Nitrogen addition simplifies micro-food webs in leaf litter habitats at humus-near stage of decomposition in a subtropical plantation

Background and aim

Litter decomposition, a key process regulating subtropical forest ecosystem carbon and nutrient cycling, is highly susceptible to increasing atmospheric N deposition and is facilitated and regulated by micro-food webs. However, responses of micro-food webs in leaf litter habitats to N deposition remain unclear, especially at humus-near stage of decomposition.

Methods

In this study, the leaf litter decomposition was subjected to experimental N addition, and the biota communities (microbes and nematodes) in leaf litter habitats and the subsequent micro-food webs were evaluated in a subtropical plantation.

Results

After a 6-year N addition, the leaf litter microbial community composition showed little change, but the leaf litter microbial G⁺/G⁻ showed significant increases. N addition increased the relative abundance of leaf litter herbivores with less resistance and decreased the OP/H. The leaf litter communities in response to N addition were driven by changes in leaf litter pH, Mn, N/Mn and P/Mn ratios. N addition decreased the leaf litter βG and AP activities, and the EI and SI relative to control plots (no N addition). These shifts were primarily controlled by the leaf litter pH, C, N, Mn, N/Mn and P/Mn ratios.

Conclusion

These findings illustrate that, in leaf litter habitats, the nematode community responses to N addition are more sensitive than the microbial community, and the micro-food webs become less enriched and less structured in response to N addition at humus-near stage of decomposition. These findings can help to better predict terrestrial biogeochemical cycling under future global change scenarios.