Interannual and seasonal variability of water use efficiency in a tropical rainforest: Results from a 9 year eddy flux time series

• Published in: Journal of geophysical research. Atmospheres 2015-01, Vol.120 (2), p.464-479
• Main Authors: Tan, Zheng-Hong, Zhang, Yi-Ping, Deng, Xiao-Bao, Song, Qing-Hai, Liu, Wen-Jie, Deng, Yun, Tang, Jian-Wei, Liao, Zhi-Yong, Zhao, Jun-Fu, Song, Liang, Yang, Lian-Yan
• Format: Article
• Language: English
• Subjects: Boreal forests; Carbon dioxide; confounding effect; Correlation; Drought; Droughts; Dry season; Eddies; environmental controls; evapotranspiration; Flux; Forests; Geophysics; gross primary production; Low temperature; Photosynthesis; Primary production; Rain forests; Rainforests; Seasonal variations; Temperate forests; Time series; Transpiration; Trends; Water use; Water use efficiency; Water vapor
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/2014JD022535

We used a continuous 9 year (2003–2011) eddy flux time series with 30 min resolution to examine water use efficiency in a tropical rainforest and determine its environmental controls. The multiyear mean water use efficiency (Wue) of this rainforest was 3.16 ± 0.33 gC per kg H2O, which is close to that of boreal forests, but higher than subtropical forests, and lower than temperate forests. The water vapor deficit (VPD) had a strong impact on instantaneous Wue, in the manner predicted by stomatal optimization theory. At the seasonal scale, temperature was the dominant controller of Wue. The negative correlation between temperature and Wue was probably caused by high continuous photosynthesis during low‐temperature periods. The VPD did not correlate with Wue at the interannual scale. No interannual trend was detected in Wue or inherent water use efficiency (Wei), either annually or seasonally. The fact that no increasing trend of Wei was found in the studied tropical rainforest, along with other evidence of CO2 stimulation in tropical rainforests, requires special attention and data validation. There was no significant difference between Wue during a drought and the 9 year mean values in the forest we studied, but we found that dry season transpiration (Tr) was consistently lower during the drought compared to the mean values. Finally, whether Wue increases or decreases during a drought is determined by the drought sensitivity of gross primary production (GPP). Key Points We did not detect increasing Wei in the forest studied The VPD did not correlate with Wue at the interannual scale Wue's response to drought is determined by GPP