Effects of nitrogen and phosphorus fertilization on soil respiration and its temperature sensitivity in grassland alfalfa soil in Northwest China

Introduction Understanding the temperature sensitivity ( Q 10 ) of soil respiration (RS) and its response to nitrogen (N) and phosphorus (P) fertilization is essential for predicting soil carbon dynamics under climate change. However, seasonal responses of RS and Q 10 to fertilization in semiarid grasslands remain insufficiently documented. Methods A two-year field experiment was conducted from April 2017 to March 2019 in an alfalfa grassland in Northwest China. Four treatments were established: control, N fertilization, P fertilization, and combined NP fertilization. Soil respiration, soil temperature and moisture, forage yield, root biomass, and key soil properties were measured during both growing and non-growing seasons. The temperature sensitivity of soil respiration was calculated using the Q 10 coefficient. Results Nitrogen, phosphorus, and NP fertilization significantly increased soil respiration during the growing season, but had no significant effect during the non-growing season. Both N and P applied individually enhanced root biomass throughout the growing season and across the entire year, whereas no significant N × P interaction was detected. Q 10 values were substantially higher during the non-growing season, ranging from 4.91 to 5.54 (mean 5.16), compared with 1.38 to 1.95 (mean 1.68) during the growing season. Fertilization increased Q 10 in both seasons, indicating greater temperature sensitivity of soil carbon release. Soil respiration increased exponentially with soil temperature at 10 cm depth and was positively associated with soil moisture, forage yield, root biomass, total phosphorus, microbial biomass carbon, and soil organic matter, but negatively correlated with soil pH. Discussion Nitrogen and phosphorus fertilization altered seasonal patterns of soil respiration and increased the temperature sensitivity of soil carbon emissions. These findings demonstrate that nutrient management can significantly influence carbon cycling and climate feedbacks in dry and semiarid grassland ecosystems.