Escribano-Rocafort Adrián G, Ventre-Lespiaucq Agustina B, Granado-Yela Carlos, Rubio de Casas Rafael, Delgado Juan A, Balaguer Luis
Department of Ecology, Faculty of Biology, Complutense University of Madrid, Jose Antonio Novais St., 28040 Madrid, Spain,
Department of Ecology, Faculty of Biology, Complutense University of Madrid, Jose Antonio Novais St., 28040 Madrid, Spain.
Ann Bot. 2016 Apr;117(4):643-51. doi: 10.1093/aob/mcw004. Epub 2016 Mar 4.
The spatial arrangement and expression of foliar syndromes within tree crowns can reflect the coupling between crown form and function in a given environment. Isolated trees subjected to high irradiance and concomitant stress may adjust leaf phenotypes to cope with environmental gradients that are heterogeneous in space and time within the tree crown. The distinct expression of leaf phenotypes among crown positions could lead to complementary patterns in light interception at the crown scale.
We quantified eight light-related leaf traits across 12 crown positions of ten isolated Olea europaea trees in the field. Specifically, we investigated whether the phenotypic expression of foliar traits differed among crown sectors and layers and five periods of the day from sunrise to sunset. We investigated the consequences in terms of the exposed area of the leaves at the tree scale during a single day.
All traits differed among crown positions except the length-to-width ratio of the leaves. We found a strong complementarity in the patterns of the potential exposed area of the leaves among day periods as a result of a non-random distribution of leaf angles across the crown. Leaf exposure at the outer layer was below 60 % of the displayed surface, reaching maximum interception during morning periods. Daily interception increased towards the inner layer, achieving consecutive maximization from east to west positions within the crown, matching the sun's trajectory.
The expression of leaf traits within isolated trees of O. europaea varies continuously through the crown in a gradient of leaf morphotypes and leaf angles depending on the exposure and location of individual leaves. The distribution of light-related traits within the crown and the complementarity in the potential exposure patterns of the leaves during the day challenges the assumption of low trait variability within individuals.
树冠内叶综合征的空间排列和表达可以反映给定环境中树冠形态与功能之间的耦合。遭受高光辐射及伴随胁迫的孤立树木可能会调整叶片表型，以应对树冠内时空异质的环境梯度。树冠不同位置叶片表型的差异表达可能导致树冠尺度上光截获的互补模式。
我们在田间对10棵孤立的油橄榄树的12个树冠位置的8个与光相关的叶片性状进行了量化。具体而言，我们研究了叶片性状的表型表达在树冠扇区和层次之间以及从日出到日落的一天中的五个时间段是否存在差异。我们研究了在一天中树木尺度上叶片暴露面积方面的结果。
除叶片长宽比外，所有性状在树冠位置间均存在差异。由于叶片角度在树冠上的非随机分布，我们发现不同时间段叶片潜在暴露面积模式具有很强的互补性。外层叶片的暴露面积低于展示面积的60%，在早晨时段达到最大截光量。从外层到内层，每日截光量增加，在树冠内从东向西位置连续达到最大值，与太阳轨迹相匹配。
油橄榄孤立树体内叶片性状的表达在树冠内连续变化，呈现出叶片形态类型和叶片角度的梯度变化，这取决于单叶的光照情况和位置。树冠内与光相关性状的分布以及白天叶片潜在暴露模式的互补性，对个体内性状变异性低这一假设提出了挑战。
