论文题目：The Functional Significance of Leaf Shape Lies in Water Relations Over Thermoregulation: A Case Study With an Arid Legume Herb
论文作者：Hui Wang*, Jian Li, Jun-Yu Chen, Min Wang, Eric Imbert, Zhao-Yang Chang
论文摘要：Leaf shape displays remarkable diversity, with its evolution hypothesized to reflect adaptive ecophysiological functions. Theoretical models propose that variation in leaf shape—particularly through modifications in effective leaf width (we)—primarily influences thermoregulation and hydraulic efficiency. However, comprehensive empirical tests of these hypotheses are lacking. Oxytropis diversifolia E. Peter (Fabaceae) has natural variation in leaf shape (1 leaflet, 1–3 leaflets, and 3 leaflets) and exhibits clinal variation, making it an ideal candidate to test those functional relationships. Here, we quantified leaf morphometrics across populations, logged in situ leaf temperature and gas exchange, and examined leaf anatomy associated with water balance. We confirmed that the production of more leaflets did reduce we. While leaves with reduced we could stay cooler during the day, the extent of leaf‐to‐air temperature difference was typically small (often within 1°C), suggesting a limited biological impact. Crucially, we identified a key anatomical trade‐off in water relations: reduced we yielded beneficial lower chlorenchyma‐to‐midrib ratios and higher vein density, but at the cost of smaller vascular dimensions. This trade‐off likely underpins the observed, context‐dependent superior gas exchange of the intermediate phenotype. We propose that the functional significance of leaf shape lies in water relations over thermoregulation, with balancing selection on the anatomical trade‐off providing a plausible mechanism maintaining the polymorphism.
叶形(leaf shape)是植物最富于变化的性状之一。由于叶的功能重要性，叶形演化被认为反映了其适应性的生理生态功能。理论研究提出，叶形变异会改变有效叶宽(we)，进而影响植物温度调节和水分输导效率。然而，这两个假说尚缺乏全面的实证检验。豆科棘豆属植物二型叶棘豆(Oxytropis diversifolia E. Peter)分布于我国西部草原荒漠地区，不同个体在叶形上存在自然变异(1小叶、1–3小叶或3小叶)。野外调查发现其居群叶形频率有自西向东的梯度变化，并与降水和温度相关的气候因子梯度变化吻合，因而是检验上述功能关系的理想材料。为全面检验这两个假说，本研究对该物种所有已知居群进行了叶宏观形态学分析，并选择4个代表性居群进行了叶温和气体交换参数测定以及水平衡相关的叶解剖结构分析。我们首先确认了小叶数目的增加确实会显著降低有效叶宽(we)。再次，我们检验了温度调节假说，发现尽管有效叶宽较小的叶可以在日间维持较低的叶温，但叶温和环境气温的差值通常较小(多在1°C以内)，生物学影响有限。最后，我们检验了水平衡假说，从而揭示了叶水分关系中一个关键的解剖学权衡：叶有效叶宽的降低带来了一些有利于水分输导的特征，如更低的叶肉组织/中脉比值和更高的叶脉密度，但是也以维管组织径级减小为代价。这一权衡很可能导致了中间表型(即1–3小叶)在特定条件下表现出更优的气体交换能力。本研究表明叶形的功能意义主要体现在水平衡而非温度调节上，而与解剖学权衡相关的平衡选择可能是维持种内叶形变异的潜在机制。
论文链接：https://onlinelibrary.wiley.com/doi/10.1111/pce.70484