晚霜冻害对黄土区苹果树水分利用能力的影响

目的]通过对比研究,明确晚霜冻害对苹果树生长季水分利用能力影响的程度与机理。方法]利用热扩散技术(TDP)对黄土区苹果树未发生霜冻年和霜冻年主要生长季边材液流速率(J_s)开展连续监测,并同步观测净辐射(R_n)、气温(T_a)等气象因子,计算大气水分亏缺(VPD)等变量。通过对比、相关分析阐明晚霜冻害对苹果树水分利用能力的影响。结果]霜冻发生后,当日午间液流速率最大值(J_(s-max))比霜冻前数日内的最大值降低9%～27%,苹果树水分利用能力(J_(s-max)/VPD)在霜冻后的数日内连续下降。霜冻后当年(2018)生长季平均液流速率比未发生霜冻年(2017)同期下降35%。在整个生长季内,液流速率日平均值(J_(s-mean))与R_n、VPD均具有显著的指数关系,但在相同的R_n或VPD水平下,霜冻年的J_(s-mean)显著低于未发生霜冻年。结论]严重低温霜冻和霜冻后快速升温共同导致了苹果树生长季水分利用能力的显著下降。研究结果为认识霜冻对苹果树水分生理的影响机制提供了理论支撑。

Effects of Late Frost Damage on Water Use of Apple Trees in Loess Plateau Area

Objective] To determine the degree and mechanism of frost damage on water use in growing season of apple trees.Method] Thermal dissipation probe (TDP) was used to monitor continuously the sap flux density (J_s) of apple trees before and after the frost during the main growing seasons for two years. The micro-meteorological factors such as net radiation (R_n), air temperature (T_a) were measured synchronously and the derived variables such as vapour pressure deficit (VPD) was calculated. The effects of late frost on water use of apple trees were analyzed.Result] The maximum sap flux density (J_s-max) around noon on the frost-occurred day decreased by 9%-27% compared with the days before the frost occurring, and J_s-max/VPD decreased continuously in the days after the frost occurring. By comparison, the average daily sap flux density (J_s-mean) in growing season of the frost year (2018) was 35% lower than that in the non-frost year (2017). In the whole main growth season, J_s-mean showed a significant exponential relationship with R_n or VPD, but the J_s-mean of frost-year was significantly lower than that of non-frost-year at the same level of R_n (or VPD).Conclusion]The severe low temperature frost with rapid rise of air temperature after frost together, will cause a significant decline in water use potential of apple trees during the growing season. The results provide support for understanding the mechanism of frost''s influence on water physiology of apple trees.