不同冠高腾冲栲叶片结构及其影响因子

树高的水力限制假说认为树木顶端的叶片受到水分胁迫后气孔导度降低,从而减少了碳积累,并限制了顶端生长和树木高生长.然而有实验表明美国黄松(Pinus ponderosa)叶片内非结构性移动碳化合物(NSC)并没有随着高度的增加而降低.为了解阔叶树种中NSC是否表现出同样的规律,以及结合NSC、叶片形态特征和水力结构来进一步综合探讨树木高生长的限制机理,我们测量了腾冲栲不同高度梯度的叶片大小、叶片表皮细胞大小、气体交换、NSC含量以及木质部导管大小.结果发现随着高度增加,叶片大小和表皮细胞大小在降低;气孔导度、单位干重和单位面积的光合速率都没有下降;单位干重和单位叶面积的可溶性糖含量在升高;单位干重和单位叶面积的淀粉含量维持在一个稳定的水平.这说明叶片和表皮细胞变小可能不是由于碳获得减少造成的,树木高生长的停滞可能并不能从单位叶片的碳积累不足角度来解释.木质部导管直径随树木长高在减小,表明水分传导能力减小,因而高处叶片可能遭受更低的水势和膨压使细胞生长受限.

A study on leaf structures of Castanopsis wattii at different crown height and the influencing factors

The Hydraulic Limitation Hypothesis predicted that stomata conductance decreases by tree height,consequently decreases carbon gain in leaves and limits the growth of the tree top,but an experiment in Pinus ponderosa demonstrated that non-structural mobile carbon compounds (NSC) did not decrease by tree height.Our objective was to understand whether leaf carbon gain show the same trend in broad-leaved species,and to understand the structural changes in leaves by tree height.We sampled the twigs which were fully sun-exposed at different height of Castanopsis wattii trees and measured the size of leaves,the size of epidermal cells, the concentration of NSC and the diameter of conduits in xylem.The size of leaves and epidermal cells decreased by height,indicating that the growth of leaves in top was limited.Leaf photosynthesis per unit mass and per unit area did not decrease.The concentration of soluble sugar per weight and per area increased by increasing height and the concentration of starch per weight and per area did not change,indicating that the limitation of tree top growth may not due to carbon gain.The diameter of xylem conduits decreased,suggesting that the ability of water conduct decreased by increasing height.Therefore,top leaves of the tree may suffer more negative water potential and lower turgor which limit the cell expansion.