Net photosynthesis and stomatal conductance of red spruce twigs before and after twig detachment

Abstract

Rates of net photosynthesis and stomatal conductance of red spruce (Picearubens Sarg.) twigs were measured in field conditions before and after twig detachment on clear midsummer days in New Brunswick. Although these variables did not change significantly within about 6 min after twig detachment, they did drop continually after detachment. Regression models for the rates of net photosynthesis and stomatal conductance were developed that can be used to simulate this drop. Photosynthetically active radiation, leaf temperature, relative humidity, and CO2 concentration were the principal covariates in these models. The regressions improved by including simulated leaf moisture values in the analysis of data obtained after twig detachment.