Large mammalian herbivores and the paradox of soil carbon in grazing ecosystems: Role of microbial decomposers and their enzymes

Roy, Shamik ORCID: https://orcid.org/0000-0002-9916-5651 and Bagchi, Sumanta (2022) Large mammalian herbivores and the paradox of soil carbon in grazing ecosystems: Role of microbial decomposers and their enzymes. Ecosystems, 25 (4). pp. 976-988. ISSN 1432-9840

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Abstract

Grazing is the dominant land use across the world, and large mammalian herbivores exert strong influence over biogeochemical cycles. Grazing ecosystems feature C-rich soils, even though herbivores consume a major fraction of plant production to reduce detrital input to soil. Yet, counter-intuitively, moderate grazing can promote net soil-C storage in many ecosystems compared to grazer-exclusion. We address this enigmatic influence of grazers on soil-C and test their indirect effect on proximate drivers of decomposition: microbial extracellular enzyme activity. We used a replicated long-term grazer-exclusion experiment to measure responses in above- and belowground plant biomass, soil-C stock, microbial biomass, labile/recalcitrant C pools and three enzymes relevant to the C-cycle: peroxidase—which initiates decomposition of recalcitrant matter, alongside beta-glucosidase and cellobiohydrolase—which act further downstream on more labile fractions. Consistent with other ecosystems, upto 12 years of herbivore exclusion did not increase soil-C in the fenced plots despite higher plant biomass and higher potential detrital C-inputs. Grazer-exclusion did not alter microbial biomass; peroxidase increased threefold and beta-glucosidase was doubled; cellobiohydrolase was unaffected. Grazer-exclusion also led to twofold increase in recalcitrant-C and in microbial respiration, but it did not influence labile-C. Structural equation models supported the hypothesis that grazing favours soil-C via its indirect effect on peroxidase, but they did not support that the effects can run in the opposite direction where soil-C affects enzymes. Grazer-mediated shifts in how microbes deploy enzymes emerge as a plausible mechanism that affects soil-C. These linkages may be important to maintain soil-C sequestration in drylands which support large mammalian herbivores.

Item Type: Article
Uncontrolled Keywords: carbon sequestration,decomposition,grassland,herbivory,lignin,soil organic matter,structural equation modelling (sem),ecology, evolution, behavior and systematics,ecology,environmental chemistry,sdg 15 - life on land ,/dk/atira/pure/subjectarea/asjc/1100/1105
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Depositing User: LivePure Connector
Date Deposited: 14 Feb 2023 16:30
Last Modified: 29 Jun 2023 15:31
URI: https://ueaeprints.uea.ac.uk/id/eprint/91130
DOI: 10.1007/s10021-021-00696-8

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