PHOTOSYNTHESIS OF INDIAN WOODOATS IN CENTRAL TEXAS WOODLANDS

Abstract

Abstract Measurements of photosynthetic rates were made on leaves of Chasmanthium latifolium (Michx.) Yates, Indian woodoats (Poaceae / Gramineae–Grass family). Plants were in the understory of Juniperus ashei/Quercus fusiformis (Ashe juniper/live oak) woodlands in central Texas. Density was low for C. latifolium in the woodlands where it was found. External light level (PFD, photosynthetic-flux density) at midday in the open, above the canopy, on a cloudless day was 1897 ± 21 μmol/m2/s (mean ± SE). Below the canopy, light level was 203 ± 28 μmol/m2/s. Leaves were exposed to light levels from zero to 2000 μmol/m2/s using a Li Cor 6400 photosynthetic meter. Photosynthetic rates were measured and used to generate light response curves. Leaf maximum photosynthetic rate (Amax) was 12.92 ± 0.50 μmol CO2/m2/s. Dark respiration was 0.08 ± 0.09 μmol CO2/m2/s. Light saturation was 1027 ± 42 μmol/m2/s or 54% of the midday maximum light level. The light compensation point was 6 ± 2 μmol/m2/s or 0.32% of the midday light level in the open, above the canopy. Thus, C. latifolium had a positive carbon uptake at very low light levels below canopies where it is usually found. Chasmanthium latifolium was able to fix carbon at light levels almost 10 times lower than some C4 grasses. Light levels below the canopy were 80% below the light saturation point of C. latifolium, which means the plants were fixing carbon at less than their Amax. However, for part of the day, if plants were in light gaps, gas exchange rates would be near the maximum rates measured.