Spatial Distribution of Organic Matter and Nitrogen in the Entic Podzols of the Prioksko-Terrasnyi Reserve and Its Relationship with the Structure of Forest Phytocenoses

Estimates of the spatial heterogeneity of the organic matter distribution in forest soils determined by the influence of the species and spatial structure of phytocenoses are relevant for many environmental problems, including the calculation of carbon sinks and modeling of the dynamics of forest ecosystems. We analyzed the data on the organic carbon (Cₒᵣg) and total nitrogen (Nₜₒₜ) contents in the O (forest litter) and AY (humus) horizons of Entic Podzols in the Prioksko-Terrasnyi Reserve (54.89° N, 37.56° E). The studied site is located in a coniferous–deciduous forest formed after overgrowing of the cutting area of pine stands. We sampled the O and AY horizons along transects between trees of different species, i.e., near the trunks, under the crown, and in the intercrown space. The contents of Cₒᵣg and Nₜₒₜ in the O horizon varied within 17.6–44.9 and 0.84–1.79%, respectively. The ranges for the AY horizon were greater: 0.71–8.5% (Cₒᵣg) and 0.035–0.33% (Nₜₒₜ). The relationship between the contents of Cₒᵣg and Nₜₒₜ in the O and AY horizons was close to linear (rₛ = 0.72 and rₛ = 0.96, respectively). We also obtained similar C : N ratios for the both horizons. The litter thickness and the content of Nₜₒₜ in the O horizon, as well as the content of Cₒᵣg in the AY horizon, significantly differed in different parts of the transects (P < 0.05). The differences in the litter thickness and the Cₒᵣg content in the O horizon under the crowns of different tree species were also significant. In samples from the AY horizon taken in intercrown spaces, the Nₜₒₜ content correlated with the demand of plant species of the ground cover for soil fertility. The data obtained reflect the influence of specific features of spatial patterns of surface and root litterfall in multispecies communities of mixed forest stands on the spatial variability of Cₒᵣg and Nₜₒₜ contents in soil.