Ol. Lange et al., FIELD-MEASUREMENTS OF WATER RELATIONS AND CO2 EXCHANGE OF THE TROPICAL, CYANOBACTERIAL BASIDIOLICHEN DICTYONEMA-GLABRATUM IN A PANAMANIAN RAIN-FOREST, Botanica acta, 107(5), 1994, pp. 279-290
Diel time courses of microclimate, hydration, and CO2 exchange of the
basidiolichen Dictyonema glabratum and its responses to experimentally
changed conditions were measured for 14 days in a clearing of a premo
ntane, tropical rainforest (Panama). Net photosynthesis (NP) was adapt
ed to high temperatures and there was no depression of CO2 uptake at t
he highest thallus hydration. The presence of a CO2 concentrating mech
anism was demonstrated. Decreased NP occurred after desiccation, and a
pparent photon yield of CO2 fixation was also sensitive to water loss.
Natural NP was controlled by the interplay of thallus hydration and r
adiation. Regular, daily desiccation and dense cloud cover suppressed
production. On average, 72% of the diurnal photosynthetic gain was los
t during the night, and there were days with negative carbon balance.
Nevertheless, total carbon gain of the lichen was extremely high. A te
ntative estimation suggests that annual carbon gain amounts to 228% of
initial thallus carbon content. Because of their strong effect on net
production, increased nocturnal temperatures as given at lower elevat
ion, would lead to a negative carbon balance. This might explain the l
ack of abundance of this and other macrolichens in warmer, lowland rai
nforests.