Abstract: The tradeoff between leaf size and leaf number reflects the highly adaptable and selfregulatory abilities of plants in response to complex environmental conditions. With the method of the standardized major axis estimation, the relationships between individual leaf area and leafing intensity of Potentilla acaulis were studied in alpine grasslands at four levels of degradation (I, II, III, IV) on the northern slope of Qilian Mountains in northwest China. The results showed that, with the aggravation of the extent of grassland degradation, the height, coverage, soil water content of the grassland communities decreased, and the height, single leaf area and petiole length of P. acaulis decreased, while its leaf number, leaf thickness and coverage increased. A significant negative relationship between the individual leaf area and the leafing intensity was found in the four alpine grasslands (P<0.05), which reflected a tradeoff between the leaf size and number. Meanwhile, an isometric relationship was found between individual leaf area and leafing intensity in lightly and moderately degraded grasslands (P<0.05), whereas an allometric relationship was found between individual leaf area and leafing intensity in nondegraded and severely degraded grasslands. In brief, the configuration mode of tradeoff between leaf size and leaf number of P. acaulis reflects its plasticity mechanism of phenotype in degraded alpine grassland.

Key words: Karst slope cropland, surface runoff and sediment yield, artificial rainfall, underground runoff and sediment yield