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

Abstract

We investigated compositions of plant communities and their abiotic determinants in the Yellow River estuary, China. Along a topographic gradient, we quantified plant compositions and abiotic factors in different vegetation zones, and examined the relationships between plant communities and abiotic factors using canonical correspondence analysis and the effects of vegetation shading using a removal experiment. The relationships between plant communities and abiotic factors differed between high elevations and low elevations. Salinity and flooding oppositely related with distributions of plant communities at low elevations, but they appeared to operate synergically at high elevations. The effects of vegetation shading were found to vary across the topographic gradient, indicating spatial variations in potential positive interactions among plants. These results suggest that spatial variations in determinants of community structure should be addressed in future studies in estuarine and coastal systems, as well as in other natural habitats.

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

“…An emerging hypothesis from these studies is that geographic variation in the mechanisms underlying salt marsh plant zonation is driven by variation in climate (Bertness & Pennings, 2000;Cui et al, 2011), tidal regime (Kunza & Pennings, 2008), and species adaptation (Sanford & Bertness, 2009). For example, low-latitude salt marshes may have steeper soil salinity and moisture gradients, with hotter climates leading to increased soil salinity at high-marsh elevations due to evaporative salt accumulation (Pennings, Selig, Houser, & Bertness, 2003).…”

“…Elevation gradients in soil salinity and moisture are typically less pronounced in colder high-latitude marshes (Bertness & Pennings, 2000). This difference in environmental stress gradients could underlie variation in the determinant of the upper limits of plants between low-and high-latitude salt marshes (Cui et al, 2011;Pennings et al, 2003). Our current understanding of geographic variation in marsh plant zonation, however, is largely based on studies from single sites.…”

Dynamics of zonal halophyte communities in salt marshes in the world

“…Determining the mechanisms underlying the growth of organisms has long been a goal of ecological research (Adams 1963;Cui et al 2011;Guo and Pennings 2012) and it is widely accepted that both abiotic and biotic factors are important in affecting the distribution of different species, but there is no consensus on how the relative role of biotic factors varies given abiotic factors. In salt marsh habitats, most research has centered on the ways in which abiotic factors affect plant zonation (Bertness and Ellison 1987;Kim and Ihm 1988;Sánchez et al 1996;Ihm and Lee 1998;Zedler et al 1999;Ko 2001;Silvestri et al 2005;Alvarez-Rogel et al 2007;Hladik and Alber 2014): topographical and climatic factors such as elevation, frequency and duration of tidal flooding, the influence of fresh water, distance from the water source (tidal effect), periods of rainfall and drought, disturbance by debris, and physical and chemical factors of soil such as salinity, moisture, type, texture, drainage, nutrient toxicity, organic content, depth of the water table, redox potential, peat accumulation, aeration, and sulfide concentration (Table 1).…”

“…Flooding establishes a strong nonresource stress gradient across salt marshes, with soil anoxia and waterlogging decreasing from the seaward edge to the terrestrial border (Mendelssohn et al 1981;Woerner and Hackney 1997;Zedler et al 1999;Cui et al 2011). …”

“…Instead, optimal growth occurs in half-and fully-flooded soil. Flooding frequency and elevation have a higher value in predicting the occurrence of dominant plant species than does elevation Armstrong et al 1985;Bertness and Ellison 1987;Sánchez et al 1996;Rogel et al 2001;Bockelmann et al 2002;Cui et al 2011). The close relationship between flooding frequency and elevation particularly applies to lower elevations, where minor changes in elevation lead to major changes in flooding frequency.…”