Climate change has intensified the frequency of extreme drought events in desert ecosystems, accompanied by uneven distribution of annual precipitation. Whether extreme precipitation events at different phenophases 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, 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 were explored, including parameters such as photosynthetic gas exchange, chlorophyll fluorescence, and antioxidant enzymes. The findings reveal that: (1) Extreme drought events at different phenophases markedly reduced the photosynthesis of A. ordosica leaves, subsequently leading to the significantly reduction in ANPP accumulation (p<0.05). With the impact degree ordered as follows: flowering and fruiting stage > sprouting stage > vegetative growth stage; (2) During extreme drought events, A. ordosica experiences a decrease in photosynthetic gas exchange capacity and an enhancement in water use efficiency, which are stomatal regulatory responses. Additionally, there is an increase in thermal dissipation, a decline in photochemical activity parameters (such as potential photosynthetic activity of PSII, initial light energy conversion efficiency, actual photochemical quantum yield, and photochemical quenching), and an augmentation of the antioxidant enzyme system, which are non-stomatal regulatory responses; (3) During extreme drought events at different phenophases, the dominant factor leading to a decline in the photosynthetic rate of A. ordosica leaves is stomatal regulation. However, there are phenological differences in the sensitivity of stomatal and non-stomatal regulation. The stomatal regulation of A. ordosica leaves during the sprouting stage is more sensitive compared to other phenophases. Non-stomatal regulation is most sensitive during the vegetative growth stage, with a heightened sensitivity in the modulation of chlorophyll fluorescence. The study reveals differences in the photosynthetic physiological regulation of desert vegetation in response to extreme drought events at different phenophases, offering an innovative perspective on the physiological and ecological regulatory mechanisms of desert ecosystems in the face of climate change.
Climate change has intensified the frequency of extreme drought events in desert ecosystems, accompanied by uneven distribution of annual precipitation. Whether extreme precipitation events at different phenophases 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, 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 were explored, including parameters such as photosynthetic gas exchange, chlorophyll fluorescence, and antioxidant enzymes. The findings reveal that: (1) Extreme drought events at different phenophases markedly reduced the photosynthesis of A. ordosica leaves, subsequently leading to the significantly reduction in ANPP accumulation (p<0.05). With the impact degree ordered as follows: flowering and fruiting stage > sprouting stage > vegetative growth stage; (2) During extreme drought events, A. ordosica experiences a decrease in photosynthetic gas exchange capacity and an enhancement in water use efficiency, which are stomatal regulatory responses. Additionally, there is an increase in thermal dissipation, a decline in photochemical activity parameters (such as potential photosynthetic activity of PSII, initial light energy conversion efficiency, actual photochemical quantum yield, and photochemical quenching), and an augmentation of the antioxidant enzyme system, which are non-stomatal regulatory responses; (3) During extreme drought events at different phenophases, the dominant factor leading to a decline in the photosynthetic rate of A. ordosica leaves is stomatal regulation. However, there are phenological differences in the sensitivity of stomatal and non-stomatal regulation. The stomatal regulation of A. ordosica leaves during the sprouting stage is more sensitive compared to other phenophases. Non-stomatal regulation is most sensitive during the vegetative growth stage, with a heightened sensitivity in the modulation of chlorophyll fluorescence. The study reveals differences in the photosynthetic physiological regulation of desert vegetation in response to extreme drought events at different phenophases, offering an innovative perspective on the physiological and ecological regulatory mechanisms of desert ecosystems in the face of climate change.
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