Distinct roles of bacteria and fungi in mediating soil extracellular enzymes under long-term nitrogen deposition in temperate plantations

Soil microbes decompose soil organic matter by producing various extracellular enzymes, and also regulate soil carbon (C) and nutrient cycles. However, how shifts in soil microbial community under long-term nitrogen (N) deposition govern soil extracellular enzyme activities (EEAs) is not known. Here, we conducted a decade-long N fertilization experiment consisting of control, low-N (2 g N m- 2 year -1), medium-N (5 g N m- 2 year -1), and high -N (10 g N m- 2 year -1) treatments in a N-limited temperate plantation in northern China. The diversity and community composition of fungi and bacteria were determined with bacterial 16S rRNA genes and fungal in-ternal transcribed spacer genes sequencing. Soil EEAs involved in C, N, and phosphorus (P) cycles were also measured. The results showed that high-N addition increased fungal diversity and altered microbial community composition. In particular, rare fungal diversity and rare bacterial community composition were more sensitive to N addition. N addition improved beta-1,4-glucosidase (BG) and acid phosphatase (AP) activities by altering bacterial community composition, and inhibited leucine aminopeptidase (LAP) and polyphenolic oxidase (PPO) activities by affecting fungal functional groups. Specifically, shifts in bacterial community composition caused by N addition were reflected in the significant increase in the dominant class Thermoleophilia, which could be an indicator of secreted hydrolase involved in C and P cycles. Symbiotrophic fungi were more closely associated with LAP for acquiring N and PPO. Our data provide a novel view of the link between major extracellular en-zymes and specific microbial taxa under the background of N deposition.

Automated summary

Soil microbes decompose soil organic matter and regulate soil carbon and nutrient cycles. The effect of long-term nitrogen deposition on soil microbial community and extracellular enzyme activities was studied. Fungal diversity and composition were most affected by nitrogen addition, while bacterial community composition played a key role in enzyme activities.