Abstract: 【Objective】Efficient genotype cotton plays important roles in promoting low phosphorus (P) stress from the perspective of the root morphology. The purpose of this study is to provide a scientific basis for identifying the main factors that affecting phosphorus absorption of cotton and improving efficiency of nutrient utilization of genetic improvement through root plasticity. 【Method】A pot experiment was carried out to test the effects of P supply levels (low P stress 0, Suitable P 150 kg·hm-2) with two P genotype （efficient XH18, CCRI-42, XLZ19; inefficient XLZ13, XLZ17）cottons on root morphology and the relationships between root morphology and P uptake. 【Result】 Cotton biomass and P uptake were significantly reduced by low P stress. Efficient genotype cotton biomass and P uptake were 1.21-2.08 and 1.35-1.91 times as much as those of inefficient genotype cotton, respectively. Phosphorus significantly increased Olsen-P content in soil. Olsen-P of P efficient genotype cotton was significantly decreased more than those of two P inefficient cottons compared with phosphorus suitable conditions under low P stress. Olsen-P in the 0-25cm layer of P efficient genotype cotton was less than P inefficient cotton, compared with XLZ13 and XLZ17 decreased by 21.1% and 30.1% in the low P stress environment. The total root length, total root surface area, total root volume and average root diameter of cotton were significantly reduced under low P stress. The total root length, total root surface area, total root volume of P efficient genotype cotton were 1.54-1.97, 1.52-1.92 and 1.47-1.84 times as much as that of those of P inefficient cotton. P efficient genotype cotton’s specific root length, specific root surface area and specific root volume were significantly higher than those of two P inefficient cottons under low P stress, were 1.10-1.25, 1.07-1.22 and 1.01-1.16 times as much as that those of P inefficient genotype cottons. The average root diameter of P efficient genotype cotton was significantly less than P inefficient cotton, which was 34.2%-70.2% of P inefficient genotype cotton in the low P stress environment. Principal component analysis showed that the total root length, total root surface area, total root volume, root dry mass, middle root length and coarse root length could be used to distinguish two P genotype cottons. General linear model variance decomposition results showed that the total root length, total root surface area, total root volume, root dry mass, middle root length and coarse root length made great contributions to P uptake of cotton. 【Conclusion】P efficient genotype cotton adapted to low P stress through greatly increasing the proportion of fine roots, reducing overall fineness root, prompting an increase of specific root length, and increasing construction efficiency of root.

Key words: cotton, phosphorus efficiency, root morphology, phosphorus uptake, biomass