Nitrogen deposition suppresses fungal biomass and oxidase activity in faeces of the millipede Spirobolus formosae in a temperate forest

Abstract

Atmospheric nitrogen (N) deposition has increased dramatically since the industrial revolution due to humanactivities. Interrestrial ecosystems, excess nitrogeninputs cangreatly affectsoil chemical properties, plant growth, and activities of soil microbes and fauna. Millipedes can fragment and consume large quantities of litter, and they regulate nutrient cycling and affect soil fertility through excretion of faeces. Many soil fauna graze on the faeces of millipedes as a part of the soil food web. The decomposition and stabilization of these millipede faeces are especially important in soil carbon dynamics and nutrient cycling, and these processes rely heavily upon microbial activity. However, very few studies have investigated how microbial community structure and oxidase activity of millipede faeces respond to climate change, especially N deposition. Therefore, we designed a microcosm study to investigate this question, which included two treatments, N addition treatment and control (without N addition). We found that: (i) microbial community structure in millipede faeces was altered and the biomass of fungi and actinomycetes in faecal pellets were significantly reduced after N addition, but bacteria still dominated in millipede faeces after N addition, (ii) oxidase activity was suppressed in response to N addition, and (iii) microbial community structure and oxidase activities were significantly correlated to organic carbon and dissolved total nitrogen of faeces. All these changes suggest that millipede excretion activities under nitrogen deposition contribute to carbon stabilization and reduction in greenhouse gas emission owing to the significant role of fungi and associated oxidase in carbon mineralization. It is noteworthy to pay more attention to the function of saprotrophic invertebrates in future N deposition studies.