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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.

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Global development has been heavily reliant on the overexploitation of natural resources since the Industrial Revolution. With the extensive use of fossil fuels, deforestation, and other forms of land-use change, anthropogenic activities have contributed to the ever-increasing concentrations of greenhouse gases (GHGs) in the atmosphere, causing global climate change. In response to the worsening global climate change, achieving carbon neutrality by 2050 is the most pressing task on the planet. To this end, it is of utmost importance and a significant challenge to reform the current production systems to reduce GHG emissions and promote the capture of CO 2 from the atmosphere. Herein, we review innovative technologies that offer solutions achieving carbon (C) neutrality and sustainable development, including those for renewable energy production, food system transformation, waste valorization, C sink conservation, and C-negative manufacturing. The wealth of knowledge disseminated in this review could inspire the global community and drive the further development of innovative technologies to mitigate climate change and sustainably support human activities.

Carbon stable isotope fractionation of tetrachloroethene (PCE) during reductive dechlorination by whole cells and crude extracts of Sulfurospirillum multivorans and Desulfitobacterium sp. strain PCE-S and the abiotic reaction with cyanocobalamin (vitamin B 12 ) was studied. Fractionation was largest during the reaction with cyanocobalamin with ␣C ‫؍‬ 1.0132. Stable isotope fractionation was lower but still in a similar order of magnitude for Desulfitobacterium sp. PCE-S (␣C ‫؍‬ 1.0052 to 1.0098). The isotope fractionation of PCE during dehalogenation by S. multivorans was lower by 1 order of magnitude (␣C ‫؍‬ 1.00042 to 1.0017). Additionally, an increase in isotope fractionation was observed with a decrease in cell integrity for both strains. For Desulfitobacterium sp. strain PCE-S, the carbon stable isotope fractionation factors were 1.0052 and 1.0089 for growing cells and crude extracts, respectively. For S. multivorans, ␣C values were 1.00042, 1.00097, and 1.0017 for growing cells, crude extracts, and the purified PCE reductive dehalogenase, respectively. For the field application of stable isotope fractionation, care is needed as fractionation may vary by more than an order of magnitude depending on the bacteria present, responsible for degradation.The chlorinated ethenes tetrachloroethene (PCE) and trichloroethene (TCE) have been used as solvents in the drycleaning industry and as metal degreasing agents and are among the most common groundwater contaminants due to spillage and leakage (12). The assessment of in situ biodegradation of groundwater contaminants is difficult since a decrease in the concentration can be a result of many factors, including dilution, sorption, and biological conversion. Monitoring and assessment of in situ microbial degradation activities of contaminants at polluted sites is therefore a major challenge. In the last few years, the application of stable isotope techniques has been suggested for assessment of the in situ biodegradation of contaminants (for a review, see references 17 and 33).Stable isotope fractionation of PCE and TCE has been observed under field conditions in contaminated aquifers as well as in laboratory studies by mixed microbial cultures and microcosms (2, 9, 39, 40); however, the factors affecting the isotope fractionation have not yet been studied systematically.Several factors may influence the degree of stable isotope fractionation, including biodegrading microorganisms, properties of the dehalogenating enzymes, and the reaction mechanism. Cobalamins are important cofactors of reductive dehalogenases in organisms capable of dehalorespiration (8,10,15,20,25,26). The microbial dehalogenation by cobalamin-containing dehalogenases has been proposed to proceed by alkylating a superreduced corrinoid containing a Co(I) species at the reactive site with the chloroethene (26). The chemical mechanism of the reductive dehalogenation of chlorinated ethenes catalyzed by cobalamin has been the subject of previous studies and has been suggested to occur via a single elect...