Partitioning root and microbial contributions to soil respiration in Leymus chinensis populations

Based on the enclosed chamber method, soil respiration measurements of Leymus chinensis populations with four planting densities (30, 60, 90 and 120 plants/0.25 m2) and blank control were made from July 31 to November 24, 2003. In terms of soil respiration rates of L. chinensis populations with four planting densities and their corresponding root biomass, linear regressive equations between soil respiration rates and dry root weights were obtained at different observation times. Thus, soil respiration rates attributed to soil microbial activity could be estimated by extrapolating the regressive equations to zero root biomass. The soil microbial respiration rates of L. chinensis populations during the growing season ranged from 52.08 to 256.35 mg CO2 m−2 h−1. Soil microbial respiration rates in blank control plots were also observed directly, ranging from 65.00 to 267.40 mg CO2 m−2 h−1. The difference of soil microbial respiration rates between the inferred and the observed methods ranged from −26.09 to 9.35 mg CO2 m−2 h−1. Some assumptions associated with these two approaches were not completely valid, which might result in this discrepancy. However, these two methods' application could provide new insights into separating root respiration from soil microbial respiration. The root respiration rates of L. chinensis populations with four planting densities could be estimated based on measured soil respiration rates, soil microbial respiration rates and corresponding mean dry root weight, and the highest values appeared at the early stage, then dropped off rapidly and tended to be constant after September 10. The mean proportions of soil respiration rates of L. chinensis populations attributable to the inferred and the observed root respiration rates were 36.8% (ranging from 9.7 to 52.9%) and 30.0% (ranging from 5.8 to 41.2%), respectively. Although root respiration rates of L. chinensis populations declined rapidly, the proportion of root respiration to soil respiration still increased gradually with the increase of root biomass.