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It is of great significance to clarify the influence of soil temperature and moisture on soil respiration rate and its characteristics in ecologically fragile regions under the background of climate change for the accurate assessment and prediction of carbon budgets in this region. The average CO 2 concentration and soil temperature and moisture at different soil depths (10, 50, and 100 cm) were measured using a CO 2 analyzer and temperature and moisture sensors. The soil respiration rate was calculated using Fick's first diffusion coefficient method. The dynamic characteristics of soil temperature, soil moisture, and soil respiration rate in different soil depths were explored, and the response of soil respiration rate to soil temperature and moisture were further analyzed. The results showed that the diurnal variation in soil respiration rate decreased significantly with the increase in soil depth ( P <0.05), and the peak time lagged behind. Soil respiration rate in adjacent soil depths (10, 50, and 100 cm) lagged 1 h from top to bottom. The monthly variation in soil respiration rate was a multi-peak curve, in which the maximum soil respiration rates of 10, 50, and 100 cm soil depths were on July 25 th , August 6 th , and August 10 th , reaching 13.96, 2.96, and 1.47 μmol·(m 2 ·s) -1 , respectively. The effect of soil temperature on soil respiration rate decreased with the increase in soil depth. Soil temperature at 50 cm and below had no significant effect on soil respiration rate ( P >0.05). The fitting index of 10 cm soil depth was the best ( R 2 =0.96), but the fitting indexes of 50 cm and 100 cm soil depths were poor ( R 2 =0.00 and R 2 =0.01, respectively). The temperature sensitivity coefficient Q 10 decreased with the increase in soil depth. Soil moisture in different soil depths had significant effects on soil respiration rate ( P <0.05), and the quadratic fitting indicated that 50 cm ( R 2 =0.35)>10 cm ( R 2 =0.22)>100 cm ( R 2 =0.31). The combined effects of soil temperature and moisture in different soil depths could explain 96%, 6%-50%, and 22%-24% of soil respiration rate, respectively. In summary, the effects of soil temperature and moisture at different soil depths of the Caragana korshinskii plantation in the loess-hilly region on soil respiration rate differed. The soil respiration rate of the 10 cm soil depth was affected by the comprehensive effect of soil temperature and moisture; however, the relative contribution of soil temperature was higher, and soil moisture at and below a soil depth of 50 cm was the key factor. These results could help improve predictions on the impact of future climate change on the carbon cycle of terrestrial ecosystems in the region and provide a theoretical basis for greenhouse gas regulation in the future.

We analyzed the changes of net primary productivity (NPP) and net ecosystem productivity (NEP) of Quercus spp. forest and Robinia pseudoacacia plantation under different future climate scenarios in Shaanxi Province during 2015-2100, using the process-based dynamic vegetation model-LPJ-GUESS. The results showed that compared with the benchmark period (1961-1990), NPP of Quercus spp. forest and R. pseudoacacia plantation in northern Shaanxi would decrease by 4.9%-29.5% and 22.5%-56.2% respectively, while that in Guanzhong and southern Shaanxi would increase by 13.0%-49.0% and 21.3%-62.9% respectively in the future. The NPP of Quercus spp. forest and R. pseudoacacia plantation under the RCP 8.5 scenario was the highest, followed by that under the RCP 4.5 and RCP 2.6 scenarios. Those two types of forest would be carbon sink in three subregions in the future. Quercus spp. forest would have stronger carbon sink function in nor-thern Shaanxi and Guanzhong, while R. pseudoacacia plantation would have stronger carbon sink function in Southern Shaanxi. Under different RCP scenarios, the NEP variation range of R. pseu-doacacia plantation was greater than that of Quercus spp. forest in three subregions.