西藏那曲地区夏季降水中生物冰核的分布特征

于2013年6~10月在高海拔的西藏那曲地区采集雨水样品,共获得6月份和7月份两个有效样品.通过液滴冻结实验,对雨水样品中大于0.22μm的气溶胶颗粒物的冰核活性进行检测,同时对不同处理(原样雨水、滤液、添加蛋白变性剂、加热煮沸)的雨水样品的冻结温度进行检测.结果显示,6月份和7月份原样雨水样品的平均冻结温度分别为-13.3℃和-8.7℃.在-10℃以上,雨水样品中存在对蛋白变性剂和加热敏感的生物冰核,但不同月份雨水中的生物冰核对雨水液滴的冻结所起的贡献不同.7月份雨水样品中的高效生物冰核对液滴在较高温度下冻结起到主要的催化作用,而6月份雨水样品中的生物冰核对液滴冻结未起到显著作用.经0.22μm滤膜过滤的雨水滤液样品中,仍然存在高效生物冰核,但目前尚未确定其主要成分.通过对雨水样品中细菌16S rRNA基因和真菌rRNA内转录间隔区及5.8S rRNA的ITS1-5.8S-ITS2基因进行克隆测序分析,获得西藏那曲地区夏季6月份和7月份雨水样品中细菌和真菌的群落组成.发现微生物群落组成中包含了具有高效生物冰核活性的假单胞菌属(Pseudomonas)细菌和镰刀菌属(Fusarium)真菌.

Distribution of biological ice nuclei in the summer precipitations of Naqu in Tibet

Precipitation sampling was took at Naqu of Tibet from June to October, 2013. Only two valid rainwater samples in June and July were got. With the experiments of droplets freezing, the average frozen temperature of droplets embedded with particulate matters (>0.22μm) of rainwater samples were tested. Meanwhile, the activity of ice nuclei in the original rainwater, filtered rainwater, rainwater added with protein denaturants, boiled rainwater had also been tested. The results indicated that the average freezing temperatures of original rainwater droplets in June and July were -13.3℃ and -8.7℃, respectively. As for samples with the average freezing temperatures above -10℃, it can be concluded that there were some biological ice nuclei in the original rainwater, which were sensitive to the protein denaturants and boiling. However, their nucleation activities were different for these two months. The biological ice nuclei played a major role in the freezing of droplets in July, but not in the June. The filtered rainwater still contained efficient biological ice nuclei, but the compositions were still unknown. Using the cloning and sequencing technology, the bacteria 16S rRNA gene and the fungi ITS1-5.8S-ITS2 gene that covered the two internal transcribed spacer and 5.8S rRNA gene were analyzed. The results indicated that the bacterial genus of Pseudomonas and the fungal genus of Fusarium were recovered in the rainwater and they were supposed to be two types of efficient biological ice nuclei.