Fig. 1.

Response of net CO₂ uptake to relative water content during drying of leafy shoots of Polytrichum formosum, measured by IRGA. All measurements were made on the same sample of eight 2-cm apical shoot lengths. Following initial weighing of the shoots at full turgor but free of superincumbent water, a measurement was made in presence of excess water on filter paper in the IRGA chamber. The shoots were blotted dry, exposed to air briefly, and then alternately weighed and returned to the IRGA chamber for measurement. Finally the shoots were oven dried at 70 °C to determine dry weight for calculation of RWC. To allow for manipulation and equilibration time at the beginning of each reading period, RWC for each reading was taken as the lower third of the interval between successive weighings. Fitted logistic curve. Error bars represent a combined estimate of the standard deviation of the sets of five individual IRGA readings on which each point is based.