Microbial necromass under global change and implications for soil organic matter

Abstract

Microbial necromass is an important source and component of soil organic matter (SOM), especially within the most stable pools. Global change factors such as anthropogenic nitrogen (N), phosphorus (P), and potassium (K) inputs, climate warming, elevated atmospheric carbon dioxide (eCO 2 ), and periodic precipitation reduction (drought) strongly affect soil microorganisms and consequently, influence microbial necromass formation. The impacts of these global change factors on microbial necromass are poorly understood despite their critical role in the cycling and sequestration of soil carbon (C) and nutrients. Here, we conducted a meta-analysis to reveal general patterns of the effects of nutrient addition, warming, eCO 2 , and drought on amino sugars (biomarkers of microbial necromass) in soils under croplands, forests, and grasslands. Nitrogen addition combined with P and K increased the content of fungal (+21%), bacterial (+22%), and total amino sugars (+9%), consequently leading to increased SOM formation. Nitrogen addition alone increased solely bacterial necromass (+10%) because the decrease of N limitation stimulated bacterial more than fungal growth. Warming increased bacterial necromass, because bacteria have competitive advantages at high temperatures compared to fungi. Other global change factors (P and NP addition, eCO 2 , and drought) had minor effects on microbial necromass because of: (i) compensation of the impacts by opposite processes, and (ii) the short duration of experiments compared to the slow microbial necromass turnover. Future studies should focus on: (i) the stronger response of bacterial necromass to N addition and warming compared to that of fungi, and (ii) the increased microbial necromass contribution to SOM accumulation and stability under NPK fertilization, and thereby for negative feedback to climate warming.

Microbial life‐history strategies mediate microbial carbon pump efficacy in response to N management depending on stoichiometry of microbial demand

“…For instance, bacteria were shown to be favored in N enriched soils . This is consistent with N addition causing a decline in the microbial biomass C/N and fungi to bacteria ratios (F/B) via increasing soil N availability (Hu et al, 2023;Zhou et al, 2017). Therefore, under N addition, bacterial taxa with high relative abundance and rapid competition for resources to invest in growth may increase the proportion of Y-strategists within the soil community.…”

Arbuscular mycorrhiza convey significant plant carbon to a diverse hyphosphere microbial food web and mineral‐associated organic matter

“…Resources derived from hyphae can increase microbial biomass, activity, frequency of interactions, and the rate of organic matter transformations (Sokol et al ., 2022). Necromass from these microbial cells is also likely a significant source of SOM and may have formed part of the mineral‐associated C that we recovered from the soil heavy fraction (Fossum et al ., 2022; Sokol et al ., 2022; Hu et al ., 2023). Future studies that compare the AMF hyphosphere with and without its microbiome would be needed to quantify this contribution.…”

Chemoautotrophic sulphur oxidizers dominate microbial necromass carbon formation in coastal blue carbon ecosystems

“…In addition to MAOM, particulate organic matter (POM) containing plant-derived compounds is also a major part of stable C pool and may be precursors of MAOM with a short residence time (Angst et al, 2023;Lavallee et al, 2020). The efficient transformation of plant-derived C into more persistent microbially derived C increase the contribution of microbial necromass to the stable C pool, which was reported to be influenced by plant diversity (Bai & Cotrufo, 2022;Prommer et al, 2020;Zhu et al, 2020) and management strategies (Hu et al, 2023;Zhou et al, 2023). As native-vegetated coastal sediment microbiomes could facilitate the transformation of plant-derived C into microbially derived C, we propose that the native-vegetated coastal sediment microbiomes with high functional potentials of C, N and S cycling may promote the deposition of microbially derived C.…”

“…For instance, microbial necromass can account for more than 50% of stable soil organic C in agricultural, grassland and forest ecosystems (Liang et al, 2019;Wang, Qu, et al, 2021). The contribution of microbial necromass to stable C pool is determined by its recycling efficiency (Buckeridge et al, 2020), microbial death pathways (Camenzind et al, 2023), soil management (Hu et al, 2023;Luo et al, 2022;Zhou et al, 2023), soil depth (He, Fang, et al, 2022) and plant diversity (Bai & Cotrufo, 2022;Prommer et al, 2020;Zhu et al, 2020).…”