Yield, growth and grain nitrogen response to elevated CO2 in six lentil (Lens culinaris) cultivars grown under Free Air CO2 Enrichment (FACE) in a semi-arid environment." European

Atmospheric CO2 concentrations have been increasing from ∼280 to 405 mmol mol−1 air from the preindustrial era until now. As this rise is a major driver for global warming and increasing variability in weather patterns, it is predicted that the frequency and duration of heat waves will continue to increase in many arable regions during this century. Lentil (Lens culinaris Medik.) is a cool‐season crop whose production has recently expanded into areas where it is subject to high temperature stress during pod filling (e.g., Australia). The objective of this experiment was to determine whether growth at elevated atmospheric CO2 concentrations (e[CO2], imposed by free‐air CO2 enrichment [FACE]) is able to compensate for the negative impact of a 3‐d heat wave event imposed at the flat pod stage on two lines of lentil. Grain yield under e[CO2] subjected to the heat wave were equivalent to grain yield under ambient without the heat wave event. The heat wave reduced grain yield by 33%, but this was not made more or less severe by e[CO2]. This reduction was attributed to a small decrease in aboveground biomass (6%) and a larger decrease in harvest index (16%) due to the heat wave event. The number of pods and grains per square meter were reduced by the heat wave (29–32%), whereas seed size was not affected. The effects of the heat wave during the event were evident on the foliar canopy temperature measured with an infrared thermometer, which increased by 6°C, and on the electron transport rate calculated from the quantum efficiency of photosystem II obtained with chlorophyll fluorescence measurements.

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Lentil (Lens culinaris Medik.) production in arable, Mediterranean-type climates is limited by heat waves and unreliable rainfall. Under climate change scenarios, increased atmospheric carbon dioxide (CO2) concentration will increase plant growth; however, the net effect of increasing occurrence and intensity of heat waves and drought is unclear. This study tested the response of combined acute high temperature (>32°C) at the early pod-filling stage and (i) crop-available soil water, and (ii) elevated CO2 on three lentil genotypes in two experiments. The three lentil genotypes selected were commercial cultivar PBA Bolt and two landraces sourced from the Australian Grains Genebank, AGG 71457 and AGG 73838. High soil-water availability (0.42 Mg m–3) throughout the growing season increased yield by 28% compared with low soil-water availability (0.35 Mg m–3). Across contrasting water treatments, there was no difference in patterns of crop response to high temperature during the early pod-filling phase (5 days at 42°C daytime, 25°C night), where yields were reduced by 45%. A significant interaction between high temperature response and genotype was observed, where reduction in grain number was higher for AGG 73838 (0.20% per degree-hour >32°C) than for AGG 71457 (0.07% per degree-hour >32°C) or PBA Bolt (0.10% per degree-hour >32°C). For heat and CO2 effects, there was no significant interaction between high temperature (3 days at 38°C daytime, ambient night temperature) and CO2 treatment on yield components. There was, however, an overall trend of increased biomass, grain number and yield due to elevated CO2. Although non-limiting soil water did not reduce the impact of high temperature in this study, the range in response across genotypes to high temperature supports opportunity for increased adaptation of lentil toward increasing yield stability under effects of climate change.

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