Effect of microtopography on soil respiration in an alpine meadow of the Qinghai-Tibetan plateau

Soil respiration is an important component of terrestrial carbon cycling and is sensitive to environmental change. Most previous studies focus on the effect of soil temperature and moisture on soil respiration, whereas the impact of spatial heterogeneity (e.g., microtopography) is seldom studied. To test the impact of microtopography on soil respiration, we performed a field investigation to examine soil respiration, soil temperature, soil water content, soil total porosity, soil organic content, and plant biomass at a hummock site (composed of grass hummocks and inter-hummock areas) and an adjacent flat meadow of the Qinghai-Tibetan plateau. Similar seasonal dynamics of soil respiration in the grass hummocks, inter-hummock areas, and flat meadow were found in the alpine meadow of the Qinghai-Tibetan plateau. However, soil respiration of the grass hummocks was 79.3% and 413.9% higher than that of the flat meadow during the growing (April, June, August) and non-growing seasons (October, December, February), respectively. Although there was no difference in soil respiration between the inter-hummock areas and the flat meadow during the non-growing season, soil respiration was 42.5% higher at the inter-hummock areas than the flat meadow during growing season. Larger soil porosity, greater surface area, and more substrate supply, but not more root growth, likely contributed to the higher soil respiration of grass hummocks. Our findings suggest that the impact of spatial heterogeneity on soil respiration should be taken into consideration to facilitate the accurate estimation of soil carbon fluxes at ecosystem and regional scales.