TITLE:
Photosynthetic Light Utilization Efficiency, Water Relations and Leaf Growth of C3 and CAM Tropical Orchids under Natural Conditions
AUTHORS:
Shawn Tay, Jie He, Tim Wing Yam
KEYWORDS:
Orchid, CAM, C3, Photosynthetic Light Utilization Efficiency, Water Relations and Leaf Growth
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.6 No.18,
November
25,
2015
ABSTRACT: Native orchid species of Singapore in their natural conditions experience stress from high irradiance,
high temperatures and periods of extended low rainfall, which impact orchid plant physiology
and lead to reduced growth and productivity. In this study, it was found that there was a reduction
in photochemical efficiency of photosystem II (PSII) in 6 native orchid species under high
light (HL) and Bulbophyllum membranaceum under low light (LL). There was chronic photoinhibition
in these 6 orchid species over a period of 3 months after transplanting onto the tree trunks
without watering and fertilization, especially in Coelogynes mayeriana and Bulbophyllum membranaceum
under both HL and LL. This chronic photoinhibition caused by sustained period of water
deficit in their natural conditions was later reversed by natural re-watering conditions from
higher rainfall. These results indicate that water deficit has a greater impact on photosynthetic
light utilization efficiency than excess light. The present study also showed that after natural rewatering,
relative water content (RWC) of leaves and pseudobulbs generally increased. During the
natural re-watering, total leaf area also gradually increased and reached maximum expansion after
7 weeks under both HL and LL, with some exceptions due to leaf abscission or decline in total
leaf area, possibly a strategy for water conservation.