Ecosystem water fluxes in response to climate warming and biofuel harvest in a tallgrass prairie

Background/Question/Methods

Evapotranspiration (ET) plays an important role in linking ecosystem water, energy and carbon cycles. However, it is not well understand how ecosystem ET and its components: soil evaporation (E) and plant transpiration (T) respond to climate warming and biofuel harvest.  We conducted a field manipulative experiments with warming and clipping treatments in a tallgrass prairie in the southern Great Plains of North America from 2009 July-2011 June.

Results/Conclusions

Warming increased E but did not change T. We explored the following potential mechanisms that caused little changes in T and ET. (1) Warming- increased vapor pressure deficit lowered stomata conductance, which depressed water release from leaves. (2) The warming-induced changes in T and ET negatively correlated with C₄ coverage across the plots, suggesting that species composition shift with more C₄ species (higher water use efficiency) in the warmed plots, contributed to little changes in T and ET. (3) ET was measured in normal days to avoid rainfall pulse effect. Within a few days after rainfall, ET positively responded to warming due to higher soil moisture.

      Clipping significantly increased T by 43-59%  and ET by 36-47%.  The positive clipping effects on ET was largely due to that clipping reduced standing and surface litter, which exposed more soil surface to air and better light condition for shorter grass. Moreover, species changing from C₄ to C₃ in the clipped plots also contributed to higher ET under chipping treatment. This study suggests that warming effects on ecosystem water cycling were complicated due to the offset impacts among different ecological processes. Biofuel harvest changes ecological hydrology more than  climate change.