Forest and Wood Technology Research Centre (CETEMAS), Pumarabule, Carbayín, s/n, 33936 Siero, Asturias, Spain; Departamento de Ciencias Agroforestales, Universidad de Huelva, Crta. Palos-La Rábida s/n, 21819 Palos de la Frontera, Spain; Dept. Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Crta. Utrera km. 1, 41013 Sevilla, Spain.
Dept. Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Crta. Utrera km. 1, 41013 Sevilla, Spain; Instituto Pirenaico de Ecología (IPE-CSIC), Avda. Montañana 1005, 50192 Zaragoza, Spain.
Sci Total Environ. 2019 Nov 10;690:1254-1267. doi: 10.1016/j.scitotenv.2019.06.515. Epub 2019 Jul 2.
Drought-induced forest dieback is causing reductions in productivity, increasing tree mortality and impairing terrestrial carbon uptake worldwide. However, the role played by long-term nutrient imbalances during drought-induced dieback is still unknown. To improve our knowledge on the relationships between dieback and nutrient imbalances, we analysed wood anatomical traits (tree-ring width and wood density), soil properties and long-term chemical information in tree-ring wood (1900-2010) by non-destructive Micro X-ray fluorescence (μXRF) and destructive (ICP-OES) techniques. We studied two major European conifers with ongoing drought-induced dieback in mesic (Abies alba, silver fir) and xeric (Pinus sylvestris, Scots pine) sites. In each site we compared coexisting declining (D) and non-declining (ND) trees. We used dendrochronology and generalized additive and linear mixed models to analyse trends in tree-ring nutrients and their relationships with wood traits. The D trees presented lower growth and higher minimum wood density than ND trees, corresponding to a smaller lumen area of earlywood tracheids and thus a lower theoretical hydraulic conductivity. These differences in growth and wood-anatomy were more marked in silver fir than in Scots pine. Moreover, most of the chemical elements showed higher concentrations in D than in ND trees during the last two-five decades (e.g., Mn, K and Mg), while Ca and Na increased in the sapwood of ND trees. The Mn concentrations, and related ratios (Ca:Mn, Mn:Al and P:Mn) showed the highest differences between D and ND trees for both tree species. These findings suggest that a reduced hydraulic conductivity, consistent with hydraulic impairment, is affecting the use of P in D trees, making them more prone to drought-induced damage. The retrospective quantifications of Mn ratios may be used as early-warning signals of impending dieback.
干旱导致的森林衰退正在降低生产力，增加树木死亡率，并在全球范围内削弱陆地碳吸收。然而，在干旱导致的衰退过程中，长期养分失衡所起的作用仍然未知。为了提高我们对衰退与养分失衡之间关系的认识，我们通过非破坏性微 X 射线荧光（μXRF）和破坏性（ICP-OES）技术，分析了木材解剖结构特征（树木年轮宽度和木材密度）、土壤特性以及树木年轮木材中的长期化学信息（1900-2010 年）。我们研究了两种在湿润（银冷杉、白冷杉）和干旱（欧洲赤松、欧洲云杉）生境中发生持续干旱导致衰退的欧洲主要针叶树。在每个地点，我们比较了共存的衰退（D）和非衰退（ND）树木。我们使用树木年代学和广义加性和线性混合模型来分析树木年轮养分的趋势及其与木材特征的关系。与 ND 树木相比，D 树木的生长较低，最小木材密度较高，这对应于早材管胞的较小腔面积，从而导致理论水力传导率降低。在银冷杉中，这些生长和木材解剖结构的差异比在欧洲云杉中更为明显。此外，在过去的两到五十年中，大多数化学元素在 D 树木中的浓度高于 ND 树木（例如，Mn、K 和 Mg），而 Ca 和 Na 在 ND 树木的边材中增加。Mn 浓度以及相关比值（Ca:Mn、Mn:Al 和 P:Mn）在两种树种的 D 树木和 ND 树木之间表现出最高的差异。这些发现表明，水力传导率降低，与水力受损一致，影响了 P 在 D 树木中的利用，使它们更容易受到干旱引起的损害。Mn 比值的回溯量化可能作为即将发生衰退的预警信号。
