance, litter quality and mass loss. Our results highlighted significant effect of litter quality on both decomposition rates and microbial biomass C, N, P. Moreover, greater microbial biomass on the tree line was not correlated with greater decom-position. Similarly, nematode abundance showed higher values on the tree line, and also for the pea litter. These first results validate our first hypothesis, showing a difference in decomposers’ functioning within our agroforestry system according to the distance from the tree line.