Effect of heat wave on N 2 fixation and N remobilisation of lentil (Lens culinaris MEDIK) grown under free air CO 2 enrichment in a mediterranean-type environment

The stimulatory effect of elevated [CO ] (e[CO ]) on crop production in future climates is likely to be cancelled out by predicted increases in average temperatures. This effect may become stronger through more frequent and severe heat waves, which are predicted to increase in most climate change scenarios. Whilst the growth and yield response of some legumes grown under the interactive effect of e[CO ] and heat waves has been studied, little is known about how N fixation and overall N metabolism is affected by this combination. To address these knowledge gaps, two lentil genotypes were grown under ambient [CO ] (a[CO ], ~400 µmol·mol ) and e[CO ] (~550 µmol·mol ) in the Australian Grains Free Air CO Enrichment facility and exposed to a simulated heat wave (3-day periods of high temperatures ~40 °C) at flat pod stage. Nodulation and concentrations of water-soluble carbohydrates (WSC), total free amino acids, N and N fixation were assessed following the imposition of the heat wave until crop maturity. Elevated [CO ] stimulated N fixation so that total N fixation in e[CO ]-grown plants was always higher than in a[CO ], non-stressed control plants. Heat wave triggered a significant decrease in active nodules and WSC concentrations, but e[CO ] had the opposite effect. Leaf N remobilization and grain N improved under interaction of e[CO ] and heat wave. These results suggested that larger WSC pools and nodulation under e[CO ] can support post-heat wave recovery of N fixation. Elevated [CO ]-induced accelerated leaf N remobilisation might contribute to restore grain N concentration following a heat wave.