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Activation Energy of Organic Matter Decomposition in Soil and Consequences of Global Warming
No full textABSTRACT The activation energy ( E a ) is the minimum energy necessary for (bio)chemical reactions acting as an energy barrier and defining reaction rates, for example, organic matter transformations in soil. Based on the E a database of (i) oxidative and hydrolytic enzyme activities, (ii) organic matter mineralization and CO 2 production, (iii) heat release during soil incubation, as well as (iv) thermal oxidation of soil organic matter (SOM), we assess the E a of SOM transformation processes. After a short description of the four approaches to assess these E a values—all based on the Arrhenius equation—we present the E a of chemical oxidation (79 kJ mol −1 , based on thermal oxidation), microbial mineralization (67 kJ mol −1 , CO 2 production), microbial decomposition (40 kJ mol −1 , heat release), and enzyme‐catalyzed hydrolysis of polymers and cleavage of mineral ions of nutrients (33 kJ mol −1 , enzyme driven reactions) from SOM. The catalyzing effects of hydrolytic and oxidative enzymes reduce E a of SOM decomposition by more than twice that of its chemical oxidation. The E a of enzymatic cleavage of mineral ions of N, P, and S from their organic compounds is 9 kJ mol −1 lower (corresponding to 40‐fold faster reactions) than the hydrolysis of N‐, P‐, and S‐free organic polymers. In soil, where organic compounds are physically protected and enzymes are partly deactivated, microbial mineralization is ~140‐fold faster compared to its pure chemical oxidation. Because processes with higher E a are more sensitive to temperature increase, global warming will accelerate the decomposition of stable organic compounds and boost the C cycle much stronger than the cycling of nutrients: N, P, and S. Consequently, the stoichiometry of microbially utilized compounds in warmer conditions will shift toward organic pools with higher C/N ratios. This will decouple the cycling of C and nutrients: N, P, and S. Overall, the E a of (bio)chemical transformations of organic matter in soil enables to assess process rates and the inherent stability of SOM pools, as well as their responses to global warming.National Key Research and Development Program of China https://doi.org/10.13039/50110001216
Microbial composition in saline and alkaline soils regulates plant growth with P-solubilizing bacteria
No full textClimate warming and agronomic practice interactively alter soil carbon stock in dry farmland in China
No full textAbstract Understanding drivers of soil organic carbon (SOC) dynamics and stocks is critical for carbon (C) neutrality in Earth’s extensive dryland croplands. Here, we analyzed 721 soil samples across northern China and revealed divergent regional dynamics of SOC stocks in topsoil (0–20 cm) over three decades. Agricultural intensification in northern China, marked by tripled productivity via strategic N-fertilization and policy-driven increases in straw return, created a major C sink (+3.1 Mg C ha −1 ), offsetting ~1.5% of China’s average annual emissions. Conversely, Northeast China experienced SOC depletion (−3.9 Mg C ha −1 ; ~12% loss since 1980s) driven by warming-enhanced decomposition of organic matter. Encouragingly, an annual straw return in excess of 270 kg C ha −1 could offset SOC losses in the face of future warming. Therefore, it is imperative to implement effective soil management practices and adaptation strategies to bolster soil resilience and health, as continued climate warming may undermine soil carbon sequestration
Glucoproteins in particulate and mineral-associated organic matter pools during grassland restoration
No full texthttp://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of Chinahttp://dx.doi.org/10.13039/501100006769 Russian Science Foundationhttp://dx.doi.org/10.13039/501100018647 RUDN Universityhttp://dx.doi.org/10.13039/501100002858 China Postdoctoral Science Foundatio
Trade-off between organic and inorganic carbon in soils under alfalfa-grass-cropland rotation
No full texthttp://dx.doi.org/10.13039/501100001659 Deutsche Forschungsgemeinschafthttp://dx.doi.org/10.13039/501100022230 Deanship of Scientific Research, Princess Nourah Bint Abdulrahman Universityhttp://dx.doi.org/10.13039/501100018647 RUDN Universityhttp://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of Chin
Effects of reindeer grazing on thermal stability of organic matter in topsoil in Arctic tundra
No full textVegetation succession on Arctic sand dunes controls organic matter accumulation and CO2 efflux from soil
No full texthttp://dx.doi.org/10.13039/100020690 Government of Tyumen Oblasthttp://dx.doi.org/10.13039/501100018647 RUDN Universityhttp://dx.doi.org/10.13039/501100006769 Russian Science Foundatio
Low carbon availability in paleosols nonlinearly attenuates temperature sensitivity of soil organic matter decomposition
Full text linkTemperature sensitivity (Q(10)) of soil organic matter (SOM) decomposition is an important parameter in models of the global carbon (C) cycle. Previous studies have suggested that substrate quality controls the intrinsic Q(10), whereas environmental factors can impose large constraints. For example, physical protection of SOM and its association with minerals attenuate the apparent Q(10) through reducing substrate availability and accessibility ([S]). The magnitude of this dampening effect, however, has never been quantified. We simulated theoretical Q(10) changes across a wide range of [S] and found that the relationship between Q(10) and the log(10)-transformed [S] followed a logistic rather than a linear function. Based on the unique Holocene paleosol chronosequence (7 soils from ca. 500 to 6900 years old), we demonstrated that the Q(10) decreased nonlinearly with soil age up to 1150 years, beyond which Q(10) remained stable. Hierarchical partitioning analysis indicated that an integrated C availability index, derived from principal component analysis of DOC content and parameters reflecting physical protection and mineral association, was the main explanatory variable for the nonlinear decrease of Q(10) with soil age. Microbial inoculation and C-13-labelled glucose addition showed that low C availability induced by physical protection and minerals association attenuated Q(10) along the chronosequence. A separate soil incubation experiment indicated that Q(10) increased exponentially with activation energy (E-a) in the modern soil, suggesting that SOM chemical complexity regulates Q(10) only when C availability is high. In conclusion, organic matter availability strongly decreased with soil age, whereas Michelis-Menten kinetics defines the Q(10) response depending on C availability, but Arrhenius equation describes the effects of increasing substrate complexity
Nitrogen fertilizer builds soil organic carbon under straw return mainly via microbial necromass formation
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