Are xylem-tapping mistletoes partially heterotrophic?

Area of Science:

• Plant biology
• Ecology
• Isotope geochemistry

Background:

• Xylem-tapping mistletoes are often considered autotrophic, relying on their own photosynthesis.
• Understanding carbon sources in parasitic plants is crucial for ecological studies.

Purpose of the Study:

• To investigate the carbon source of the xylem-tapping mistletoe Phoradendron juniperinum.
• To determine the extent of host-derived carbon assimilation in mistletoes.

Main Methods:

• Measurement of carbon isotope ratios in mistletoe and host tissues.
• Gas exchange analysis to assess photosynthesis and transpiration rates.
• Comparison of observed isotope ratios with theoretical predictions.

Main Results:

• Host tissue carbon isotope ratios aligned with gas exchange predictions.
• Mistletoe carbon isotope ratios significantly deviated from predictions, suggesting an alternative carbon source.
• Evidence indicates 62±2% of mistletoe carbon originates from the host xylem.

Conclusions:

• Phoradendron juniperinum assimilates significant amounts of organic carbon from its host's xylem water.
• Mistletoes exhibit high transpiration and low photosynthetic rates, increasing dependence on host carbon.
• Xylem-tapping mistletoes may be partially heterotrophic, deriving substantial carbon from hosts.