Habitat filtering and exclusion of weak competitors jointly explain fern species assemblage along a light and water gradient

Hui Zhang,Robert John,Hui Liu,Shidan Zhu,Qing Ye,Ronghua Li

doi:10.1038/s41598-017-00429-9

Abstract

Fern species are an important component of the diversity of forest plant communities, but very little is known about how fern communities assemble in different environments. In this study, we use multiple trait-based tests to examine the relationships between several key eco-physiological traits which are direct indicators of shade and drought tolerance, and the abundance of fern species in pine forest (PF), pine and mixed broad leaf forest (PMBF) and matured broad leaf forest (MBF) in southern China. These forests are characterized by decreasing light but increasing water availability during succession, and the fern communities correspondingly differ in species composition. We tested community assembly using functional trait distributions and found that habitat filtering and exclusion of weak competitive traits among coexisting species jointly explain fern shade tolerance as measured by photosynthetic capacity (PR), photosynthetic nutrient efficiency (PNUE and PPUE) and water use efficiency as measured by carbon isotope ratio (CIR), and constitute important determinants of fern community assembly in all three forests. These observed fern plant strategies are consistent with known responses of other plant taxa such as flowering plants in similar successional environments and illustrate the value of functional trait based analyses to study community assembly.

Highlights

Identifying the mechanisms generating changes in species abundances in space and time is a central question in ecology[1]
We found that very few species were shared among the three forest types, with only 2 species shared between pine forest (PF) and pine and mixed broad leaf forest (PMBF), no species shared between PF and matured broad leaf forest (MBF), and 2 species shared between PMBF and MBF
We found statistically significant positive correlations between species abundance and traits for photosynthetic rate (PR), Photosynthetic nitrogen use efficiency (PNUE) and phosphorus use efficiency (PPUE), but significant negative correlations between abundance and trait values for carbon isotope ratio (CIR) of fern species in PF and PMBF forest (Fig. 1)

Summary

Introduction

Identifying the mechanisms generating changes in species abundances in space and time is a central question in ecology[1]. Stochastic processes invoke ecological drift as the main factor that determines species abundances, where trait differences are uncorrelated with species abundances and species are considered ecologically equivalent[13, 14] Such species may coexist for long periods of time but are not expected to show significant convergence or divergence in functional trait dispersion patterns. We measured photosynthesis rate (PR), photosynthetic nitrogen use efficiency (PNUE), photosynthetic phosphorus use efficiency (PPUE), and water use efficiency, measured as carbon isotope ratio (CIR) (δ13C) of leaves The selection of these four traits is based on the observations of decreased light but increased water availability in the understory environment from PF to MBF forest[25, 26], which is expected to influence the physiology and function of fern species[22, 27,28,29,30,31]. We hypothesize that 1) abundant fern species in early successional communities tend to have high photosynthetic capacity (high PR) and high photosynthetic nutrient efficiency (high PPUE and PNUE), but may suffer lower long-term water use efficiency, whereas the dominant fern species in late successional communities would have low photosynthetic capacity (low PR), low photosynthetic nutrient efficiency (low PPUE and PNUE) and high long-term water use efficiency, and 2) that the strong environmental effects of light and water availability would lead to trait convergence due to habitat filtering in all four traits

Methods

Results

Discussion

Conclusion