Field Measurement of Photosynthesis in a Forage Grass Breeding Program1

A system for rapid measurement of net carbon exchange (NCE) by leaves of clonal lines of forage grasses growing in the fidd has been developed. Air‐sealed leaf chambers of laminated construction connected to a manifold permit the determination of the average NCE of several leaves measured simultaneously. With 4 replications and more than 10 genotypes, the average NCE from 6 individual leaf measurements per plot was adequate to detect statistical differences of 2.0 mg dm−2 hour−1 between 2 genotypes with 83% power. Two units of six leaf chambers, each operating simultaneously, are monitored by one infrared CO2 analyzer, allowing the average NCE rates of 20 plots/hour to be accurately measured. The system is reliable, rapid, relatively simple, and uses intact leaves for field measurement. The technique is being used to determine genetic variability, heritability, and potential use of NCEin a tall fescue (Festuca arundinacea Schreb.) breeding program.