Elevated temperature shifts soil N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification across global terrestrial ecosystems

Abstract

We assessed the response of soil microbial nitrogen (N) cycling and associated functional genes to elevated temperature at the global scale. A meta-analysis of 1,270 observations from 134 publications indicated that elevated temperature decreased soil microbial biomass N and increased N mineralization rates, both in the presence and absence of plants. These findings infer that elevated temperature drives microbially mediated N cycling processes from dominance by anabolic to catabolic reaction processes. Elevated temperature increased soil nitrification and denitrification rates, leading to an increase in N 2 O emissions of up to 227%, whether plants were present or not. Rates of N mineralization, denitrification and N 2 O emission demonstrated significant positive relationships with rates of CO 2 emissions under elevated temperatures, suggesting that microbial N cycling processes were associated with enhanced microbial carbon (C) metabolism due to soil warming. The response in the abundance of relevant genes to elevated temperature was not always consistent with changes in N cycling processes. While elevated temperature increased the abundances of the nirS gene with plants and nosZ genes without plants, there was no effect on the abundances of the ammonia-oxidizing archaea amoA gene, ammonia-oxidizing bacteria amoA and nirK genes. This study provides the first global-scale assessment demonstrating that elevated temperature shifts N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification in terrestrial ecosystems. These findings infer that elevated temperatures have a profound impact on global N cycling processes with implications of a positive feedback to global climate and emphasize the close linkage between soil microbial C and N cycling.

Warming leads to more closed nitrogen cycling in nitrogen‐rich tropical forests

“…The decline in microbial biomass N may derive from the inhibited construction of microbial skeletons due to low soil moisture (Figure S2) and labile carbon (Fang et al., 2020) under warming. The possibly depressed microbial N immobilization (Dai et al., 2020) and/or microbial N fixation (Sorensen et al., 2012) under warming could be also important reasons for the decreased microbial biomass N. Third, mycorrhizal contribution to N supply can be another important source for plants in ecosystems when N is depleted. Warming decreased AMF abundance at our site dominated by AMF species, indicating that the mycorrhizal contribution to N supply was likely restricted.…”

Early Spring Snowmelt and Summer Droughts Strongly Impair the Resilience of Key Microbial Communities in Subalpine Grassland Ecosystems

“…Determining the resilience including the resistance and recovery capabilities at subalpine grassland ecosystems is crucial to understand since these ecosystems are under drastic influence of global climatic changes which ultimately may disrupt their functioning and the linked ecosystem services (Berauer et al, 2019; Bernard et al, 2019; Schirpke et al, 2013; Wipf and Rixen, 2010; Vittoz et al, 2009). This work demonstrates the impact of successive droughts and early snowmelt climatic extremes on subalpine grassland ecosystem functioning focusing on nitrification and denitrification as model processes since these give valuable insights into overall N cycling (Chen et al, 2020; Dai et al, 2020).…”

“…Similarly, the weather extremes directly influencing the plant community may also impact the microbes (Bardgett et al, 2013; de Vries and Shade, 2013, Saccone et al, 2013). Earlier, summer droughts in subalpine grasslands are reported to increase leaf senescence while reducing plant productivity (Benot et al, 2014), as well as affecting N cycling-related microbial community and functions (Dai et al, 2020; Cantarel et al, 2012).…”

“…, respiration, decomposition) and specialized soil processes ( e.g. (de)nitrification), may respond differentially to various perturbations (Dai et al, 2020; Jusselme et al, 2016; Chaer et al, 2009; Wertz et al, 2007), we conducted our work both at broad and functional scales. Investigating the response of these grasslands is crucial since the variable impact of natural and manmade perturbations might have considerably influenced the nutrient cycling including that of N (Galloway et al, 2004), but also the involved microbial functional guilds.…”

“…First, we tested how total bacterial community (16S rRNA ) and related substrate-induced respiration (SIR) were influenced under droughts, snow removal and their cumulative impact and how they recovered from these stresses. Then we investigated the nitrogen (N) cycling (that is critical in ecosystem sustainability (Chen et al, 2020; Kuypers et al, 2018)) processes by determining the abundances (nitrifiers (nxrA, NS) , denitrifiers (nirK, nirS, nosZ) ) and activities (nitrification and denitrification enzyme activities - NEA and DEA, respectively) of the involved microbial communities, since they carry implications for plant productivity (loss of N - an important plant nutrient) and environment (N 2 O emissions-global warming) (Dai et al, 2020; Galloway et al, 2004).…”