Soil humus composition in mountain grasslands with different land-use intensity

摘要

Soil humus is a dynamic characteristic greatly vulnerable to land use and climate and with important feedbacks to the atmospheric greenhouse gas balance and the rate of climate change. The increased demand for accurate soil carbon stocks assessments and predictions of its changes as a result of land use/cover and climate change has triggered large-scale and long-term measurements of soil organic matter specifics. We studied the soil humus composition is four mountain grasslands, differentiated according to the land-use sub-type and land-use intensity. Two pastures – with intensive (Pi) and extensive grazing (Pe) and two meadows- managed (Mm) and unmanaged (Mu) were objects of present study. Humus composition was analyzed following the methodology of Kononova-Belchikova. Our results showed that the highest total carbon content was localized in the organic-mineral soil horizon and decreased toward deeper soil. The aggressive and mobile fulvic acids predominated in Pi, Mm and Mu, while humic acids were higher in Pe. Humic acids are “free” and bonded with R3O3 and no Ca-bonded humic acids were established. The values of total org.C and C-extracted by 0.1 N NaOH was similar in most of studied horizons. The highest total carbon content estimated at 14.04 % was determined in A-horizon of soil in pasture with extensive grazing, compared with other studied sites, including the intensive pasture, where this value was 4.8 %. The higher grazing disturbance in Pi leads to increase root biomass in patch areas and in inter-patch upper soil related with decrease of soil humus content. We supposed that the reduced amount of litter input with increased recalcitrance to decomposition provoked the reduction of organic carbon content and in changes in its composition under intensive grazing. The extensive pasture in mountain areas is better land-use approach in the perspective of soil humus quality improvement. The managed meadow in mountain areas accumulated more carbon in superficial soil, but the composition of soil humus is similar to this in unmanaged grassland.