Temperature and pH mediate stoichiometric constraints of organically derived soil nutrients

• Published in: Global change biology Vol. 28; no. 4; pp. 1630 - 1642
• Main Authors: Souza, Ligia F. T., Billings, Sharon A.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-02-2022; John Wiley and Sons Inc
• Subjects: Acid phosphatase; Availability; Bioavailability; Biosphere; Carbon; Climate change; Constraint modelling; Decay; Ecosystem; Environmental conditions; Enzymatic activity; Enzyme activity; Enzyme kinetics; Enzymes; flow ratios; global change; Hydrogen-Ion Concentration; Kinetics; Microorganisms; Mineral nutrients; Nutrient availability; Nutrients; N‐acetyl‐glucosaminidase; Organic matter; Organic soils; pH effects; Phosphatase; Primary; Primary s; Ratios; Resources; Sensitivity; Soil; Soil - chemistry; soil enzyme activity; Soil Microbiology; Soil nutrients; Soil organic matter; Soil pH; Soil temperature; Soils; Stoichiometry; Temperature; Temperature effects; Terrestrial environments; warming; β‐glucosidase; N-acetyl-glucosaminidase; global change; soil enzyme activity; soil pH; warming; acid phosphatase; flow ratios; β-glucosidase; nutrient availability
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.15985

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.
We explored the degree to which increases in temperature by the end of the century may change the stoichiometry of bioavailable resources from soil exoenzyme activity. Spatial representation of enzyme kinetics revealed the power of soil pH as a regulator of the relative bioavailability of C, N, and P as decay proceeds. The work, thus, offers proof of concept of the importance of quantifying intrinsic biochemical responses of organic matter decay to constrain model projections of future bioavailable soil, and the potential consequences for terrestrial productivity and feedbacks to climate change.