Objectives Breeding rice materials with high phosphorus (P) uptake efficiency is an effective way to use the soil P resources. Rice root is the most important organ for P absorption and studying the root morphological and structural characteristics can reveal the mechanisms of P-efficient uptake.

Methods A hydroponic experiment was conducted with 40 rice materials under low P (0.003 mmol/L) and normal P (0.3 mmol/L) treatment, and the rice plants were sampled at the tillering stage for determination of shoot biomass and P concentration. Through cluster analysis of shoot P accumulation and biomass, R527 and IR58025 were identified as high-P efficiency and low-P efficiency materials, respectively. The root morphology, and root anatomical structure of the two rice materials were further determined to elucidate the relationship between rice root development characteristics and P uptake.

Results 1) Under low P conditions, the 40 rice materials showed significantly different biomass and P accumulation, ranging from 0.11 to 0.93 g/plant in biomass and 0.07 to 0.58 mg/plant in P accumulation, with coefficients of variation of 49.41% and 49.55%, respectively. 2) Under low P conditions, the biomass (0.83 g/plant) and P accumulation (0.46 mg/plant) of R527 were 6.38 and 5.75 times higher than those of IR58025. 3) The total root length, root surface area, adventitious root length, lateral root length, and lateral root surface area of R527 under low P conditions was 61.79%, 38.12%, 60.44%, 67.99% and 186.67% higher than under normal P conditions. And the total root length, root surface area, root volume, average root diameter, adventitious root length, lateral root length, adventitious root surface area and lateral root surface area of R527 under low P stress were 2.62, 2.87, 3.22, 1.18, 4.41, 2.97, 3.97 and 1.45 times of those in IR58025. 4) Under low P conditions, the proportions of stele, epidermis, cortex in R527 were 1.11, 0.67 and 1.05 times of those in IR58025. 5) Under low P conditions, total root length, root surface area, root volume, average root diameter, adventitious root length, adventitious root surface area, lateral root length, lateral root surface area, cortex proportion, and stele proportion of rice showed positive correlation with biomass and P accumulation, while epidermis and endodermis proportions showed negative correlation.

Conclusions The growth of high-P efficiency rice material R527 is less inhibited than low-P efficiency material IR58025 under low P conditions, due to the significantly higher biomass and P accumulation. Under low P conditions, R527 could develop large total root length, root surface area, root volume, adventitious root length, lateral root length, adventitious root surface area, lateral root surface area, and cortex proportion, as well as lower epidermis and endodermis proportions, which is contributed to its efficient P uptake.