Massonnet C, Regnard J L, Lauri P E, Costes E, Sinoquet H
INRA, SupAgro, UMR 1098 DAP, Equipe Architecture et Fonctionnement des Espèces Fruitières, Montpellier Cedex 1, France.
Tree Physiol. 2008 May;28(5):665-78. doi: 10.1093/treephys/28.5.665.
Both the spatial distribution of leaves and leaf functions affect the light interception, transpiration and photosynthetic capacities of trees, but their relative contributions have rarely been investigated. We assessed these contributions at the branch and tree scales in two apple cultivars (Malus x domestica Borkh. 'Fuji' and 'Braeburn') with contrasting architectures, by estimating their branch and tree capacities and comparing them with outputs from a radiation absorption, transpiration and photosynthesis (RATP) functional-structural plant model (FSPM). The structures of three 8-year-old trees of each cultivar were digitized to obtain 3-D representations of foliage geometry. Within-tree foliage distribution was compared with shoot demography, number of leaves per shoot and mean individual leaf area. We estimated branch and tree light interception from silhouette to total leaf area ratios (STAR), transpiration from sap flux measurements and net photosynthetic rates by the branch bag method. Based on a set of parameters we previously established for both cultivars, the outputs of the RATP model were tested against STAR values, sap fluxes and photosynthetic measurements. The RATP model was then used to virtually switch foliage distribution or leaf functions (stomatal and photosynthetic properties), or both, between cultivars and to evaluate the effects on branch and tree light interception, transpiration and photosynthetic capacities in each cultivar. 'Fuji' trees had a higher proportion of leaf area borne on long shoots, fewer leaves per unit shoot length and a larger individual leaf area than 'Braeburn' trees. This resulted in a lower leaf area density and, consequently, a higher STAR in 'Fuji' than in 'Braeburn' at both branch and tree scales. Transpiration and photosynthetic rates were significantly higher in 'Fuji' than in 'Braeburn'. Branch heterogeneity was greater in 'Braeburn' than in 'Fuji'. An analysis of the virtual switches of foliage distribution or leaf function showed that differences in leaf spatial distribution and functions had additive effects that accounted for the lower transpiration and photosynthetic rates of branches and trees of 'Braeburn' compared with 'Fuji'. Leaf distribution had a more important role at the branch scale than at the tree scale, but the leaf function effect exceeded the leaf distribution effect at both scales. Our study demonstrated the potential of FSPM to disentangle physiological differences between cultivars through in silico scenarios.
叶片的空间分布和叶功能都会影响树木的光截获、蒸腾作用和光合能力，但其相对贡献很少得到研究。我们通过估算两个苹果品种（苹果属苹果种‘富士’和‘澳洲青苹’）在枝条和整株尺度上的能力，并将其与辐射吸收、蒸腾和光合作用（RATP）功能-结构植物模型（FSPM）的输出结果进行比较，评估了这两个具有不同树形结构的品种在枝条和整株尺度上的这些贡献。对每个品种的三棵8年生树的结构进行数字化处理，以获得叶片几何形状的三维表示。将树内叶片分布与新梢数量统计、每个新梢的叶片数量和平均单叶面积进行比较。我们通过轮廓到总叶面积比（STAR）估算枝条和整株的光截获，通过液流通量测量估算蒸腾作用，并采用枝条套袋法测定净光合速率。基于我们之前为两个品种建立的一组参数，将RATP模型的输出结果与STAR值、液流通量和光合测量结果进行对比测试。然后，利用RATP模型在品种间虚拟切换叶片分布或叶功能（气孔和光合特性），或两者同时切换，并评估其对每个品种枝条和整株的光截获、蒸腾作用和光合能力的影响。‘富士’树在长枝上着生的叶面积比例更高，单位新梢长度上的叶片数量更少，单叶面积比‘澳洲青苹’树更大。这导致‘富士’树的叶面积密度较低，并因此在枝条和整株尺度上的STAR均高于‘澳洲青苹’。‘富士’的蒸腾速率和光合速率显著高于‘澳洲青苹’。‘澳洲青苹’的枝条异质性比‘富士’更大。对叶片分布或叶功能的虚拟切换分析表明，叶片空间分布和功能的差异具有累加效应，这解释了与‘富士’相比，‘澳洲青苹’枝条和整株的蒸腾速率和光合速率较低的原因。叶片分布在枝条尺度上比在整株尺度上发挥更重要的作用，但在两个尺度上叶功能的影响均超过叶片分布的影响。我们的研究证明了功能-结构植物模型通过计算机模拟情景解析品种间生理差异的潜力。
