Abstract: Tradeoff is the basis of the theory on plant life-history strategies, and the trade-off between flower size and flower number is an important determinant of flower biomass allocation. In this study, GIS and the method of experimental ecology were used to study the relationship between flower size and number of Zygophyllum xanthoxylum in response to slope aspects located in desert grasslands on the northern slope of Qilian Mountains, Northwest China. The results showed that the height, density, aboveground biomass, soil moisture content of the plant community and flower size, twig number, dry weight of Z. xanthoxylum displayed a pattern of gradual decrease with the aspect turning from north, east, west to south, while the flower number and reproductive allocation of Z. xanthoxylum displayed a pattern of gradual increase. The flower size was highly significantly negatively correlated with flower number on the north slope and south slope (P<0.01), and the slopes of the regressions were significantly less than -1, whereas it was significantly negatively correlated with flower number on the east slope and west slope (P<0.05), and the slopes of the regressions were close to -1. The trade-off relationship of resource allocation between the flower size and flower number of Z. xanthoxylum in different slope aspects reflected the population reproduction strategy via optimizing habitat adaptability of plant.

Key words: rice, tillering stage, submergence stress, variety type, loss rate.