Department of Biology and Kevo Subarctic Research Institute, University of Turku, FIN-20500, Turku, Finland.
Microb Ecol. 1993 Nov;26(3):227-34. doi: 10.1007/BF00176955.
Endophytes were frequently isolated from mountain birch (Betula pubescens var. tortuosa (Ledeb.) Nyman) leaves at a subarctic site where natural air pollution is low. We tested whether simulated acid rain had any influence on the occurrence of endophytes. Dry controls with only ambient rain and irrigated controls treated with spring water of pH 6 were compared with acid treatments at pH 3 and pH 4, prepared by adding both sulphuric and nitric acids. Treatments began in 1985 and leaf samples were taken twice during the summer of 1992. Leaves were surface sterilized, five leaf disks from each leaf placed on malt extract agar, and growing colonies were counted and identified. The most frequently isolated endophyte from birch leaves was a Fusicladium anamorph of Venturia sp. (88% of all the isolates in July and 75% of all the isolates in August), followed by a sterile mycelium and Melanconium sp. The number of endophytes isolated and the species number increased from July to August. Endophytes were most frequently isolated from the basal part of the midrib. The percentage of colonization by endophytes was similar in short and long shoots. More endophytes were isolated from leaves of branches taken at 1 m height than at 2 m height. The stronger acid rain treatment (pH 3) reduced by approximately 25% the number of isolated endophytes in August. Treatments did not have any effect on species composition of endophyte assemblages in birch leaves.
内生真菌常从亚北极地区的山桦（Betula pubescens var. tortuosa (Ledeb.) Nyman）叶片中分离出来，该地区的自然空气污染水平较低。我们测试了模拟酸雨是否会对内生真菌的发生产生影响。与仅用环境雨水处理的干燥对照和用 pH 值为 6 的泉水处理的灌溉对照相比，用添加硫酸和硝酸制成的 pH 值为 3 和 pH 值为 4 的酸处理进行了对比。处理于 1985 年开始，1992 年夏季期间进行了两次叶片样本采集。叶片经过表面消毒，将每个叶片的五个叶圆盘放在麦芽提取物琼脂上，并对生长的菌落进行计数和鉴定。从桦树叶中分离出的最常见的内生真菌是属于角斑病菌属（Venturia sp.）的 Fusicladium 无性型（7 月所有分离物的 88%和 8 月所有分离物的 75%），其次是无菌菌丝和 Melanconium 属。从 7 月到 8 月，分离出的内生真菌数量和物种数量有所增加。内生真菌最常从中脉基部分离出来。短枝和长枝上内生真菌的定殖率相似。从 1 米高的树枝上采集的叶片中分离出的内生真菌比从 2 米高的树枝上采集的叶片中多。更强的酸雨处理（pH 值为 3）使 8 月分离出的内生真菌数量减少了约 25%。处理对桦树叶内生真菌组合的物种组成没有影响。
