Effect of stomatal control onPopulus simonii Carrstand transpiration in farmland shelterbelt, China's semi-arid region

Farmland shelterbelt is an important biome for protecting the oasis agricultural system, andPopulus simonii Carris the main tree species of farmland shelterbelt. The unknown mechanism of controlling tree transpiration under different drought conditions restricted the development of farmland shelterbelt. In this study, we applied sap flow to measure stand transpiration, coupled with calculating canopy conductance, aerodynamic conductance and the decoupling coefficient, to identify the effect of environmental change on farmland shelterbelt transpiration and protection. Results showed stand transpiration of the farmland shelterbelt increased with soil water content rising, the stand transpiration was 7.69 L d(-1), 10.48 L d(-1)and 15.96 L d(-1)at heavy drought, medium drought and wet period, respectively; the daily canopy conductance ranged from 5.32 x 10(-5)to 5.24 x 10(-4) ms(-1). Climate change and water stress affected farmland shelterbelt transpiration by changing stomata and leaf area index. Stomata controls most of the stand transpiration in heavy dry and wet periods, while temperature, relative humid and solar radiation play more important roles in moderately dry periods. In the shelterbelt, it is the atmospheric demand and vapor pressure deficit that control farmland shelterbelt stand transpiration. This investigation provides a preliminary interpretation of the mechanism of the motion of shelterbelt transpiration in China's semi-arid region.