Effects of Soil Organic Matter Properties and Microbial Community Composition on Enzyme Activities in Cryoturbated Arctic Soils

Abstract

Enzyme-mediated decomposition of soil organic matter (SOM) is controlled, amongst other factors, by organic matter properties and by the microbial decomposer community present. Since microbial community composition and SOM properties are often interrelated and both change with soil depth, the drivers of enzymatic decomposition are hard to dissect. We investigated soils from three regions in the Siberian Arctic, where carbon rich topsoil material has been incorporated into the subsoil (cryoturbation). We took advantage of this subduction to test if SOM properties shape microbial community composition, and to identify controls of both on enzyme activities. We found that microbial community composition (estimated by phospholipid fatty acid analysis), was similar in cryoturbated material and in surrounding subsoil, although carbon and nitrogen contents were similar in cryoturbated material and topsoils. This suggests that the microbial community in cryoturbated material was not well adapted to SOM properties. We also measured three potential enzyme activities (cellobiohydrolase, leucine-amino-peptidase and phenoloxidase) and used structural equation models (SEMs) to identify direct and indirect drivers of the three enzyme activities. The models included microbial community composition, carbon and nitrogen contents, clay content, water content, and pH. Models for regular horizons, excluding cryoturbated material, showed that all enzyme activities were mainly controlled by carbon or nitrogen. Microbial community composition had no effect. In contrast, models for cryoturbated material showed that enzyme activities were also related to microbial community composition. The additional control of microbial community composition could have restrained enzyme activities and furthermore decomposition in general. The functional decoupling of SOM properties and microbial community composition might thus be one of the reasons for low decomposition rates and the persistence of 400 Gt carbon stored in cryoturbated material.

Properties and bioavailability of particulate and mineral‐associated organic matter in Arctic permafrost soils, Lower Kolyma Region, Russia

“…There was a general decrease in the C:N ratio of bulk OM from organic layers to topsoil mineral horizons, subsoil horizons and to the permafrost (Figure ; Schnecker et al ., ), indicating a preferential loss of carbon relative to nitrogen. The decline of C:N ratios was accompanied by an enrichment of both 13 C and 15 N (Figure a, b), suggesting an on‐going decomposition and subsequent enrichment of isotopically heavy microbial products with soil depth.…”

Species interactions and distinct microbial communities in high Arctic permafrost affected cryosols are associated with the CH4 and CO2 gas fluxes

“…The IWP isolates contained genes for degradation of complex carbohydrates and aromatic compounds. This corresponds to studies that have found extracellular enzyme activities in mineral cryosols, including cellobiohydrolase and phenol oxidases (Schnecker et al ., ; Gittel et al ., ). In addition, Arctic mineral soil horizons contain relatively high levels polysaccharides and phenolic compounds compared to other organic carbon sources (Xu et al ., ).…”

Ectomycorrhizal fungi and soil enzymes exhibit contrasting patterns along elevation gradients in southern Patagonia

“…Previous studies clarified the role of SOM composition (i.e. C and N content in organic horizons) as the main driver of EEAs at high latitudes (Schnecker et al ., ; Waldrop et al ., ), whereas EEAs seemed relatively insensitive to temperature in a tropical nonECM Peruvian forest (Nottingham et al ., ). The contribution of ECM fungi to SOM recycling has been demonstrated (Lindahl & Tunlid, ) and, in some cases, was comparable to saprotrophic fungi (Phillips et al ., ).…”