Long-term nitrogen addition enhances the energy fluxes of soil macro-food webs in young but not mature forest plantations

Abstract

Forest plantations play a critical role in restoring ecosystems and mitigating environmental change. While soil fauna communities represent a key driver of belowground ecosystem dynamics, we know little about the structure and functioning of soil macro-food webs in plantation systems and their responses to changes in environmental conditions. In this study, we used data from a 14-year nitrogen addition experiment in larch plantations to investigate how nitrogen addition influenced the diversity and energetic processes of soil macro-food webs in young and mature plantations. We found that low and high nitrogen addition treatments promoted biodiversity (by 23% and 19%), total biomass (56% and 31%), and energy fluxes (42.5% and 39.5%) of soil macro-food webs in young plantations, but they had no significant impacts on soil macro-food webs in mature plantations. The increase in total energy fluxes was partially mediated by nitrogen-induced changes in consumer biomass. Specifically, total energy fluxes increased with the biomass of secondary consumers (e.g., Carabidae), although the biomass of primary consumers (e.g., Lumbricidae) showed a weaker correlation. The age-specific responses may be understood from the varying nitrogen demands between young and mature plantations. Our findings highlight the need to integrate soil food web dynamics into forest management and underscore the necessity of adopting age-specific strategies in nitrogen management in plantations.

Graphical abstract

Keywords

forest age / nitrogen deposition / soil macro-food web / energy flux

Highlight

	● Nitrogen addition enhanced soil macro-food webs biodiversity, biomass, and energy fluxes in young but not mature larch plantations.
	● In young forests, soil fauna biomass increased more under low nitrogen addition, suggesting nitrogen availability limits soil fauna growth.
	● Energy flux in soil macro-food webs was driven by biomass distribution across trophic levels, with weak effects of taxonomic diversity.

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