|Authors: ||D.E. Deyton, S.K. Hunt, C.E. Sams|
|Keywords: ||Rubus idaeus, light saturation curve, photosynthesis, diurnal response, leaf age|
Trials were conducted to characterize net photosynthesis (Pn) of red raspberry (Rubus idaeus) primocane leaves.
Twelve tissue cultured 'Titan' plants were planted in 38-L pots on May 10. The lowest node of primocanes having leaflets large enough to fill a Parkinson photosynthesis chamber were selected on each plant and monitored outdoors for 10 days starting on June 10. Maximum Pn rates of terminal and side leaflets were reached when leaflets were ≈80% expanded and remained high for about five days.
Side leaflets had numerically higher Pn rates than terminal leaflets when newly fully expanded.
By June 26, Pn rates of terminal and side leaflets had declined to 41 and 72%, respectively, of their previous highest rates.
Terminal leaflets had higher Pn rates than side leaflets on June 26 and July 9. As the primocanes grew, the Pn of the terminal leaflet (fully expanded) at every fourth node was determined.
At the last measurement date (September 26), leaflets in the mid plant zone of nodes 28 through 40 had higher Pn rates than lower leaves or leaves at nodes 48 and 52. The Pn response to photosynthetically active radiation (PAR) was determined by placing plants under metal-halide lamps and varying light intensity.
The Pn rate of terminal leaflets increased with increasing light intensity until reaching a maximum at 1400 to 1500 µE m2 s-1. The diurnal Pn response of fully expanded terminal leaflets in outdoor light peaked at about 1000 HR EDT and gradually declined throughout the afternoon.
For plants placed indoors under lights, the diurnal Pn response started with 15 mg CO2 dm2 h-1 at 700 HR, peaked at 1000 HR, gradually declined until about 1600 HR, and then remained steady at about 8 mg CO2 dm2 h-1 until the last measurement at 2100 HR.
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