Data from: Early stages of sea-level rise lead to decreased salt marsh plant diversity through stronger competition in Mediterranean-climate marshes

Climate change shuffles species ranges and creates novel interactions that may either buffer communities against climate change or exacerbate its effect. For instance, facilitation can become more prevalent in salt marshes under stressful conditions while competition is stronger in benign environments. Sea-level rise (SLR) is a consequence of climate change that affects the distribution of stress from inundation and salinity. To determine how interactions early in SLR are affected by changes in these two stressors in Mediterranean-climate marshes, we transplanted marsh turfs to lower elevations to simulate SLR and manipulated cover of the dominant plant species, Salicornia pacifica (formerly Salicornia virginica). We found that both S. pacifica and the subordinate species were affected by inundation treatments, and that subordinate species cover and diversity were lower at low elevations in the presence of S. pacifica than when it was removed. These results suggest that the competitive effect of S. pacifica on other plants is stronger at lower tidal elevations where we also found that salinity is reduced. As sea levels rise, stronger competition by the dominant plant will likely reduce diversity and cover of subordinate species, suggesting that stronger species interactions will exacerbate the effects of climate change on the plant community.气候变化会重塑物种分布范围，并催生新的种间相互作用，这类作用既可能缓冲群落应对气候变化的压力，也可能加剧气候变化的负面影响。例如，在胁迫程度更高的盐沼生境中，物种间的促进作用会更为普遍，而在环境适宜的生境中，种间竞争则更为激烈。海平面上升（sea-level rise, SLR）是气候变化的产物之一，它会改变淹水和盐度带来的胁迫分布格局。为探明地中海气候盐沼中，海平面上升早期阶段的种间相互作用如何受这两类胁迫因子变化的调控，我们将盐沼草皮移植到更低海拔处以模拟海平面上升，并对优势植物种Salicornia pacifica（原名为Salicornia virginica）的盖度进行了人为操控。研究发现，Salicornia pacifica与从属伴生物种均受到淹水处理的影响；且在保留Salicornia pacifica的样地中，从属物种的盖度与多样性均显著低于其被移除的样地，尤其在低海拔区域这一差异更为明显。此外我们还发现，低潮汐海拔处的盐度水平更低，而此处Salicornia pacifica对其他植物的竞争抑制作用也更强。随着海平面上升，优势植物种更强的竞争作用可能会降低从属物种的盖度与多样性，这表明更强的种间相互作用会加剧气候变化对植物群落的负面影响。