Abstract
Many terrestrial plants are C3 plants that evolved in the Mesozoic Era when atmospheric CO2 concentrations ([CO2]) were high. Given current conditions, C3 plants can no longer benefit from high ambient [CO2]. Kaempferia marginata Carey is a unique understory ginger plant in the tropical dry forests of Thailand. The plant has two large flat leaves that spread on the soil surface. We found a large difference in [CO2] between the partly closed space between the soil surface and the leaves (638 µmol mol−1) and the atmosphere at 20 cm above ground level (412 µmol mol−1). This finding indicates that the plants capture CO2 efflux from the soil. Almost all of the stomata are located on the abaxial leaf surface. When ambient air [CO2] was experimentally increased from 400 to 600 μmol mol−1, net photosynthetic rates increased by 45 to 48% under near light-saturated conditions. No significant increase was observed under low light conditions. These data demonstrate that the unique leaf structure enhances carbon gain by trapping soil CO2 efflux at stomatal sites under relatively high light conditions, suggesting that ambient air [CO2] can serve as an important selective agent for terrestrial C3 plants.
Highlights
Many terrestrial plants are C3 plants that evolved in the Mesozoic Era when atmospheric CO2 concentrations ([CO2]) were high
We report the discovery of an understory ginger plant, Kaempferia marginata Carey (Zingiberaceae), which effectively traps soil-efflux CO2 in the closed space between the soil surface and its leaves
The ginger plant has a unique leaf structure; the individual plant has two flat leaves that spread on the soil surface, and the leaf edges are often curled downward to capture the air under its leaf blades (Fig. 1)
Summary
Many terrestrial plants are C3 plants that evolved in the Mesozoic Era when atmospheric CO2 concentrations ([CO2]) were high. The increase in light-saturated net photosynthesis under doubled [CO2] was 13% in C3 crops and 47% in C3 trees[3] This finding may indicate that C3 plants in the past exhibited increased carbon (C) gain and that more extensive C cycling occurred in forest ecosystems compared with the present era. We report the discovery of an understory ginger plant, Kaempferia marginata Carey (Zingiberaceae), which effectively traps soil-efflux CO2 in the closed space between the soil surface and its leaves. This plant enhances photosynthesis by 45 to 48% under relatively high light conditions. Based on measurements of ambient air [CO2], photosynthetic capacity, and the stable carbon isotope ratios in the lamina, we demonstrate that this ginger plant makes effective use of high [CO2] on the forest floor
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