Evapotranspiration and water use efficiency in relation to climate and canopy nitrogen in U.S. forests. Issue 10 (17th October 2016)

• Record Type: Journal Article
• Authors: Guerrieri, Rossella; Lepine, Lucie; Asbjornsen, Heidi; Xiao, Jingfeng; Ollinger, Scott V.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 10(2016:Oct.)
• Page Start: 2610
• Page End: 2629
• Publication Date: 2016-10-17
• Subjects: GPP -- ET -- WUE -- nitrogen -- stable isotopes -- AmeriFlux; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/2016JG003415
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Understanding relations among forest carbon (C) uptake and water use is critical for predicting forest‐climate interactions. Although the basic properties of tree‐water relations have long been known, our understanding of broader‐scale patterns is limited by several factors including (1) incomplete understanding of drivers of change in coupled C and water fluxes and water use efficiency (WUE), (2) difficulty in reconciling WUE estimates obtained at different scales, and (3) uncertainty in how evapotranspiration (ET) and WUE vary with other important resources such as nitrogen (N). To address these issues, we examined ET, gross primary production (GPP), and WUE at 11 AmeriFlux sites across North America. Our analysis spanned leaf and ecosystem scales and included foliar δ 13 C, δ 18 O, and %N measurements; eddy covariance estimates of GPP and ET; and remotely sensed estimates of canopy %N. We used flux data to derive ecosystem WUE (WUEe ) and foliar δ 13 C to infer intrinsic WUE. We found that GPP, ET, and WUEe scaled with canopy %N, even when environmental variables were considered, and discuss the implications of these relationships for forest‐atmosphere‐climate interactions. We observed opposing patterns of WUE at leaf and ecosystem scales and examined uncertainties to help explain these opposing patterns. Nevertheless, significant relationship between C isotope‐derived ci / ca and GPP indicates that δ 13 C can be an effective predictor of forest GPP. Finally, we show that incorporating species functional traits—wood anatomy, hydraulic strategy, and foliar %N—into a conceptual model improved the interpretation of Δ 13 C and δ 18 O vis‐à‐vis leaf to canopy water‐carbon fluxes. Key Points: ET and WUE scaled with canopy N with important implication on vegetation‐climate interactions Carbon isotope‐derived ci/ca reconcile leaf and ecosystem carbon uptake Combining foliar isotopes and tree functional traits allowed to link leaf and canopy water‐carbon relations