Quantitative assessment of microbial necromass contribution to soil organic matter

Abstract

Soil carbon transformation and sequestration have received significant interest in recent years due to a growing need for quantitating its role in mitigating climate change. Even though our understanding of the nature of soil organic matter has recently been substantially revised, fundamental uncertainty remains about the quantitative importance of microbial necromass as part of persistent organic matter. Addressing this uncertainty has been hampered by the absence of quantitative assessments whether microbial matter makes up the majority of the persistent carbon in soil. Direct quantitation of microbial necromass in soil is very challenging because of an overlapping molecular signature with nonmicrobial organic carbon. Here, we use a comprehensive analysis of existing biomarker amino sugar data published between 1996 and 2018, combined with novel appropriation using an ecological systems approach, elemental carbon–nitrogen stoichiometry, and biomarker scaling, to demonstrate a suit of strategies for quantitating the contribution of microbe‐derived carbon to the topsoil organic carbon reservoir in global temperate agricultural, grassland, and forest ecosystems. We show that microbial necromass can make up more than half of soil organic carbon. Hence, we suggest that next‐generation field management requires promoting microbial biomass formation and necromass preservation to maintain healthy soils, ecosystems, and climate. Our analyses have important implications for improving current climate and carbon models, and helping develop management practices and policies.

Soil carbon loss with warming: New evidence from carbon‐degrading enzymes

“…Indeed, soil C stocks are determined by the balance between plant litter that is decomposed and transformed into SOM versus the amount that is mineralized (Cotrufo et al, 2015;Jenkinson, 1990;Kallenbach et al, 2016;Kleber & Johnson, 2010). Thus, other soil processes, for example, warming-induced changes in litter input, root exudation, the formation of stable SOM from microbial products and C leaching could also contribute to changes in soil C storage with warming (Liang, Amelung, Lehmann, & Kästner, 2019;Pausch & Kuzyakov, 2018), while those process are not considered in this meta-analysis. Moreover, even though the enzymes considered in this meta-analysis can indirectly affect the decomposition of bulk soil C, they are mostly involved in the decomposition of plant litter and particulate SOM (Lavallee, Soong, & Cotrufo, 2019).…”

Dark microbial CO2 fixation in temperate forest soils increases with CO2 concentration

“…Although the rates of dark microbial fixation in the temperate forest soils studied here were small compared to the respiration rates, our findings indicate that organic matter formed by microorganisms from CO 2 contributes to the soil organic matter pool. Dead microbial biomass (microbial necromass) is a very important source of soil organic matter since it is relatively stable in soil compared to plant detritus (Liang, Amelung, Lehmann, & Kästner, 2019;Miltner, Bombach, Schmidt-Brücken, & Kästner, 2012;Schimel & Schaeffer, 2012). Thus, C that enters the soil through the microbial biomass pool likely remains much longer in soil than C that enters the soil as plant detritus and mostly leaves the soil again in the form of CO 2 after only a few years (Sierra, Hoyt, He, & Trumbore, 2018).…”

The soil microbial carbon pump: From conceptual insights to empirical assessments

“…These differences would introduce uncertainties when the conversion factors were used to assess microbial necromass. However, the stability of conversion factors has been clarified by Appuhn and Joergensen (2006), and their applications and values have been recognized and acknowledged in recent years (Joergensen, 2018;Liang et al, 2019).…”