Abstract: From 1988 to 1990, the ecological and physiological effects on root systems of wheat were studied under different soil water conditions. Results showed that the development of root systems could be inhibited by deficiency and oversupply of soil water. Drought might lead to the reduction of roots in the surface layer and the increase of the ratio of the roots in the deeper layer. When the relative soil water content was below 60%, the number of secondary roots of the individual plant decreased obviously. When it was below 50%,the root system reduced significantly.Less activity of root systems resulted from the higher severity soil water stress, and the least activity wax found in the flowering period. The wound sap flow of the single plant was in extremely significant positive correlation with the content of soil water. However, there existed an extremely significant negative correlation between the root-top ratio and the soil water content. It was found that the 40% relative soil water content was the lower limit index for severe drought in the later growing stage of wheat.

Key words: Wheat, Root system, Soil water content, Water stress, Ecological and physiological effects