Response of soybean genotypes to iron limiting stress in calcareous vertisol under ambient and elevated CO2 and temperature conditions

Aim: To compare the relative performance of two contrasting genotypes of soybean to iron limiting conditions under ambient and elevated CO2 and temperature conditions. Methodology: A pot culture experiment was performed using calcareous vertisol soil. The environmental factors viz. CO2 and temperature were combined and applied as a single factor with two levels: a-[CO2+T] (400 +/- 10 mu mol mol(-1), day/night temperature 30 degrees C/22 degrees C) and e-[CO2+T] (610 +/- 10 mu mol mol(-1), day/night temperature 34 degrees C/26 degrees C). Soybean genotype that differed in iron use efficiency was used as another factor and two contrasting genotypes were used as two levels viz. iron efficient and responsive (FeER) and iron inefficient and responsive (FeIR). Results: The higher partial pressure of CO2 under elevated carbon dioxide and temperature condition (P-CO2 = 61.8 Pa) dissolved the native CaCO3 from calcareous vertisol soil and thereby resulted in higher HCO3- ion concentration. The antagonistic interaction between Fe2+ with HCO3- ion resulted in greater iron stress. As compared to ambient condition, seed yield was significantly reduced under more stressed e-[CO2+T] condition and resulted in similar to 1.4 and similar to 1.9 times drop in FeER and FeIR genotypes, respectively. Iron efficient and responsive (FeER) genotype recorded an impressive performance, as compared to the iron inefficient and responsive (FeIR) genotype, in counteracting iron deficiency stress, both under ambient and elevated conditions. Interpretation: The intra-specific variability between soybean genotypes and their response to elevated CO2 and temperature can be exploited to remediate the emerging iron deficiency stress in soybean plants and suggest ways to structure the future breeding programmes to adapt to the climate change.