Montgomery Botanical Center , 11901 Old Cutler Road, Miami, FL 33156 , USA.
AoB Plants. 2011;2011:plr022. doi: 10.1093/aobpla/plr022. Epub 2011 Aug 12.
The basic set of adaptations necessary for salinity tolerance in vascular plants remains unknown. Although much has been published on salinity stress, almost all studies deal with spermatophytes. Studies of salinity tolerance in pteridophytes are relatively rare but hold promise for revealing the fundamental adaptations that all salt-tolerant vascular plants may share. The most basal pteridophytes to exhibit salinity tolerance are members of the genus Equisetum, including the giant horsetail, Equisetum giganteum, the only pteridophyte to occur in salinity-affected regions of the Atacama Desert valleys of northern Chile. Here it can constitute a significant vegetation component, forming dense stands of shoots >4 m high.
Physiological parameters (stomatal conductances; efficiency of photosystem II; sap osmotic potential) were measured in E. giganteum populations in northern Chile across a range of groundwater salinities at 11 sites. In addition, Na, K, electrical conductivity and total plant water potential were measured in the plants and groundwater from each site.
Equisetum giganteum exhibits similar stomatal conductances and photochemical efficiencies of photosystem II across a wide range of groundwater salinities. It lowers cell sap osmotic potential with increasing salinity and produces positive root pressure, as evidenced by guttation, at the full range of salinities experienced in the Atacama Desert. Equisetum giganteum maintains low Na concentrations in its xylem fluid and cell sap when soil water Na is high. It also maintains high K/Na ratios in xylem fluid and cell sap when soil water has low K/Na ratios.
Equisetum giganteum is well adapted to salinity stress. Efficient K uptake and Na exclusion are important adaptations and closely similar to those of the facultative halophyte fern Acrostichum aureum.
血管植物耐盐性所需的基本适应机制仍不清楚。尽管已有大量关于盐胁迫的研究，但几乎所有研究都涉及有性植物。关于蕨类植物耐盐性的研究相对较少，但有望揭示所有耐盐性血管植物可能共有的基本适应机制。表现出耐盐性的最基础的蕨类植物是木贼属植物，包括巨型木贼，即唯一一种出现在智利北部阿塔卡马沙漠山谷受盐影响地区的蕨类植物。在这里，它可以构成一个重要的植被组成部分，形成超过 4 米高的密集的枝条。
在智利北部的 11 个地点，对跨越一系列地下水盐度范围的巨型木贼种群的生理参数（气孔导度；光合作用 II 系统的效率；叶汁渗透压）进行了测量。此外，还测量了每个地点的植物和地下水中的 Na、K、电导率和总植物水势。
巨型木贼在广泛的地下水盐度范围内表现出相似的气孔导度和光合作用 II 的光化学效率。随着盐度的增加，它降低了细胞汁液渗透压，并在阿塔卡马沙漠经历的全盐度范围内产生正根压，表现为吐水。当土壤水中的 Na 含量高时，巨型木贼在木质部液和叶汁中保持低的 Na 浓度。当土壤水中的 K/Na 比值较低时，它还在木质部液和叶汁中保持高的 K/Na 比值。
巨型木贼很好地适应了盐胁迫。高效的 K 吸收和 Na 排斥是重要的适应机制，与兼性盐生蕨类植物肾蕨的适应机制非常相似。
