Nitrogen addition stimulated soil respiration more so than carbon addition in alpine meadows

The soil carbon (C) and nitrogen (N) availability are important in the regulation of soil C cycling under climate change. Fertilizers alter soil C and N availability, which can affect C balance. However, the impact of fertilizers on C balance in grassland restoration has been equivocal and warrants more research. We determined the direct and indirect effects of the addition of three levels of C (sucrose) (0, 60, and 120 kg C ha-1 yr- 1), three levels of N (urea) (0, 50, and 100 kg N ha-1 yr- 1), and a combination of C plus N at each of the levels on soil respiration (Rs) dynamics and C balance in an alpine meadow in northern Tibet (4700 m above sea level). This study was undertaken during the middle of the growing season in 2011-2012. The addition of C and/or N stimulated CO2 emission, which was 2-fold greater in 2011 (102-144 g C m- 2) than in 2012 (43-54 g C m- 2). The rate of Rs increased with the addition of N, but was not affected with the addition of C plus N. Microbial biomass C, dissolved organic C and inorganic N were the main drivers of Rs. We concluded that N addition stimulated Rs to a greater extent than C addition in the short term. The application of fertilizer in the restoration of degraded grassland should be re-considered.

Automated summary

The impact of fertilizers on carbon balance in grassland restoration is uncertain and requires further research. In an experiment conducted in an alpine meadow on the Tibetan Plateau, the addition of carbon and/or nitrogen stimulated soil respiration, with nitrogen having a greater effect. Therefore, the application of fertilizer in restoring degraded grassland should be re-evaluated.