Photosynthesis in a sub-Antarctic shore-zone lichen

Area of Science:

• Plant Physiology
• Ecology
• Biochemistry

Background:

• Turgidiusculum complicatulum, a lichen species, is a potential new introduction to Marion Island.
• Understanding its physiological responses is crucial for assessing its ecological impact.

Purpose of the Study:

• To investigate the photosynthetic responses of Turgidiusculum complicatulum to environmental factors.
• To determine the optimal conditions for photosynthesis in this lichen species.

Main Methods:

• Measurements of net CO2 exchange and chlorophyll fluorescence.
• Controlled experiments varying moisture, light intensity (PPFD), temperature, salinity, and nitrogen fertilization (NH4NO3).

Main Results:

• Optimal net photosynthesis occurred at moisture content of 225-346%.
• Net photosynthesis saturated at low PPFD (<300 µmol m⁻² s⁻¹), but electron transport rate (ETR) increased up to ~900 µmol m⁻² s⁻¹.
• NH4NO3 significantly depressed net photosynthesis, except at 100% seawater salinity, while increasing ETR and respiration.

Conclusions:

• Turgidiusculum complicatulum exhibits a strong temperature-dependent respiration.
• The lichen's photosynthetic capacity is well-suited to the sub-Antarctic microclimate.
• Sufficient hydration allows for near-maximal photosynthesis for approximately 75% of the year.