Woody tissue photosynthesis delays drought stress inPopulus tremulatrees and maintains starch reserves in branch xylem tissues

摘要

Photosynthesis in woody tissues (P-wt) is less sensitive to water shortage than in leaves, hence,P(wt)might be a crucial carbon source to alleviate drought stress. To evaluate the impact ofP(wt)on tree drought tolerance, woody tissues of 4-m-tall drought-stressedPopulus tremulatrees were subjected to a light-exclusion treatment across the entire plant to inhibitP(wt). Xylem water potential (psi(xylem)), sap flow (FH2O), leaf net photosynthesis (P-n,P-l), stem diameter variations (Delta D),in vivoacoustic emissions in stems (AEs) and nonstructural carbohydrate concentrations ([NSC]) were monitored to comprehensively assess water and carbon relations at whole-tree level. Under well-watered conditions,P(wt)kept psi(xylem)at a higher level, loweredFH2Oand had no effect on [NSC]. Under drought,psi(xylem),FH2OandP(n,l)in light-excluded trees rapidly decreased in concert with reductions in branch xylem starch concentration. Moreover, sub-daily patterns of Delta D,FH2Oand AEs were strongly related, suggesting thatin vivoAEs may inform not only about embolism events, but also about capacitive release and replenishment of stem water pools. Results highlight the importance ofP(wt)in maintaining xylem hydraulic integrity under drought conditions and in sustaining NSC pools to potentially limit increases in xylem tension.