• Increases in leaf mass per area (LMA) are commonly observed in response to environmental stresses and are achieved through increases in leaf thickness and/or leaf density. Here, we investigated how the two underlying components of LMA differ in relation to species native climates and phylogeny, across deciduous and evergreen species.
• Using a phylogenetic approach, we quantified anatomical, compositional and climatic variables from 40 deciduous and 45 evergreen Quercus species from across the Northern Hemisphere growing in a common garden.
• Deciduous species from shorter growing seasons tended to have leaves with lower LMA and leaf thickness than those from longer growing seasons, while the opposite pattern was found for evergreens. For both habits, LMA and thickness increased in arid environments. However, this shift was associated with increased leaf density in evergreens but reduced density in deciduous species.
• Deciduous and evergreen oaks showed fundamental leaf morphological differences that revealed a diverse adaptive response. While LMA in deciduous species may have diversified in tight coordination with thickness mainly modulated by aridity, diversification of LMA within evergreens appears to be dependent on the infrageneric group, with diversification in leaf thickness modulated by both aridity and cold, while diversification in leaf density is only modulated by aridity.

中文翻译：

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落叶和常绿橡树在整个环境中的每单位面积叶片质量上显示出不同的适应性响应

• 通常在响应环境压力时观察到每单位面积叶片质量（LMA）的增加，并且可以通过增加叶片厚度和/或叶片密度来实现。在这里，我们调查了在落叶和常绿物种中，LMA的两个基本组成部分与物种的自然气候和系统发育的关系是如何不同的。
• 使用系统发育方法，我们量化了北半球在共同花园中生长的40种落叶和45种常绿栎属物种的解剖，组成和气候变量。
• 生长季节较短的落叶树种叶片的LMA和叶厚度往往比生长季节较长的落叶树低，而常绿的树种则相反。对于这两种习惯，在干旱环境中，LMA和厚度都会增加。但是，这种变化与常绿植物的叶片密度增加但落叶树种的密度降低有关。
• 落叶和常绿橡树显示出基本的叶片形态差异，从而揭示了多种适应性反应。落叶树种中的LMA可能与主要受干旱调节的厚度紧密协调地发生了变化，而常绿植物中LMA的多样性似乎取决于亚种群，而干旱和寒冷调节了叶子的厚度，而叶片密度的变化是仅由干旱调节。