Characteristics of pea leaves and their relationships to photosynthetic CO2 exchange in the field

Photosynthetic CO2 exchange rate (CER) was determined in attached leaflets of field-grown peas (Pisum sativum L.) Three populations of genotypes were studied in different field locations and years. In 1 year, CER, leaf characteristics, and meteorological factors were measured in parallel at different times of the day and season. Differences in CER across environments or time of day were related to differences in stomatal resistance; however, changes during the season, which might be of environmental or developmental origin, were not. Genotype ranking for CER was largely independent of measuring time, field location, and year. None of the leaf characters which have been suggested as simple assays for photosynthetic ability (specific leaf weight, chlorophyll content, stomatal resistance) was consistently related to CER over several tests. In the single experiment in which they were determined, ribulose bisphosphate carboxylase activity, leaf soluble protein content, and the difference in CER at 2 and 20 kPa...