Impact of elevated atmospheric CO2 on radiation utilization and related plant biophysical properties in pigeon pea (Cajanus cajan L.)

An open top chamber (OTC) study was conducted with two replications to investigate the impact of elevated CO2 (580 ppm) on canopy radiation interception and its use in relation to yield components of two pigeon pea (Cajanus cajan L) cultivars Pusa-992 and PS-2009. Two OTCs with ambient CO2 of 380 ppm were used as control. The LAI and above ground biomass were significantly higher during most of the growth stages for plants exposed to higher CO2 concentration. The canopy radiation extinction coefficient (k) values for both the cultivars were lower for plants exposed to elevated CO2 than for control plants, indicating a more erect structure of these plants. However, the radiation use efficiency (RUE) was 52.3% higher for plants grown under elevated CO2 than for plants grown under ambient CO2 for both the cultivars. The canopy temperature of plants grown under elevated CO2 was found to be lower throughout the growing period. Correspondingly, these plants were supported by higher soil moisture depletion from deeper soil layers. In cultivar Pusa-992, seed yield increased by 12.0% under elevated CO2 because of increase in pod numbers and weight. But in this cultivar, the significant increase (40.6%) in biomass under elevated CO2 did not translate into a corresponding increase in seed yield due to lower harvest index and less numbers of seed per pod. Under elevated CO2, the other cultivar PS-2009 became indeterminate and did not mature, resulting in undeveloped pods. Hence in PS-2009, elevated CO2 resulted in poor seed yield, pod numbers and pod weight even though the biomass produced was higher. Elevated CO2 in the future may result in higher biomass production and higher RUE in pigeon pea due to carbon fertilization, but may not cause a corresponding gain in grain yield because it may lower harvest index. (C) 2012 Elsevier B.V. All rights reserved.