Photosynthetic Responses to Irradiance in Three Forest Understory Species of the C4 Grass Genus Muhlenbergia

Abstract

Three species of the C4 grass genus Muhlenbergia—M.frondosa, M. sobolifera, and Af. schreberi—were collected from forest understory habitats in Kansas and grown in a growth chamber at 1,500, 150, and 15- 25 |xmol m"2 s"1 photosynthetic photon flux density (PPFD). Assimilation (A), conductance to C02 , intercellular C02 concentration, chlorophyll (chl) concentrations, and photosystem I electron-transport capacity were determined and compared with results for Af. cuspidata, which occurs only in open, prairie areas. All of the shade species exhibited more shade tolerance than the prairie species: they had lower maximum A, saturation of A, and photosystem I electron transport with respect to PPFD, higher quantum yields that increased with decreasing growth PPFD, and increasing chl concentrations with decreasing PPFD.