Photosynthetic characteristics of the shade‐adapted C4grassMuhlenbergia sobolifera(Muhl.) Trin.: control of development of photorespiration by growth temperature

ABSTRACT Muhlenbergia sobolifera(Muhl.) Trin., a C4grass, occurs in understory habitats in the northeastern United States. Plants ofM. soboliferawere grown at 23 and 30°C at 150 and 700 μmol photons m−2s−1. The photosynthetic CO2compensation point, maximum CO2assimilation, dark respiration and the absorbed quantum use efficiency (QUE) were measured at 23 and 30°C at 2 and 20% O2. Photosynthetic CO2compensation points ranged from 4 to 14mm3dm−3CO2and showed limited O2sensitivity. The mean photosynthetic CO2compensation point of plants grown at 30°C (4·5 mm3dm−3) was 57% lower and 80% less inhibited by O2than that of plants grown at 23°C. Photosynthesis was similarly affected by growth temperature, with 70% more O2inhibition in plants grown at 23°C; suppression over all treatments ranging from 2 to 11%. Unlike typical C4species, plants ofM. soboliferafrom both temperature regimes exhibited higher CO2assimilation rates when grown at low light. Growth temperature and light also affected QUE; plants grown at low light and 23°C had the highest value (0·068 mol CO2/mol quanta). Measurement temperature and growth light regime significantly affected dark respiration; however, O2did not affect QUE or dark respiration under any growth or measurement conditions. The results indicate thatM. soboliferais adapted to low PPFD, and that complete suppression of photorespiration is dependent upon high growth temperature.