Rising atmospheric carbon dioxide concentration should stimulate biomass production directly via biochemical stimulation of carbon assimilation, and indirectly via water savings caused by increased plant water-use efficiency. Because of these water savings, the CO 2 fertilization effect (CFE) should be stronger at drier sites, yet large differences among experiments in grassland biomass response to elevated CO 2 appear to be unrelated to annual precipitation, preventing useful generalizations. Here, we show that, as predicted, the impact of elevated CO 2 on biomass production in 19 globally distributed temperate grassland experiments reduces as mean precipitation in seasons other than spring increases, but that it rises unexpectedly as mean spring precipitation increases. Moreover, because sites with high spring precipitation also tend to have high precipitation at other times, these effects of spring and non-spring precipitation on the CO 2 response offset each other, constraining the response of ecosystem productivity to rising CO 2 . This explains why previous analyses were unable to discern a reliable trend between site dryness and the CFE. Thus, the CFE in temperate grasslands worldwide will be constrained by their natural rainfall seasonality such that the stimulation of biomass by rising CO 2 could be substantially less than anticipated.
Bibliographical noteFunding Information:
We thank R. Brinkhoff for assistance with collating the data for this analysis. This research was initiated at the workshop ‘Using results from global change experiments to inform land model development and calibration’, which was co-sponsored by the US-based INTERFACE Research Coordination Network and Research Group of Global Change Ecology at Henan University (funded by MOST2013CB956300 and NSFC41030104/ D0308).
© 2019, The Author(s), under exclusive licence to Springer Nature Limited.