Characterization and comparison of soil and vegetation carbon stocks in natural grassland and afforestation

In this study, we examined and compared the characteristics and processes directly influencing soil carbon content and carbon turnover in a slightly sodified, haevy textured soil in a near-natural sodic grassland and a 100-year-old oak afforestation established in its immediate vicinity, originally with identical soil conditions. We compared the amount of carbon stored at the two sites in the above ground living phytomass, in the organic matter accumulated in the litter layer (dead wood, litter), and in the living root biomass in the upper 10 cm layer of the soil. In the soil samples, we analyzed the soil organic carbon content, the microbial biomass, the dehydrogenase and sacharase activities by sampling in 10 cm thick layers between 0-40 cm, replicated per season. We measured the CO₂ emission of the soil surface replicated per season.

In the 100th year after afforestation, soil pH and base saturation were lower in the forest area. Carbon stock was higher in the near-natural grassland area (0-40 cm: 1144±35 g∙m²) than in the planted forest (973±34 g∙m²). At the same time, the C content of the living phytomass increased to 14,712 g∙m² in the forest area, compared to 298±65 g∙m² measured in the grassland. The amount of C stored in the litter in the afforested area was 4 482±1 018 g∙m², and in the grassland 162±61 g∙m². The C content stored in the root system was higher in the grassland, 1676±988 g∙m², compared to 94±57 g∙m² in the forest. Microbial biomass and enzyme activity were higher in the grassland in all seasons and in all layers, and CO₂ emissions were also higher in the grassland (0.235 g∙m²∙h^-1) compared to the forest (0.337 g∙m²∙h^-1).

According to our studies, the rearrangement of surface and subsurface carbon storage processes changes significantly over 100 years and affects the chemical and biological processes of the soil as well.