Opposing community assembly patterns for dominant and non-dominant plant species in herbaceous ecosystems globally

Dominant and non-dominant plants could be subject to different biotic and abiotic influences, partially because dominant plants modify the environment where non-dominant plants grow, causing an interaction asymmetry. Among other possibilities, if dominant plants compete strongly, they should deplete most resources forcing non-dominant plants into a more constrained niche space. Conversely, if dominant plants are constrained by the environment, they might not fully deplete available resources but instead ameliorate some of the environmental constraints limiting non-dominants. Hence, the nature of the interactions between the non-dominants could be modified by dominant species. However, when plant competition and environmental constraints have similar effects on dominant and non-dominant species no difference is expected. By estimating phylogenetic dispersion in 78 grasslands across five continents, we found that dominant species were clustered (underdispersed), suggesting dominant species are likely organized by environmental filtering, and that non-dominant species were either randomly assembled or overdispersed. Traits showed similar trends, but insufficient data prevented further analyses. Furthermore, several lineages scattered in the phylogeny had more non-dominant species, suggesting that traits related to non-dominants are phylogenetically conserved and have evolved multiple times. We found some environmental drivers of the dominant—non-dominant disparity. Our results indicate that assembly patterns for dominants and non-dominants are different, consistent with asymmetries in assembly mechanisms. Among the different mechanisms we evaluated, the results suggest two complementary hypotheses seldom explored: (1) Non-dominant species include lineages adapted to thrive in the environment generated by the dominant species. (2) Even when dominant species reduce resources to non-dominant ones, dominant species could have a stronger effect on—at least—some non-dominants by ameliorating the impact of the environment on them, than by depleting resources and increasing the environmental stress to those non-dominants. The results show that the dominant–non-dominant asymmetry has ecological and evolutionary consequences fundamental to understand plant communities.

Biotic–Abiotic Influences on Modern Ca–Si-Rich Hydrothermal Spring Mounds of the Pastos Grandes Volcanic Caldera (Bolivia)

The lacustrine-to-palustrine Pastos Grandes Laguna (Bolivia) is located in a volcanic caldera fed by active hot springs, with a carbonate crust extending over 40 km2. An integrated approach based on geology and hydrochemistry was used to characterize La Salsa, one of its hydrothermal systems, composed of a flat mound with a hydrothermal discharge. The mound is composed of carbonate–diatom aggregates, forming muds that accumulate and undergo slight swelling. The discharge area along the hydrothermal pathway exhibits several facies and microfabrics, with considerable biological activity and microbialite development. Both the downstream evolution of carbonate and silica content in sediments and the distribution of microbialites can be linked to changes in biotic-abiotic processes occurring along the pathway. The spatial distribution of microbialites and their morphologies are related to hydrodynamic conditions, the nature of the substrate on which they grow and, to a lesser extent, to the accommodation space available. The evolution of the physicochemical properties of the water and biological activity mainly impact mineral precipitation but also affect microbialite morphologies and microstructures. This atypical Si- and Ca-rich hydrothermal system therefore provides insights into the diversity of environmental, chemical, and biotic factors controlling mineralization, which also responds to independent thermodynamic controls.

JASSY, a chloroplast outer membrane protein required for jasmonate biosynthesis

Jasmonates are vital plant hormones that not only act in the stress response to biotic and abiotic influences, such as wounding, pathogen attack, and cold acclimation, but also drive developmental processes in cooperation with other plant hormones. The biogenesis of jasmonates starts in the chloroplast, where several enzymatic steps produce the jasmonate precursor 12-oxophytodienoic acid (OPDA) from α-linolenic acid. OPDA in turn is exported into the cytosol for further conversion into active jasmonates, which subsequently induces the expression of multiple genes in the nucleus. Despite its obvious importance, the export of OPDA across the chloroplast membranes has remained elusive. In this study, we characterized a protein residing in the chloroplast outer membrane, JASSY, which has proven indispensable for the export of OPDA from the chloroplast. We provide evidence that JASSY has channel-like properties and propose that it thereby facilitates OPDA transport. Consequently, a lack of JASSY in Arabidopsis leads to a deficiency in accumulation of jasmonic acids, which results in impaired expression of jasmonate target genes on exposure to various stresses. This results in plants that are more susceptible to pathogen attack and also exhibit defects in cold acclimation.