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Historic iWUE Trends in Far Northeastern China

Paper Reviewed
Liu, X., Zhao, L., Voelker, S., Xu, G., Zeng, X., Zhang, X., Zhang, L., Sun, W., Zhang, Q., Wu, G. and Li, X. 2019. Warming and CO2 enrichment modified the ecophysiological responses of Dahurian larch and Mongolia pine during the past century in the permafrost of northeastern China. Tree Physiology 39: 88-103.

Atmospheric CO2 concentrations have risen some 45% since the dawn of the Industrial Revolution. In light of numerous scientific studies that show rising atmospheric CO2 enhances plant water use efficiency (see the many reviews posted on this topic under the heading of Water Use Efficiency on this page), it stands to reason that there should be some evidence of that benefit out in the real world of nature. And there is (see here, here and here, as examples).

Another recent study that presents evidence of a CO2-induced increase in plant water use efficiency comes from Liu et al. (2019). Working in the far northeastern region of China, the team of eleven scientists examined tree-ring cores from Dahurian larch and Mongolian pine trees in the permafrost region of the norther Great Higgnan Mountains, producing a record of intrinsic water use efficiency (iWUE) for each species over the period 1901-2010. The data are presented in Figure 1.

As illustrated there, the iWUE of larch and pines increased by 22.7% and 31.8% over the 110-year period, during which time the CO2 concentration of the atmosphere rose some 30%. With respect to the cause(s) of the increasing iWUE, Liu et al. say that it was a combination of rising CO2 and climate variability, where warming temperatures and higher CO2 levels both acted to reduce leaf stomatal openings on the trees, thereby helping to reduce transpiration, which ultimately improved iWUE.

And thus we find yet another real world example that rising atmospheric CO2 is benefitting vegetation across the globe by helping to improve plant iWUE. Since 1900, the intrinsic water use efficiencies of larch and pine trees have risen by 22.7% and 31.8%, thanks to the supposed twin evils of the radical environmental movement: rising temperatures and rising atmospheric CO2. How ironic is that?

Figure 1. Intrinsic water-use efficiency (iWUE) of Dahurian Larch and Mongolia pine trees in northeastern China since 1900. Adapted from Supplemental Figure 5 from Liu et al. (2019).

Posted 25 March 2020