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The seasonal and diurnal variation in transpiration rate and stomatal conductance of four dominant shrub species (Caragana intermedia, Hippophae rhamnoides, Hedysarum leave, Salix psammophyla) planted in schemes designed to restore vegetation and conserve water in the arid soils of northwest China were studied. Transpiration rates were measured at the leaf scale using a porometer and then combined with data on leaf area, leaf mass, and remotely sensed information on shrub stand size, to scale-up the leaf-based estimates to the individual and stand scale. The results showed that the leaf daily transpiration rates per dry leaf mass of H. leave and H. rhamnoides was greater than that of C. intermedia and S. psammophyla. For C. intermedia, the most drought-adapted species at the individual plant scale, has the lowest daily transpirational water consumption (2808 g). The total diurnal transpirational water consumption of three shrubs stands at the Wufendi small catchment was 74 tonnes of water in August 2002. C. intermedia is a more suitable species for planting in ecological restoration schemes in chestnut soils in northwest China. However, for long-term ecosystem stability and health at the catchment scale, a more diverse selection of shrubs should be used in the eco-reclamation programs. [ABSTRACT FROM AUTHOR]

Abstract: The net CO2 exchange between the atmosphere and an alpine meadow ecosystem (NEE) was measured by Eddy covariance technique in Damxung county (30°25′N, 91°05′E, 4333ma.s.l.), Tibet, China for three continuous growing seasons from 2003 to 2005. The apparent quantum use efficiency (α) of alpine meadow was derived based on the linear function between NEE and photosynthetically active radiation (PAR) under low light. A model driven by the main ecological factors, such as temperature, CO2 concentration was further adapted for α modeling at stand level. The key parameter of this model was the maximum apparent quantum use efficiency (α 0), which could be inversed with the model. As a parameter for the growth status of a plant community, α 0 changed in accord with leaf area index (LAI), and the maximum for alpine meadow was about 0.016μmolCO2 μmol−1 PAR. If considered by the soil moisture (θ), α 0 was linearly correlated with θ when the soil moisture was lower than 0.2m3 m−3, and α 0 leveled off gradually when θ was higher than 0.2m3 m−3. This model provides a method to simulate α at stand level and can be applicable to different communities. When the CO2 concentration is double in the future, the α of alpine meadow will increase by 7%, and the tendency might be strengthened by the global warming. [Copyright &y& Elsevier]