Nonrandom variation of gas exchange within arctic lichens

Nonrandom variation in gas exchange of the three arctic lichens Cladonia rangiferina (L.) Wigg., Cladonia stellaris (Opiz) Brodo, and Parmelia separata Th. Fr. is documented through a combination of field and laboratory studies. The highest rates of both photosynthesis and respiration occur in the youngest, actively growing sections of the thalli and both parameters decrease progressively into the older sections. For the two Cladonia species gross photosynthesis is shown to vary directly as a function of chlorophyll a and b concentration as found in a vertical profile through the lichen mat.