Nitrogen and water availability control plant carbon storage with warming

Plants may slow global warming through enhanced growth, because increased
levels of photosynthesis stimulate the land carbon (C) sink. However, how
climate warming affects plant C storage globally and key drivers
that determining the response of plant C storage to climate warming
remains unclear, causing uncertainty in climate projections. We performed
a comprehensive meta-analysis, compiling 393 observations from 99 warming
studies to examine the global patterns of plant C storage responses to
climate warming and explore the key drivers. Warming significantly
increased total biomass (+8.4%), aboveground biomass (+12.6%) and
belowground biomass (+10.1%). The effect of experimental warming on plant
biomass was best explained by the availability of soil nitrogen
(N) and water. Across the entire dataset, warming-induced changes
in total, aboveground and belowground biomass all positively
correlated with soil C:N ratio, an indicator of soil N
availability. In addition, warming stimulated plant biomass more strongly
in humid than in dry ecosystems, and warming tended to decrease root:shoot
ratios at high soil C:N ratios. Together, these results suggest dual
controls of warming effects on plant C storage; warming increases plant
growth in ecosystems where N is limiting plant growth, but it reduces
plant growth where water availability is limiting plant growth. Together,
these findings suggested that warming effects on plant C storage largely
depend on soil N and water status, which should be considered into
 Earth system models to improve the future prediction of
C-climate change feedbacks.