School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province, China.
PLoS One. 2013 Jun 11;8(6):e66016. doi: 10.1371/journal.pone.0066016. Print 2013.
Leaf physiology determines the carbon acquisition of the whole plant, but there can be considerable variation in physiology and carbon acquisition within individual leaves. Alocasia macrorrhiza (L.) Schott is an herbaceous species that can develop very large leaves of up to 1 m in length. However, little is known about the hydraulic and photosynthetic design of such giant leaves. Based on previous studies of smaller leaves, and on the greater surface area for trait variation in large leaves, we hypothesized that A. macrorrhiza leaves would exhibit significant heterogeneity in structure and function. We found evidence of reduced hydraulic supply and demand in the outer leaf regions; leaf mass per area, chlorophyll concentration, and guard cell length decreased, as did stomatal conductance, net photosynthetic rate and quantum efficiency of photosystem II. This heterogeneity in physiology was opposite to that expected from a thinner boundary layer at the leaf edge, which would have led to greater rates of gas exchange. Leaf temperature was 8.8°C higher in the outer than in the central region in the afternoon, consistent with reduced stomatal conductance and transpiration caused by a hydraulic limitation to the outer lamina. The reduced stomatal conductance in the outer regions would explain the observed homogeneous distribution of leaf water potential across the leaf surface. These findings indicate substantial heterogeneity in gas exchange across the leaf surface in large leaves, greater than that reported for smaller-leafed species, though the observed structural differences across the lamina were within the range reported for smaller-leafed species. Future work will determine whether the challenge of transporting water to the outer regions can limit leaf size for plants experiencing drought, and whether the heterogeneity of function across the leaf surface represents a particular disadvantage for large simple leaves that might explain their global rarity, even in resource-rich environments.
叶片生理学决定了整株植物的碳获取量，但在单个叶片内，生理学和碳获取量可能存在相当大的差异。象耳芋（Alocasia macrorrhiza (L.) Schott）是一种草本植物，可以发育出长达 1 米的巨大叶片。然而，对于如此巨大的叶片的水力和光合作用设计知之甚少。基于先前对较小叶片的研究，以及较大叶片在性状变异方面具有更大的表面积，我们假设象耳芋叶片在结构和功能上会表现出显著的异质性。我们发现，叶片外区的水力供应和需求减少；叶面积质量、叶绿素浓度和保卫细胞长度降低，气孔导度、净光合速率和光系统 II 的量子效率降低。这种生理学上的异质性与叶片边缘较薄的边界层所预期的相反，这将导致气体交换速率增加。下午，叶片外区的温度比中心区高 8.8°C，这与外层叶片水力限制导致的气孔导度和蒸腾作用降低一致。外层叶片气孔导度的降低可以解释观察到的叶片表面水势的均匀分布。这些发现表明，在大型叶片中，气体交换在叶片表面存在显著的异质性，比报道的小型叶物种更为显著，尽管在叶片上观察到的结构差异在报道的小型叶物种范围内。未来的工作将确定向叶片外区输送水分的挑战是否会限制经历干旱的植物的叶片大小，以及叶片表面功能的异质性是否代表大型简单叶片的一个特殊劣势，这可能解释了它们在全球的稀有性，即使在资源丰富的环境中也是如此。
