Niessner Armin, Ehekircher Stefan, Zimmermann Reiner, Horna Viviana, Reichle Daniel, Land Alexander, Spangenberg Göran, Hein Sebastian
Department of Silviculture, University of Applied Forest Sciences, Rottenburg am Neckar, Germany.
Ecological Botanical Gardens ÖBG, University of Bayreuth, Bayreuth, Germany.
Front Plant Sci. 2024 Aug 6;15:1401833. doi: 10.3389/fpls.2024.1401833. eCollection 2024.
Soil drought during summer in Central Europe has become more frequent and severe over the last decades. European forests are suffering increasing damage, particularly Norway spruce. Douglas-fir ( (Mirbel) Franco), a non-native tree species, is considered as a promising alternative to build drought-resilient forests. The main goal of this study was to investigate the intraannual radial stem growth and sap flow performance of Douglas-fir along a precipitation gradient across Germany under severe drought.
Sap flow and stem radial changes of up to ten trees each at four sites with different precipitation regimes were measured in combination with volumetric soil water content during the growing season of 2022. Measurements of stem radial changes were used to calculate the trees' stem water deficit, a proxy for tree water status and drought stress.
The severe summer drought of 2022 led to an early growth cessation and a significant reduction in daily sap flow at all four sites monitored. We could identify a site-specific threshold in soil water availability ranging between 21.7 and 29.6% of relative extractable water (REW) under which stem water reserves cannot be replenished and thereby inhibiting radial growth. We could also demonstrate that at this threshold, sap flow is heavily reduced to between 43.5 and 53.3%, and for a REW below 50%, sap flow linearly decreases by 1.1-2.0% per 1% reduction in REW. This reduction tends to follow the humidity gradient, being more pronounced at the most oceanic characterized site and suggesting an adaptation to site conditions. Even though Douglas-fir is considered to be more drought stress resistant than Norway spruce, growth and sap flow are greatly reduced by severe summer drought, which became more frequent in recent years and their frequency and intensity is likely to increase.
Our results suggest that timber production of Douglas-fir in Central Europe will decline considerably under projected climate change, and thus pointing to site specific growth constraints for a so far promising non-native tree species in Europe.
在过去几十年中，中欧夏季的土壤干旱变得更加频繁和严重。欧洲森林正遭受越来越大的损害，尤其是挪威云杉。花旗松（（米尔贝尔）佛朗哥），一种非本土树种，被认为是构建抗旱森林的有前景的替代树种。本研究的主要目标是调查在严重干旱条件下，德国各地降水梯度上花旗松的年内径向茎干生长和液流表现。
在2022年生长季节，对四个不同降水模式地点的多达十棵树的液流和茎干径向变化进行了测量，并结合土壤体积含水量。茎干径向变化的测量用于计算树木的茎干水分亏缺，这是树木水分状况和干旱胁迫的一个指标。
2022年夏季的严重干旱导致所有四个监测地点的树木早期生长停止，每日液流显著减少。我们可以确定土壤水分可利用性的一个特定地点阈值，相对可提取水量（REW）在21.7%至29.6%之间，低于该阈值，茎干水分储备无法补充，从而抑制径向生长。我们还可以证明，在这个阈值下，液流大幅减少至43.5%至53.3%之间，对于低于REW 50%的情况，液流每降低1%的REW就线性减少1.1 - 2.0%。这种减少倾向于遵循湿度梯度，在最具海洋性特征的地点更为明显，表明对地点条件的适应性。尽管花旗松被认为比挪威云杉更耐干旱胁迫，但严重的夏季干旱使生长和液流大幅减少，近年来这种干旱变得更加频繁，其频率和强度可能会增加。
我们的结果表明，在预计的气候变化下，中欧花旗松的木材产量将大幅下降，因此指出了一种迄今在欧洲有前景的非本土树种在特定地点的生长限制。
