Earthworm communities in conventional and organic fruit orchards under two different climates

Climate strongly influences the distribution of soil organisms in agroecosystems, but local agricultural practices can also alter the natural composition of soil communities. Conventional (CONV) practices usually cause long-term negative effects in soil agroecosystems, by reducing soil biodiversity and altering edaphic processes, while organic (ORG) practices promote soil health and the diversity and abundance of fauna. Here, we used distributional and multivariate analyses to compare the species composition and ecological structure of earthworm communities in four fruit orchards (kiwifruit, grapevine, clementine, and olive) cultivated under CONV and ORG practices and located in two different biogeographic regions of the Iberian Peninsula (Atlantic and Mediterranean). Results indicated that the interaction among the three factors studied (biogeographic region, agricultural management and fruit tree orchard) caused a significant effect on all parameters analyzed (abundance, biomass, diversity, earthworms communities, and earthworms life strategies). More earthworms were collected in Atlantic (7160 ind m(-2)) than Mediterranean (5576 ind m(-2)) region, although no differences were found between CONV and ORG practices. However, agricultural practices caused an important effect on earthworm diversity, with significant reductions in species richness (S), diversity (H' index) and mature earthworms in the dryer and warmer climate under CONV practices. The multivariate analysis reflected those dissimilarities in ecological structure between biogeographic regions (95%) and agricultural practices (> 82%). Finally, the comparison of the abundance and biomass curves confirmed that ORG practices were beneficial for earthworm populations, showing moderate or absence of ecological perturbation, and consequently, they diverted more energy to individual growth than to reproduction. Therefore, the positive effects of implementing more sustainable agricultural practices in agroecosystems will depend on their interactive effects with environmental factors, being especially useful in the dryer and warmer climates, such as in the Mediterranean region.