Background Coastal wetlands are threatened by the increased salinity that may result from sea level rise. Salinity stress alters species zonation patterns through changes in competitive outcome between species differing in salinity tolerance. This study therefore aimed to understand how salinity and light affect two dominant and competing coastal wetland grasses that differ in salt tolerance, height and photosynthetic metabolism. Methods The C4 species Spartina anglica and the C3 species Phragmites australis were grown at five salinity levels (0, 7, 14, 21 and 28 ppt) and two light fluxes (100 % and 50 % of natural daylight) in an outdoor experimental setup for 102 d with full access to nutrients. Key Results Salinity reduced the biomass, height and shoot density of P. australis from 81.7 g dry weight (DW), 0.73 m and 37 shoots per pot at a salinity of 0 ppt to 16.8 gDW, 0.3 m and 14 shoots per pot at a salinity of 28 ppt. Biomass, height and shoot density of S. anglica did not respond or were only slightly reduced at the highest salinity of 28 ppt. High salinity also resulted in a higher tissue concentration of N and P in P. australis. Both species had low ability to acclimate to the lower light flux. Shade acclimation in S. anglica occurred via modest changes in specific leaf area, pigment content and biomass allocation. Conclusions High salinity reduced traits important for light competition and increased the nutrient concentration in P. australis leaf and root biomass, while this was overall unaffected in S. anglica. This is likely to reduce the competitive ability of P. australis over S. anglica for light because at high salinities the former cannot effectively shade the lower-growing S. anglica. Neither species effectively acclimates to shade, which could explain why S. anglica does not occur in the understorey of P. australis at low salinities.

中文翻译：

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两种主要滨海湿地草的阴影和盐度响应：对过渡区光竞争的影响

背景 沿海湿地受到海平面上升可能导致盐度增加的威胁。盐分胁迫通过改变耐盐性不同物种之间的竞争结果来改变物种分区模式。因此，本研究旨在了解盐度和光照如何影响两种在耐盐性、高度和光合代谢方面不同的优势和竞争滨海湿地草。方法 C4 种 Spartina anglica 和 C3 种 Phragmites australis 在室外实验装置中在五个盐度水平（0、7、14、21 和 28 ppt）和两种光通量（自然日光的 100% 和 50%）下生长102 d 充分获得营养。主要结果 盐度降低了 P. australis 的生物量、高度和枝条密度，从 81.7 g 干重 (DW)，0。在 0 ppt 至 16.8 gDW 的盐度下，每盆 73 m 和 37 个芽，在 28 ppt 的盐度下，每盆 0.3 m 和 14 个芽。S. anglica 的生物量、高度和枝条密度在 28 ppt 的最高盐度下没有反应或仅略微降低。高盐度还导致澳大利亚南芥中较高的 N 和 P 组织浓度。这两个物种对较低光通量的适应能力都很低。S. anglica 的阴影适应通过特定叶面积、色素含量和生物量分配的适度变化发生。结论 高盐度降低了对光竞争很重要的性状，增加了南洋杉叶片和根生物量中的养分浓度，而这在黄杨中总体上不受影响。这可能会降低 P. australis 对 S. australis 的竞争能力。anglica 用于光照，因为在高盐度下，前者不能有效地遮蔽生长较低的 S. anglica。这两个物种都不能有效地适应阴影，这可以解释为什么在低盐度的 P. australis 的下层中不会出现 S. anglica。