Lovelock Catherine E, Clough Barry F
Australian Institute of Marine Science, PMB 3, Q4810, Townsville, MC, Australia.
Oecologia. 1992 Oct;91(4):518-525. doi: 10.1007/BF00650325.
Mangroves have similar xanthophyll cycle components/chlorophyll ratios [i.e. (V+A+Z)/chl] to other plant species. (V+A+Z)/chl ratios were sensitive to the light environment in which leaves grew, decreasing as light levels decreased over a vertical transect through a forest canopy. The (V+A+Z)/chl ratio also varied among species. However, in sun leaves over all species, the (V+A+Z)/chl ratios correlate with the proportion of leaf area displayed on a horizontal plane, which is determined by leaf angle. Thus, leaf angle and the xanthophyll cycle may both be important in providing protection from high light levels in mangrove species. A canopy survey assessed whether (V+A+Z)/chl ratios could be correlated with species dominance of exposed positions in forest canopies.Rhizophora mangroves, with near-vertical leaf angles, andBruguiera parviflora, with small, horizontal, xanthophyllrich leaves, dominated the canopy, whileB. gymnorrhiza, a species with large, horizontally arranged leaves, was less abundant at the top of the canopy. Thus, two different strategies for adapting to high solar radiation levels may exist in these species. The first strategy is avoidance through near vertical leaf angles, and the second is a large capacity to dissipate energy through zeaxanthin. The (V+A+Z)/chl ratio was also negatively correlated with the epoxidation state of the xanthophyll cycle pool (the proportion present as violaxanthin and half that present as antheraxanthin) at midday. This suggested that the requirement for dissipation of excess light (represented by the midday epoxidation state) may influence the (V+A+Z)/chl ratio.
红树林与其他植物物种具有相似的叶黄素循环组分/叶绿素比率[即(V+A+Z)/chl]。(V+A+Z)/chl比率对叶片生长所处的光照环境敏感，在穿过森林冠层的垂直样带上，随着光照水平降低而下降。(V+A+Z)/chl比率在不同物种间也存在差异。然而，在所有物种的阳生叶中，(V+A+Z)/chl比率与在水平面上展示的叶面积比例相关，该比例由叶角决定。因此，叶角和叶黄素循环在保护红树林物种免受高光强影响方面可能都很重要。一项冠层调查评估了(V+A+Z)/chl比率是否与森林冠层中暴露位置的物种优势度相关。具有近乎垂直叶角的红树属红树林以及具有小而水平、富含叶黄素叶片的小花木榄属植物占据了冠层，而具有大的水平排列叶片的裸花白骨壤在冠层顶部的数量较少。因此，这些物种可能存在两种适应高太阳辐射水平的不同策略。第一种策略是通过近乎垂直的叶角进行躲避，第二种策略是通过玉米黄质具有强大的能量耗散能力。(V+A+Z)/chl比率在中午时还与叶黄素循环池的环氧化状态（以紫黄质形式存在的比例以及以中间型叶黄素形式存在比例的一半）呈负相关。这表明对过剩光能耗散的需求（由中午的环氧化状态表示）可能会影响(V+A+Z)/chl比率。
