Niche separation and weak interactions in the high tidal zone of saltmarsh-mangrove mixing communities

Abstract

Saltmarsh-mangrove ecotones occur at the boundary of the natural geographic distribution of mangroves and salt marshes. Climate warming and species invasion can also drive the formation of saltmarsh-mangrove mixing communities. How these coastal species live together in a "new" mixed community is important in predicting the dynamic of saltmarsh-mangrove ecosystems as affected by ongoing climate change or human activities. To date, the understanding of species interactions has been rare on adult species in these ecotones.Two typical coastal wetlands were selected as cases to understand how mangrove and saltmarsh species living together in the ecotones. The leaves of seven species were sampled from these coastal wetlands based on their distribution patterns (living alone or coexisting) in the high tidal zone, and seven commonly used functional traits of these species were analyzed.We found niche separation between saltmarsh and mangrove species, which is probably due to the different adaptive strategies they adopted to deal with intertidal environments.Weak interactions between coexisting species were dominated in the high tidal zone of the two saltmarsh-mangrove communities, which could be driven by both niche differentiation and neutral theory.Synthesis. Our field study implies a potential opportunity to establish a multispecies community in the high tidal zone of saltmarsh-mangrove ecotones, where the sediment was characterized by low salinity and high nitrogen.

Keywords: adult species interaction; coastal wetland species; coexistence; niche differentiation; niche width; plant functional traits.

FIGURE 1

The distribution and formation of saltmarsh‐mangrove community

FIGURE 2

The species collected from (a) Quanzhou Bay Mangrove Reserve and (b) Minjiang Estuary wetlands

FIGURE 3

The trait space constructed by common coastal wetland species (close and open symbols represent the niche of the species when living alone and when living with other species, respectively; the same color indicates the coexisting species pair; violet and sienna circles indicate the two wetlands in Quanzhou Bay and Minjiang Estuary, respectively)

FIGURE 4

Trait comparison between saltmarsh and mangrove species in Quanzhou Bay wetlands. Leaf area (a), SLA (b), LDMC (c), Leaf biomass (d), Leaf N (e), Leaf P (f), and Leaf C (g). The following colors represent green (A. corniculatum), blue (A. marina), yellow (K. obovata), and red (S. alterniflora). The interval plot (NPC) and box plots show standards boxes summarize median, first, and third quartile, while whiskers represent value range (minimum and maximum). The red points and the curved line represent the distribution of the data. The symbols with different letters denote significantly different from each other at p < .05, while the same letters denote no significant difference (p > .05)

FIGURE 5

Trait comparison between saltmarsh and mangrove species in Minjiang Estuary wetlands. Leaf area (a), SLA (b), LDMC (c), Leaf biomass (d), Leaf N (e), Leaf P (f), and Leaf C (g). Green and blue colors represent P. australis and S. alterniflora, respectively. The box plots show standards boxes summarize median, first, and third quartile, while whiskers represent value range (minimum and maximum). The red points and the curved line represent the distribution of the data. The symbols with different letters denote significantly different from each other at p < .05, while the same letters denote no significant difference (p > .05)

FIGURE 6

Trait distance when species coexisting and living alone. The asterisk * and ** indicate significant difference at p < .05 and p < .01, respectively. The colored asterisk represents divergent variation, and the dark color represents trait convergent. The dash line denotes the threshold between divergence and convergence in trait variation. Only when the data within the top‐left space, it means species coexistence leading to divergent variation of a given trait

FIGURE 7

The interactions between species of each trait based on the index of RNE (a), LnRR (b) and RII (c)