Previous studies have reported that the establishment of rubber plantations in Xishuangbanna has made local people face water shortages during the dry season, which seldom occurred prior.
Despite the belief that rubber plantations cause water shortages, little is known regarding the coupling between the carbon and water cycles in the case of rubber trees, although the plantations represent a substantial carbon sink in this part of China.
Researchers from Global Change Ecology Group of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to examine the annual and interannual dynamics of water use efficiency (WUE) during the growing season and the interannual trend of WUE in rubber plantations. They also wanted to explore the environmental and biological factors that control the variation in monthly WUE.
The researchers used a four-year (2013–2016) continuous biometric survey along with sap flow data recorded at a monthly resolution in Xishuangbanna.
They observed a pattern in annual water use efficiency characterized by peak values generally occurring around August during the growing season from April to December. The multi-year mean WUE of rubber plantations was markedly lower than the annual mean WUE values reported for evergreen broadleaved and tropical forests.
The results showed that WUE related more to both air temperature and net radiation than other factors. WUE depended more on growth rate of the diameter than other biological factors. WUE was determined more by the carbon gain rather than water consumption.
Their results indicated that the coupling processes between the carbon and water cycles of the rubber plantations might be mainly controlled by factors that affect the carbon sequestration rather than water consumption in Southwest China, while the latter might tend to decrease the strength of the coupling processes when it exceeded a certain threshold.