Anest, A., Charles-Dominique, T., Maurin, O., Millan, M., Edelin, C. and Tomlinson, K.W. (2021), Evolving the structure: climatic and developmental constraints on the evolution of plant architecture. A case study in Euphorbia. New Phytol, 231: 1278-1295. https://doi.org/10.1111/nph.17296

Summary

• Plant architecture strongly influences ecological performance, yet its role in plant evolution has not been explored in depth. By testing both phylogenetic and environmental signals, it is possible to separate architectural traits into four categories: development constraints (phylogenetic signal only); convergences (environmental dependency only); key confluences to the environmental driver (both); unknown (neither).
• We analysed the evolutionary history of the genus Euphorbia, a model clade with both high architectural diversity and a wide environmental range. We conducted comparative analyses of 193 Euphorbia species world-wide using 73 architectural traits, a dated phylogeny, and climate data.
• We identified 14 architectural types in Euphorbia based on trait combinations. We found 22 traits and three types representing convergences under climate groups, 21 traits and four types showing phylogenetic signal but no relation to climate, and 16 traits and five types with both climate and phylogenetic signals.
• Major drivers of architectural trait evolution likely include water stress in deserts (selected for succulence, continuous branching), frost disturbance in temperate systems (selected for simple, prostrate, short-lived shoots) and light competition (selected for arborescence). Simple architectures allowed resilience to disturbance, and frequent transitions into new forms. Complex architectures with functional specialisation developed under stable climates but have low evolvability.

Chaturvedi, R.K.*, Tripathi, A., Raghubanshi, A.S. & Singh, J.S., 2021. Functional traits indicate a continuum of tree drought strategies across a soil water availability gradient in a tropical dry forest. Forest Ecology and Management 482: 118740. DOI:  10.1016/j.foreco.2020.118740

Abstract

This study evaluates drought survival mechanisms of tropical dry forest (TDF) trees based on their functional traits (FTs). We addressed the following questions: (i) What are the dominant functional guilds (FGs) of tree species across a soil water availability gradient in TDF? (ii) What are the important FTs influencing tree species assemblage in different FGs? (iii) What is the functional composition of different FGs in the study sites, and how are they influencing biomass accumulation capacity (BAC) across the soil water availability gradient?

We selected 12 FTs associated with plant water use strategies, viz., canopy cover intensity (CC), wood specific gravity (WSG), saturated stem water content (QWsat), leaf size or leaf area (LA), specific leaf area (SLA), relative water content (RWC), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), maximum saturated stomatal conductance (Gs_max), maximum saturated photosynthetic rate (A_max), and intrinsic water use efficiency (WUEi). By using these FTs, we classified 47 tree species by HCPC (hierarchical clustering on principal components) into three FGs, viz, drought avoiding (DAFG), drought resistant (DRFG), and drought tolerant (DTFG). For species grouping, QWsat was the most significant for DAFG, impacts of A_max, LPC, Gs_max and LNC were significant for DRFG, while LDMC and CC were significant for DTFG. Across the five forest fragments, along a soil moisture content (SMC) gradient, the three FGs exhibited significant differences in species richness, stem density, aboveground biomass, and biomass accumulation capacity (BAC). We observed increasing dominance of DAFG towards drier sites, while the abundance of DRFG and DTFG was higher towards moister sites. Among the three FGs, DTFG showed highest biomass and BAC in our study region. Strategies of DAFG were more associated with savanna habitats, while DRFG and DTFG exhibited strategies important for TDFs. Our findings could help forest managers in restoration and conservation of TDFs.