Fluctuations in climatic conditions during the growing season are recorded in Mediterranean tree-rings and often result in intra-annual density fluctuations (IADFs). Dendroecology and quantitative wood anatomy analyses were used to characterize the relations between the variability of IADF traits and climatic drivers in Pinus pinaster Aiton and Quercus ilex L. growing at sites with different water availability on the Elba island in Central Italy. Our results showed that both species present high xylem plasticity resulting in the formation of L-type IADFs (L-IADFs), consisting of earlywood-like cells in latewood. The occurrence of such IADFs was linked to rain events following periods of summer drought. The formation of L-IADFs in both species increased the hydraulic conductivity late in the growing season, due to their larger lumen area in comparison to “true latewood”. The two species expressed greater similarity under arid conditions, as unfavorable climates constrained trait variation. Wood density, measured as the percentage of cell walls over total xylem area, IADF frequency, as well as conduit lumen area and vessel frequency, specifically in the hardwood species, proved to be efficient proxies to encode climate signals recorded in the xylem. The response of these anatomical traits to climatic variations was found to be species- and site-specific.

中文翻译：

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松树和栎栎的木质部可塑性在地中海地区水量不同的地区生长：年内密度波动与环境条件之间的关系

在地中海的树木年轮中记录了生长季节期间气候条件的波动，并经常导致年内密度波动（IADF）。利用树状生态学和定量的木材解剖学分析来表征生长在意大利中部厄尔巴岛上水量不同的地点的Pinus pinaster Aiton和Quercus ilex L.的IADF性状的变异性与气候驱动因素之间的关系。我们的结果表明，这两个物种都表现出较高的木质部可塑性，导致形成L型IADF（L -IADF），后者由晚木中的早木样细胞组成。这种IADF的发生与夏季干旱后的降雨事件有关。L的形成-与“真正的晚材”相比，这两个物种的IADF都在生长期后期增加了水力传导率，这是因为它们的管腔面积更大。由于不利的气候限制了性状的变异，这两个物种在干旱条件下表现出更大的相似性。木材密度（以细胞壁占木质部总面积的百分比，IADF频率以及导管内腔面积和容器频率（特别是硬木树种）的百分比来衡量）被证明是编码木质部中记录的气候信号的有效代理。这些解剖特征对气候变化的响应被发现是特定物种和特定地点的。