Abstract
Leaf gas exchange is closely associated with water relations; however, less attention has been given to this relationship over successive drought events. Dynamic changes in gas exchange and water potential in the seedlings of two woody species, Amorpha fruticosa and Robinia pseudoacacia, were monitored during recurrent drought. The pre-dawn leaf water potential declined in parallel with gas exchange in both species, and sharp declines in gas exchange occurred with decreasing water potential. A significant correlation between pre-dawn water potential and gas exchange was observed in both species and showed a right shift in R. pseudoacacia in the second drought. The results suggested that stomatal closure in early drought was mediated mainly by elevated foliar abscisic acid (ABA) in R. pseudoacacia, while a shift from ABA-regulated to leaf-water-potential-driven stomatal closure was observed in A. fruticosa. After re-watering, the pre-dawn water potential recovered quickly, whereas stomatal conductance did not fully recover from drought in R. pseudoacacia, which affected the ability to tightly control transpiration post-drought. The dynamics of recovery from drought suggest that stomatal behavior post-drought may be restricted mainly by hydraulic factors, but non-hydraulic factors may also be involved in R. pseudoacacia.
Highlights
Water availability is one of the principal factors limiting terrestrial biological activity in ecosystems[1]
A similar pattern of gas exchange response to Ψp during the drought cycles was observed in both species, which were fit with exponential sigmoid models
The two species investigated in this study are preferred species for afforestation because of their high drought resistance, and have been planted widely in the Loess Plateau region. Ψp declined in both species in parallel with gas exchange due to the course of soil water depletion, which is typical of plants’ responses to drought[28, 30]
Summary
Water availability is one of the principal factors limiting terrestrial biological activity in ecosystems[1]. It is important to understand the regulation mechanisms of leaf water potential (Ψleaf) on gas exchange during recovery from drought and over recurrent drought cycles. Understanding the correlations of A and gs with Ψleaf would permit an estimation of the limitation of photosynthesis in plants grown under drought stress via stomatal closure and reduced mesophyll conductance www.nature.com/scientificreports/. Metabolic impairment[17, 20] It remains unclear how Ψleaf controls gas exchange during the re-watered period and subsequent drought and whether the relations between Ψleaf and gas exchange are shifted during recurrent drought cycles[11, 21]. The decline of A in response to mild-to-moderate water stress occurs because of increased diffusive resistance within the leaf as well as decreased mesophyll conductance of CO226. An accurate description of the relationship between gas exchange performance and water potential during recovery from drought and a subsequent drought cycle would significantly improve our understanding of plant responses to drought stress
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