ABSTRACT
The Loess Plateau in the northwestern part of China is a typical semiarid area. Some local varieties of spring wheat have a long cultivated history and have adapted to the drought prone environment. An experiment was conducted to explore the daily and seasonal variation in photosynthesis of spring wheat. The results showed that the daily change of photosynthesis peaked between 10 a.m. and 11 a.m., decreased to a very low value at midday, then gradually recovered. The maximal peak value of photosynthesis was 14.8 CO2 μ mol m'2 s*1, which appears during the jointing stage. Leaf-air water vapor deficit and soil water stress at midday decreased photosynthesis by 29.8% and 32.6%, respectively. A combination of leaf-air water vapor deficit and soil water stress reduced photosynthesis by 61.8%. The limitations imposed by the semiarid conditions of the Loess Plateau on single leaf photosynthesis and on the peak energy conversion rate also are discussed.
