Responses of net photosynthetic rate related to anatomical adaptations of cocksfoot leaves grown under different fluctuating light regimes in New Zealand.

PERI P.L.; MOOT D.J.; LUCAS R.J.; MCNEIL D.

Orlando, Florida, USA

Congreso; 1st World Congress of Agroforestry, Session VI Tree Domestication and Management; 2004

University of Florida

Net photosynthetic rate was measured from the youngest fully expanded leaves of cocksfoot (Dactylis glomerata L.) grown under different fluctuating light regimes (24, 43, 58 and 100% transmissivity) in the field at the Lincoln University silvopastoral experiment (New Zealand). The light-saturated rate of net photosynthesis (Pmax), photosynthetic efficiency (á) and convexity (è) of the light-response curve were derived from fitted non-rectangular hyperbola functions. The main features related to the effect of leaf adaptation to different light regimes on leaf photosynthesis were: (i) Pmax in full sun conditions was double that under severe shade; (ii) when re-exposed to full sunlight, plants previously grown under shade had lower Pmax and á values, showing they were photosynthetically less efficient than those grown in full sunlight; (iii) when plants were exposed to severe shade, leaves adapted to severe shade conditions (24% transmissivity) had the highest Pmax, á and è, and saturated at a lower PPFD value compared with others shaded treatments (43% and 58% transmissivity). These changes were attributed to a reduction in stomatal conductance (gs), the mesophyll surface area to leaf surface area ratio (Ames/A) and maintenance respiration for shade adapted plants. The reduction in gs was attributed to a reduction in stomata density (total pore space) in the abaxial surface of leaves grown at low light intensity. Also, plants grown under shade invested leaf nitrogen (N) to total chlorophyll and decreased the chlorophyll a:b ratio which may improve the light absorptance per unit N invested in light harvesting at low light levels. These results emphasise the physiological adaptation of coksfoot leaves under different light regimes.