Light use efficiency of dry matter gain in five macro-lichens: relative impact of microclimate conditions and species-specific traits

Relations between irradiance (I) and lichen growth were investigated for fi ve macro-lichens growing at two sites in Sweden. The lichens represented di fferent mycobiont-photobiont associations, two morphologies (foliose, fruti cose) and two life forms (epiphytic, terricolous). The lichens were transpl anted at two geographically distant sites in Sweden (1000 km apart) from Se pt 1995 to Sept 1996 in their typical microhabitats, where microclimate and growth were followed. Between April/May and Sept 96, the terricolous speci es had a dry matter gain of 0.2 to 0.4 g (g DW)(-1) and the epiphytes 0.01 to 0.02 g (g DW)(-1). When related to area, growth amounted to 30 to 70 g m (-2) for the terricolous species and to 1 to 4 g m(-2) for the epiphytes. T here was a strong correlation between growth and intercepted irradiance whe n the lichens were wet (I-wet), with 0.2 to 1.1 g lichen dry matter being p roduced per MJ solar energy. Across the 10 sets of transplants, light use e fficiencies of dry matter yield (e) ranged between 0.5 and 2%, using an ene rgy equivalent of 17.5 kJ g(-1) of lichen dry matter. The higher productivi ty of the terricolous species was due to longer periods with thallus water contents sufficient for metabolic activity and because of the higher mean p hoton flux densities of their microhabitat. A four-fold difference in photo synthetic capacity among the species was also important. It is concluded th at lichen dry matter gain was primarily related to net carbon gain during m etabolically active periods, which was determined by light duration, photon flux density and photosynthetic capacity.