Cardoso Amanda A, Visel Dominik, Kane Cade N, Batz Timothy A, García Sánchez Clara, Kaack Lucian, Lamarque Laurent J, Wagner Yael, King Andrew, Torres-Ruiz José M, Corso Déborah, Burlett Régis, Badel Eric, Cochard Hervé, Delzon Sylvain, Jansen Steven, McAdam Scott A M
Purdue Center for Plant Biology, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, 47907, USA.
Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany.
New Phytol. 2020 Sep;227(6):1804-1817. doi: 10.1111/nph.16649. Epub 2020 Jun 13.
Lycophytes are the earliest diverging extant lineage of vascular plants, sister to all other vascular plants. Given that most species are adapted to ever-wet environments, it has been hypothesized that lycophytes, and by extension the common ancestor of all vascular plants, have few adaptations to drought. We investigated the responses to drought of key fitness-related traits such as stomatal regulation, shoot hydraulic conductance (K ) and stem xylem embolism resistance in Selaginella haematodes and S. pulcherrima, both native to tropical understory. During drought stomata in both species were found to close before declines in K , with a 50% loss of K occurring at -1.7 and -2.5 MPa in S. haematodes and S. pulcherrima, respectively. Direct observational methods revealed that the xylem of both species was resistant to embolism formation, with 50% of embolized xylem area occurring at -3.0 and -4.6 MPa in S. haematodes and S. pulcherrima, respectively. X-ray microcomputed tomography images of stems revealed that the decline in K occurred with the formation of an air-filled lacuna, disconnecting the central vascular cylinder from the cortex. We propose that embolism-resistant xylem and large capacitance, provided by collapsing inner cortical cells, is essential for Selaginella survival during water deficit.
石松类植物是现存最早分化的维管植物谱系，是所有其他维管植物的姊妹类群。鉴于大多数物种适应于常年湿润的环境，有人推测石松类植物，以及由此推断的所有维管植物的共同祖先，对干旱的适应性较差。我们研究了热带林下原生的血红卷柏和美丽卷柏中与关键适合度相关性状对干旱的响应，这些性状包括气孔调节、枝条水力导度（K）和茎木质部抗栓塞能力。在干旱期间，发现两个物种的气孔在K下降之前就关闭了，血红卷柏和美丽卷柏的K分别在-1.7和-2. MPa时损失50%。直接观察方法表明，两个物种的木质部都抗栓塞形成，血红卷柏和美丽卷柏栓塞木质部面积分别在-3.0和-4.6 MPa时达到50%。茎的X射线微计算机断层扫描图像显示，K的下降伴随着充满空气的腔隙的形成，使中央维管束与皮层断开连接。我们提出，抗栓塞的木质部和由内皮层细胞塌陷提供的大电容，对于卷柏在水分亏缺期间的存活至关重要。
