Organic Matter Content and Standard Material Decomposition Rate in Soils of High-Mountain Plant Communities of the Teberda National Park

Soils of high mountains significantly differ in the soil organic matter (SOM) content, but the factors of such diversity are still not completely known. We have studied physicochemical and microbiological soil properties and have estimated parameters of standard material decomposition based on the Tea bag index (TBI)—stabilization factor (STBI) and decomposition constant (kTBI)—in 16 subalpine, alpine, and subnival plant communities of the Teberda National Park (northwestern Caucasus) We tested the following hypotheses: (1) SOM is one of predictors of STBI and kTBI in the high-mountain zone along with other physicochemical soil properties; (2) the SOM content is greater at high STBI and low kTBI; (3) the SOM content correlates with belowground plant productivity. The main gradients of the studied soils include moisture content (automorphic vs. hydromorphic soils) and the concurrent SOM accumulation, as well as the altitudinal gradient (a decrease of soil basal respiration with altitude). The enrichment in nitrogen (e.g. the SOM quality) of the labile fraction is the best predictor of the decomposition rate. The parameter STBI decreases with the increase in the total carbon content and loss on ignition, while the correlation between kTBI and SOM is positive only in automorphic soils. Thus, the soils rich in organic matter are characterized by low stabilization factor and relatively high decomposition rate. The SOM content in plant communities with herbaceous dominants is in positive correlation with the production of fine roots, which reflects the important role of productivity in organic matter accumulation.