Spatial variability of soil organic carbon fractions and aggregate stability along an elevation gradient in the alpine meadow grasslands of the Qilian Mountains, China

Grasslands contain substantial amount of soil organic C (SOC) and thus have a key function in global C cycle. Thus knowledge on SOC contents and aggregate stability is vital in exploring their impact as a C storage or source under climate change simulations. The research investigated the spatial variability of SOC and its fractions and stability of aggregates and their relationships with factors like vegetation, climate and soil conditions along an elevation gradient of the alpine meadow grassland (3105-4200 m a.s.l.) The SOC concentrations had an increasing trend with elevation from 76.04 g kg-1 at 3105 m a.s.l. up to 110.42 g kg-1 at 3710 m a.s.l. and 103.87g kg-1 and then decreased to 71.25 g kg-1 at the peak of the slope at 4200 m a.s.l. The results indicated that macro- and micro-aggregate organic C, mean weight diameter, geometric weight diameter, percentage of > 0.25 mm water-stable aggregates (W0.25), and stability of water-stable aggregates ratio increased with increasing elevation, attaining a peak at 3710 or 3925 m a.s.l. and afterwards decreased. The findings of this research show that prospective global climate warming could have a telling effect on SOC and soil aggregate stability by affecting the distribution of aboveground biomass. Due to the low structural stability of soils at the lower parts of the elevations, we proposed that these areas should be barred from continuous grazing to enhance high grassland productivity and be able to cope with prospective climate change in this area.