Mycorrhizal type regulates trade-offs between plant and soil carbon in forests

Forest ecosystems store ~80% of the carbon in terrestrial ecosystems, but their long-term carbon sequestration depends partly on how plant biomass and soil carbon stocks will respond to global changes. Although the stimulation of plant growth by global change drivers has been widely observed, the response of soil carbon stock to global changes remains uncertain. Here we conducted a meta-analysis on experimental observations of plant and soil carbon-related data worldwide. We found that plant biomass and soil carbon stock increased more under elevated CO2 than under nitrogen deposition and warming. Under nitrogen deposition and warming, soil carbon stock depended on mycorrhizal associations, decreasing in forests dominated by arbuscular mycorrhizal tree species while increasing in forests dominated by ectomycorrhizal tree species. These results suggest a mycorrhizae-mediated trade-off between plant biomass and soil carbon sequestration in forest ecosystems under nitrogen deposition and warming conditions. The impact of climate change on soil carbon remains uncertain. This study shows that soil carbon in forests increases in response to elevated CO2, but the response to warming and nitrogen deposition depends on mycorrhizal associations, indicating a trade-off between soil and plant carbon.