Tree-scale spatial variation of soil respiration and its influence factors in apple orchard in Loess Plateau

Although small-scale spatial variation of soil respiration has been studied in a wide variety of ecosystems, there are few studies investigating the spatial variation of soil respiration at tree-scale. An inaccurate estimation of soil respiration would be obtained if the spatial variation of soil respiration was ignored. Soil respiration, soil temperature, soil moisture and fine roots biomass were measured in different directions (0, 120, and 240A degrees) at different distances (0.5 and 2 m radial distance) from the trunk of three representative trees for the period 2011-2013 in a mature apple orchard established on the Loess Plateau in 2000. The mean soil respiration rate at 0.5 m-distance was 21, 35 and 42 % higher, respectively. The cumulative soil respiration at 0.5 m-distance was 20, 31, and 38 % higher; and the temperature sensitivity of soil respiration (Q (10)) at 0.5 m-distance was 15, 30 and 12 % higher than that at 2 m-distance in 2011, 2012, and 2013, respectively. There was no significant difference in soil temperature and moisture between 0.5 m- and 2 m-distance, whereas fine root biomass at 0.5 m-distance was 64, 108, and 114 % higher than that at 2 m-distance in 2011-2013, respectively. Fine root biomass had a positive linear relationship with accumulative soil respiration and Q (10). Mean annual cumulative soil respiration was 0.46, 0.45, and 0.57 kg C m(-2) year(-1) in 2011-2013, respectively. Fine root biomass contributed to the spatial variation of soil respiration in apple orchard, and soil respiration at 2 m-distance could represent the C respired in orchard level.