EFFECT OF ELEVATED CARBON-DIOXIDE ON THE PHOTOSYNTHESIS AND EARLY GROWTH OF MANGOSTEEN (GARCINIA-MANGOSTANA L)

Mangosteen is a potentially important new crop for tropical northern Australia if its long establishment time can be substantially reduced. The effect of enriching the atmosphere with up to 1000 μbar CO2 on the growth and photosynthesis of mangosteen seedlings was examined over the course of a year in an attempt to accelerate early plant development. It was initially found to be necessary to reduce photon irradiance from 450 to 200 μmol photons m-2 s-1 (400-700 nm) to overcome photoinhibition of photosynthesis, and to reduce CO2 from 1000 to 800 μbar to encourage greening of newly formed leaves. A major effect of CO2 enrichment was to stimulate earlier lateral branching which accelerated the development of leaf area and plant carbon gain. Photosynthetic rates of mangosteen leaves were found to be very low and the 800-μbar CO2 atmosphere increased CO2 fixation by 40-60% compared to control leaves measured at 400 μbar CO2. As a result, total plant dry weight increased by 77%. The stimulatory effect of CO2 was greatest on root and stem dry weight, which doubled. Although a smaller proportion of dry weight was partitioned into leaves compared with the control plants, CO2 enrichment increased average leaf size by ∼ 10%, specific leaf dry weight by 17% and total leaf area by 28%. By comparison, plants from the same apomictic seedling population grown under shadehouse conditions in Darwin, Australia, developed more slowly, consistent with descriptions in the literature, and were substantially smaller and lower in dry weight compared to the plants grown under controlled conditions, even in the absence of CO2 enrichment, and had not developed lateral branches by harvest time. Reasons for this difference are suggested which may enable improvement of the early growth of mangosteen plants under field nursery conditions. © 1990.