遮荫和环剥对刺槐、侧柏苗木碳素分配和水力学特性的影响

Effects of Shading and Girdling on Carbon Allocation and Hydraulic Architecture of Robinia pseudoacacia and Platycladus orientalis Seedlings

【目的】通过分析碳限制条件下2种植物的碳素分配和水分关系,研究碳限制对树木水力学特性的影响,以期更深入了解碳限制对水力学特性的影响模式,揭示水力学失败和碳饥饿的交互作用方式。【方法】采用遮荫和环剥处理对刺槐和侧柏造成碳限制,测定2个树种生物量分配、不同部位非结构性碳(NSC)浓度,并测定根系系导水率、枝条凌晨和正午水势、粗根和枝条导水率损失值(PLC)、叶片气孔导度。【结果】遮荫和环剥均显著降低刺槐和侧柏不同部位的生物量,尤其是细根生物量降幅最大;遮荫和环剥使2个树种根NSC浓度显著降低,环剥使侧柏茎NSC浓度显著增加;2种处理均导致刺槐和侧柏根系导水率显著下降,遮荫和环剥处理刺槐的根系导水率分别为对照的3.7%和2.9%,侧柏为21.0%和7.6%;2种处理均导致2个树种根和茎PLC显著增加,以及枝条凌晨和正午水势显著降低;遮荫和环剥处理均导致2个树种气孔导度显著下降,刺槐气孔导度分别为对照的33.7%和26.1%,侧柏分别为对照的46.9%和23.4%。【结论】碳限制会减少光合产物向根部的分配,抑制新根的发生,降低根的水分吸收和输导能力,影响根和茎的水力学特性,反过来又限制植物的碳同化,以致影响植物在逆境下的存活。

【Objective】Carbon balance and the maintenance of hydraulic architecture are indispensable for plants＇ survival. Correspondently,carbon starvation and hydraulic failure are the main physiological mechanisms of droughtinduced tree mortality. Recent researches have showed that the interaction of the two mechanisms may play a more important role in the death of trees under drought stress. However,it is still blurry about how carbon starvation affects hydraulic failure. This study explored the effect of carbon limitation on hydraulic architecture by analyzing the changes of hydraulic architecture in Robinia pseudoacacia and Platycladus orientalis seedlings exposed to carbon limitation conditions.This study would facilitate us to further understand the effects of carbon limitation on hydraulic architecture,and also to reveal the interaction between carbon starvation and hydraulic failure. 【Method】Shading and girdling were conducted on R. pseudoacacia and P. orientalis seedlings to create carbon limitation. Biomass allocation,nonstructural carbohydrates（ NSC） concentration in different tissues,root hydraulic conductivity,percentage loss of conductivity（ PLC） in coarse roots and branches,predawn and midday twig water potential,and leaf stomatal conductance of the seedlings were detected. 【Result】For both species,biomass in all organs,especially in fine roots,was significantly reduced by shading and girdling. NSC concentration in roots of the two species was markedly decreased by shading and girdling,and NSC concentration in stem was increased. Root hydraulic conductivity of R. pseudoacacia seedlings with shading and girdling treatments accounted for 3. 7% and 2. 9% of the control,respectively,and that of P. orientalis with shading and girdlingtreatments accounted for 21. 0% and 7. 6% of the control,respectively. For the two species,the root and branch PLC significantly increased in shading and girdling treatments with the root PLC greater than the branch. Meanwhile predawn and midday water potential significantly decreased. Stomatal conductance was also significantly reduced,and with shading and girdling treatments R. pseudoacacia accounted for 33. 7% and 26. 1% of the control,respectively,and P. orientalis accounted for 46. 9% and 23. 4% of the control,respectively. 【Conclusion】Both shading and girdling greatly reduced NSC in roots,and the carbon limitation constrained the growth of new roots,hence reduced the ability of water uptake and transport in roots,which deteriorated hydraulic architecture of roots and stem,and further impeded long-distance water transport. As a result,carbon uptake was in turn constrained. Thus,plant ＇s survival under adverse conditions was influenced. In addition,girdling-induced NSC accumulation above girdles could not alleviate stem PLC for both species.