Robustness of trait connections across environmental gradients and growth forms

Abstract

Aim Plant trait databases often contain traits that are correlated, but for whom direct (undirected statistical dependency) and indirect (mediated by other traits) connections may be confounded. The confounding of correlation and connection hinders our understanding of plant strategies, and how these vary among growth forms and climate zones. We identified the direct and indirect connections across plant traits relevant to competition, resource acquisition and reproductive strategies using a global database and explored whether connections within and between traits from different tissue types vary across climates and growth forms. Location Global. Major taxa studied Plants. Time period Present. Methods We used probabilistic graphical models and a database of 10 plant traits (leaf area, specific leaf area, mass‐ and area‐based leaf nitrogen and phosphorous content, leaf life span, plant height, stem specific density and seed mass) with 16,281 records to describe direct and indirect connections across woody and non‐woody plants across tropical, temperate, arid, cold and polar regions. Results Trait networks based on direct connections are sparser than those based on correlations. Land plants had high connectivity across traits within and between tissue types; leaf life span and stem specific density shared direct connections with all other traits. For both growth forms, two groups of traits form modules of more highly connected traits; one related to resource acquisition, the other to plant architecture and reproduction. Woody species had higher trait network modularity in polar compared to temperate and tropical climates, while non‐woody species did not show significant differences in modularity across climate regions. Main conclusions Plant traits are highly connected both within and across tissue types, yet traits segregate into persistent modules of traits. Variation in the modularity of trait networks suggests that trait connectivity is shaped by prevailing environmental conditions and demonstrates that plants of different growth forms use alternative strategies to cope with local conditions.

Plant Trait Networks: Improved Resolution of the Dimensionality of Adaptation

“…Indeed, for more than two decades studies have suggested that the relationships among plant traits may be visualized as a network or correlogram, and sometimes analyzed using path analysis or structural equation models [21,26,[37][38][39][40][41][42][43]. Recent studies [40,44] have quantified parameters to describe the network topology and the interdependency of traits.…”

“…Plant traits can be biologically or statistically correlated; however, not all traits directly connect in all PTNs. Consequently, PTNs with higher edge density, shorter average path length, and shorter diameter imply a stronger coordination among multiple traits [44] (Y. Li, dissertation, Beijing Forestry University, 2020).…”

Optimal Community Assembly Related to Leaf Economic- Hydraulic-Anatomical Traits

“…A lack of coupling between these traits is consistent with their contrasting impacts on leaf level function (Li et al, 2015). Indeed, decoupled relationships between leaf economic and hydraulic traits potentially allow greater evolvability for more combinations of leaf traits to adapt to multifarious niche dimensions, resulting in many plant species that coexist within communities in tropical-subtropical forests (Li et al, 2015;Flores-Moreno et al, 2019). Trait-trait relationships represent coordinated ecological strategies and trade-offs of plants, due to the different strategies that could facilitate co-existence (Bruelheide et al, 2018).…”

“…In this study, we found that the influence of leaf economic-hydraulic trait moments (mean, variance, skewness, and kurtosis) on GPP in observed communities were significantly higher than those in the null communities, indicating that assembly of leaf economic and hydraulic traits within community optimized their productivity. Further, the strong coordination between leaf economic and hydraulic traits at the community level allows plant communities to function efficiently and take up resources faster (Flores-Moreno et al, 2019). This would directly affect ecosystem productivity.…”

“…Indeed, leaf economic and hydraulic traits were decoupled across species from tropical and subtropical forests (Li et al, 2015). By contrast, coupling of such traits in low resource communities would provide greater efficiency with respect to carbon cost (Flores-Moreno et al, 2019) and could help plants adapt to drought stressed environments (Yin et al, 2018). Here, we assume that the coupling of leaf economic and hydraulic traits through filtering specific plant species might be an adaptation strategy of plant communities.…”