The rise in atmospheric levels of carbon dioxide over the past century has driven an increase in the intrinsic water use efficiency of trees worldwide, a study finds. Intrinsic water use efficiency is the ratio of carbon uptake through photosynthesis to water vapor release through transpiration. Small changes in the water use efficiency of trees can have a major impact on carbon and water fluxes, but relatively little is known about the environmental factors that affect water use efficiency across large spatial scales, or the underlying plant physiological mechanisms. Justin Mathias and Richard Thomas analyzed previously published data on carbon and oxygen isotopes from 113 tree ring chronologies for 36 species across 10 biomes at 84 sites around the world. Between 1901 and 2015, the intrinsic water use efficiency of trees worldwide rose by approximately 40%, in conjunction with an increase of approximately 34% in atmospheric carbon dioxide. The results suggest that the rise in carbon dioxide is the main environmental factor driving the increase in water use efficiency. Additional analysis suggests that an increase in photosynthesis is primarily responsible for the rise in intrinsic water use efficiency. According to the authors, the study could help improve Earth system models for predicting the effects of climate change on global carbon and water cycles.
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Article #20-14286: "Global tree intrinsic water use efficiency is enhanced by increased atmospheric CO2 and modulated by climate and plant functional types," by Justin Mathias and Richard Thomas.
MEDIA CONTACT: Justin Mathias, University of California, Santa Barbara, CA; email: < justinmathias@ucsb.edu >
Proceedings of the National Academy of Sciences