Elevated temperature increases the accumulation of microbial necromass nitrogen in soil via increasing microbial turnover

Abstract

Microbial-derived nitrogen (N) is now recognized as an important source of soil organic N. However, the mechanisms that govern the production of microbial necromass N, its turnover, and stabilization in soil remain poorly understood. To assess the effects of elevated temperature on bacterial and fungal necromass N production, turnover, and stabilization, we incubated 15 N-labeled bacterial and fungal necromass under optimum moisture conditions at 10°C, 15°C, and 25°C. We developed a new 15 N tracing model to calculate the production and mineralization rates of necromass N. Our results showed that bacterial and fungal necromass N had similar mineralization rates, despite their contrasting chemistry. Most bacterial and fungal necromass 15 N was recovered in the mineral-associated organic matter fraction through microbial anabolism, suggesting that mineral association plays an important role in stabilizing necromass N in soil, independently of necromass chemistry. Elevated temperature significantly increased the accumulation of necromass N in soil, due to the relatively higher microbial turnover and production of necromass N with increasing temperature than the increases in microbial necromass N mineralization. In conclusion, we found elevated temperature may increase the contribution of microbial necromass N to mineral-stabilized soil organic N.

High temperatures enhance the microbial genetic potential to recycle C and N from necromass in high‐mountain soils

“…Therefore, despite overall C limitation, the fast-growing taxa prevalent at 35°C may have benefitted from a high N acquisition potential, enabling rapid growth fueled from necromass N. In line with this view, fast-growing microorganisms have been proposed to have a relatively high N demand (Fierer et al, 2007;. Wang et al (2020) (2020), mineralization of necromass N may also explain the strong increase in NH 4 + concentrations at 35°C in this study. As microbial biomass is rich in N (Xu et al, 2013), and the fast-growing high-temperature community is assumed to have a high energy demand, recycling of microbial necromass is expected to exacerbate the C limitation in the studied soil, which is supported by the decreased DOC:DON ratio at 35°C compared with 4°C as well as by the strong increase in inorganic N at 35°C (Table 1).…”

Large‐scale importance of microbial carbon use efficiency and necromass to soil organic carbon

“…This might explain the positive relationship between clay content and soil AS content (Table S5). However, very few studies have quantified the decomposition rate of microbial necromass and its temperature sensitivity (Wang, Wang, Cotrufo, et al, 2020; Wang, Wang, Pei, et al, 2020). Future research is needed to study this parameter and its response to environmental factors in order to better incorporate the microbial necromass pool in ESMs.…”

“…Results from models indicated that the contribution of microbially derived necromass C to the formation of SOC could be from 10% to 80% (Fan et al, 2021; Liang et al, 2019; Simpson et al, 2007). Moreover, this C has been found to have different structural components and different decomposition patterns from plant‐derived C (Simpson et al, 2007; Wang, Wang, Cotrufo, et al, 2020; Wang, Wang, Pei, et al, 2020). Therefore, the high contribution of microbial necromass to SOC could be due to their relative slow decomposition rate or the higher chance of mineral protection from decomposition by microorganisms or both (Hagerty et al, 2014; Li et al, 2018; Miltner et al, 2012; Wang, Wang, Cotrufo, et al, 2020; Wang, Wang, Pei, et al, 2020).…”

“…Moreover, this C has been found to have different structural components and different decomposition patterns from plant‐derived C (Simpson et al, 2007; Wang, Wang, Cotrufo, et al, 2020; Wang, Wang, Pei, et al, 2020). Therefore, the high contribution of microbial necromass to SOC could be due to their relative slow decomposition rate or the higher chance of mineral protection from decomposition by microorganisms or both (Hagerty et al, 2014; Li et al, 2018; Miltner et al, 2012; Wang, Wang, Cotrufo, et al, 2020; Wang, Wang, Pei, et al, 2020). In addition, microbial physiology parameters, such as biomass turnover rate, defined as the rate of microbial growth per unit microbial biomass, and C use efficiency (CUE) could indirectly impact SOC via their impacts on microbial biomass and necromass.…”

“…If microbial necromass was readily recycled into microbial biomass and decomposed, it would not contribute significantly to the stable SOM pool. However, recent studies suggest that the decomposition rate of microbial necromass could be quite low once it is protected by soil minerals and oxides (Wang, Wang, Cotrufo, et al, 2020; Wang, Wang, Pei, et al, 2020), making it necessary to model microbial necromass as a separate pool from plant‐derived SOC. Secondly, microbial CUE, defined as the proportion of substrate C that microorganisms assimilate for growth out of total uptake C, has been shown to be an important microbial physiology parameter to improve the performance of model prediction of SOC variations under global climate changes (Frey et al, 2013; Georgiou et al, 2017; Malik et al, 2018).…”