摘叶造成的碳限制对刺槐碳素分配和水力学特性的影响

Effects of defoliation-induced carbon limitation on carbon allocation and hydraulic architecture of Robinia pseudoacacia Linn. seedlings

以3年生刺槐(Robinia pseudoacacia Linn.)为研究对象,通过对其进行连续3次摘叶造成严重碳限制,检测摘叶后刺槐的生物量分配、叶片形态和不同部位的非结构性碳(NSC)浓度,同时检测其根压和根系导水率、枝条水势和导水率损失值(PLC)及茎的抗栓塞能力,研究摘叶造成的碳限制对刺槐碳素分配和水力学特性的影响。结果显示,摘叶显著降低了刺槐不同部位的生物量,其中细根生物量降低程度最大;摘叶还造成了刺槐不同部位NSC浓度显著降低,茎韧皮部、茎木质部、根韧皮部和根木质部的NSC浓度分别为对照的29.6%、20.2%、10.2%和8.7%,且根部NSC的降低程度显著高于茎;碳限制显著降低了刺槐苗木的根压和根系导水率,增加了枝条凌晨和正午的PLC,降低了其抗栓塞能力。研究结果表明摘叶造成的碳限制改变了刺槐的碳素分配模式,限制了碳素向根的分配,抑制细根的发生,进而限制根的水分吸收能力,加重枝条栓塞程度,同时还会导致枝条抗栓塞能力下降,从而降低植物水分输导的安全性。

This study aimed to explore how carbon limitation affects the carbon allocation and hydraulic characteristics of trees. It was conducted on three-year-old Robinia pseudoacacia Linn. seedlings by three-time artificial defoliation. Biomass allocation, leaf morphology, nonstructural carbohydrate （NSC） concentration in different tissues, root pressure, root hydraulic conductivity, branch water potential, branch percentage loss of conductivity （PLC）, and xylem vulnerability to embolism were measured after defoliation. The biomasses of all organs, especially that of fine roots, were significantly reduced. Defoliation-induced carbon limitation significantly reduced NSC concentration in all tissues. NSC in the branch phloem,branch xylem, root phloem, and root xylem accounted for 29.6%, 20.2%, 10.2%, and 8.7% of the control, respectively. The reduction in NSC concentration in the roots was more severe than that in the branches. Root pressure and root hydraulic conductivity were also significantly reduced. Predawn and midday branch PLC was significantly increased, and xylem cavitation resistance was significantly decreased compared with that of the control. Results indicated that defoliation-induced carbon limitation reduced the ability of water uptake in the roots due to decreased biomass in the fine roots and decreased NSC. The reduced capacity of root water uptake further deteriorated hydraulic function of the roots and stems, which impeded long- distance water transport. Carbon limitation also reduced the safety of water transport by damaging cavitation resistance.