COS 71-4 - CANCELLED - The effect of environmental gradients on water use efficiency across National Ecological Observatory Network, USA

Background/Question/Methods

Water use efficiency (WUE) is central to the coupled carbon-water cycling as an integrated measure of the relative efficiency of carbon gain through photosynthesis to the water loss through transpiration. Knowledge gaps still exist about the relative importance of different environmental drivers, and the interspecific variation of WUE at a large scale. In this study, the stable isotopes of carbon in sunlit foliage samples were used to quantify the intrinsic water use efficiency (iWUE) of woody plants at 44 sites across National Ecological Observatory Network (NEON), USA. We hypothesize that: 1) iWUE varies with the climate factors across different eco-climatic domains at a continental scale but is significantly influenced by soil conditions within eco-climatic domains; 2) evergreen needleleaf trees (ENT) have larger mean iWUE while deciduous broadleaf trees (DBT) have smaller mean iWUE; 3) Isohydric species has wider range of iWUE whereas anisohydric species has narrower range of iWUE.

Results/Conclusions

Results showed that 1) mean annual precipitation is the dominant controlling climatic factor for iWUE across eco-climatic domains while soil texture and hydraulic conductivity significantly influence the iWUE within eco-climatic domains; 2) among the three pervasive genera (Acer, Pinus, and Quercus), Pinus (ENT, isohydric) has largest mean value of 71.3 mmol mol^-1 and its iWUE ranges from 22.7 to 124.0 mmol mol^-1 with minimum and maximum in D08 Ozarks Complex and D13 Southern Rockies & Colorado Plateau, respectively; Acer (DBT, isohydric) has least mean value of 63.7 mmol mol^-1 and its iWUE ranges from 20.3 to 101.7 mmol mol^-1 with minimum and maximum in D08 Ozarks Complex and D05 Great Lakes, respectively; Quercus (DBT, anisohydric) has smaller mean value of 65.3 mmol mol^-1 and its iWUE ranges from 32.3 to 106.5 mmol mol^-1 with minimum and maximum in D08 Ozarks Complex and D17 Pacific Southwest, respectively. The differences of iWUE across species may be due to species-specific water-use strategies as a result of adaptive evolution under different environmental conditions. The results also suggested that stable isotopes of carbon in foliage samples is a good approach to quantify the spatial variation of iWUE and its response to environmental gradients.