Options
Photosynthetic characteristics of green leaves and green pseudobulbs of Coelogyne rochussenii orchid and their responses to different growth irradiance and drought stress
Author
Tan, Geraldine Shu Hui
Supervisor
He, Jie
Abstract
The epiphytic Necklace Orchid (Coelogyne rochussenii) is one of Singapore’s native orchids currently being reintroduced to the urban habitat. Field observations have shown that some of these plants displayed visible signs of leaf curling and extreme dryness during midday that may have resulted from excess light or water deficit or the combination of both. To ensure the sustainable reintroduction of C. rochussenii in Singapore, this project investigated how C. rochussenii behaved in terms of water relations and photosynthetic physiology under natural conditions in Pasir Ris Park and towards a combination of drought stress (DS) and light stress in the greenhouse. Green leaves (GL) of C. rochussenii followed a typical C(sub)3s) and WC were not significantly different for GPSB grown under the different light intensities. Despite conferring more qP and NPQ, the photosynthetic machinery in GL appeared to be stressed under HL conditions with a lower ETR. In addition, all GL had a midday leaf RWC greater than 80% indicating that there was no severe water deficit stress regardless of their growth irradiance under natural conditions. After 42 days of different combinations of water and growth irradiance treatments, GL in well-watered (WW) plants had higher Fv/Fm ratio, leaf RWC and WC than DS plants. There were no observable light saturated photosynthetic CO2 assimilation (A sat) and gs sat of GL in DS plants after the onset of the experiment. The leaf area of young expanding leaves was greatest in WWIL (intermediate light) plants but lowest in WWHL plants and DS plants, implying that growth was most optimum under WWIL conditions. GL of DSHL plants suffered a decrease in Car content causing the Chl/Car ratio to increase implying that their photosynthetic machinery had been damaged. However, DS and HL stress respectively increased Car content in young expanding leaves to confer more photoprotection. DS plants had lower ETR and NPQ than WW plants. GL and GPSB of DSHL plants have significantly lower ETR and qP than WWHL plants. There were no differences in the dawn/dusk fluctuation of TA in GPSB across all treatments. Experimental findings suggested that the photosynthetic physiology of C. rochussenii was at its optimum under WW conditions between 200 μmol m-2 s-1 to 500 μmol m-2 s-1 of PPFD. GPSB are vital organs ensuring high leaf RWC and WC in GL in times of drought.
Date Issued
2013
Call Number
QK495.O64 Tan
Date Submitted
2013