Are ecophysiological adaptive traits decoupled from leaf economics traits in wetlands?

Abstract

Wetland plants have developed a suite of traits, such as aerenchyma, radial oxygen loss and leaf gas films, to adapt to the wetland environment characterised by, for example, a low redox potential and a lack of electron acceptors. These ecophysiological traits are critical for the survival and physiological functioning of wetland plants. Most studies on these traits typically focus on a single trait and a single or few species at the time. Next to these traits, traits of the leaf economics spectrum (LES) that reflect resource acquisition and allocation in plant species have also been frequently measured in wetlands. However, the performance of the LES has rarely been examined among wetland plants. Both suites of traits are critical for—but affect different aspects of—wetland plant functioning and survival. The interactions between them, potentially causing synergies or trade‐offs, reflect wetland plant strategies to simultaneously deal with stress tolerance and resource utilization, and have ramifications for the functioning of wetland ecosystems. Based on a literature review and quantitative analysis of available data, we provide evidence suggesting that LES and ecophysiological traits may be decoupled (e.g., for root porosity and radial oxygen loss vs. leaf nitrogen) or coupled (e.g., for iron tolerance vs. specific leaf area) in wetlands, depending on the trait combination concerned. This rather complex relationship between wetland adaptive traits and LES traits indicates that there can be multiple mechanisms behind the strategies of wetland plants. We further illustrate how adaptive and LES traits together contribute to wetland ecosystem functions, such as denitrification and methane emission. We highlight that both suites of traits should be considered simultaneously when applying trait‐based methods to wetland ecology.

Drivers of plant traits that allow survival in wetlands

“…We therefore expect to see a decoupled pattern between some of the wetland adaptive traits. Along with the evidence that some wetland adaptive traits tend to be orthogonal to LES traits (Pan et al, ), our current results support the idea that these three (and potentially others as well) wetland adaptive traits are relatively cheap to develop, and therefore are not to a large‐extent constrained by other adaptive traits or by LES traits.…”

“…Wetland adaptive traits are the premise of survival under the adverse conditions present in wetlands (Moor et al, ; Pan et al, ; Voesenek & Bailey‐Serres, ). The identified environmental filters in wetlands select plants with suitable adaptive traits, along with other factors including soil fertility, light radiation, competition/facilitation in communities (Luo et al, ).…”

“…To cope with these adverse conditions, wetland plants have developed a suite of adaptive traits (Pan, Cieraad, & van Bodegom, ; Voesenek, Colmer, Pierik, Millenaar, & Peeters, ; Winkel et al, ). Examples of adaptive traits include the following: enhanced shoot and root porosity (aerenchyma formation) to facilitate internal oxygen transportation, ameliorate oxygen concentration in the root zone and aid (root) respiration and oxidation (Colmer, ; Mcdonald, Galwey, & Colmer, ; Visser, Colmer, Blom, & Voesenek, ); shoot elongation to allow leaves to access atmospheric oxygen; decreased root/shoot ratios to create a better balance between gas transport capacity (oxygen source) and root oxygen consumption (oxygen sink; van Bodegom, Kanter, Bakker, & Aerts, ; Jung, Hoffmann, & Muller, ); and a root radial oxygen loss (ROL) barrier to reduce diffusion of precious oxygen to the rhizosphere (Armstrong, Cousins, Armstrong, Turner, & Beckett, ; Colmer, ).…”

Global patterns of the leaf economics spectrum in wetlands

“…LES traits in wetlands are likely to play a role in these ecosystem processes and services 11,12 . While the wide fertility gradient across different wetland types theoretically provides a natural gradient for the expression of LES from the acquisitive to conservative strategies 13 , additional constraints induced by adverse environmental conditions in wetlands compared to non-wetland systems mean that it cannot be taken for granted that LES traits will show similar patterns.…”

“…To survive in such an adverse environment, wetland plants have developed a suite of adaptive strategies 15 . Whether the LES also exists in wetlands depends, to a large extent, on whether the prevalent adaptive strategies of plants to environmental stressors are generally costly or cheap 13 . If adaptations are cheap, the LES should be unaffected and similar to non-wetland ecosystems.…”