Peanut Leaf Photosynthetic Activity in Cool Field Environments

Abstract

Controlled environment studies have shown that peanut (Arachis hypogaea L.) leaf CO2 exchange rates (CER) are sensitive to night temperatures <20 °C and that genotypes vary in their ability to acclimate after exposure to continuous cool nights. Our objectives were to investigate the relationship between minimum air temperature (Tmin) and leaflet CER for peanut genotypes grown in the field and to determine the extent of differences between Tmin and minimum canopy temperatures under existing climatic conditions. Eight peanut genotypes were grown in the field at Delhi, Ontario, in 1991 and six genotypes common to the 1991 study were sown in 1992. Leaflet CER was recorded on a number of occasions in both seasons, and canopy temperatures were recorded under both clear and overcast conditions at night during 1992. Variation in leaflet CER between sampling dates was large in 1992 (e.g., 1.5–36.0 μmol m−2 s−1 for Early Bunch) but small in 1991. Effects of Tmin could account for 73 to 95% of the CER variation in 1992, depending on genotype. Genotypes differed significantly in CER response to Tmin in 1992, with relative tolerance to low Tmin of OAC Ruby > OAC Garroy > all other genotypes. The cultivar OAC Ruby showed a reduction in CER of ≈25% when Tmin fell from 20 to 5 °C. In contrast, Early Bunch, Chico, VA910212, and OAC Tango did not differ from each other and were relatively sensitive to low Tmin, with CER reduced by approximately 55% for the same reduction in Tmin. After Tmin of 20 °C, however, CER of sensitive genotypes was 17% higher than that of OAC Ruby. Canopy minimum temperatures at Delhi were 1 to 3°C cooler than Tmin, primarily due to radiative cooling. Microclimate differences between environments will affect the magnitude of differences between Tmin and Tmin (leaf) and therefore affect the utility of Tmin‐CER relationships developed here.