Divergent responses of the soil bacteria community to multi‐level nitrogen enrichment in temperate grasslands under different degrees of degradation

Abstract

AbstractNitrogen (N) enrichment has been reported to affect the soil bacteria community in natural temperate grasslands. However, it remains unknown how the bacteria community responds to N enrichment in degraded grasslands. Here, we established multi‐level N enrichment experiments in temperate grasslands under non‐degraded (ND), moderately degraded (MD), severely degraded (SD), and extremely degraded (ED) sites in northern China. The bacteria community was investigated by high‐throughput sequencing and linked to major abiotic and biotic factors. We found bacterial diversity was lower in ED grassland than the other grasslands, and community composition highly varied across the four degrees of degradation. Change in bacterial diversity was due to the different variations in dominant phyla, and soil phosphorus content contributed to the variation in community composition across grasslands under increasing degradation. In ND, MD, and SD grasslands, bacterial diversity was not significantly altered by N enrichment below 30 g‐N m−2 yr−1 but declined when N enrichment was greater than 30 g‐N m−2 yr−1. The bacterial diversity loss was associated with the decreased soil pH under N enrichment. However, in ED grassland, bacterial diversity decreased when N enrichment was below 30 g‐N m−2 yr−1 and remained unchanged when N enrichment was greater than 30 g‐N m−2 yr−1. Change in bacterial diversity was modulated by soil N availability. Besides, N enrichment shifted bacterial community composition via changing soil N availability. Our study identified bacterial diversity loss in ED grassland and differently nonlinear responses of bacterial diversity to multi‐level N enrichment in grasslands under different degrees of degradation.