Juárez-López Francisco José, Escudero Alfonso, Mediavilla Sonia
Colegio de Postgraduados-Campus Tabasco, Avd. Periférico Carlos A. Molina s/n, Carretera Cardenas-Huimanguillo, 86500 Tabasco, Mexico.
Tree Physiol. 2008 Mar;28(3):367-74. doi: 10.1093/treephys/28.3.367.
A quantitative analysis was applied to the stomatal and biochemical limitations to light-saturated net photosynthesis under optimal field conditions in mature trees and seedlings of the co-occurring evergreen oak, Quercus ilex L., and the deciduous oak, Q. faginea Lam. Stomatal limitation to photosynthesis, maximal Rubisco activity and electron transport rate were determined from assimilation versus intercellular leaf carbon dioxide concentration response curves of leaves that were subsequently analyzed for nitrogen (N) concentration, mass per unit area, thickness and percent internal air space. In both species, seedlings had a lower leaf mass per unit area, thickness and leaf N concentration than mature trees. The root system of seedlings during their third year after planting was dominated by a taproot. A lower leaf N concentration of seedlings was associated with lower maximal Rubisco activity and electron transport rate and with assimilation rates similar to or lower than those of mature trees, despite the higher stomatal conductances and potential photosynthetic nitrogen-use efficiencies of seedlings. Consequently, stomatal limitation to photosynthesis increased with tree age in both species. In both seedlings and mature trees, a lower assimilation rate in Q. ilex than in Q. faginea was associated with lower stomatal conductance, N allocation to photosynthetic functions, maximal Rubisco activity and electron transport rate, and potential photosynthetic nitrogen-use efficiency but greater leaf thickness and leaf mass per unit area. Tree-age-related changes differed quantitatively between species, and the characteristics of the two species were more similar in seedlings than in mature trees. Despite higher stomatal conductances, seedlings are more N limited than adult trees, which contributes to lower biochemical efficiency.
对同域生长的常绿栎树（冬青栎，Quercus ilex L.）和落叶栎树（法氏栎，Q. faginea Lam.）的成熟树木和幼苗在最佳田间条件下光饱和净光合作用的气孔和生化限制进行了定量分析。通过叶片同化作用与细胞间叶二氧化碳浓度响应曲线确定光合作用的气孔限制、最大核酮糖-1,5-二磷酸羧化酶（Rubisco）活性和电子传递速率，随后对叶片进行氮（N）浓度、单位面积质量、厚度和内部空气空间百分比分析。在这两个物种中，幼苗的单位面积叶质量、厚度和叶N浓度均低于成熟树木。种植后第三年幼苗的根系以主根为主。尽管幼苗的气孔导度较高且潜在光合氮利用效率较高，但其较低的叶N浓度与较低的最大Rubisco活性和电子传递速率以及与成熟树木相似或更低的同化率相关。因此，两个物种的光合作用气孔限制均随树龄增加。在幼苗和成熟树木中，冬青栎的同化率低于法氏栎，这与较低的气孔导度、光合功能的N分配、最大Rubisco活性和电子传递速率以及潜在光合氮利用效率有关，但叶厚度和单位面积叶质量更大。物种间与树龄相关的变化在数量上有所不同，并且两个物种在幼苗中的特征比在成熟树木中更相似。尽管气孔导度较高，但幼苗比成年树木更受N限制，这导致生化效率较低。
