Short-term phosphorus addition increases soil respiration by promoting gross ecosystem production and litter decomposition in a typical temperate grassland in northern China

Anthropogenic activities have increased phosphorus (P) deposition and affect ecosystem carbon cycles. Although soil respiration (Rs) is a vital part of terrestrial C fluxes, the responses of Rs to altered substrate supply, inputs, and decomposition rates under P addition are not fully understood. Here, we conducted a 2-year field experiment with P fertilization rates ranging from 0 to 12.5 g P m−2 yr−1 to explore the effects on the Rs of a temperate grassland in Inner Mongolia, northern China. P addition increased Rs and annual Rs ranged from 413.04 to 938.83 g C m−2 yr−1. Soil heterotrophic respiration (Rh) increased after P addition, and its contribution to Rs ranged from 65.5% to 71.4%, possibly due to the increased litter input and microbial biomass. P addition increased soil P availability and the net N mineralization rate, thereby mitigating microbial nutrient limitations, and increased the maximum net photosynthetic rate of the dominant species and gross ecosystem production, which was strongly correlated with Rs. P addition increased litter quantity and improved litter quality, with decreased litter C:N and C:P ratios, and generally increased the activities of the soil enzymes β-1,4-glucosidase, polyphenol oxidase, leucine aminopeptidase, and alkaline phosphatase. This accelerated litter decomposition and increased Rh. Soil autotrophic respiration reached a maximum at 2.5 g P m−2 yr−1, possibly due to the decreased transportation of photosynthate to roots at high P. Our results suggest that Rs in temperate grassland responds sensitively to P addition and highlight the regulation of Rs by biotic factors under P fertilization.