Yield, growth and grain nitrogen response to elevated CO₂ of five field pea (Pisum sativum L.) cultivars in a low rainfall environment

Atmospheric CO₂ concentrations have been increasing from about 280 ppm to 400 ppm from the pre-industrial era until now. If intraspecific variability in the response to elevated CO₂ (e[CO₂]) can be found, then it should be possible to select for greater responsiveness in crop breeding programs. Our experiment aimed to determine the effects of e[CO₂] on the yield, biomass, leaf and grain nitrogen content of a range of field pea (Pisum sativum L.) cultivars subjected to rainfed and supplemental irrigation conditions. Plants were grown under Free Air CO₂ Enrichment (FACE) at the Australian Grains FACE facility in Horsham, Victoria, Australia under e[CO₂] (550 ppm) or at ambient CO₂ (390–400 ppm) under rainfed conditions and supplemental irrigation during three seasons, 2010–2012. Yields were significantly increased by 26% under e[CO₂] due to an increase in the number of pods per area. Grain size, the number of grains per pod and the harvest index remained unaffected by e[CO₂]. Grain nitrogen concentration ([N]) was slightly, but significantly, decreased by e[CO₂], but this was not consistent across cultivars under all water regimes. The dual purpose cultivar PBA Hayman consistently maintained grain [N] in response to e[CO₂] while the response in grain [N] in the cultivars Sturt and PBA Twilight depended on the irrigation treatment. While there was no evidence for consistent differences in seed yield response to e[CO₂] for the chosen cultivars, understanding the mechanisms for why some cultivars are able to maintain [N] under e[CO₂] would allow breeding programs to develop varieties resistant to decreases in [N] under e[CO₂].