Worthy Fiona Ruth, Schaefer Douglas Allen, Wanasinghe Dhanushka, Xu Jian Chu, Wang Li Song, Wang Xin Yu
Yunnan Key Laboratory for Fungal Diversity and Green Development, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan 650201, China.
Honghe Centre for Mountain Futures, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan 650201, China.
AoB Plants. 2024 Apr 29;16(3):plae025. doi: 10.1093/aobpla/plae025. eCollection 2024 Jun.
Cyanobacteria require liquid water for photosynthesis, whereas green algae can photosynthesise with water vapour alone. We discovered that several spp. which normally have cyanobacteria as the sole photobiont, in some regions of the trans-Himalayas also harboured green algae. We tested whether green algal acquisition was: limited to high elevations; obtained from neighbouring chloro- species; enabled photosynthesis at low humidity. spp. were collected from 2000 to 4000 m elevation. Spectrophotometry quantified green algal abundance by measuring chlorophyll (absent in cyanobacteria). Thalli cross-sections visually confirmed green algal presence. We sequenced gene regions: (), green algae () and (). Phylogenetic analysis determined myco-photobiont associations. We used a custom closed-circuit gas exchange system with an infrared gas analyser to measure CO exchange rates for desiccated specimens at 33%, 76%, 86% and 98% humidity. Cross-sections revealed that the photobiont layers in putative cyano contained both cyanobacteria and green algae, indicating that they should be considered chloro-cyanolichens. Chloro- had no visible cephalodia nor cyanobacteria in the photobiont layer. Chloro- and chloro-cyano- had comparable levels of chlorophyll . Chloro- usually contained Chloro-cyano- mainly associated with and ; infrequently with , , . Sequences from two green algal genera were obtained from within some thalli. Desiccated specimens of every species could attain net photosynthesis with light exposure and 33% humidity. CO exchange dynamics over a five-day period differed between species. At all elevations, chloro-cyano- spp. had abundant green algae in the photobiont layer, but green algal strains mostly differed to those of chloro- spp. Both chloro- and chloro-cyano- were capable of conducting photosynthesis without liquid water. The data strongly suggest that they attained positive net photosynthesis.
蓝藻进行光合作用需要液态水，而绿藻仅靠水蒸气就能进行光合作用。我们发现，在跨喜马拉雅山脉的一些地区，有几种通常以蓝藻作为唯一光合共生体的地衣物种，也含有绿藻。我们测试了绿藻的获取是否：仅限于高海拔地区；从邻近的含氯物种中获得；在低湿度条件下能够进行光合作用。从海拔2000米至4000米采集了地衣物种。分光光度法通过测量叶绿素a（蓝藻中不存在）来量化绿藻丰度。地衣体横截面通过肉眼确认了绿藻的存在。我们对基因区域进行了测序：核糖体DNA（rDNA）、绿藻的18S核糖体RNA（18S rRNA）和线粒体细胞色素氧化酶亚基I（COI）。系统发育分析确定了菌藻光合共生体的关联。我们使用了一个配备红外气体分析仪的定制闭路气体交换系统，来测量在33%、76%、86%和98%湿度条件下干燥标本的二氧化碳交换率。横截面显示，假定为蓝藻型地衣的光合共生体层中同时含有蓝藻和绿藻，这表明它们应被视为含氯蓝藻地衣。含氯地衣在光合共生体层中没有可见的假杯点，也没有蓝藻。含氯地衣和含氯蓝藻地衣的叶绿素a水平相当。含氯地衣通常含有绿藻纲；含氯蓝藻地衣主要与刚毛藻属和鞘毛藻属相关联；很少与石莼属、浒苔属、礁膜属相关联。从一些地衣体内部获得了两个绿藻属的序列。每个地衣物种的干燥标本在光照和33%湿度条件下都能实现净光合作用。不同物种在五天时间内的二氧化碳交换动态有所不同。在所有海拔高度，含氯蓝藻地衣物种的光合共生体层中都有丰富的绿藻，但绿藻菌株大多与含氯地衣物种的不同。含氯地衣和含氯蓝藻地衣都能够在没有液态水的情况下进行光合作用。数据有力地表明它们实现了正的净光合作用。
