Species Survey of Leaf Hyponasty Responses to Warming Plus Elevated CO2

Abstract

Atmospheric carbon dioxide (CO₂) concentrations are increasing and may exceed 800 ppm by 2100. This is increasing global mean temperatures and the frequency and severity of heatwaves. Recently, we showed for the first time that the combination of short-term warming and elevated carbon dioxide (eCO₂) caused extreme upward bending (i.e., hyponasty) of leaflets and leaf stems (petioles) in tomato (Solanum lycopersicum), which reduced growth. Here, we examined additional species to test the hypotheses that warming + eCO₂-induced hyponasty is restricted to compound-leaved species, and/or limited to the Solanaceae. A 2 × 2 factorial experiment with two temperatures, near-optimal and supra-optimal, and two CO₂ concentrations, ambient and elevated (400, 800 ppm), was imposed on similarly aged plants for 7-10 days, after which final petiole angles were measured. Within Solanaceae, compound-leaf, but not simple-leaf, species displayed increased hyponasty with the combination of warming + eCO₂ relative to warming or eCO₂ alone. In non-solanaceous species, hyponasty, leaf-cupping, and changes in leaf pigmentation as a result of warming + eCO₂ were variable across species.

Keywords: climate change; hyponasty; leaf angle; morphology.

Figure 1

Average petiole angle in solanaceous crops, by species and treatment. From top to bottom: pepper (C. annuum), ground cherry (P. pruinosa), tomato (S. lycopersicum), eggplant (S. melongena), and potato (S. tuberosum). Plants were grown for 7 days under control (optimal temperature and 400 ppm CO₂), warming (8 °C over optimal temperature and 400 ppm CO₂), eCO₂ (optimal temperature and 800 ppm CO₂), or warming + eCO₂ conditions (8 °C over optimal temperature and 800 ppm CO₂). Results are means + 1 SD, with significant differences among treatments indicated by different letters above bars within each graph.

Figure 2

Average petiole angle in non-solanaceous plants, by species and treatment. From top to bottom: bush bean (P. vulgaris), hibiscus (H. rosa-sinensis), and nasturtium (T. majus). Plants were grown for 7 days under control (optimal temperature and 400 ppm CO₂), warming (8 °C over optimal temperature and 400 ppm CO₂), eCO₂ (optimal temperature and 800 ppm CO₂), or warming + eCO₂ conditions (8 °C over optimal temperature and 800 ppm CO₂). Results are means + 1 SD, with significant differences among treatments indicated by different letters above bars within each graph.

Figure 3

Leaf curving or leaf cupping index of species (the ratio of flattened leaf length to curled leaf length, minus 1). From top to bottom: bush bean (P. vulgaris), mint (M. × piperita), and rose (R. multiflora). Plants were grown for 7 days under control (optimal temperature and 400 ppm CO₂), warming (8 °C over optimal temperature and 400 ppm CO₂), eCO₂ (optimal temperature and 800 ppm CO₂), or warming + eCO₂ conditions (8 °C over optimal temperature and 800 ppm CO₂). Results are means + 1 SD, with significant differences among treatments indicated by different letters above bars within each graph.

Figure 4

Visual comparison of leaf pigmentation under control (optimal temperature and 400 ppm CO₂; (left)) and warming + eCO₂ (8 °C over optimal temperature and 800 ppm CO₂; (right)) treatments. From top to bottom: pepper (C. annuum), hibiscus (H. rosa-sinensis), mint (M. × piperita), and nasturtium (T. majus).

Figure 5

Shoot biomass of plants grown for 7 days under control (optimal temperature and 400 ppm CO₂), warming (8 °C over optimal temperature and 400 ppm CO₂), eCO₂ (optimal temperature and 800 ppm CO₂), or warming + eCO₂ conditions (8 °C over optimal temperature and 800 ppm CO₂): pepper (C. annuum), hibiscus (H. rosa-sinensis), mint (M. × piperita), bush bean (P. vulgaris), rose (R. multiflora), tomato (S. lycopersicum), eggplant (S. melongena), potato (S. tuberosum), and nasturtium (T. majus). Ground cherry (P. pruinosa) biomass not collected. Results are means + 1 SD, with significant differences among treatments indicated by different letters above bars within each graph.