Interactive effects of nitrogen addition and litter on soil nematodes in grassland

Abstract

Soil nematodes are ubiquitous in terrestrial ecosystems. Nematodes are one of the most abundant groups of soil invertebrates, and they influence ecosystem processes and functions. Plant litter is a fundamental factor in controlling the structure of belowground communities. The addition of nitrogen (N) can restructure soil nematode communities by affecting the quantity and quality of litter input into soil. However, little is known about how N and litter interact to affect nematode communities. We examined the response of soil nematodes to the addition of N and litter manipulation (i.e. initial litter, removal, addition) in a 6‐year field experiment in grassland, and quantified the effects of additions of N and litter on nematode abundance, diversity and community structure through the plant community and nutrients in soil. There were interactive effects between additions of N and litter on nematode numbers and trophic group abundance, the Shannon–Wiener index (H′) and the maturity index. The addition of litter without that of N increased the total and trophic group abundance, whereas the addition of N and litter decreased nematode H′ and the maturity index. Structural equation modelling (SEM) revealed that the addition of N decreased herbivore abundance through increasing plant N concentration, and directly decreased fungivore abundance and indirectly decreased bacterivore and omnivore predator abundance through fungivores. The positive effects of litter addition on nematodes without the addition of N and its negative effects on treatments with the addition of N suggested that without added N, increased litter accumulation could benefit the soil nematode community. However, under scenarios of N deposition, grassland management that reduced litter accumulation, such as grazing and mowing, could also benefit soil nematode communities.Highlights There were interactive effects between additions of N and litter on nematode community N addition decreased nematode abundance and diversity in litter addition treatments Without N addition, litter addition increased nematode abundance and diversity Nematodes were affected mainly through decreased fungivore abundance