WATER RELATIONS AND CO2 EXCHANGE OF TROPICAL BRYOPHYTES IN A LOWER MONTANE RAIN-FOREST IN PANAMA

For 6 tropical bryophytes, measurements of the diel courses in water s tatus and net CO2 exchange were made in a submontane tropical rain for est in Panama. In addition, the response of gas exchange to changes in photon flux density (PPFD) and thallus water content (WC) was studied under controlled conditions. Diel variation of WC was pronounced, and both low and high WC limited carbon gain considerably. Low PPFD, e.g. during rain storms, was less important in limiting CO2 exchange. More than half of the mean diurnal carbon gain of 2.9 mg C per g thallus c arbon was lost during the night as respiration. Assuming that the aver age 24-h carbon gain was representative for the entire year, we estima ted the net annual primary productivity of the mosses and liverworts t o be 45% of the initial plant carbon content.