Water-use efficiency and its relationship with environmental and biological factors in a rubber plantation.

Water-use efficiency ( WUE ) at the whole-plant level plays as an important role as an indicator of both the water-use strategy of the plant, and the ecophysiological processes linking the carbon and water cycles. However, the variation in the annual pattern of WUE , the interannual trends, and the regulating factors of WUE in rubber plantations remain poorly understood. Here, we used a four-year (2013–2016) continuous biometric survey along with sap flow data recorded at a monthly resolution to examine the annual and interannual dynamics of WUE and the relationships of WUE with environmental and biological factors in rubber ( Hevea brasiliensis ) plantations in Southwest China. The results showed that (1) there was no definitive pattern in WUE between April and December, but the peak WUE values generally occurred around August; (2) the multi-year mean WUE was 2.34 ± 0.19 g C·kg −1 H 2 O, and a negative correlation of WUE to photosynthetically active radiation was found at the interannual scale ( r  = −0.962, P  < 0.05); and (3) a moderate, significant and parabolic relationship of WUE with air temperature ( R 2  = 0.40), net radiation ( R 2  = 0.37) and growth rate of the diameter at breast height ( R 2  = 0.35) was observed at the monthly scale during the growing season ( P  < 0.001). These findings indicate that WUE might be regulated by factors affecting the carbon sequestration rather than water consumption, and it will provide a deeper understanding of the ecohydrological and coupled processes between the carbon and water cycles of rubber plants. [ABSTRACT FROM AUTHOR]