Photosynthesis-light curves of 3 seeded species in a Conservation Reserve Program study field. Dong, Xuejun^*,1, Nyren, Paul ¹, Patton, Bob¹, Nyren, Anne¹, ¹ 4824 48th Ave SE, Streeter, ND, USA

ABSTRACT- Grass-legume mixtures are preferred in grasslands for grazing or haying. The self-regulation and dynamics of the grass-legume mixtures involve the legume-based nitrogen fixation and the competitive utilization of soil resources and solar radiation through photosynthesis. Quantitative data on the comparative photosynthetic light use capacity between the grass and the legume components is useful for better understanding and management of the grass-legume mixtures. This study compared intrinsic species differences in photosynthetic light use capacity on two grasses, tall wheatgrass (Agropyron elongatum (Host) Beauv.) and intermediate wheatgrass (Agropyron intermedium (Host) Beauv.), and a legume, purple-flowered alfalfa (Medicago sativa L.) grown in a Conservation Reserve Program (CRP) study field in South-Central North Dakota. The results show that both alfalfa and tall wheatgrass had a high photosynthetic capacity in the less stressful June and July measurement periods in 2003. Alfalfa plants exhibited an advantageous stomatal control under changing light conditions. The less tight stomatal control observed in tall wheatgrass may be considered a contributing factor to why tall wheatgrass has a high transpiration rate and limited drought tolerance in dry soils. Intermediate wheatgrass tended to have a lower photosynthetic capacity compared with alfalfa and tall wheatgrass, which seemed to be related to its earlier maturing.

KEY WORDS: Grasslands, Rapid photosynthesis-light curves, Equilibrium vs non-equilibrium stomatal response, Field crops