Abstract
This study investigated the physiological and ecological changes in P. sepium Bunge and elucidated the physiological regulatory mechanisms underlying the adaptation of P. sepium to drought stress in shell sand. Drought stress led to a significant decrease in the net photosynthesis rate (Pn) and respiration rate of leaves and a decrease in low-intensity light-use efficiency (LUE) and light ecological amplitude. An increase in drought stress led to a considerable decrease in the photosynthetic electron transport rate in the P. sepium leaves and a significant increase in the amount of light energy dissipated as heat. In addition, the photosynthesis process suffered from severe photoinhibition. P. sepium plants counteracted the effects of drought stress primarily by increasing their peroxidase (POD) activity and by regulating membrane lipid peroxidation by secreting greater numbers of osmotic adjustment substances (proline (Pro) and soluble sugars (Ss)) and malondialdehyde (MDA). As drought stress increased, both the stem sap flow rate and the cumulative sap flow of P. sepium decreased considerably. P. sepium Bunge adapts to drought stress through interregulatory activity between photosynthesis, water-related physiological activities, and physiological and biochemical processes, and this species exhibits relatively high adaptive plasticity to drought.
Highlights
Shell ridges are unique beach ridge landforms near the high tide line that forms from the accumulation of residual shells from dead mollusks and their fragments, which are transported by waves
There was a significant difference in the extent of the decreases in the photosynthesis rate (Pn) and Gs between the P. sepium leaves in the shell sand habitats under different drought stress conditions
As the degree of drought in shell sand area increased, a significant decrease in the Pn, transpiration rate (Tr), Gs, and light energy for photosynthesis of P. sepium Bunge leaves occurred, and an increased amount of light energy was dissipated as heat
Summary
Shell ridges are unique beach ridge landforms near the high tide line that forms from the accumulation of residual shells from dead mollusks and their fragments, which are transported by waves. How changes in the water contents of shell sand affect the photosynthesis, water transport, and physiological and biochemical processes of the dominant species P. sepium Bunge along the shell ridges in the Yellow River Delta as well as the tolerance and adaptability of P. sepium Bunge to drought stress in shell sand remain unknown. The physiological and ecological regulatory mechanisms through which P. sepium Bunge adapts to drought stress in shell sand remain unclear These factors somewhat hinder water management and the selection of habitats with suitable soil water contents, both of which are vital for guiding the planting of P. sepium Bunge in the degraded ecosystem of the shell ridges along the Yellow River Delta. This study investigated four-year-old seedlings of P. sepium Bunge, a typical xerophytic shrub species that grows along the shell ridges in the Yellow River Delta, on four simulated shell sand habitats whose water conditions differ. This study aimed to provide a reference for the water management of plant resources in dry shell sand habitats
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