Linking nitrogen- and straw-sensitive indicator species and their co-occurrences to priming effect in agricultural soil exposed to long-term nitrogen fertilization

The increasing input of nitrogen (N) fertilizers has a considerable impact on agricultural soil carbon (C) cycling due to its influence on soil microbial abundance and assemblages. However, the microbial mechanism underlying the response of straw-induced priming effect to long-term N application remains an open question. Here, using soils with three N fertilization levels (0, 300, and 570 kg N ha(-1) y(-1)) from a long-term experimental site, we established a 40-day microcosm experiment to investigate the priming effect of straw addition on SOM miner-alization and the associated microbial activity and community composition. We found that long-term N appli-cation significantly inhibited soil respiration while increasing straw-induced priming effect. The soil microbial biomass (including bacterial and fungal abundance) decreased with increasing N levels, accompanied by decreased bacterial alpha-diversity and altered beta-diversity. In addition, the N fertilization level significantly influ-enced bacterial and fungal indicator species that were sensitive to straw addition (siOTUs) and long-term N fertilization (niOTUs), as well as their co-occurrence patterns. In the first three days of straw decomposition, long-term N fertilization decreased the oligotroph-to-copiotroph ratio of bacterial siOTUs. In contrast, long-term N fertilization increased this ratio on days 20 and 40, along with facilitated microbial investment in extracellular enzymes and microbial N demand. This caused a stronger N mining process and consequently enhanced the priming effect in soil exposed to long-term N fertilization at the later stage of incubation. Linking indicator species analysis with priming effect, these results advance our understanding of the complex C cycling in agricultural soils undergoing long-term nitrogen management.

Automated summary

Long-term nitrogen fertilization inhibits soil respiration and increases straw-induced priming effect, decreasing microbial biomass and altering microbial diversity and co-occurrence patterns. The oligotroph-to-copiotroph ratio of bacterial indicator species decreases in the early stage of straw decomposition but increases in the later stage, leading to enhanced microbial investment in extracellular enzymes and nitrogen demand, and consequently stronger nitrogen mining process and priming effect.