High Night Temperature Induced Alterations in Post Flowering Carbon Balance and Its Impact on Yield in Winter Wheat.

Carbon losses in response to increasing night temperatures can induce significant decline in wheat productivity. Growth chamber studies were carried out using six diverse winter wheat genotypes (Guymon, Tascosa, Carson, TX86A5606, 2174-05 and Gage) to determine high night temperature (HNT) induced changes in the ratio of photosynthesis and night respiration (C balance). High night (23^oC) and optimum (15^oC) temperature responses starting from heading till physiological maturity were documented among the genotypes. Night respiration or photosynthesis measurements were recorded every 2 hours throughout the 24 hours cycle on the fourth day of stress, to determine the time of night or day when maximum carbon was lost to night respiration and the possible influence of HNT on succeeding day’s photosynthesis. Succeeding temporal gas exchange measurements were recorded at 4 day intervals until physiological maturity, at specific time period during the night identified with highest respiration and during the day with stable photosynthetic rate. HNT during the reproductive and ripening stages significantly reduced the grain filling duration, lowered the above-ground biomass by reducing the number of productive tillers or plant height and increasing unproductive tillers. On average, across genotypes, HNT resulted in up to 67 and 73 % reduction in total seed number and seed weight per plant, respectively. A significant increase in night respiration induced carbon loss was observed with HNT exposure during the post-flowering stages and genetic diversity for the trait was observed. Only Guymon and TX86A5606 had a pronounced decline in photosynthetic rate. Interestingly, five of the six tested genotypes recorded significant increase in night respiration after four days of HNT stress exposure, with all the cultivars regulating C loss and demonstrating different degree of acclimation to extended HNT exposure. These findings are currently being validated and mechanistic basis of HNT induced yield loss will be discussed.