Interspecific trait integration increases with environmental harshness: A case study along a metal toxicity gradient

Unforeseen plant phenotypic diversity in a dry and grazed world

Earth harbours an extraordinary plant phenotypic diversity1 that is at risk from ongoing global changes2,3. However, it remains unknown how increasing aridity and livestock grazing pressure-two major drivers of global change4-6-shape the trait covariation that underlies plant phenotypic diversity1,7. Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity8-10. They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification.

Phylogenetic conservatism and coordination in traits of Chinese woody endemic flora

Range-limited endemic species, often labeled as endangered due to their low adaptability to climate change, exhibit unclear evolutionary mechanisms influencing their distribution. This study explores the relationship between leaf length, maximum height, and seed diameter and their linkage to phylogeny and climate in the macroecology of 1,370 woody endemics. Using Bayesian analytical method that allows partitioning phylogenetic and environmental variances and covariance, we revealed moderate to high phylogenetic signals in these traits, indicating evolutionary constraints potentially impacting climate change adaptability. The study uncovered a phylogenetically conserved coordination between height and leaf length which showed to be independent of macroecological patterns of temperature and precipitation. These findings emphasize the role of phylogenetic ancestry in shaping the distribution of woody endemics, highlighting the need for prioritized in-situ conservation and providing insights for ex situ conservation strategies.

Root morphological and physiological traits and arbuscular mycorrhizal fungi shape phosphorus-acquisition strategies of 12 vegetable species

Trait plasticity and integration mediate vegetable adaptive strategies. However, it is unclear how patterns of vegetables in root traits influence vegetable adaptation to different phosphorus (P) levels. Nine root traits and six shoot traits were investigated in 12 vegetable species cultivated in a greenhouse with low and high P supplies to identify distinct adaptive mechanisms in relation to P acquisition (40 and 200 P mg kg^-1 as KH₂PO₄). At the low P level, a series of negative correlations among root morphology, exudates and mycorrhizal colonization, and different types of root functional properties (root morphology, exudates and mycorrhizal colonization) respond differently to soil P levels among vegetable species. non-mycorrhizal plants showed relatively stable root traits as compared to solanaceae plants that showed more altered root morphologies and structural traits. At the low P level, the correlation between root traits of vegetable crops was enhanced. It was also found in vegetables that low P supply enhances the correlation of morphological structure while high P supply enhances the root exudation and the correlation between mycorrhizal colonization and root traits. Root exudation combined with root morphology and mycorrhizal symbiosis to observe P acquisition strategies in different root functions. Vegetables respond highly under different P conditions by enhancing the correlation of root traits. Low P supply could significantly improve the direct and indirect ways of mycorrhizal vegetable crops' root traits axis on shoot biomass, and enhance the direct way of non-mycorrhizal vegetable crops' root traits axis and reduce the indirect way of root exudates.

Changes in trait covariance along an orographic moisture gradient reveal the relative importance of light- and moisture-driven trade-offs in subtropical rainforest communities

A range of functional trait-based approaches have been developed to investigate community assembly processes, but most ignore how traits covary within communities. We combined existing approaches - community-weighted means (CWMs) and functional dispersion (FDis) - with a metric of trait covariance to examine assembly processes in five angiosperm assemblages along a moisture gradient in Australia's subtropics. In addition to testing hypotheses about habitat filtering along the gradient, we hypothesized that trait covariance would be strongest at both ends of the moisture gradient and weakest in the middle, reflecting trade-offs associated with light capture in productive sites and moisture stress in dry sites. CWMs revealed evidence of climatic filtering, but FDis patterns were less clear. As hypothesized, trait covariance was weakest in the middle of the gradient but unexpectedly peaked at the second driest site due to the emergence of a clear drought tolerance-drought avoidance spectrum. At the driest site, the same spectrum was truncated at the 'avoider' end, revealing important information about habitat filtering in this system. Our focus on trait covariance revealed the nature and strength of trade-offs imposed by light and moisture availability, complementing insights gained about community assembly from existing trait-based approaches.

Global patterns of leaf construction traits and their covariation along climate and soil environmental gradients

Leaf functional traits and their covariation underlie plant ecological adaptations along environmental gradients, but there is limited information on the global covariation patterns of key leaf construction traits. To explore how leaf construction traits co-vary across diverse climate and soil environmental conditions, we compiled a global dataset including cell wall mass per unit leaf mass (CW_mass ), leaf carbon (C) and calcium (Ca) concentrations, and specific leaf area (SLA) for 2348 angiosperm species from 340 sites world-wide. Our results demonstrated negative correlations between leaf C and Ca concentrations and between leaf C and SLA across diverse nongraminoid angiosperms. Leaf C concentration increased with increasing mean annual temperature (MAT) and mean annual precipitation (MAP) and with decreasing soil pH and calcium carbonate (CaCO₃ ) concentration, whereas leaf Ca concentration and SLA exhibited the opposite responses to these environmental variables. The covariations of leaf Ca-C and of leaf SLA-C were stronger in habitats with lower MAT and MAP, and/or higher soil CaCO₃ content. This global-scale analysis demonstrates that the leaf C and Ca concentrations and SLA together govern the C and biomass investment strategies in leaves of nongraminoids. We conclude that environmental conditions strongly shape leaf construction traits and their covariation patterns.

Macroscopic variation in Arabidopsis mutants despite stomatal uniformity across soil nutrient environments

Stomata are essential pores flanked by guard cells that control gas exchange in plants. We can utilize stomatal size and density measurements as a proxy for a plant's capacity for gas exchange. While stomatal responses to stressful environments are well studied; data are lacking in the responses across mutant genotypes of the same species in these trait and treatment interactions or genetic variation in phenotypic plasticity. We evaluated the effects of soil nutrient variation on macroscopic and stomatal traits of Arabidopsis thaliana T-DNA insertion mutants for which prior performance in a single benign growing condition were available. Nutrient-induced stress significantly impacted traits including plant biomass, height, fruit number, and leaf number which we denote as macroscopic traits. We found evidence that genotype by environment effects exist for macroscopic traits, yet total stomatal area variation, or "microscopic variation" across environments was modest. Divergence from the wildtype line varied by mutant background and these responses were variable among traits. These findings suggest that Arabidopsis employs a strategy of physiological compensation, sacrificing morphological traits to maintain stomatal production.

Functional assembly of tropical montane tree islands in the Atlantic Forest is shaped by stress tolerance, bamboo presence, and facilitation

AIMS

Amidst the Campos de Altitude (Highland Grasslands) in the Brazilian Atlantic Forest, woody communities grow either clustered in tree islands or interspersed within the herbaceous matrix. The functional ecology, diversity, and biotic processes shaping these plant communities are largely unstudied. We characterized the functional assembly and diversity of these tropical montane woody communities and investigated how they fit within Grime's CSR (C-competitor, S-stress-tolerant, R-ruderal) scheme, what functional trade-offs they exhibit, and how traits and functional diversity vary in response to bamboo presence/absence.

METHODS

To characterize the functional composition of the community, we sampled five leaf traits and wood density along transects covering the woody communities both inside tree islands and outside (i.e., isolated woody plants in the grasslands community). Then, we used Mann-Whitney test, t test, and variation partitioning to determine the effects of inside versus outside tree island and bamboo presence on community-weighted means, woody species diversity, and functional diversity.

RESULTS

We found a general SC/S strategy with drought-related functional trade-offs. Woody plants in tree islands had more acquisitive traits than those within the grasslands. Trait variation was mostly taxonomically than spatially driven, and species composition varied between inside and outside tree islands. Leaf thickness, wood density, and foliar water uptake were unrelated to CSR strategies, suggesting independent trait dimensions and multiple drought-coping strategies within the predominant S strategy. Islands with bamboo presence showed lower Simpson diversity, lower functional dispersion, lower foliar water uptake, and greater leaf thickness than in tree islands without bamboo.

CONCLUSIONS

The observed functional assembly hints toward large-scale environmental abiotic filtering shaping a stress-tolerant community strategy, and small-scale biotic interactions driving small-scale trait variation. We recommend experimental studies with fire, facilitation treatments, ecophysiological and recruitment traits to elucidate on future tree island expansion and community response to climate change.

Individual-level leaf trait variation and correlation across biological and spatial scales

Even with increasing interest in the ecological importance of intraspecific trait variation (ITV) for better understanding ecological processes, few studies have quantified ITV in seedlings and assessed constraints imposed by trade-offs and correlations among individual-level leaf traits. Estimating the amount and role of ITV in seedlings is important to understand tree recruitment and long-term forest dynamics. We measured ten different size, economics, and whole leaf traits (lamina and petiole) for more than 2,800 seedlings (height ≥ 10 cm and diameter at breast height < 1 cm) in 283 seedling plots and then quantified the amount of ITV and trait correlations across two biological (intraspecific and interspecific) and spatial (within and among plots) scales. Finally, we explored the effects of trait variance and sample size on the strength of trait correlations. We found about 40% (6%-63%) variation in leaf-level traits was explained by ITV across all traits. Lamina and petiole traits were correlated across biological and spatial scales, whereas leaf size traits (e.g., lamina area) were weakly correlated with economics traits (e.g., specific lamina area); lamina mass ratio was strongly related to the petiole length. Trait correlations varied among species, plots, and different scales but there was no evidence that the strength of trait relationships was stronger at broader than finer biological and spatial scales. While larger trait variance increased the strength of correlations, the sample size was the most important factor that was negatively related to the strength of trait correlations. Our results showed that a large amount of trait variation was explained by ITV, which highlighted the importance of considering ITV when using trait-based approaches in seedling ecology. In addition, sample size was an important factor that influenced the strength of trait correlations, which suggests that comparing trait correlations across studies should consider the differences in sample size.