Evapotranspiration and water yield of a pine‐broadleaf forest are not altered by long‐term atmospheric [CO 2 ] enrichment under native or enhanced soil fertility

Abstract

Changes in evapotranspiration ( ET ) from terrestrial ecosystems affect their water yield ( WY ), with considerable ecological and economic consequences. Increases in surface runoff observed over the past century have been attributed to increasing atmospheric CO 2 concentrations resulting in reduced ET by terrestrial ecosystems. Here, we evaluate the water balance of a Pinus taeda (L.) forest with a broadleaf component that was exposed to atmospheric [CO 2 ] enrichment (ECO 2 ; +200 ppm) for over 17 years and fertilization for 6 years, monitored with hundreds of environmental and sap flux sensors on a half‐hourly basis. These measurements were synthesized using a one‐dimensional Richard's equation model to evaluate treatment differences in transpiration ( T ), evaporation ( E ), ET , and WY . We found that ECO 2 did not create significant differences in stand T, ET , or WY under either native or enhanced soil fertility, despite a 20% and 13% increase in leaf area index, respectively. While T , ET , and WY responded to fertilization, this response was weak ( E responded to ECO 2 in the first 7 years of the study, this effect was of negligible magnitude ( P. taeda , our results imply that recent observations of increased global streamflow cannot be attributed to decreases in ET across all ecosystems, demonstrating a great need for model–data synthesis activities to incorporate our current understanding of terrestrial vegetation in global water cycle models.

Bibliographic Information