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Abstract Extracellular enzymes play a key role in microbe‐mediated organic matter decomposition in soils, and the efficiency of these enzymes in substrate decomposition depends on their mobility and specific activity in soils. In this work, we explored the influence of biochar adsorption on extracellular enzyme activity across a spectrum of environmental conditions, from simple to complex. Batch adsorption results showed that biochar adsorption of two hydrolytic enzymes—α‐amylase and amyloglucosidase (AMG)—similarly decreases with pH and follows the Langmuir isotherm, suggesting electrostatic interaction between them. Activity of AMG and alkaline phosphatase (ALP), which belong to carbon and phosphorus cycling enzymes, was measured using a novel calorimetric method. The technique demonstrated advantages over conventional enzyme assays, such as in situ real‐time measurement of reaction rate and the ability to identify potential interferences. The technique enabled the measurement of specific activity of biochar‐adsorbed AMG, which ranged from 10% to 90% of that of free AMG. The effect of substrate adsorption on activity measurement was demonstrated through the examination of two substrates for ALP, which suggested the use of effective substrate concentration (instead of nominal concentration) in calculating enzyme activity kinetics. Soil column experiments showed that biochar amendment can affect the activity of AMG in starch hydrolysis through changing the mobility of AMG (and accessibility to substrate) and its specific activity. Results from this work improve our understanding of the effects of biochar adsorption on enzyme activity and suggest the need to appropriately interpret enzyme activity data and account for confounding processes.
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Temperature and pH mediate stoichiometric constraints of organically derived soil nutrients
Abstract It remains unclear how warming will affect resource flows during soil organic matter (SOM) decomposition, in part due to uncertainty in how exoenzymes produced by microbes and roots will function. Rising temperatures can enhance the activity of most exoenzymes, but soil pH can impose limitations on their catalytic efficiency. The effects of temperature and pH on enzyme activity are often examined in environmental samples, but purified enzyme kinetics reveal fundamental attributes of enzymes’ intrinsic temperature responses and how relative release of decay‐liberated resources (their flow ratios) can change with environmental conditions. In this paper, we illuminate the principle that fundamental, biochemical limitations on SOM release of C, N, and P during decay, and differential exoenzymes’ responses to the environment, can exert biosphere‐scale significance on the stoichiometry of bioavailable soil resources. To that end, we combined previously published intrinsic temperature sensitivities of two hydrolytic enzymes that release C and N during decay with a novel data set characterizing the kinetics of a P‐releasing enzyme (acid phosphatase) across an ecologically relevant pH gradient. We use these data to estimate potential change in the flow ratios derived from these three enzymes’ activities (C:N, C:P, and N:P) at the global scale by the end of the century, based on temperature projections and soil pH distribution. Our results highlight how the temperature sensitivity of these hydrolytic enzymes and the influence of pH on that sensitivity can govern the relative availability of bioavailable resources derived from these enzymes. The work illuminates the utility of weaving well‐defined kinetic constraints of microbes’ exoenzymes into models that incorporate changing SOM inputs and composition, nutrient availability, and microbial functioning into their efforts to project terrestrial ecosystem functioning in a changing climate.
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- Award ID(s):
- 1656006
- PAR ID:
- 10372348
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 28
- Issue:
- 4
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 1630-1642
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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