Carbon assimilation strategies in lichenized ascomycetes

Problem definition
The Antarctic terrestrial environment has only recently been colonized by phototrophic terrestrial organisms. Most of the taxa encountered in Antarctic vegetation have colonized their habitat within the last 15.000 years after the last glaciation of Antarctica. A critical step in colonizing a habitat for lichens, which dominate Antarctic vegetation, is to find a compatible algal partner. Some species solve this problem by producing vegetative propagules containing both photobiont and mycobiont. Sexually reproducing species depend on relichenisation in order to sucessfully colonize a habitat. Free-living photobionts are scarce in extreme environments. Therefore it might be of advantage for mycobionts to be able to use alternative sources of organic carbon i.e. sources other than the compatible mycobiont.

Objectives
How autotrophic are lichens (during different stages of development)?
Is the degree of autotrophy related to selectivity and specificity of the mycobiont towards the photobiont?
Do these characteristics influence the genetic variability of the mycobionts? And is this variability connected to the Carbon source?

Approach
For this project the SIRR equipment (see below), developed by T. Bouma, will be adapted and subsequently simultaneous measurements on CO₂ exchange will be performed.

International co-operation
University of Düsseldorf, Germany.

The SIRR equipment. has been adapted from a measurement system for root respiration. It measures simultaneously CO₂ and H₂0 concentration. The left hand installation (in a climate room) houses the air stream regulation through the cuvettes. The right hand installation (outside the climate room) produces an air stream with preset CO₂ and H₂0 concentration, analyses the CO₂ and H₂0 concentration and stores the data in a computer.