Abstract
Soil fungi play critical roles in ecosystem processes and are sensitive to global changes. Elevated atmospheric nitrogen (N) deposition has been well documented to impact on fungal diversity and community composition, but how the fungal community assembly responds to the duration effects of experimental N addition remains poorly understood. Here, we aimed to investigate the soil fungal community variations and assembly processes under short- (2 years) versus long-term (13 years) exogenous N addition (∼100 kg N ha–1 yr–1) in a N-rich tropical forest of China. We observed that short-term N addition significantly increased fungal taxonomic and phylogenetic α-diversity and shifted fungal community composition with significant increases in the relative abundance of Ascomycota and decreases in that of Basidiomycota. Short-term N addition also significantly increased the relative abundance of saprotrophic fungi and decreased that of ectomycorrhizal fungi. However, unremarkable effects on these indices were found under long-term N addition. The variations of fungal α-diversity, community composition, and the relative abundance of major phyla, genera, and functional guilds were mainly correlated with soil pH and NO3––N concentration, and these correlations were much stronger under short-term than long-term N addition. The results of null, neutral community models and the normalized stochasticity ratio (NST) index consistently revealed that stochastic processes played predominant roles in the assembly of soil fungal community in the tropical forest, and the relative contribution of stochastic processes was significantly increased by short-term N addition. These findings highlighted that the responses of fungal community to N addition were duration-dependent, i.e., fungal community structure and assembly would be sensitive to short-term N addition but become adaptive to long-term N enrichment.
Highlights
As one of the major global change drivers, reactive nitrogen (N) from fertilizer application and fossil fuel combustion has increased by 120% over the past few decades (Galloway et al, 2004) and is expected to increase or at least not decrease rapidly in the near future (Yu et al, 2019; Wen et al, 2020)
At the functional guild level, approximately 43.4% sequences were categorized into EcM fungi, and the shortterm N addition significantly decreased the relative abundance of this group by 26.13% (Supplementary Figure 2A)
Only 3.5% of sequences were classified as saprotrophic fungi, and the short-term N addition significantly increased the relative abundance of this group (Supplementary Figure 2B)
Summary
As one of the major global change drivers, reactive nitrogen (N) from fertilizer application and fossil fuel combustion has increased by 120% over the past few decades (Galloway et al, 2004) and is expected to increase or at least not decrease rapidly in the near future (Yu et al, 2019; Wen et al, 2020). Previous studies suggested that experimental N addition or fertilization generally shifts the fungal community composition directly by affecting their nutrient supply and indirectly by altering edaphic conditions (Yang Y. et al, 2020; Cui et al, 2021). The relative abundance and diversity of mycorrhizal fungi decreased, whereas that of saprotrophic fungi increased with experimental N addition (Weese et al, 2015; Morrison et al, 2016), resulting in the shifts of community composition. Knowledge of how soil fungal communities respond to N addition is critical for predicting ecosystem responses and for managing plant–fungi interactions under the context of global environmental changes and maintaining sustainable agriculture and forestry (Bissett et al, 2013; Dessaux et al, 2016)
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