Precipitation manipulation and terrestrial carbon cycling: the roles of treatment magnitude, experimental duration, and local climate

Aim: Precipitation manipulation experiments have shown diverse terrestrial
carbon (C) cycling responses when the ecosystem is subjected to different
magnitudes of altered precipitation, various experimental durations, or
heterogeneity in local climate. However, how these factors combine to
affect C cycle responses to changes in precipitation remains unclear.
Location: Global. Time period: 1990–2019. Major taxa studied: Terrestrial
ecosystems. Methods: Using observations from 230 published studies in
which precipitation was manipulated and terrestrial C cycling variables
were measured, we conducted a global meta-analysis to investigate
responses of diverse C cycle processes to altered precipitation, including
gross ecosystem productivity, ecosystem respiration, net ecosystem
productivity, ecosystem carbon use efficiency, net primary productivity,
aboveground and belowground net primary productivity, aboveground and
belowground biomass, shoot:root ratio, soil respiration, and soil
microbial biomass C. Results:  We found that C cycling responses
correlated linearly and positively with the magnitude of precipitation
treatments. We also detected that the responses of net primary
productivity (NPP) and its aboveground component (ANPP) to altered
precipitation weakened with experimental duration. Furthermore, gross
ecosystem productivity, ecosystem respiration, and net ecosystem
productivity had larger responses to precipitation treatments of greater
magnitude over shorter time periods. The response of soil respiration, a
key component of the C budget in most terrestrial ecosystems, particularly
depended on the local climate. Local temperature and precipitation not
only influenced the magnitude of the response of soil respiration to
altered precipitation but also affected its sensitivity to the magnitude
of the precipitation treatments, with higher sensitivities in the response
of soil respiration to treatment magnitude at drier and colder sites. Main
conclusions:  Our findings highlight the importance of
the interactions between the magnitude of precipitation treatments, their
duration, and local climate in the response of ecosystem C cycling to
altered precipitation, which is critical to better understanding and
projecting ecosystem C processes and functioning under changing
precipitation regimes.