Ecophysiological Responses of desert shrub to rainfall addition for Reaumurica soongorica in desert ecosystem

Desert environments are characterized by limited and highly variable rainfall, which is an intermittent source of water critical to the evolution of the structure and functioning of desert ecosystems. The present study was to assess the effects of different amounts of rainfall received through discrete rainfall events and of the ecophysiological responses for Reaumurica soongorica along multiple average precipitation (MAP) gradient. A field experiment was performed under seven simulated rainfall amounts (0 - 40 mm) with Reaumurica soongorica at respective High-P (120 mm), Middle-P (67 mm), and Low-P (35 mm) sites along middle and lower reach of Heihe River Basin in July, 2015. Pre-dawn plant water potential (ψ_pd), the rates of photosynthesis and stomatal conductance were measured synchronously. Results showed that: photosynthetic response of R.soongorica to rainfall pulse was significant different. The mean daily leaf gas exchange and maximum photosynthesis rate (P_n-max) of R.soongorica were decreased obviously with decreasing MAP. Vapour pressure deficit (VPD) was the predominant factor for gas exchange limiting. Under the control of VPD, stomatal conductance was pregressively reduced with decreasing ψ_pd, which was functioned as limiting P_n-max and further increasing water use efficiency (WUE). However, when MAP was declined below 35 mm, the response of stomatal conductance to ψ_pd was weakened, from which P_n-max began to increase again. 2 to 4 days hystereric response of R.soongorica ψ_pd to various rainfall events was found in High-P. Stomatal conductance was then increased linearly with increasing ψ_pd, from which P_n-max was also enhanced linearly. While weakly response of ψ_pd to similar rainfall events was observed in Low-P, where stomatal conductance and P_n-max was maintained stable after rain. Mentioned above, the effective rainfall pluse, induced by obvious physiological response of R. soongorica, was 3.63-6.73 mm and 6.73-10.09 mm for Linze and Ejina, respective. Our results provided comprehensively understanding in the consequences of long-term variability in rainfall for the physiology of desert plants and species dynamics in desert ecosystems.