As sea-level rises, low-salinity tidal marshes experience greater flooding with more saline water. In the Chesapeake Bay estuary, we compared the 1980 and 2014 tidal marsh inventories (TMIs) of plant communities from James City County, Virginia, USA, with respect to the spatial distribution of two species—the invasive reed Phragmites australis and native salt marsh grass Spartina alterniflora–plus overall species richness. Since the 1980 TMI, the total area of low-salinity tidal marshes in which P. australis occurred increased from 0.46 km² to 6.30 km² in 2014. Between TMIs, however, the total area of low-salinity marshes occupied by S. alterniflora increased by only 0.02 km². Species richness in low-salinity tidal marshes decreased from 41 to 25 between TMIs. To assess seedling emergence under increased flooding and salinity, we completed two seed bank germination experiments using soil samples collected from six low-salinity marshes containing established P. australis stands. In the first experiment, more seedlings emerged in the two low-salinity (0 vs. 5 ppt) treatments after seven weeks, irrespective of flooding (water 3.75 cm below vs. at soil surface), but no P. australis or S. alterniflora germinated. For the second experiment, we added seeds of P. australis and S. alterniflora to soils exposed to the same flooding and salinity treatments to test the impact of these plant competitors on seedling emergence. No difference in number of seedlings was detected among treatments, but the number of species and their relative abundance was significantly affected by flooding (ANOSIM, R = 0.138, P < 0.001). The presence of P. australis and S. alterniflora seedlings appeared to shift the physical factor more influential on seedling emergence from salinity to flooding. For both seed bank experiments, more seedlings but not more species emerged from soils collected from marshes where P. australis coverage was <50%. High diversity plant communities of low-salinity tidal marshes along the upper reaches of this estuary are gradually being replaced by those dominated by P. australis and S. alterniflora—a trend expected to continue here and in other riverine estuaries of the Atlantic and Gulf Coasts.

中文翻译：

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低盐度潮汐沼泽植物群落响应海平面上升的变化

随着海平面的上升，低盐度的潮汐沼泽会遭受更大的洪水和更多的咸水。在切萨皮克湾河口，我们比较了 1980 年和 2014 年美国弗吉尼亚州詹姆斯城县植物群落的潮汐沼泽清单 (TMI)，这两个物种的空间分布是入侵芦苇和原生盐沼草。互花米草——加上整体物种丰富度。自 1980 年 TMI 以来，P的低盐度潮汐沼泽总面积。australis在 2014 年从 0.46 km ²增加到 6.30 km ²。然而，在 TMI 之间，S .互花米草仅增加了 0.02 km ²。低盐度潮汐沼泽的物种丰富度在 TMI 之间从 41 减少到 25。为了评估洪水和盐度增加下的幼苗出苗，我们使用从六个含已建立的P的低盐度沼泽收集的土壤样品完成了两个种子库发芽实验。澳大利亚站。在第一个实验中，七周后在两个低盐度（0 对 5 ppt）处理中出现了更多的幼苗，而与洪水无关（水深 3.75 厘米与土壤表面），但没有出现P. australis或S。互花米草发芽了。在第二个实验中，我们添加了P. australis 的种子和小号。对暴露于相同洪水和盐度处理的土壤进行互花蜜的检测，以测试这些植物竞争者对幼苗出苗的影响。处理间未检测到幼苗数量差异，但物种数量及其相对丰度受洪水影响显着（ANOSIM，R  = 0.138，P  < 0.001）。P. australis和S的存在。互花米草幼苗似乎将影响幼苗出苗的物理因素从盐度转变为洪水。对于这两个种子库实验，从沼泽收集的土壤中出现了更多的幼苗，但没有更多的物种。覆盖率<50%。沿着这条河口上游低盐度潮沼的高度多样性的植物群落正逐渐被那些由主导替代芦苇和小号。互花米草——这一趋势预计将继续在这里以及大西洋和墨西哥湾沿岸的其他河口。