Spatial structure and soil properties shape local community structure of plant-parasitic nematodes in cultivated olive trees in southern Spain

Abstract

Numerous studies have documented the distribution of plant and animal communities with respect to spatial structure; however, relatively little is known about the involvement of spatial structures in the diversity of soil organisms such as plant-parasitic nematodes (PPN). Host plants such as olive trees are of particular interest because they host a large number of PPN and have a high economic and cultural importance. In this study, we investigated how different aspects of the environment (i.e. the factors soil, above-ground environment, and agricultural management) and spatial structure shaped the variation of species composition (expressed as beta diversity) and species richness of plant-parasitic nematodes infesting the soil rhizosphere in 376 commercial olive orchards in the south of Spain. We used variation partitioning to assess the relative importance of the unique and shared contributions of the factors describing the environment and spatial structure. To identify sites and species of particular interest, we partitioned beta diversity into local and species contributions.Contrary to our expectation that soil and agricultural management would largely determine the community structure of PPN, more than two-thirds of the variation remained unexplained. Spatial structure and soil were the most important factors shaping species richness and beta diversity. Surprisingly, the effects of agricultural management on species richness were lower than expected, and null [or nonexistent, or nonsignificant] on beta diversity. We found relatively high levels of shared contributions of the different factors, especially in combination with spatial structure, indicating the presence of spatial gradients of the variables describing the environmental factors.Species contributions to beta diversity (SCBD) were positively correlated with nematode prevalence and density range; thus, SCBD could be related to the niche position as reported in other ecosystems. Local contributions to beta diversity (LCBD) were mainly related with habitat filtering mechanisms (e.g. soil physiochemical and agronomic management predictors), suggesting a relationship between nematode total biomass and ecological gradients. Overall, we revealed novel insights into the spatial structure of PPN communities and showed that its beta diversity is less structured by spatial and environmental factors compared to other organism types.