Organic Matter Pools in Soddy-Podzolic Soil: A Comparison of Sites under Different Land Uses along a Regional Transect

Abstract— The study focused on soddy-podzolic soils (Albic Retisol, WRB) from three regions along a latitudinal transect (~200 km) crossing Tver oblast and the central and southern parts of Moscow oblast, under three land-use types (forest, grassland, arable land). The following SOM pools were determined: particulate organic matter (C-POM), mineral-associated organic matter (C-MAOM), potentially mineralizable organic matter (C-PM), microbial biomass (C-MB), and permanganate-oxidizable organic matter (C-POX). It is shown that SOM in soddy-podzolic soils is a dynamic, structurally and functionally heterogeneous system that is sensitive to land-use change and, to a lesser extent, to moderate geographic gradients. Latitudinal differentiation of SOM along the transect was expressed less in the absolute size of individual pools than in their covarying variability. Soil texture and pH across sites acted as significant factors controlling the distribution of carbon among pools; they initiated different mechanisms of SOC stabilization. The C-POM pool decreases from north to south, whereas the C-MAOM pool remains relatively constant. The transition from forest to grassland and arable land is accompanied by a decrease in SOC content by factors of 1.52 and 1.74, respectively, as well as by a reduction in the size of the C-POM pool and all process-related pools, along with an increase in the proportion of mineral-associated carbon. It is emphasized that the size and ratio of pools is a more sensitive indicator of SOM changes than total SOC content, and that land use is the primary factor determining both the content and quality composition of organic matter in soddy-podzolic soils.