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

Abstract

Nitrogen (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 highthroughput 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.

Selection of r-K strategies by soil bacterial communities in response to grassland degradation

“…In the present study, we investigated bacterial community dynamics at phylum level in degraded grasslands. Previous studies have reported that different soil bacterial phyla display different responses in abundance in grasslands following shifts in nutrient conditions (Zeng et al, 2015;Dong, Shi, et al, 2021).…”

“…Previous studies that have investigated the influence of soil nutrient loss on soil microbial community structure under grassland degradation have concluded that soil nutrients regulate microbial biomass, diversity, and community composition in grasslands (Hu et al, 2014;Dong, Shi, et al, 2021); however, it is not clear how microbial community assembly in turn respond to grassland degradation. Some studies have suggested that the reason for the microbial community dynamics in degraded grasslands are associated with different responses of different phyla to soil nutrient loss and decrease in available substrate (Delgado-Baquerizo et al, 2016; Dong, Shi, et al, 2021); furthermore, biotic interactions such as facilitation, niche complementation, and competition, as major drivers of community assembly (Dong et al, 2019), influence the responses of microbial communities to modulate resource-use efficiency (Yu, Polz, et al, 2019).…”

“…Such studies highlight the importance of microbial life strategies in facilitating responses to environmental change. Therefore, considering the underlying mechanisms via which microbial communities respond to grassland degradation remain poorly understood (Luo et al, 2020;Dong, Shi, et al, 2021;Ren et al, 2021), more studies should explore the response strategies of communities and the dominant community assembly processes in the course of grassland degradation to elucidate the responses of microbial communities across environments with different levels of degradation (Yang et al, 2013). The results of such studies could facilitate further studies as well as grassland ecosystem management activities.…”

Shift in soil bacterial communities from K‐ to r‐strategists facilitates adaptation to grassland degradation

“…In addition, soil pH has strong effects on microorganisms, determining soil biological activity and imposing selection pressure on certain bacterial taxa, thereby regulating community composition (Fan et al, 2018; B. Ren et al, 2018; Zhalnina et al, 2015). Previous studies have highlighted the roles of environmental factors in regulating microbial biomass, diversity, and soil microbial community structure in grassland ecosystem (C. Dong, Shi, et al, 2021; Y. Hu et al, 2014; Widdig et al, 2020); however, it is not clear how microbial community assembly specifically responds to grassland degradation.…”

“…Ren et al, 2018;Zhalnina et al, 2015). Previous studies have highlighted the roles of environmental factors in regulating microbial biomass, diversity, and soil microbial community structure in grassland ecosystem (C. Dong, Shi, et al, 2021;Y. Hu et al, 2014;Widdig et al, 2020); however, it is not clear how microbial community assembly specifically responds to grassland degradation.…”