Institute of Biochemical Plant Pathology, Helmholtz Zentrum München, Allergens in Ecosystems, Neuherberg, Germany.
Forest Growth and Yield Science, Technische Universität München, Freising, Germany.
Glob Chang Biol. 2018 Feb;24(2):e560-e576. doi: 10.1111/gcb.13957. Epub 2017 Nov 15.
Forest ecosystems in central Europe are predicted to face an increasing frequency and severity of summer droughts because of global climate change. European beech and Norway spruce often coexist in these forests with mostly positive effects on their growth. However, their different below-ground responses to drought may lead to differences in ectomycorrhizal (ECM) fungal community composition and functions which we examined at the individual root and ecosystem levels. We installed retractable roofs over plots in Kranzberg Forest (11°39'42″E, 48°25'12″N; 490 m a.s.l.) to impose repeated summer drought conditions and assigned zones within each plot where trees neighboured the same or different species to study mixed species effects. We found that ECM fungal community composition changed and the numbers of vital mycorrhizae decreased for both tree species over 3 drought years (2014-2016), with the ECM fungal community diversity of beech exhibiting a faster and of spruce a stronger decline. Mixed stands had a positive effect on the ECM fungal community diversity of both tree species after the third drought year. Ectomycorrhizae with long rhizomorphs increased in both species under drought, indicating long-distance water transport. However, there was a progressive decline in the number of vital fine roots during the experiment, resulting in a strong reduction in enzyme activity per unit volume of soil. Hydrolytic enzyme activities of the surviving ectomycorrhizae were stable or stimulated upon drought, but there was a large decline in ECM fungal species with laccase activity, indicating a decreased potential to exploit nutrients bound to phenolic compounds. Thus, the ectomycorrhizae responded to repeated drought by maintaining or increasing their functionality at the individual root level, but were unable to compensate for quantitative losses at the ecosystem level. These findings demonstrate a strong below-ground impact of recurrent drought events in forests.
由于全球气候变化，中欧的森林生态系统预计将面临夏季干旱频率和严重程度的增加。欧洲山毛榉和挪威云杉通常在这些森林中共同存在，对其生长有积极影响。然而，它们对干旱的地下反应不同可能导致外生菌根（ECM）真菌群落组成和功能的差异，我们在个体根和生态系统水平上对此进行了研究。我们在克兰茨贝格森林（11°39'42″E，48°25'12″N；490 米海拔）的样地安装了可伸缩的屋顶，以施加反复的夏季干旱条件，并在每个样地内分配树木相邻的同一或不同物种的区域，以研究混合物种的影响。我们发现，在 3 个干旱年份（2014-2016 年）中，两种树种的 ECM 真菌群落组成都发生了变化，重要菌根的数量减少了，山毛榉的 ECM 真菌群落多样性下降得更快，云杉的下降得更强。混合林在第三个干旱年后对两种树种的 ECM 真菌群落多样性都有积极影响。在干旱条件下，两种树种的长根状菌根数量都增加了，表明进行了长距离水分运输。然而，在实验过程中，重要的细根数量逐渐减少，导致单位体积土壤的酶活性大幅降低。干旱条件下，存活的外生菌根的水解酶活性稳定或受到刺激，但具有漆酶活性的 ECM 真菌物种大量减少，表明从与酚类化合物结合的养分中获取营养的潜力降低。因此，外生菌根通过在个体根水平上维持或增加其功能来应对反复干旱，但无法补偿生态系统水平上的定量损失。这些发现表明，森林中反复发生的干旱事件对地下有强烈的影响。
