A STUDY ON THE RELATION BETWEEN THE DECLINE IN PHOTOSYNTHESIS AT MIDDAY AND ECOLOGICAL FACTORS FOR ANEUROLEPIDIUM CHINENSE AND STIPA GRANDIS
羊草和大针茅光合作用午间降低与生态因子关系的研究

This study shows that under fine-weather conditions due to difference of soil moisture content the diurnal course of photosynthesis of Aneurolepidium Chinense and Stipa Grandis has two types. When the soil moisture is sufficient, there is the monopeak type with a peak occurring before midday. When the soil is dry, there is the double peak type. In both the two types, the photosynthesis is low at midday.A comparison has been made between the two species, When the soil is dry, the decline in photosynthesis of Aneurolepidium Chinense at midday is much greater than that of Stipa Grandis. When the soil is sufficient, their declines are sinilar. No matter what the soil moisture condition may be, the low atmospheric humidity is a main ecological factor of the decline in photosynthesis at midday. The intense sunlight is a direct ecological factor of the decline in photosynthesis at midday only when the soil is dry. So the occurrence of the peak after midday is due to the decline in intensity of the sunlight.The dry soil and the low atmospheric humidity together increase the degree of the decline in photosynthesis at midday. The range of decline increases as the soil moisture decreases. Therefore, increasing the soil moisture content is the main ecological way to decrease the degree of decline in photosynthesis at midday.