Zhang Lan, Copini Paul, Weemstra Monique, Sterck Frank
Forest Ecology and Forest Management Group, Wageningen University and Research Centre, PO Box 47, 6700 AA, Wageningen, the Netherlands.
Alterra, Wageningen University and Research Centre, PO Box 47, 6700 AA, Wageningen, the Netherlands.
New Phytol. 2016 Mar;209(4):1566-75. doi: 10.1111/nph.13731. Epub 2015 Nov 3.
Leaf, xylem and phloem areas drive the water and carbon fluxes within branches and trees, but their mutual coordination is poorly understood. We test the hypothesis that xylem and phloem areas increase relative to leaf area when species are selected for, or branches are exposed to, higher levels of light intensity. Trees of 10 temperate, broadleaved and deciduous, tree species were selected. Fifty-centimetre-long branches were collected from shaded and exposed conditions at a height of 3-4 m. We measured the total leaf area, xylem area, phloem area and leaf traits, as well as the area of the constituent cell types, for a stem section at the branch base. Xylem area : leaf area and phloem area : leaf area ratios did not differ consistently between sun and shade branches, but, as expected, they decreased with species' shade tolerance. Similar trends were observed for conductive cell areas in xylem and phloem. Trees of light-demanding species maintain higher water loss and carbon gain rates per leaf area by producing more xylem area and phloem area than shade-tolerant species. We call for more comparative branch studies as they provide an integrated biological perspective on functional traits and their role in the ecology of tree species.
叶片、木质部和韧皮部面积驱动着树枝和树木内部的水分和碳通量，但它们之间的相互协调作用却鲜为人知。我们检验了这样一个假设：当选择物种或树枝暴露于更高光照强度下时，木质部和韧皮部面积相对于叶面积会增加。选取了10种温带阔叶落叶树种的树木。在3 - 4米高的位置，从遮荫和暴露环境中采集了50厘米长的树枝。我们测量了树枝基部茎段的总叶面积、木质部面积、韧皮部面积和叶片性状，以及组成细胞类型的面积。木质部面积与叶面积之比和韧皮部面积与叶面积之比在向阳枝和背阴枝之间并没有始终存在差异，但正如预期的那样，它们随着物种耐荫性的增加而降低。在木质部和韧皮部的传导细胞面积方面也观察到了类似趋势。与耐荫物种相比，喜光物种的树木通过产生更多的木质部面积和韧皮部面积，维持了更高的单位叶面积水分损失和碳获取速率。我们呼吁开展更多的比较性树枝研究，因为它们能为功能性状及其在树种生态学中的作用提供一个综合的生物学视角。
