Water use efficiency (WUE) has been recognized as an effective trait for assessing ecosystem response to climate change. It quantifies how much water an ecosystem uses relative to carbon gained. A widespread and severe drought occurred in southwestern China in 2009 and 2010, providing a unique opportunity to directly evaluate how WUE changes with drought stress in the Ailaoshan primary subtropical forest.
Prof. ZHANG Yiping and his team of Xishuangbanna Tropical Botanical Garden (XTBG) calculated water use efficiency using measures of gross primary production (GPP) and evapotranspiration (ET) from five years of continuous eddy covariance measurements (2009–2013) obtained over the Ailaoshan primary subtropical forest. They analyzed eddy-covariance (EC) measurements of carbon and water vapor exchange.
The researchers evaluated the diurnal, seasonal and inter-annual variations of WUE and underlying water use efficiency (UWUE) of the Ailaoshan primary subtropical forest. Instantaneous WUE during the wet and dry season showed a varied diurnal cycle trend, with a primary WUE maximum in the early morning and a secondary maximum in the evening.
WUE exhibited considerable seasonal variation, with the highest values during the wet season and the lowest values during the later dry season. WUE in the wet season was always higher than that in the dry season, due to the more increased GPP in the wet season.
Annual gross ecosystem primary productivity responded less to drought stress than evapotranspiration in 2009.
During the leaf emergence stage, the variation of WUE could be suitably explained by water-related variables (relative humidity, soil water content at 100 cm, solar radiation and the green index).
The study showed that the water use efficiency in Ailaoshan primary subtropical forest were highly variable at different time scales. The findings highlighted the complexities involved in climatic and biotic factors in the different time scales.
ZHANG Yiping Ph.D Principal Investigator Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China Tel: 86-871-65160904 E-mail: email@example.com
Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences. Menglun, Mengla, Yunnan 666303, China
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