Niinemets Ulo, Cescatti Alessandro, Christian Rochelle
Department of Plant Physiology, Institute of Molecular and Cell Biology, University of Tartu, Riia 23, Tartu 51010, Estonia.
Tree Physiol. 2004 Jun;24(6):617-30. doi: 10.1093/treephys/24.6.617.
Shoot architecture may significantly alter mean quantum flux on foliage and thus, photosynthetic productivity. There is currently only limited information about plastic alterations in shoot structure caused by within-canopy variation in mean integrated irradiance (Q(int)) in broad-leaved trees. We studied leaf and shoot structure, and nitrogen and carbon content in late-successional, widely distributed, temperate, broad-leaved Nothofagus taxa to determine the architectural controls on light harvesting and photosynthetic performance. Nothofagus fusca (Hook. f.) Oersted has larger leaves and less densely leaved shoots than the N. solandri varieties. Nothofagus solandri var. solandri (Hook. f.) Oersted is characterized by rounder leaves that potentially have a larger overlap than the ovate-triangular leaves of N. solandri var. cliffortioides (Hook. f.) Poole. Leaf dry mass (M(A)) and nitrogen content (N(A)) per unit area increased with increasing Q(int) in all species, demonstrating enhanced investment of photosynthetic biomass in high light. Although M(A) differed between species at a common irradiance, there was a uniform relationship between N(A) and Q(int) across species. Leaf carbon content per dry mass and leaf dry mass to fresh mass ratio also scaled positively with irradiance, suggesting greater structural investments in high light. In all species, shoots became more horizontal and flatter at lower Q(int), implying an enhanced use efficiency of direct irradiance in natural leaf positions. In contrast, irradiance effects on leaf aggregation varied among species. Across the data, leaf overlap or leaf area density was often greater at lower irradiances, possibly as a result of limited carbon availability for shoot axis extension growth. In N. fusca, leaves of which were more aggregated in high light, the shoot silhouette to total leaf area ratio (S(S)) declined strongly with increasing irradiance, demonstrating a lower light harvesting efficiency at high Q(int). This effect was only moderate in N. solandri var. cliffortioides and S(S) was independent of Q(int) in N. solandri var. solandri. Although the efficiency of light interception at high irradiances was lowest in N. fusca, this species had the greatest nitrogen content per unit shoot silhouette area (2N(A)/S(S)), indicating superior shoot-level photosynthetic potential. These data collectively demonstrate that shoot architecture significantly affects light interception and photosynthesis in broad-leaved trees, and that structural carbon limitations may constrain leaf light harvesting efficiency at low irradiance.
枝条结构可能会显著改变叶片上的平均量子通量，进而影响光合生产力。目前，关于阔叶树树冠内平均积分辐照度（Q(int)）变化引起的枝条结构可塑性变化的信息有限。我们研究了处于演替后期、分布广泛的温带阔叶假山毛榉类群的叶片和枝条结构，以及氮和碳含量，以确定对光捕获和光合性能的结构控制。与索氏假山毛榉变种相比，福氏假山毛榉（Hook. f.）Oersted的叶片更大，枝条的叶密度更低。索氏假山毛榉变种索氏（Hook. f.）Oersted的特点是叶片更圆，与悬崖假山毛榉变种（Hook. f.）Poole的卵状三角形叶片相比，可能具有更大的重叠度。所有物种中，单位面积的叶片干质量（M(A)）和氮含量（N(A)）均随Q(int)的增加而增加，表明在高光条件下光合生物量的投资增加。尽管在相同辐照度下不同物种的M(A)有所不同，但各物种的N(A)与Q(int)之间存在统一的关系。叶片干质量碳含量和叶片干质量与鲜质量比也与辐照度呈正相关，表明在高光条件下有更大的结构投资。在所有物种中，在较低的Q(int)下，枝条变得更水平、更扁平，这意味着在自然叶片位置上对直射辐照度的利用效率提高。相比之下，辐照度对叶片聚集的影响因物种而异。综合所有数据来看，在较低辐照度下，叶片重叠或叶面积密度通常更大，这可能是由于枝条轴延伸生长的碳供应有限所致。在福氏假山毛榉中，其叶片在高光下更聚集，枝条轮廓与总叶面积比（S(S)）随辐照度增加而强烈下降，表明在高Q(int)下光捕获效率较低。这种效应在悬崖假山毛榉变种中仅为中等程度，而在索氏假山毛榉变种中S(S)与Q(int)无关。尽管在高辐照度下，福氏假山毛榉的光拦截效率最低，但该物种单位枝条轮廓面积的氮含量最高（2N(A)/S(S)），表明其枝条水平的光合潜力 superior。这些数据共同表明，枝条结构显著影响阔叶树的光拦截和光合作用，并且结构碳限制可能会在低辐照度下限制叶片的光捕获效率。
