Partitioning the respiratory components of soil surface CO_2 efflux is important in understanding carbon turnover and in identifying the soil carbon sink/source function in response to land-use change. The sensitivities of soil respiration components on changing climate patterns are currently not fully understood. We used trench and isotopic methods to separate total soil respiration into autotrophic(RA) and heterotrophic components(R_H). This study was undertaken on a Robinia pseudoacacia L. plantation in the southern Taihang Mountains, China. The fractionation of soil^(13)CO_2 was analyzed by comparing the δ^(13) C of soil CO_2 extracted from buried steel tubes with results from Gas Vapor Probe Kits at a depth of 50 cm at the preliminary test(2.03%). The results showed that the contribution of autotrophic respiration(f R_A) increased with increasing soil depth.The contribution of heterotrophic respiration(f R_H) declined with increasing soil depth. The contribution of autotrophic respiration was similar whether estimated by the trench method(f RA, 23.50%) or by the isotopic method in which a difference in value of^(13) C between soil and plant prevailed in the natural state(R_C, 21.03%). The experimental error produced by the trench method was insignificant as compared with that produced by the isotopic method, providing a technical basis for further investigations.
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