EFFECTS OF WATER STRESS ON PHOTOSYNTHESIS OF WHEAT LEAVES AND THEIR RELATION TO DROUGHT RESISTANCE nteractive Effect of Split Application of Nitrogen and CO2 Elevation on Photosynthesis,Matter Accumulation and Yield of Winter Wheat COMPARISONS OF BIOMASS AND PHOTOSYNTHETIC ACTIVITY AMONG MUTANT LINES OF SPARTINA PATENS INDUCED BY LOW ENERGY HEAVY ION Winter inhibition in photosynthetic ability of Changbai Mountain evergreen conifers