Photosynthetic Rates of Two Species of Malvaceae, Malvaviscus arboreus var. drummondii (Wax Mallow) and Abutilon theophrasti (Velvetleaf)

Abstract We examined two co-occurring species of Malvaceae in the savanna of central Texas to determine their photosynthetic response to varying levels of light. Abutilon theophrasti had a mean (±1 SD) density of 4 ± 4 plants/m2 in the open-grassland phase of the savanna, and a density of 1 ± 2 plants/m2 under canopy of woody mottes. Malvaviscus arboreus var. drummondii was not in the open-grassland phase and had a density of 3 ± 6 plants/m2 under canopy of woody mottes. Mean midday levels of light in the open and canopy were significantly different at 2,004 versus 192 µmol/m2/s, respectively. Maximum photosynthetic rate of A. theophrasti (34.6 ± 3.6 µM CO2/m2/s) occurred at a photosynthetic-flux density of 2,000 ± 0.0 µM /m2/s and was significantly greater than the maximum photosynthetic rate of M. arboreus var. drummondii (14.8 ± 2.2 µM CO2/m2/s), which occurred at a photosynthetic-flux density of 1,350 ± 173.0 µM /m2/s. Light saturation, light-compensation point, dark respiration rates, stomatal conduc...