Instituto de Investigación Interdisciplinaria (I3), Vicerrectoría Académica, Universidad de Talca, Campus Lircay, Talca 3460000, Chile.
Instituto Pirenaico de Ecología (IPE-CSIC), Avda. Montañana 1005, E-50192 Zaragoza, Spain.
Ann Bot. 2023 Jul 10;131(6):941-951. doi: 10.1093/aob/mcad053.
The vulnerability and responsiveness of forests to drought are immensely variable across biomes. Intraspecific tree responses to drought in species with wide niche breadths that grow across contrasting climatically environments might provide key information regarding forest resistance and changes in species distribution under climate change. Using a species with an exceptionally wide niche breath, we tested the hypothesis that tree populations thriving in dry environments are more resistant to drought than those growing in moist locations.
We determined temporal trends in tree radial growth of 12 tree populations of Nothofagus antarctica (Nothofagaceae) located across a sharp precipitation gradient (annual precipitation of 500-2000 mm) in Chile and Argentina. Using dendrochronological methods, we fitted generalized additive mixed-effect models to predict the annual basal area increment as a function of year and dryness (De Martonne aridity index). We also measured carbon and oxygen isotope signals (and estimated intrinsic water-use efficiency) to provide potential physiological causes for tree growth responses to drought.
We found unexpected improvements in growth during 1980-1998 in moist sites, while growth responses in dry sites were mixed. All populations, independent of site moisture, showed an increase in their intrinsic water-use efficiency in recent decades, a tendency that seemed to be explained by an increase in the photosynthetic rate instead of drought-induced stomatal closure, given that δ18O did not change with time.
The absence of drought-induced negative effects on tree growth in a tree species with a wide niche breadth is promising because it might relate to the causal mechanisms tree species possess to face ongoing drought events. We suggest that the drought resistance of N. antarctica might be attributable to its low stature and relatively low growth rate.
森林对干旱的脆弱性和响应在不同生物群落中差异巨大。在具有广泛生态位宽度且在截然不同气候环境中生长的物种中，种内树木对干旱的响应可能为了解森林在气候变化下的抵抗力和物种分布变化提供关键信息。本研究使用一个生态位宽度异常广泛的物种，检验了以下假设，即在干旱环境中茁壮成长的树木种群比生长在潮湿环境中的树木种群更能抵御干旱。
我们测定了智利和阿根廷一个急剧降水梯度（年降水量 500-2000 毫米）上 12 个 Nothofagus antarctica（山毛榉科）种群的树木径向生长的时间趋势。使用树木年代学方法，我们拟合了广义可加混合效应模型，以预测年基面积增量作为年和干旱（De Martonne 干燥度指数）的函数。我们还测量了碳和氧同位素信号（并估计了内在水分利用效率），以提供树木对干旱生长响应的潜在生理原因。
我们发现，1980-1998 年期间，潮湿地区的生长出乎意料地有所改善，而干旱地区的生长响应则参差不齐。所有种群，无论其所处地点的湿度如何，在最近几十年都表现出内在水分利用效率的提高，这种趋势似乎是由于光合速率的增加而不是干旱引起的气孔关闭所致，因为 δ18O 并没有随时间而变化。
在一个具有广泛生态位宽度的树种中，树木生长没有受到干旱的负面影响，这是令人鼓舞的，因为这可能与树木物种具有的应对持续干旱事件的因果机制有关。我们认为，N. antarctica 的耐旱性可能归因于其矮小的体型和相对较低的生长速度。
