Forest soils are an important but under-studied part of forest ecosystems. The effects of O(3) on below-ground processes in a mature forest have only received limited attention so far. In our study, we have analysed the community of ectomycorrhizal fungi and beech fine root dynamics over two growing seasons (2003 - 2004) in a 70-year old mixed spruce-beech forest stand, in which two groups of five adult beech trees were either fumigated by 2 x ambient ozone concentration or used as control. The main difference between previous studies and our approach was that previous studies were performed on seedlings in pot experiments or in closed or open top chambers, and not IN SITU, in a mature forest stand. Although beech is a relatively unresponsive species to tropospheric O(3), we found a pronounced effect of 2 x O(3) on the number of vital ectomycorrhizal root tips and non-turgescent fine roots. Both categories of roots were significantly increased when compared to controls in two consecutive years at each sampling event. The number of types of ectomycorrhizae and species richness increased in 2004, but not in the extremely dry year 2003. We hypothesised that the observed changes might be an expression of a transitional state in below-ground succession of niches caused by an O(3) induced effect on carbon allocation to roots and the rhizosphere. We have detected changes in ectomycorrhizal species level, however Shannon-Weavers species diversity index and percentage of types of ectomycorrhizae did not change significantly in any sampling year thus indicating our results cannot be unequivocally explained by summer drought in year 2003 or by O(3) exposure alone.

译文

森林土壤是森林生态系统中一个重要但研究不足的部分。到目前为止,O(3) 对成熟森林地下过程的影响仅受到有限的关注。在我们的研究中,我们分析了70年历史的云杉-山毛榉混合林分中两个生长季节 (2003-2004年) 的外生菌根真菌群落和山毛榉细根动态,其中两组五棵成年山毛榉树被2倍环境臭氧浓度熏蒸或用作对照。以前的研究与我们的方法之间的主要区别在于,以前的研究是在盆栽实验中或在封闭或开放的顶部腔室中对幼苗进行的,而不是在成熟的林分中进行的。尽管山毛榉是对流层O(3) 相对无反应的物种,但我们发现2 x O(3) 对重要的外生菌根根尖和非膨胀细根的数量有明显影响。在每个采样事件中,连续两年与对照组相比,两类根均显着增加。外生菌根的种类和物种丰富度2004年增加,但在极端干燥的2003年中却没有增加。我们假设观察到的变化可能是由O(3) 诱导的对根和根际碳分配的影响引起的生态位地下演替中的过渡状态的表达。我们已经检测到外生菌根物种水平的变化,但是Shannon-Weavers物种多样性指数和外生菌根类型的百分比在任何采样年份都没有显着变化,因此表明我们的结果不能通过2003年夏季干旱或O(3) 来明确解释。单独暴露。

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