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Canopy temperature is a result of the canopy energy balance and is driven by climate conditions, plant architecture, and plant-controlled transpiration. Here, we evaluated canopy temperature in a rubber plantation (RP) and tropical rainforest (TR) in Xishuangbanna, southwestern China. An infrared temperature sensor was installed at each site to measure canopy temperature. In the dry season, the maximum differences (T − T) between canopy temperature (T) and air temperature (T) in the RP and TR were 2.6 and 0.1 K, respectively. In the rainy season, the maximum (T − T) values in the RP and TR were 1.0 and −1.1 K, respectively. There were consistent differences between the two forests, with the RP having higher (T − T) than the TR throughout the entire year. Infrared measurements of T can be used to calculate canopy stomatal conductance in both forests. The difference in (T − T) at three g levels with increasing direct radiation in the RP was larger than in the TR, indicating that change in (T − T) in the RP was relatively sensitive to the degree of stomatal closure. [ABSTRACT FROM AUTHOR]

We calculated water use efficiency (WUE) using measures of gross primary production (GPP) and evapotranspiration (ET) from five years of continuous eddy covariance measurements (2009-2013) obtained over a primary subtropical evergreen broadleaved forest in southwestern China. Annual mean WUE exhibited a decreasing trend from 2009 to 2013, varying from ~2.28 to 2.68 g C kg H2O−1. The multiyear average WUE was 2.48 ± 0.17 (mean ± standard deviation) g C kg H2O−1. WUE increased greatly in the driest year (2009), due to a larger decline in ET than in GPP. At the diurnal scale, WUE in the wet season reached 5.1 g C kg H2O−1 in the early morning and 4.6 g C kg H2O−1 in the evening. WUE in the dry season reached 3.1 g C kg H2O−1 in the early morning and 2.7 g C kg H2O−1 in the evening. During the leaf emergence stage, the variation of WUE could be suitably explained by water-related variables (relative humidity (RH), soil water content at 100 cm (SWC_100)), solar radiation and the green index (Sgreen). These results revealed large variation in WUE at different time scales, highlighting the importance of individual site characteristics. [ABSTRACT FROM AUTHOR]