Instituto Pirenaico de Ecología (CSIC), Avda. Montañana 1005, Apdo. 202, 50192 Zaragoza, Spain.
Tree Physiol. 2012 May;32(5):585-98. doi: 10.1093/treephys/tps031. Epub 2012 Apr 25.
Forest decline has been attributed to the interaction of several stressors including biotic factors such as mistletoes and climate-induced drought stress. However, few data exist on how mistletoes are spatially arranged within trees and how this spatial pattern is related to changes in radial growth, responses to drought stress and carbon use. We used dendrochronology to quantify how mistletoe (Viscum album L.) infestation and drought stress affected long-term growth patterns in Pinus sylvestris L. at different heights. Basal area increment (BAI) trends and comparisons between trees of three different infestation degrees (without mistletoe, ID1; moderately infested trees, ID2; and severely infested trees, ID3) were performed using linear mixed-effects models. To identify the main climatic drivers of tree growth tree-ring widths were converted into indexed chronologies and related to climate data using correlation functions. We performed spatial analyses of the 3D distribution of mistletoe individuals and their ages within the crowns of three severely infested pines to describe their patterns. Lastly, we quantified carbohydrate and nitrogen concentrations in needles and sapwood of branches from severely infested trees and from trees without mistletoe. Mistletoe individuals formed strongly clustered groups of similar age within tree crowns and their age increased towards the crown apex. Mistletoe infestation negatively impacted growth but this effect was stronger near the tree apex than in the rest of sampled heights, causing an average loss of 64% in BAI (loss of BAI was ∼51% at 1.3 m or near the tree base). We found that BAI of severely infested trees and moderately or non-infested trees diverged since 2001 and such divergence was magnified by drought. Infested trees had lower concentrations of soluble sugars in their needles than non-infested ones. We conclude that mistletoe infestation causes growth decline and increases the sensitivity of trees to drought stress.
森林衰退归因于多种胁迫因子的相互作用，包括生物因子如槲寄生和气候引起的干旱胁迫。然而，关于槲寄生在树木内的空间排列方式以及这种空间模式如何与径向生长变化、对干旱胁迫的响应和碳利用相关的数据很少。我们使用树木年代学来量化槲寄生（Viscum album L.）感染和干旱胁迫如何影响不同高度的欧洲赤松（Pinus sylvestris L.）的长期生长模式。使用线性混合效应模型对无槲寄生（ID1）、中度感染树（ID2）和重度感染树（ID3）三种不同感染程度的树木的基面积增量（BAI）趋势和比较进行了分析。为了确定树木生长的主要气候驱动因素，将树木年轮宽度转换为索引年表，并使用相关函数将其与气候数据相关联。我们对树冠内 3 棵重度感染松树的槲寄生个体及其年龄的 3D 分布进行了空间分析，以描述其模式。最后，我们量化了重度感染树木和无槲寄生树木的针叶和边材中的碳水化合物和氮浓度。槲寄生个体在树冠内形成了年龄相似的强烈聚类群，其年龄向树冠顶点增加。槲寄生感染对生长有负面影响，但这种影响在树顶附近比在采样高度的其他部位更强，导致 BAI 平均损失 64%（在 1.3 米或靠近树基处，BAI 损失约为 51%）。我们发现，自 2001 年以来，重度感染树和中度或未感染树的 BAI 出现分歧，干旱加剧了这种分歧。感染树木的针叶中可溶性糖浓度低于未感染树木。我们的结论是，槲寄生感染会导致生长下降，并增加树木对干旱胁迫的敏感性。
