Comparison of methods for estimating surface area of water-stressed and fully hydrate pine needle segments for gas exchange analysis

A nondestructive technique for repeatedly estimating total surface area of water-stressed pine (Pinus taeda L.) fascicle segments was evaluated. Fascicle radius was measured with a digital caliper and needle surface area calculated on the assumption that the needles were segments of a cylinder. High correlations (r greater than or equal to 0.94) were found between surface area estimated in this way and surface area calculated (a) from needle displacement, also on the assumption that needles are segments of a cylinder, and (b) from needle dry weight using a regression between dry weight and surface area estimated from needle displacement. The caliper-radius method gave slightly lower estimates of surface area than the other methods. However, differences among surface area estimates made with the three methods and between estimates made on water-stressed and fully hydrated needles were small relative to variances of leaf gas exchange measurements.