Contributions of aboveground litter to soil respiration in coniferous and deciduous plantations

Aboveground litter is of great importance in the study of carbon cycle in terrestrial ecosystem. However, current understandings of the contribution of aboveground litter to soil respiration are far too limited. In order to investigate the degree of contribution of aboveground litter to soil respiration, three treatments of non-litter (NL), cover litter (CL) and the control (C, natural litter cover) were set up in ten-year old Pinus tabulaeform and Populus plantations in Beijing-Tianjin sandstorm source area. Each treatment was replicated three times in galvanized sheet irons of size of 40 cm × 40 cm × 9 cm, 4 cm of which was above ground surface. Polyvinyl chloride (PVC) collars (with 10 cm inside diameter) were installed in each plot for soil respiration measurements. The field experiments were conducted from March 2013 to November 2013 and measurements taken only on days without precipitation and/or high winds to minimize equipment damage and measurement error. Soil respiration rates (R_s) were measured approximately once a month during the period of the experiment using Li-6400 portable CO₂ infrared gas analyzer (IRGA) equipped with Li-6400-09 chamber (Li-COR IC., LiColn, NE, USA). R_s was continuously measured in three cycles at each collar and the three measurements averaged for the collar mean. Soil temperature was monitored simultaneously along soil respiration using a thermocouple penetration probe inserted in the soil to the depth of 5 cm in the vicinity of the respiration chamber. Soil moisture in the top soil layer (0-5 cm) was monitored using the oven-dry method. Results showed that soil respiration was significantly different among different treatments (P < 0.05). The mean soil respiration rates (R_s, μmol·m^-2·s^-1) under P. tabulaeform and Populus plantations in the NL, CL, C treatments were respectively 2.28, 2.81, 2.55, and 2.13, 2.62, 2.32., indicating that CL > C > NL. Soil respiration was positively correlated with soil temperature at 5 cm soil depth (R² = 0.54 to 0.88, P < 0.05), but not with soil moisture at 5 cm soil depth. The order of sensitivity to temperature of soil respiration (Q₁₀) was NL < CL < C. The contribution rates of aboveground litter to soil respiration under P. tabulaeform and Populus plantations were 20.78% and 20.75%, respectively, suggesting little difference in litter contribution to soil respiration between P. tabulaeform and Populus. The results of the study could have significant implications for future study on soil respiration and the estimation of carbon sequestration of young coniferous and deciduous plantations in the Beijing-Tianjin sandstorm source area.