DOI: 10.5061/dryad.51c59zw9v
title: Leading trait dimensions in flood-tolerant plants

description: Background and Aims While trait-based approaches have provided critical
 insights into general plant functioning, we lack a comprehensive
 quantitative view on plant strategies in flooded conditions. Plants
 adapted to flooded conditions have specific traits (e.g. root porosity,
 low root/shoot ratio and shoot elongation) to cope with the environmental
 stressors including anoxic sediments, and the subsequent presence of
 phytotoxic compounds. In flooded habitats, plants also respond to
 potential nutrient and light limitations, e.g. through the expression of
 leaf economics traits and size-related traits, respectively. However, we
 do not know whether and how these trait dimensions are connected. Methods
 Based on a trait dataset compiled on 131 plant species from 141 studies in
 flooded habitats, we quantitatively analysed how flooding-induced traits
 are positioned in relation to the other two dominant trait dimensions:
 leaf economics traits and size-related traits. We evaluated how these key
 trait components are expressed along wetness gradients, across habitat
 types and among plant life forms. Key Results We found that
 flooding-induced traits constitute a trait dimension independent from leaf
 economics traits and size-related traits, indicating that there is no
 generic trade-off associated with flooding adaptations. Moreover,
 individual flooding-induced traits themselves are to a large extent
 decoupled from each other. These results suggest that adaptation to
 stressful environments, such as flooding, can be stressor specific without
 generic adverse effects on plant functioning (e.g. causing trade-offs on
 leaf economics traits). Conclusions The trait expression across multiple
 dimensions promotes plant adaptations and coexistence across multifaceted
 flooded environments. The decoupled trait dimensions, as related to
 different environmental drivers, also explain why ecosystem functioning
 (including, for example, methane emissions) are species and habitat
 specific. Thus, our results provide a backbone for applying trait-based
 approaches in wetland ecology by considering flooding-induced traits as an
 independent trait dimension.
description: Data
 compilation We compiled functional traits on plants recorded
 in flooded habitats, following the definition of the international Ramsar
 Convention (Ramsar
 Convention Secretariat 2013) and the terminology guidance on the definition
 of ‘flooding’ (Sasidharan
 <em>et al</em>. 2017), under both field and laboratory measurements
 based on a combination of expert knowledge of existing literature and
 systematic searches in Web of Science and Google Scholar. The literature
 search included, but was not limited to, the following keywords: wetland,
 marsh, bog, floodplain, macrophytes, aquatic plants, hydrophyte,
 submerged, floating-leaved, emergent, isoetid, mangrove, root porosity,
 root/shoot ratio, shoot elongation, leaf N, leaf P, specific leaf area
 (SLA), leaf dry matter per unit area (LMA), plant height. We also checked
 the references of several important reviews of eco-physiological traits
 for wetlands and flooding events in the recent 15 years
 (e.g. Voesenek
 <em>et al</em>., 2006; Bailey-Serres & Voesenek, 2008;
 Voesenek & Bailey-Serres, 2015). Moreover, we circulated enquiries around our
 network of wetland/aquatic plant experts for recommendations for
 literature that we possibly had overlooked. We used The Plant List to
 eliminate synonyms in species names from our database
 (http://www.theplantlist.org). Root porosity was quantified mainly as either the percentage of the hollow area in the root cross-section or the ratio of hollow volume to the whole root volume. These two methods generally show agreement in air-filled root porosity (Van Noordwijk & Brouwer, 1988). Root/shoot ratio was defined as the root dry mass divided by the shoot dry mass. Shoot elongation was calculated as the percentage of the maximum shoot length increase after submergence/flooding. We are aware that there are various other flooding-induced traits (e.g., radial oxygen loss, leaf gas films) that have been emphasized in eco-physiological studies. However, they are either qualitative, or represented in our database by too few consistently measured observations to be included in our statistical analysis. To evaluate potential drivers of trait-trait relationships, we included habitat wetness, habitat type and growth form in our analysis. The Ellenberg moisture indicator values provide insights in the extent to which species are known to occur at different extents of wetness of the habitat (Ellenberg 1988). These indicator values are based on expert knowledge of the generic distribution of plant species along a gradient of habitat wetness, categorized into 12 levels from very dry habitats (level 1) to strictly aquatic (level 12). To make the Ellenberg moisture indicator applicable for a global analysis, we related the Ellenberg moisture indicator values to the USDA wetland plant classification to derive Ellenberg values for the flora of the USA (see details in Appendix A). To obtain more comprehensive insights in the relationships between the traits of the species and the ecological backgrounds relevant to wetland conditions, we also recorded the habitat type for each trait observation according to a modified Ramsar classification as presented in Pan <em>et al.</em> (2020) and we added life form to each plant species based on the descriptions in the original literature. For this study, we took species mean trait values to allow analysing trait-trait relationships as individual studies did not provide all traits for the same situation (the distribution map of the sampling sites across the globe is shown in Fig. 2). Our analysis covered a total of 131 species of six life form categories (grass, sedge, emergent, submerged, floating-leaved and shrub/tree), with 113 species for root porosity, 60 species for root/shoot ratio, and 32 species for shoot elongation (A list of the data sources and plant species can be found in Appendix B).