Soil carbon efflux is an important component of the terrestrial carbon cycle. For accurate regional carbon estimation, it is urgent to understand the spatial and temporal variabilities of soil carbon efflux. In areas with complex terrain, topography can complicate the spatial and temporal variations through its effects on the abiotic and biotic factors, but the factors that control the spatial and temporal variations keep unknown.  

In order to identify the topographic effects on soil carbon efflux, the Global Change Biology Group led by Prof. LIU Feng of Wuhan Botanical Garden investigated soil respiration along topographic transects with ridge, middle slope, lower slope and valley positions to assess the driving factors of the variations in soil respiration.   

The results showed that soil respiration rates had strong temporal and spatial variations. Both soil temperature and soil moisture could well explain the temporal variation. Soil respiration rates also showed clear topographic pattern and decreased significantly from the ridge to valley soils. The spatial variation of soil respiration could be explained by multiple parameters associated with soil temperature, vegetation cover, carbon sources and soil physico-chemical properties. The topography controlled the spatial variation mainly through its effects on the carbon sources and soil physico-chemical properties.   

These results further emphasized the ridge position was a potential hot spot for future environmental changes. Further more, these results suggested that soil respiration of the sloping landscape was affected by geomorphological, biogeochemical and hydrological processes, and future studies on the soil carbon efflux should take into account the topographic effects.    

This work was supported by the National Natural Science Foundation of China and the Chinese National Key Development Program for Basic Research. Relevant research results have been published in Biogeochemistry entitled "Topographic controls on the variability of soil respiration in a humid subtropical forest".  

Soil respiration rates at the four landscape positions (a) and the spatiotemporal variability of soil respiration (b)(Image by WBG) 

Path analysis diagrams (a) and total effects (b) of each factor on spatial variation in soil respiration (Image by WBG)