Grassland soil organic carbon stocks along management intensity and warming gradients

Grasslands are a major terrestrial ecosystem type and store large amounts of soil organic carbon (SOC) per unit area. Quantitative and mechanistic knowledge on the effects of management on SOC stocks in grasslands is limited. Also, climate change can be seen as an indirect anthropogenic threat to SOC stocks, with warming effects on grassland SOC being currently understudied. Here, several studies investigating the effects of management and warming on SOC stocks are summarised, with a central to northern European focus. SOC sequestration increased with management intensity, i.e. cutting frequency and mineral fertilisation, even without external C inputs. This was partly explicable by increased productivity in more intensively managed grasslands. In addition, the availability of nutrients was found to foster microbial anabolism, leading to a more efficient build-up of SOC in fertilised as compared to unfertilised soils. Interestingly, the addition of 1 kg nitrogen as NPK fertiliser consistently led to approximately 1 kg of additional SOC. Sequestration of SOC might thus compensate for a major part of the increased greenhouse gas emissions associated with highly intensive grassland management. Including perennial grasses in agricultural crop rotations is multi-beneficial and proved to be a very efficient measure to increase SOC stocks. At the same time, soil warming depleted SOC, both in natural subarctic as well as in managed temperate grasslands. Climate change can thus be expected to counterbalance efforts of SOC build-up to some extent. Future research should focus on the interactive effects of climate change and management, which will be important for future management decisions.