Water-and carbon-related physiological mechanisms underlying the decline of wild apricot trees in Ili,Xinjiang,China
Aims Wild apricot(Prunus armeniaca var.ansu)in Xinjiang of China,one of the origin species of apricot cultivars around the world,has important economical and ecological values,whereas natural apricot forests in Xinjiang have experienced serious decline and mortality in recent years.It is of great significance to carry out research on the underlying mechanisms for the conservation and recovery of wild apricots in Xinjiang.Methods In the present study,the xylem hydraulic properties and tissue non-structural carbohydrate(NSC)contents of relatively healthy(dead branches ≤30％)and seriously declined(dead branches ≥70％)wild apricot trees in Ili,Xinjiang were compared to analyze the potential role of hydraulic dysfunction and carbon imbalance in mediating the decline and mortality of this species.Important findings The results showed that the seriously declined apricot trees had significantly lower leaf area at the branch level,but there were no significant differences in leaf mass per area,relative chlorophyll content and stomatal conductance between the severely declined and relatively healthy trees.The midday leaf water potential,branch hydraulic efficiency and embolism resistance of seriously declined apricot trees were significantly lower than those of relatively healthy ones,indicating an evident xylem hydraulic impairment.The total NSC content of seriously declined trees was lower than that of relatively healthy trees,but the soluble sugar-to-starch content ratio in the stem xylem of seriously declined trees was significantly higher.Impaired hydraulic functioning was accompanied by decreased carbon assimilation capacity and reduced NSC reserve.On top of hydraulic dysfunction,carbon imbalance further contributed to the weakening of tree defense against scale insects,eventually leading to the decline and mortality of apricot trees due to the interplay between plant water relations and carbon economy.
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