What was done
Noting that "among the major limiting factors to plant growth, water availability most strongly limits vegetation growth over 40% of the earth's vegetated surface (Nemani et al., 2003)," the authors used the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM) -- which had been calibrated and validated for the whole of China's vegetated land surface -- to investigate the temporal and spatial changes in evapotranspiration (ET), runoff, soil moisture, and resultant limitations on photosynthesis and transpiration throughout the 20th and 21st centuries under a set of eight different climate change scenarios that were derived from combinations of two GCMs and four IPCC emission scenarios.

What was learned
Tao et al. say their findings indicate that "the response of China's terrestrial ecosystem hydrological cycles to future climate change could be considerable," noting that "vegetation water stress on plant growth could be generally eased by climate changes and rising CO2." More specifically, they report that "the net impact of physiological and structural vegetation responses to elevated CO2 resulted in ... a decrease in mean ET, as well as an increase in mean soil moisture and runoff across China's terrestrial ecosystem in the 21st century," largely as a result of the fact that "under elevated CO2, stomatal apertures on plant leaves are observed to close partially -- suppressing transpiration and, consequently, increasing runoff -- together with precipitation increase (e.g., Gedney et al., 2006; Betts et al., 2007)."

What it means
The two Chinese researchers contend that the results of their study "can be used with some confidence as a guide for policy making." And seeing that projected greenhouse gas-induced climate changes and CO2-induced plant productivity changes come together to produce a net increase in soil moisture and runoff across the whole of China throughout the 21st century, one would think that any related policy decisions would not include a hurried attempt to limit anthropogenic CO2 emissions, as those CO2-induced soil moisture and runoff increases will likely figure highly in China's ability to adequately feed its future population.

References
Betts, R.A., Boucher, O., Collins, M., Cox, P.M., Falloon, P.D., Gedney, N., Hemming, D.L., Huntingford, C., Jones, C.D., Sexton, D.M.H. and Webb, M.J. 2007. Projected increase in continental runoff due to plant responses to increasing carbon dioxide. Nature 448: 1037-1041.

Gedney, N., Cox, P.M., Betts, R.A., Boucher, O., Huntingford, C. and Stott, P.A. 2006. Detection of a direct carbon dioxide effect in continental river runoff records. Nature 439: 835-838.

Nemani, R.R., Keeling, C.D., Hashimoto, H., Jolly, W.M., Piper, S.C., Tucker, C.J., Myneni, R.B. and Running. S.W. 2003. Climate-driven increases in global terrestrial net primary production from 1982 to 1999. Science 300: 1560-1563.