Effect of a Heat Wave on Lentil Grown under Free‐Air CO₂ Enrichment (FACE) in a Semi‐Arid Environment

Abstract

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.

Impact of heat stress during seed filling on seed quality and seed yield in lentil (Lens culinarisMedikus) genotypes

“…35 Heat stress damaged the leaf membranes (as electrolyte leakage) and reduced chlorophyll concentration, PSII function and photosynthesis in both lentil genotypes, which was associated with a significant reduction in leaf water content and stomatal conductance, especially in HS genotypes. Damage to leaf membranes due to heat stress has been reported previously, 18,38 and may be due to direct effects of high temperature such as photo-oxidation of chlorophyll pigments, 39 impaired electron flow, 23,39 inhibition of carbon fixation 13 or to indirect effects such as water loss from the leaves. 40 Membrane damage impairs the production of photo-assimilates in leaves, 19 eventually decreasing their availability and mobilization to developing seeds.…”

“…Heat stress reduced the seed number per plant due to reduced pod set and fewer filled pods, which agrees with previous observations on chickpea, 36 mungbean 37 and lentil. 19,23,24 Heat stress also reduced seed size, resulting in much lower seed weights per plant and individual seed weights, which appears to be related to a reduction in the seed filling rate and duration. In general, the phenology of legumes is accelerated under high temperature.…”

“…Temperatures above 32/20 °C (max./min.) at the time of flowering and pod filling in lentil can drastically reduce seed yield and quality . In 2009, across southeastern Australia, a heat wave (35 °C for 6 days) reduced lentil yields by 70% …”

“…18,19 Lentil requires low temperatures at the time of vegetative growth but warm temperatures to mature; optimum growth occurs from 18-30 ∘ C. 20,21 Lentil is also grown in relatively warmer regions in various parts of India and Australia, where the crop is exposed to supra-optimal temperatures at the time of seed filling that reduce its yield potential. 18,19,22,23 Moreover, chilling periods are becoming shorter and heat periods are becoming longer in northern parts of India and elsewhere in the world, resulting in the exposure of cool-season crops to heat stress, especially through reproductive and seed-filling stages. 4 Temperatures above 32/20 ∘ C (max./min.)…”

“…at the time of flowering and pod filling in lentil can drastically reduce seed yield and quality. 23,24 In 2009, across southeastern Australia, a heat wave (35 ∘ C for 6 days) reduced lentil yields by 70%. 24 Considering the sensitivity of lentil to high temperatures, this study was undertaken to investigate the effects of heat stress during seed filling on the quantitative and qualitative aspects of lentil seeds involving heat-sensitive and heat-tolerant genotypes.…”