Contrasts among cationic phytochemical landscapes in the southern United States

Abstract

Understanding the phytochemical landscapes of essential and nonessential chemical elements to plants provides an opportunity to better link biogeochemical cycles to trophic ecology. We investigated the formation and regulation of the cationic phytochemical landscapes of four key elements for biota: Ca, Mg, K, and Na. We collected aboveground tissues of plants in Atriplex, Helianthus, and Opuntia and adjacent soils from 51, 131, and 83 sites, respectively, across the southern United States. We determined the spatial variability of these cations in plants and soils. Also, we quantified the homeostasis coefficient for each cation and genus combination, by using mixedeffect models, with spatially correlated random effects. Additionally, using random forest models, we modeled the influence of bioclimatic, soil, and spatial variables on plant cationic concentrations. Sodium variability and spatial autocorrelation were considerably greater than for Ca, Mg, or K. Calcium, Mg, and K exhibited strongly homeostatic patterns, in striking contrast to non-homeostatic Na. Even so, climatic and soil variables explained a large proportion of plants' cationic concentrations. Essential elements (Ca, Mg, and K) appeared to be homeostatically regulated, which contrasted sharply with Na, a nonessential element for most plants. In addition, we provide evidence for the No-Escape-from-Sodium hypothesis in real-world ecosystems, indicating that plant Na concentrations tend to increase as substrate Na levels increase.

Low sodium availability in hydroponically manipulated host plants promotes cannibalism in a lepidopteran herbivore

“…2 c) also increased as sodium in the hydroponic solution increased. The values for plant-sodium concentrations across treatments fall within the range of concentrations observed for sunflower foliar tissues in the wild and across the geographic range of C. lacinia (minimum = 3 ppm, maximum = 29,791 ppm) 10 . We found no significant differences in plant-tissue concentrations for Ca, C, Cu, Fe, Mg, Mn, N, P, K, S, and Zn, none of which varied among the hydroponic solutions used to produce the host plants (Supplementary Table S2 ).…”

“…Therefore, our study suggests that plant-sodium concentrations can have variable and important influences on animal behaviour and performance. Sources of sodium for animal consumers are highly variable across the terrestrial phytochemical landscape 10 , 67 , 68 , which can be consequential for micro- and macroevolutionary processes, local adaptation, community assembly, food web structure, and eco-evolutionary dynamics.…”

“…As an essential element for animals, sodium plays an important role in osmoregulatory processes, promotes muscle and neural tissue development, and controls blood movement, among other functions 7 – 9 . Posing challenges for animal foragers, the availability of sodium across terrestrial environments (e.g., soils and plants) is highly heterogeneous 10 – 13 .…”

“…To our knowledge, no study of insect herbivore behaviour or performance has manipulated plant-tissue-incorporated sodium concentrations. Our hydroponic method aimed to present variation of dietary sodium in host tissue as the herbivore has experienced it in nature, i.e., they do not feed on artificial diets nor generally encounter sodium sprayed onto leaves in the field, except in coastal habitats through aerosol deposition 10 . We manipulated tissue sodium of common sunflowers ( Helianthus annuus, Asteraceae) to test whether plant sodium concentration would influence an herbivore's cannibalistic behaviour and survival.…”