Impacts of extreme drought events at each phenophase on the Aboveground net primary productivity and its photosynthetic physiological regulatory process of sandy semi-shrubs.

Climate change has intensified the frequency of extreme drought events in desert ecosystems, accompanied by uneven distribution of annual precipitation. Whether extreme drought events at each phenophase have equivalent impacts on desert plants is an unverified topic, yet it is crucial for understanding the mechanisms of vegetation adaptation to changes in precipitation. This study focuses on the typical desert plant Artemisia ordosica and employs in situ precipitation control experiments using rain shelters to simulate extreme drought events (30 consecutive days of precipitation removal) at three phenophases: the sprouting stage, vegetative growth stage, and flowering and fruiting stage. Against this backdrop, we explored phenological differences in the leaf photosynthetic physiological regulatory mechanisms that affect the accumulation of Aboveground Net Primary Productivity (ANPP) in A. ordosica under extreme drought events. The parameters examined included photosynthetic gas exchange, chlorophyll fluorescence, and antioxidant enzymes activities. The findings reveal that: (1) Extreme drought events at each phenophase significantly suppressed the photosynthesis of A. ordosica leaves, leading to a marked decrease in ANPP accumulation (p < 0.05). The impact severity was ordered as follows: flowering and fruiting stage > sprouting stage > vegetative growth stage; (2) A. ordosica experiences both stomatal regulatory responses, and non-stomatal regulatory responses,to adapt to the extreme drought events. The stomatal regulation of A. ordosica leaves during the sprouting stage is more sensitive. Non-stomatal (chlorophyll fluorescence) regulation is most sensitive during the vegetative growth stage. These findings highlight the variations in the photosynthetic physiological regulation of desert vegetation in response to extreme drought events at each phenophase, providing an innovative perspective on the physiological and ecological regulatory mechanisms of desert ecosystems under climate change.