What confines an annual plant to two separate zones along coastal topographic gradients?

Abstract

We investigated the roles of flooding, salinity, and plant competition in creating a bimodal zonation pattern of the marsh dominant annual plant, Suaeda salsa, along coastal topographic gradients on the Pacific coast of northern China. In two consecutive years, we manipulated salinity and flooding, salinity, and competition for S. salsa seedlings that had been transplanted into the mudflat, the high marsh, and the upland, respectively. S. salsa plants that had been transplanted into the mudflat were completely eliminated in the non-elevated treatments whereas they performed much better in the 10 cm elevated treatments, regardless of salinity treatments. Although the performance of S. salsa transplanted into the high marsh did not differ between the fresh (watered) and the salt (control) treatments, S. salsa seedling emergence in the high marsh was nearly completely inhibited in the salt treatments. In contrast, a large number of S. salsa seedlings did emerge in the fresh treatments. S. salsa transplanted into the upland performed well when neighbors were removed, whereas it appeared to be strongly suppressed when neighbors were present. These data indicated that flooding, salinity, and competition all played a role in determining the zonation pattern of S. salsa. Furthermore, the importance of salinity was found to vary with life-history stage. Based on the results from these field manipulative experiments, we suggest that the marsh plant zonation paradigm may hold true for plant distributions along landscape-scale topographic gradients from mudflats to uplands in general. The relative importance of flooding, salinity, and competition, however, may vary at different elevations within a site and between sites.

Testing the importance of plant strategies on facilitation using congeners in a coastal community

“…This emphasizes the essence of the physiological-ecologicalamplitude concept, and extends it to stress gradients biotically created by a third species. Furthermore, by showing that S. salsa dominating saline marshes was competitively restricted from the low-salinity upland, our study suggests that this concept may be applicable to broad stress gradients that encompass coastal marsh and terrestrial habitats (also see He et al 2009). …”

“…Fieldwork was conducted at upper elevations of a coastal marsh-upland ecosystem in the Yellow River Delta, northeast China (see He et al [2009] for a map). The climate is warm-temperate.…”

Biogeography of salt marsh plant zonation on the Pacific coast of South America

“…The lower limits of plants are thought to be determined by physical stress, while the upper limits of plants are determined by interspecific plant competition. This simple community assembly model has been tested in California (Pennings & Callaway, 1992), Spain (Castellanos, Figueroa, & Davy, 1994;Castillo, Fernandez-Baco, Castellanos, & Davy, 2000), Brazil (Costa, Marangoni, & Azevedo, 2003), China (He, Cui, Bertness, & An, 2012;He et al, 2009), Argentina (Alberti et al, 2010;Idaszkin, Bortolus, & Bouza, 2011, and Chile (Farina, Silliman & Bertness, 2009). …”

Community Structure and Abiotic Determinants of Salt Marsh Plant Zonation Vary Across Topographic Gradients

“…Lines a-e, divisions between mudflat and Spartina low marsh, Spartina low marsh and Suaeda low marsh, Suaeda low marsh and high marsh, high marsh and terrestrial border, and terrestrial border and upland, respectively. Refer to He et al (2009a) for the location of the study site on the western Pacific coast estuary, becoming a dominant species in these habitats and is moving up rapidly. Other plant species including Salicornia europaea, Scripus spp., and Juncus spp.…”

“…In a Californian salt marsh, Pennings and Callaway (1992) indicated that although flooding, soil salinity, and competition all interacted to determine plant zonation patterns, the relative importance of these factors differed at different elevations. Moreover, the precise roles of the two main physical stressors, salinity and flooding, in mediating plant zonation were also suggested to vary with elevation in a Chinese salt marsh (He et al 2009a).…”