Quercus suber decline alters soil food webs as indicated by soil nematodes

Abstract

In the last decades many forests worldwide have experienced an increase in tree defoliation and mortality associated to global change drivers. The implications of tree decline for the structure and function of soil communities is however poorly understood. In this work we analyze the impacts of the decline of Quercus suber in the Iberian Peninsula on the structure of soil food webs as indicated by soil nematodes. Soil nematodes comprise different trophic groups and are strongly linked to the microbial community; therefore they are considered valuable bio-indicators of the response of soil food webs to changes in environmental conditions. We took soil samples in four different forest sites using a spatially-explicit design and identified nematodes to the genus level. We used neighborhood models to predict the abundance, diversity and trophic structure of the nematode community as a function of the distribution and health status of the tree and shrub community. Our results did not support any effect of neighbor health or identity on nematode abundance and diversity. However, we found that tree neighborhoods dominated by defoliated and dead Q. suber trees showed higher abundance of bacterial-feeding nematodes, higher values of the Enrichment Index (indicative of an increment of opportunistic nematodes), and lower values of the Channel Index (indicative of the predominance of the bacterial decomposition pathway) than healthy neighborhoods. Overall, our results suggest that the decline of Q. suber causes major shifts in the structure of nematode communities and the channeling of energy through decomposer food webs.