Dependence of the South African geophyte Boweia volubilis on its inflorescence for plant carbon gain

Abstract

The largest organ of the eastern South African geophyte Boweia volubilis (climbing or sea onion) is the green inflorescence; leaves are small, ephemeral, and only occasionally produced. The reticulated inflorescence is also succulent. The goals of this study were to determine if the inflorescence of this plant is its sole source of energy and carbon, and if the inflorescence is capable of CAM photosynthesis. CO2 exchange of all plant organs was measured and, using their total biomass, used to calculate their contribution to the carbon budget of the whole plant. Diel fluctuations in tissue acidity were also measured in the organs.The large, green inflorescence of B. volubilis accounts for nearly two-thirds of the total biomass of the plant, while its occasional, linear leaves are small and ephemeral. The dominance of the inflorescence in the plant's biomass, coupled with its relatively high photosynthetic rate, illustrates the reliance of this plant on its inflorescence for nearly all its carbon gain. Although the upper part of the plant bulb is green, it cannot photosynthesize (no daytime CO2 uptake and no O2 release) and, thus, does not contribute to plant carbon gain. The small cotyledon and the succulent inflorescence undergo CAM-cycling, which may benefit the plant when drought-stressed.