Effects of elevated carbon dioxide (CO₂) on flowering traits of three horticultural plant species

Carbon dioxide (CO₂) has been increasing homogeneously worldwide since industrial revolution. Current CO₂ concentrations are around 400 ppm, which may increase over this century to 430 ppm (best scenario) to > 1000 ppm (worst scenario) (IPCC, 2013). Species-level responses of plant traits to elevated carbon dioxide (eCO₂), especially those that affect interactions with pollinators, could potentially have flow-on effects to both ecological communities and horticultural industries. The impacts of eCO₂ on flowering traits in pepper (Capsicum annuum - Giant Bell), tomato (Lycopersicon lycopersicum- var. Tomato Roma) and zucchini (Cucurbita pepo - Zucchini Blackjack), all economically important horticultural species, were investigated. Twenty plants of each species were grown under two treatments: 1) two glasshouses with ambient CO₂ (400 ppm), and 2) two with eCO₂ (555 ppm). For both treatments, we measured the number of flowers, flower longevity and dry biomass for all species; pollen diameter and number of pollen grains for tomato and zucchini and the sucrose concentration and nectar production in zucchini. Elevated CO₂ had few significant effects on the measured traits, the main exceptions being in zucchini, which produced more male flowers, fewer pollen grains per plant and fewer female flowers under this treatment. Pepper also produced fewer flowers at eCO₂ while tomato was the least sensitive species. Future studies could be aimed at testing sensitivity of different varieties of these important commercial species to eCO₂.