关键词: 刺槐, 侧柏, 碳限制, 碳素分配, 气穴栓塞, 根系导水率, 气孔导度

Abstract: [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 drought-induced 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 girdling treatments 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.

Key words: Robinia pseudoacacia, Platycladus orientalis, carbon limitation, carbon allocation, embolism, root hydraulic conductivity, stomatal conductance