Effects of elevated temperature and carbon dioxide on seed-set and yield of kidney bean (Phaseolus vulgaris L.)

It is important to quantify and understand the consequences of elevated temperature and carbon dioxide (CO2) on reproductive processes and yield to develop suitable agronomic or genetic management for future climates. The objectives of this research work were (a) to quantify the effects of elevated temperature and CO2 on photosynthesis, pollen production, pollen viability, seed‐set, seed number, seeds per pod, seed size, seed yield and dry matter production of kidney bean and (b) to determine if deleterious effects of high temperature on reproductive processes and yield could be compensated by enhanced photosynthesis at elevated CO2 levels. Red kidney bean cv. Montcalm was grown in controlled environments at day/night temperatures ranging from 28/18 to 40/30 °C under ambient (350 µmol mol−1) or elevated (700 µmol mol−1) CO2 levels. There were strong negative relations between temperature over a range of 28/18–40/30 °C and seed‐set (slope, − 6.5% °C−1) and seed number per pod (− 0.34 °C−1) under both ambient and elevated CO2 levels. Exposure to temperature > 28/18 °C also reduced photosynthesis (− 0.3 and − 0.9 µmol m−2 s−1 °C−1), seed number (− 2.3 and − 3.3 °C−1) and seed yield (− 1.1 and − 1.5 g plant−1 °C−1), at both the CO2 levels (ambient and elevated, respectively). Reduced seed‐set and seed number at high temperatures was primarily owing to decreased pollen production and pollen viability. Elevated CO2 did not affect seed size but temperature > 31/21 °C linearly reduced seed size by 0.07 g °C−1. Elevated CO2 increased photosynthesis and seed yield by approximately 50 and 24%, respectively. There was no beneficial interaction of CO2 and temperature, and CO2 enrichment did not offset the negative effects of high temperatures on reproductive processes and yield. In conclusion, even with beneficial effects of CO2 enrichment, yield losses owing to high temperature (> 34/24 °C) are likely to occur, particularly if high temperatures coincide with sensitive stages of reproductive development.