Grazing Mammals Steer the Microbial Enzymes That Govern Soil Carbon

Deep in the Trans-Himalayan rangelands of Spiti, where yak, ibex, and wild ungulates have grazed for millennia, an invisible chemical economy is running beneath the surface. Soil microbes deploy suites of extracellular enzymes to break down organic matter, and the composition of that enzymatic arsenal determines how fast carbon is unlocked from the ground and released back into the atmosphere. A new study published in the journal Biogeochemistry by Shamik Roy and Sumanta Bagchi shows that large mammalian herbivores, long recognized as shapers of plant communities, also exert a profound and predictable influence on this subterranean enzyme economy. The findings suggest that the fate of soil carbon in grazed ecosystems is not written solely by plants and climate, but by a three-way negotiation among herbivores, plant litter quality, and the foraging strategies of microbial communities.

Large grazers are a planetary force. Their ranges once covered, and still cover, roughly forty percent of the terrestrial surface, and through defecation, urination, trampling, and selective feeding they have regulated biogeochemical cycles for thousands of years. Scientists have made considerable progress in understanding how grazing alters the quantity and chemistry of organic matter entering the soil. What has remained far murkier is the downstream half of the story: how grazing reshapes the way microbes actually forage for nutrients once that organic matter is deposited. This gap matters because extracellular enzymes are the critical link between cellular-scale microbial demands and ecosystem-scale flows of carbon, nitrogen, and phosphorus. Enzymes secreted by bacteria and fungi into the soil solution cleave large polymers into small molecules that cells can assimilate, and which enzymes a community invests in determines whether carbon is efficiently incorporated into biomass or respired away as carbon dioxide.

To probe this hidden layer, the researchers capitalized on a rare asset in ecology: a fourteen-year-old long-term grazer-exclusion experiment in the Trans-Himalayan ecosystem. By comparing soils where large herbivores had been fenced out for over a decade with soils that continued to receive natural grazing pressure, they could isolate the signature of mammalian herbivory on microbial enzyme deployment. They measured the activities of seven enzymes involved in acquiring carbon, nitrogen, and phosphorus from organic substrates, tracking them across the growing season. The results revealed a striking temporal architecture. Rather than rising and falling in unison, the seven enzymes peaked in different months, in an asynchronous pattern, indicating that microbial nutrient demand shifts through the season and that no single snapshot can capture the functional state of the soil community.

The most dramatic effects emerged when the researchers examined how exclusion changed the enzymatic portfolio. Removing grazers shifted microbial investment from nitrogen acquisition in spring toward carbon and phosphorus acquisition in summer and autumn. Two enzymes told an especially vivid story. Peroxidase activity, a marker of oxidative depolymerization of tough, recalcitrant carbon compounds, increased by 124.7 percent in grazer-excluded soils. Beta-glucosidase, which cleaves simple cellulose-derived sugars, rose by a more modest 16.7 percent. In other words, when large herbivores vanished from the landscape, the microbial community responded by ramping up its machinery for attacking chemically difficult carbon, not merely by digesting more of the easy material. About half of the variation in the overall enzyme portfolio could be explained by seasonal differences in grazer effects, underscoring how strongly the animal presence is woven into the seasonal rhythm of soil chemistry.

Exclusion did more than change average enzyme activities; it changed the spread. Grazer-excluded soils showed greater variability in their enzyme portfolios, meaning microbes had to forage across a larger portion of the available functional space to meet their demands. The authors interpret this as a sign of deteriorating foraging conditions. When resources are chemically diverse, patchy, and recalcitrant, microbes cannot rely on a small set of specialized enzymes and must instead maintain a broader, more expensive toolkit. This has energetic consequences. Producing a wide array of extracellular enzymes diverts resources away from growth, and a community forced into broad foraging is typically one that processes carbon less efficiently.

Why would removing grazers degrade the quality of the raw material reaching the soil? The structural equation models built by the team pointed to a chain of causation running through plant tissue chemistry. Grazer exclusion led to an 18 percent increase in acid-unhydrolysable carbon, a chemically resistant fraction of plant biomass that resists breakdown. Grazing, it turns out, acts as a quality filter on litter: herbivores preferentially consume palatable tissue, stimulate regrowth of nutrient-rich vegetation, and deposit waste that is comparatively easy for microbes to decompose. When that pressure is lifted, vegetation shifts toward more lignified, recalcitrant biomass, and the organic matter entering the soil becomes tougher fare. Consistent with patterns documented in other ecosystems, this decline in substrate quality pushed the microbial community to invest more heavily in generic depolymerizing enzymes, which crudely break down complex polymers, relative to specialized enzymes that release readily assimilable end-products.

This shift carries a potentially significant climatic implication. Greater investment in generic depolymerizers may reduce microbial carbon use efficiency, the proportion of consumed carbon that microbes convert into their own biomass rather than respiring as carbon dioxide. Lower carbon use efficiency means more of the soil’s organic carbon is mineralized and lost to the atmosphere rather than stabilized in microbial residues, which are a major route by which carbon persists in soils. In this way, the presence or absence of large herbivores could ripple upward from enzyme kinetics to the carbon balance of entire rangeland ecosystems. The study frames this within the emerging field of zoogeochemistry, which treats animals as active agents in elemental cycling rather than passive participants, and connects to the concept of the carbon pump, the suite of processes that move carbon into long-lived soil pools.

Crucially, the team did not rely on field correlations alone. In a second line of evidence, laboratory incubations demonstrated that soil enzymes are inducible or repressible in response to experimental manipulation of biomass quality. When the researchers altered the quality of organic inputs under controlled conditions, microbial enzyme deployment shifted in ways that mirrored the field observations. This convergence is what elevates the study from description to mechanism. It shows that microbial responses are not idiosyncratic accidents of a particular Himalayan valley but predictable, generalizable reactions to substrate quality, reproducible across spatial scales from a laboratory flask to a whole ecosystem. The same regulatory logic that governs enzyme induction in a jar appears to govern enzyme portfolios across hundreds of square kilometers of rangeland.

The practical implications reach into one of the most active arenas of conservation science: rewilding and natural climate solutions. As governments and organizations increasingly promote the restoration of large mammal populations as a strategy for climate mitigation and biodiversity recovery, questions about the consequences for soil carbon have loomed large. This study suggests that fostering healthy grazer populations may help maintain microbial functions that favor efficient carbon processing, by sustaining the quality of organic inputs and keeping microbial foraging focused and specialized. Conversely, simply excluding animals from rangelands, a common conservation and land-management assumption, may inadvertently push soil communities toward less efficient carbon processing. The authors argue that explicitly incorporating microbial function into the design of rewilding and restoration programs could enhance the scope and efficacy of nature-based climate strategies.

What makes the work resonant beyond its Himalayan field site is the reframing it demands. Soil carbon models have traditionally treated herbivores, if at all, as modifiers of plant biomass, and have treated microbial enzymes as a black box responding only to temperature and moisture. Roy and Bagchi’s results show that the enzymatic machinery itself is a responsive, seasonally structured, herbivore-sensitive system, and that roughly half of its variation tracks the seasonal interplay between animals and their forage. With large grazers having shaped biogeochemical cycles across vast portions of the planet for millennia, understanding how their presence tunes the molecular tools of decomposition may prove essential for predicting how rangeland carbon stocks will respond to the ongoing global upheaval in mammal populations, from catastrophic declines of wild herbivores to ambitious rewilding programs on multiple continents.

Subject of Research: Effects of large mammalian herbivores on microbial extracellular enzyme deployment and soil carbon cycling

Article Title: Large mammalian herbivores influence the deployment of microbial extracellular enzymes to control soil carbon cycling

Article References: Roy, S., & Bagchi, S. (2026). Large mammalian herbivores influence the deployment of microbial extracellular enzymes to control soil carbon cycling. Biogeochemistry, 169(5), Article 62. https://doi.org/10.1007/s10533-026-01378-0

Image Credits: AI Generated

DOI: 10.1007/s10533-026-01378-0

Keywords: soil carbon, extracellular enzymes, large herbivores, grazing, microbial ecology, zoogeochemistry, Trans-Himalaya, rewilding, carbon use efficiency, biogeochemistry, natural climate solutions, enzyme stoichiometry