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

Root functional traits are important predictors for plant resource acquisition strategies in subtropical forests

Intercorrelated aboveground traits associated with costs and plant growth have been widely used to predict vegetation in response to environmental changes. However, whether underground traits exhibit consistent responses remains unclear, particularly in N-rich subtropical forests. Responses of foliar and root morphological and physiological traits of tree and herb species after 8-year N, P, and combined N and P treatments (50 kg N, P, N and P ha-1 year-1) were examined in leguminous Acacia auriculiformis (AA) and nonleguminous Eucalyptus urophylla (EU) forests in southern China. N addition did not significantly impact all leaf and root traits except root N concentration per root length. Root traits responded to P addition more than leaf traits in trees; however, both traits responded similarly to P addition in herbs. Tree species deviated from the expected leaf economics spectrum; however, all species aligned with the root economics spectrum. The P and combined N and P treatments significantly altered the position of principal components analysis of root functional traits for herb species compared to the control. However, these changes did not reflect a classic shift in nutrient acquisition strategy within the root economics spectrum. As leguminous species experienced greater P limitation, AA responded more to P addition than EU; their understories indicated no significant differences. This study reveals how plant aboveground and underground traits adapt to nutrient-rich environments. These findings highlight the importance of incorporating plant underground traits, which show significant and specific responses to nutrient additions, into Earth system models for accurately predicting plant responses to global change.

Global change and plant-ecosystem functioning in freshwaters

Freshwater ecosystems are of worldwide importance for maintaining biodiversity and sustaining the provision of a myriad of ecosystem services to modern societies. Plants, one of the most important components of these ecosystems, are key to water nutrient removal, carbon storage, and food provision. Understanding how the functional connection between freshwater plants and ecosystems is affected by global change will be key to our ability to predict future changes in freshwater systems. Here, we synthesize global plant responses, adaptations, and feedbacks to present-day and future freshwater environments through trait-based approaches, from single individuals to entire communities. We outline the transdisciplinary knowledge benchmarks needed to further understand freshwater plant biodiversity and the fundamental services they provide.

Choose Wisely: Great Variation among Genotypes of Promising Paludiculture Crop Phragmites australis

Measures mitigating the climate crisis, such as paludiculture, which is the agriculture on rewetted peatlands, are urgently needed. The cosmopolitan species Phragmites australis has the potential to be used in paludiculture worldwide but is known for its high intraspecific variation. This raises the questions of whether (i) P. australis genotypes differ even at a regional scale, making them differently well suited for paludiculture and (ii) P. australis performance can be predicted by linking the variation in genotypes to strategies in the plant economics spectrum. Five P. australis genotypes from Mecklenburg-Western Pomerania were cultivated in two 10-month mesocosm experiments along gradients of water level and nutrient addition. We compared growth, morphology (height, growing density), above- and belowground biomass, functional and ecophysiological traits (SLA, LDMC, SRL, RDMC, root porosity, photosynthetic rate) as well as gene expression. Our results demonstrate a high variability of P. australis genotypes even at a regional scale, revealing genotype-specific productivity, morphology, and gene expression and implying that the selection of suitable genotypes will be crucial for the success of a paludiculture. However, trait covariation did not indicate distinct plant economic strategies to predict genotype performance. Instead, large-scale genotype trials are needed to select suitable genotypes for paludiculture.

The global spectrum of plant form and function: enhanced species-level trait dataset

Here we provide the 'Global Spectrum of Plant Form and Function Dataset', containing species mean values for six vascular plant traits. Together, these traits -plant height, stem specific density, leaf area, leaf mass per area, leaf nitrogen content per dry mass, and diaspore (seed or spore) mass - define the primary axes of variation in plant form and function. The dataset is based on ca. 1 million trait records received via the TRY database (representing ca. 2,500 original publications) and additional unpublished data. It provides 92,159 species mean values for the six traits, covering 46,047 species. The data are complemented by higher-level taxonomic classification and six categorical traits (woodiness, growth form, succulence, adaptation to terrestrial or aquatic habitats, nutrition type and leaf type). Data quality management is based on a probabilistic approach combined with comprehensive validation against expert knowledge and external information. Intense data acquisition and thorough quality control produced the largest and, to our knowledge, most accurate compilation of empirically observed vascular plant species mean traits to date.

Leading trait dimensions in flood-tolerant plants

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.

Flooding and Soil Properties Control Plant Intra- and Interspecific Interactions in Salt Marshes

The stress gradient hypothesis (SGH) states that plant-plant interactions shift from competition to facilitation in increasing stress conditions. In salt marshes, edaphic properties can weaken the application of the SGH by amplifying the intensity of flooding and controlling plant zonation. We identified facilitative and competitive interactions along flooding gradients and tested the role of edaphic properties in exacerbating stress and shaping plant-plant interactions. Morphological traits of two target halophytes (Limonium narbonense and Sarcocornia fruticosa), flooding intensity, soil texture and soil organic C were recorded. The relative plant fitness index was assessed for the two species based on the relative growth in plurispecific rather than monospecific plant communities. Plant fitness increased with increasing stress supporting the SGH. L. narbonense showed larger fitness in plurispecific stands whereas S. fruticosa performed better in conspecific stands. Significant intra- or interspecific interactions were observed along the stress gradient defined by the combination of flooding and clay content in soil. When considering the limited soil organic C as stressor, soil properties were more important than flooding in defining plant-plant interactions. We highlight the need for future improvements of the SGH approach by including edaphic stressors in the model and their possible interactions with the main abiotic drivers of zonation.

Physiological Adaptation and Plant Distribution along a Steep Hydrological Gradient

Plant species often separate strongly along steep environmental gradients. Our objective was to study how coupling between plant physiology and environmental conditions shapes vegetation characteristics along a distinct hydrological gradient. We therefore investigated species photosynthesis in air and under water within a limited area from dry-as-dust to complete submergence in a nutrient-poor limestone habitat on Öland's Alvar, Sweden. We found structural and physiological adaptations of species to endure water limitation at the dry end (e.g., moss cushions and CAM-metabolism) and diffusive carbon limitation (e.g., bicarbonate use) at the submerged end of the gradient. As anticipated, mean photosynthesis in air increased 18-fold from the species-poor assembly of cushion-mosses and Sedum CAM-species on mm-thin limestone pavements to the species-rich assembly of C-3 terrestrial plants in deeper and wetter soils. A GLM-model indicated that 90% of the variation in species richness could be explained by a positive effect of soil depth, a negative effect of the duration of water cover and their interaction. In water, mean photosynthesis was highest among aquatic species, low among Sedum species and cushion mosses, and negligible among C-3 terrestrial plants. While aquatic species dried out in air, drought-resistant small species were probably competitively excluded from the more suitable terrestrial habitats on deeper soils with moderate flooding by taller species of high photosynthetic capability. In conclusion, the clear distribution of species along the steep hydrological gradient reflects distinct structural and physiological adaptations, environmental filtering and interspecific competition.

Leaf reflectance can surrogate foliar economics better than physiological traits across macrophyte species

BACKGROUND

Macrophytes are key players in aquatic ecosystems diversity, but knowledge on variability of their functional traits, among and within species, is still limited. Remote sensing is a high-throughput, feasible option for characterizing plant traits at different scales, provided that reliable spectroscopy models are calibrated with congruous empirical data, but existing applications are biased towards terrestrial plants. We sampled leaves from six floating and emergent macrophyte species common in temperate areas, covering different phenological stages, seasons, and environmental conditions, and measured leaf reflectance (400-2500 nm) and leaf traits (dealing with photophysiology, pigments, and structure). We explored optimal spectral band combinations and established non-parametric reflectance-based models for selected traits, eventually showing how airborne hyperspectral data could capture spatial-temporal macrophyte variability.

RESULTS

Our key finding is that structural-leaf dry matter content, leaf mass per area-and biochemical-chlorophyll-a content and chlorophylls to carotenoids ratio-traits can be surrogated by leaf reflectance with normalized error under 17% across macrophyte species. On the other hand, the performance of reflectance-based models for photophysiological traits substantively varies, depending on macrophyte species and target parameters.

CONCLUSIONS

Our main results show the link between leaf reflectance and leaf economics (structure and biochemistry) for aquatic plants, thus envisioning a crucial role for remote sensing in enhancing the level of detail of macrophyte functional diversity analysis to intra-site and intra-species scales. At the same time, we highlighted some difficulties in establishing a general link between reflectance and photosynthetic performance under high environmental heterogeneity, potentially opening further investigation directions.

Urban growth drives trait composition of urban spontaneous plant communities in a mountainous city in China

Urban ecosystems feature intense anthropogenic activities and environmental stressors that filter species with varying life-history traits. The traits therefore provide an essential aspect to understanding how species respond to urban environments. We conducted this study in Chongqing, a mountainous city in southwestern China, and tested the hypothesis that the velocity of urban growth can alter functional compositions of urban plant communities through selection on species' taxonomic distributions and functional traits. We found that for most traits, their values spanned a wide range across the 70 spontaneous species in this study, and seed size and leaf element composition played a key role in contributing to the functional differentiation among species. At the same time, urban growth intensity was negatively correlated with leaf N concentration, the N:P ratio, and specific leaf area (SLA), and positively correlated with the leaf C:N ratio. This suggests that species in urban centers are associated with an acquisitive nutrient-use strategy and may gain strong competitive strategies to be favored by greater selective pressure in those long-term urban centers. Lastly, we show that urbanization as a strong filter tends to reduce the chance of species with unique traits for the spontaneous plant communities. Our study offers insights into mechanisms through which spontaneous plant communities are filtered by urbanization with a special focus on the ecological consequences of the velocity of urban growth.

Plant trait-environment trends and their conservation implications for riparian wetlands in the Yellow River

Determining the relationship between plant functional traits and the environment are key for the protection and sustainable utilization of riparian wetlands. In the middle and lower reaches of the Yellow River, riparian wetlands are divided into seasonal floodplain wetlands (natural) and pond-like wetlands or paddy fields (artificial). Here, species composition differences were catalogued based on plant functional traits including origin, life history, and wetland affinity in natural and artificial wetlands. Wetland physicochemical characteristics and regional socio-economic parameters collected as indicators of environmental variables were used to analyze the plant functional trait-environment relationship. The results reveal that plant functional traits in the seasonal floodplain wetland are impacted by physicochemical characteristics of habitat. The abundance of annual plants tends to decrease with concentration of heavy metals, while species diversity is mainly determined by soil physical and chemical properties, especially soil pH and temperature. Specifically, wetland-obligate species (not in water) are more resistant to heavy metal content in water than species with other types of wetland affinity. Life history strategies of species in artificial sites tend to be significantly associated with animal husbandry and artificial populations, while the wetland affinity of species is mainly determined by regional agriculture, especially the installation of agricultural covered areas. Furthermore, water quality and nutrients in suspended sediments from the Yellow River affected species diversity and life history strategies by affecting water and soil conditions of surrounding wetlands, especially conductivity and phosphorus levels.

Global patterns of the leaf economics spectrum in wetlands

The leaf economics spectrum (LES) describes consistent correlations among a variety of leaf traits that reflect a gradient from conservative to acquisitive plant strategies. So far, whether the LES holds in wetland plants at a global scale has been unclear. Using data on 365 wetland species from 151 studies, we find that wetland plants in general show a shift within trait space along the same common slope as observed in non-wetland plants, with lower leaf mass per area, higher leaf nitrogen and phosphorus, faster photosynthetic rates, and shorter leaf life span compared to non-wetland plants. We conclude that wetland plants tend to cluster at the acquisitive end of the LES. The presented global quantifications of the LES in wetland plants enhance our understanding of wetland plant strategies in terms of resources acquisition and allocation, and provide a stepping-stone to developing trait-based approaches for wetland ecology.

Leaf economics spectrum theory has greatly advanced understanding of plant functional ecology, but it is unclear whether its predictions hold in wetland communities. Here, Pan and colleagues analyse leaf economics traits in wetland plants, showing that their trait relationships deviate from fully terrestrial plants, particularly by clustering towards acquisitive plant strategies.