FIELD EVALUATION OF GROWTH AND NITROGEN FIXATION IN PEAS SELECTED FOR HIGH AND LOW PHOTOSYNTHETIC CO2 EXCHANGE
Six genotypes of pea (Pisum sativum L.), selected for either high or low CO2 exchange rate per unit leaf area (CER) on the basis of field measurements, were grown in field plots during 1978 and 1979. During two growing seasons, CER was determined in leaves of different physiological age at several times of the day and season. Dry weights, leaf areas and node numbers were determined 4, 7 and 10 wk after planting, and again after pod ripening. C2H2 reduction by detached roots was measured 5, 6, 8 and 9 wk after planting. Despite the large variability in CER with years, leaf numbers, and times of measurement, the mean CER of the three genotypes selected for high rates was always greater than that of the low selected group. CER was significantly correlated with growth per unit leaf area (E) and the high to low group ratios averaged 1.4 for CER and 1.3 for E. C2H2 reduction on an equivalent leaf area basis was not different in the two groups. On a land area basis, the low CER group had a significantly greater leaf area index which compensated for the decreased CER, and estimates of total CO2 exchange, growth and C2H2 reduction were similar in the two groups. Total aboveground dry matter and seed yields were greater in the low CER group, but harvest index was generally greater in those genotypes selected for high CER.