Abstract only

Daily dynamics of CO2 gas exchange is of much importance for assessment of adaptation and comparison ofthe assimilating activity of various winter wheat genotypes under the moisture stress. Data on maximum and minimum photosynthetic activity and its dynamics during the day have been obtained through analyzing the curves of the daily course of photosynthesis. Daily changes in photosynthetic intensity of the both investigated varieties (Baraketli-95 and Girmizi-bugda), irrespective of the leaf, are expres- sed as the curves with a peak in the morning hours, depression at the noon and a relatively lower and shorter rise and faster drop associated with the sunset. Photosynthesis starts at 7:00 with the sunrise, sharply intensifies and reaches its maximum in varieties Baraketli-95 by noon, with the values being equal to 22.5 and 2] .2 mg CO2/dm2 hr in the irrigated (check) and moisture stress treatments, respective]y. Thereafter it gradually degreases, falling down at 15 :00 to as low as 16.1 and 9.8 mg CO2/dm2, under irrigation and moisture stress, respective]y. The daytime photosynthesis depression rate estimated based on the maximum morning values is equal to 70% and 52% for the variants with irrigation and moisture stress, respectively. After the midday depression, another peak of photosynthetic activity is observable, which raises photosynthesis under irrigation and water stress to 83% and 50% of the morning values, respectively. In the evening, together with the reduction of solar radiation the photo- synthetic intensity goes down, and by 20:00 point of the compensation is observed, after which the photosynthetic gas exchange passes to respiratory gas exchange with the resultant release of CO2. The gas-exchange dynamics in variety Gir- mizi-bugda has a steep rise in the morning, reaching maximum value under irrigation and water stress as high as 19.5 mg CO2/dm2 h rand 24.0 mgCO2/dm2 hr, respectively. Photosynthesis depression under irrigation and water stress begins at 12:00 and 11 :00, respectively. The values of depression are estimated as 34% and 46% of the morning values, respectively. After depression, the rise in photosynthesis makes up 18.4 and 16.0 mgCO2/dm2 hour, under irrigation and moisture stress, respectively. With the sunset the release of CO2 from leaves begins as a result of respiration. The dark-time respiration intensity of leaves reaches its maximum at 1 :00 PM, equaling to 2.8 and 1.8 mgCO2/dm2 hour under irrigation and moisture stress, respectively. The latter may experi- ence further 30%-decline due to moisture stress. Total CO2 /dm2 assimilation of the 8th leaf of Baraketli-95 and Girmizi-bugda under moisture stress and irrigation was equal to 103 and 113 mg CO2/dm2 day and 72 and 93 mgCO2/dm2 day, res- pectively. While the hourly average intensity of photosynthesis was estimated to be 7.8 and 8.4 mg CO2/dm2 hour forBaraketli-95 and 6.2 and 7.1 mg CO2/dm2 hour for Girmizi-bugda, under moisture stress and irrigation respectively. The study results show that varieties Baraketli-95 and Girmizi-bugda have similar values for the daily gas-exchange dynamics, photosynthesis rate, total assimilated CO2 and its hourly average. Also, water stress impact on photosynthetic activity as well as the critical period of water stress is similarly reflected by the photosynthetic parameters in both genotypes.

English

0409|AGRIS 0401|AL-Wheat Program

Juan Carlos Mendieta

CIMMYT Publications Collection