ENVIRONMENTAL-INFLUENCES ON CARBON RECYCLING IN A TERRESTRIAL CAM BROMELIAD, BROMELIA-HUMILIS JACQ

The effects of night-time temperature, leaf-to-air vapour pressure deficit (VPD) and water stress on CO2 recycling in Bromelia humilis Jacq. grown under two light and nitrogen regimes were investigated. At night-time temperatures above 30-degrees-C, integrated net dark CO2 uptake was severely reduced and CO2 for malate synthesis was mainly derived from dark respiration. At 35-degrees-C, up to 84% of the CO2 liberated by dark respiration was refixed into malic acid. Below 30-degrees-C only nitrogen deficient plants showed significant recycling. No significant differences were observed between high and low light grown plants in CO2 recycling. A doubling of leaf-to-air VPD from 7.46 Pa kPa-1 to 15.49 Pa kPa-1 resulted in a 2- to 20-fold decrease in leaf conductance and about 50 to 65% reduction in integrated dark CO2 uptake. However, about twice as much CO2 was recycled at the higher VPD as in the lower. Ten days of water stress resulted in 80 to 100% recycling of respiratory CO2. Under high VPD and water stress treatments, the amount of water potentially saved through recycling of CO2 reached 2- to 6-fold of the actual transpiration. In general, nitrogen deficient plants had higher per cent recycling of respiratory CO2 in response to high night-time temperature, increased VPD or water stress. The results emphasize the ecological relevance of carbon recycling in CAM plants.