Photosynthetic difference among genotypes and the effect of red and far-red light on diurnal photosynthesis of Phalaenopsis in reproductive stage

MSc-thesis abstract (submitted 12 February 2018):
This study investigates the effect of red and far-red light on the spike growth and diurnal photosynthesis of Phalaenopsis.
Plants were grown under three red and far-red light conditions:
PSS (phytochrome photostationary state) 0.88, 0.83 and 0.72.

A lower PSS value increased diurnal photosynthesis. This was because lower PSS value increased the duration of CAM phase II and had positive effect on spike volume so that sink strength was increasing and the suppression in photosynthesis was released. Besides, it was found red and far-red light had no effect on stomata development.

In order to investigate the relation between sink strength and cumulative CO2 exchange in depth, this study also compared the diurnal CO2 uptake among genotypes with different growth rate. The plants for genotype comparing were grown with light treatment of 0.83 PSS, no difference of diurnal CO2 uptake per unit leaf area was found.

It was concluded that genotypes had different strategy of assimilates partitioning because genotype showed largest leaf area did not have largest spike volume. Additionally, the genotype showed larger spike volume had shorter duration of phase II and IV than other genotypes, therefore, it had lower cumulative CO2 uptake in phase II and IV.

Keywords: Phalaenopsis, photosynthesis, stomatal conductance, spike, genotype