Response of Leaf Photosynthesis–Transpiration Coupling to Biotic and Abiotic Factors in the Typical Desert Shrub Artemisia ordosica

Abstract

The environmental regulatory mechanism underlying the coupling of leaf photosynthesis and transpiration in Artemisia ordosica, a typical desert shrub in China, remains unclear. To understand this mechanism, we measured the net leaf photosynthetic rate (Pn), transpiration rate (E), and stomatal conductance (gs) from May to October 2019 using a portable photosynthesis analyser. Photosynthetically active radiation, air temperature, relative humidity, and soil water content were simultaneously measured. Both E and Pn are positively correlated with gs. Pn and E exhibited a nonlinear quadratic correlation from May to July and a linear correlation in August and September. The changes in the maximum photosynthetic (Pn−max) and carboxylation rates were mainly affected by air temperature and light. Seasonally, Pn−max initially exhibited an increasing trend, peaking in June and then decreasing. Under low temperature and light conditions, Pn−E was linearly correlated and the coupling relationship was stable. Under higher temperatures and radiation, Pn−E exhibited a nonlinear quadratic correlation, and decoupling occurred with increasing temperature and light intensity. The results of this study provide a better understanding of the responses of desert shrub ecosystems to climate change.