Partial mycoheterotrophy in the leafless orchid Cymbidium macrorhizon

Area of Science:

• Plant evolutionary biology
• Mycoheterotrophy
• Orchidaceae family

Background:

• Full mycoheterotrophy is a key topic in plant evolution.
• The leafless orchid Cymbidium macrorhizon is often presumed fully mycoheterotrophic.
• This species possesses a green stem and fruit capsule, suggesting potential for autotrophy.

Purpose of the Study:

• To assess the trophic status of Cymbidium macrorhizon.
• To determine if the species is fully or partially mycoheterotrophic.
• To investigate carbon acquisition strategies during different life stages.

Main Methods:

• Analysis of chlorophyll content in sprouting and fruiting individuals.
• Measurement of natural carbon-13 (¹³C) and nitrogen-15 (¹⁵N) isotopic abundance.
• Comparison with neighboring autotrophic and partially mycoheterotrophic plants.

Main Results:

• Fruiting C. macrorhizon exhibited significantly higher chlorophyll content than sprouting individuals.
• ¹³C abundance indicated partial carbon gain from mycorrhizal fungi (approx. 73.7%) in fruiting plants.
• Sprouting plants showed isotopic signatures closer to autotrophic standards.

Conclusions:

• Cymbidium macrorhizon demonstrates significant carbon fixation via photosynthesis during its fruiting stage.
• Photosynthetic activity likely supports fruit and seed production.
• The species is best classified as partially mycoheterotrophic, particularly when fruiting.