关键词: 黑沙蒿, 水分利用效率, 季节变化, 环境调控

Abstract: Water use efficiency (WUE) is a key indicator for predicting the impacts of climate change on ecosystem carbon and water cycles. Most studies have explored the changes in the response environment of WUE at a particular scale. Few studies have examined how WUE responds to environments at multiple scales, thus limiting our in-depth understanding of the cross-scale carbon and water cycles. In this study, we measured photosynthesis and transpiration in situ periodically and continuously from June to October 2022 in a community dominated by Artemisia ordosica in Mu Us Sandy Land, and analyzed the seasonal variations in WUE at leaf, canopy, and ecosystem scales. The results showed there were significant seasonal variations in leaf water use efficiency (WUE_L), canopy water use efficiency (WUE_T), and ecosystem water use efficiency (WUE_E). WUE_L was large in June and small in both August and September, ranging from 0.73-2.98 μmol·mmol^-1. Both WUE_T and WUE_E were lowest in June and highest in July and August, ranging from 0.10-7.00 and 0.06-6.25 μmol·mmol^-1. WUE_L was significantly negatively correlated with stomatal conductance. WUE_T was significantly positively correlated with canopy conduc-tance and soil water content, and negatively correlated with vapor pressure deficit (VPD). There was a significant positive correlation between WUE_E and soil water content (SWC₁₀) in 10 cm soil depth. The structural equation model showed that SWC₁₀ and air temperature affected net photosynthetic rate and transpiration rate by modifying stomatal conductance, and thus affecting WUE_L. VPD and SWC₁₀ affected WUE_T by altering transpiration. SWC₁₀, air temperature, and VPD affected WUE_E by regulating ecosystem gross primary productivity. The modelling of carbon and water cycles should thoroughly consider the path and intensity of the effect of environmental factors on WUE at multiple scales.

Key words: Artemisia ordosica, water use efficiency, seasonal variation, environmental regulation