Effect of Soil Drought Stress on the Ultramicrostructures of Chloroplasts and Mitochondria in Three Desert Plants with Different Photosynthetic Types C4 Photosynthetic Enzymes and Antioxidant Enzymes Activities in Two Photosynthetic Subtypes of C4 Desert Plants under Soil Drought Stress Differences Responses of Ornamental Crabapple Cultivars to Soil Drought Stress Effect of soil drought stress on leaf coloration-emerging of Prunus cistenena cv. Pissardii Comprehensive Evaluation on Drought Resistance of Early Fruiting Walnut Cultivars Comprehensive Evaluation on Drought Resistance of Early Fruiting Walnut Cultivars