Jordan Gregory J, Brodribb Timothy J
School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia.
Funct Plant Biol. 2007 Oct;34(10):918-924. doi: 10.1071/FP07166.
This paper examines physiological characteristics of the leaves of Agastachys odorata R.Br., a wet-climate sclerophyllous shrub with very long-lived leaves. It addresses the hypothesis that cuticles become leakier to water vapour as leaves age. Astomatous cuticular conductance, whole-leaf minimum epidermal conductance, leaf damage and accumulation of epiphylls all increased several-fold with leaf age from first year growth to 10 years of age. Maximum carbon assimilation peaked 1 year after full leaf expansion, then declined. Intrinsic water use efficiency was highest in mid-aged leaves and declined markedly in the oldest leaves. Stomatal density, stomatal size and cuticle thickness did not vary significantly among ages. The older leaves were less effective at controlling water loss, resulting in decreases in water use efficiency. A differential increase in the conductance of the stomatal surface of the leaves relative to astomatous surface suggested that stomatal leakiness was significant in leaves over five years old. Although data for other species is ambiguous, the deterioration in A. odorata appears to be consistent with changes in the oldest leaves of other species. Thus, decreasing ability to use water efficiently appears to be a consequence of accumulated damage and may contribute to the need for leaf senescence in evergreen species with little self shading.
本文研究了长叶排草（Agastachys odorata R.Br.）叶片的生理特征，长叶排草是一种生长在湿润气候下的硬叶灌木，其叶片寿命极长。本文探讨了如下假说：随着叶片衰老，角质层对水蒸气的渗透性会增加。从第一年生长到10年生，无气孔角质层导度、全叶最小表皮导度、叶片损伤以及叶附生物的积累均随叶龄增加了几倍。最大碳同化作用在叶片完全展开1年后达到峰值，随后下降。内在水分利用效率在中年叶片中最高，在最老叶片中显著下降。气孔密度、气孔大小和角质层厚度在不同叶龄间无显著差异。较老的叶片在控制水分流失方面效果较差，导致水分利用效率降低。叶片气孔表面相对于无气孔表面导度的差异增加表明，五年以上叶片的气孔渗漏很显著。尽管其他物种的数据尚不明确，但长叶排草的这种退化似乎与其他物种最老叶片的变化一致。因此，水分利用效率下降似乎是累积损伤的结果，可能促使几乎没有自我遮荫的常绿树种出现叶片衰老现象。
