Objectives Organic phosphorus (P) is an important component of soil P pools. Observing the response difference in root morphology of plants when exposured to low organic P stress will help understanding the mechanism of plant genotype P use efficiency in the environment.

Methods A hydroponic experiment was conducted with P-efficient genotypes (IS-22-25 and IS-22-30) and P-inefficient genotype (IS-07-07) as test materials and with phytate sodium as organic P source. Five phytate-P levels were set up in the nutrition solution: 0.1, 0.2, 0.3, 0.4 and 0.5 mmol/L. The root length, surface area and volume were analyzed using a root scanning system, and the activities of acid phosphatase and phytase were determined in roots of both wild barley genotypes.

Results The total root length, surface area and volume in the P-efficient wild barley genotypes were increased gradually in response to the reduced organic P supply levels. In the low organic P level, the total root lengths in the P-efficient wild barley genotypes were increased by 139.7%-146.0% compared to those in the normal organic P condition (0.4 mmol/L), and the lengths were increased by 8.6%-60.4% in relative to that in the P-inefficient genotype. In the low organic P condition, the lengths of the roots (D < 0.16 mm) in the P-efficient wild barley genotypes were 156.8%-161.5% higher than those in the normal organic P condition. Increases of 83.5%-117.5% and 80.7%-119.3% were observed in total surface area and total volume in the P-efficient wild barley in response to the reduction of organic P concentration, which were 14.0%-46.4% and 19.6%-150.0% higher than those in the P-inefficient wild barley, respectively. In addition, the activities of acid phosphatase and phytase were significantly reduced with the increasing levels of the organic P. In the low organic P condition, the activities of acid phosphoatase and phytase of the P-efficient wild barley were increased by 163.3%-172.2% and 98.6%-121.2%, which were 14.4%-41.2% and 23.1%-37.2% higher than those in the P-inefficient genotype, respectively. Meanwhile, the activities of acid phosphatase and phytase excreted by root in the P-efficient genotypes were increased by 157.8%-193.4% and 172.4%-183.4%, which were 20.2%-15.7% and 24.7%-51.4% higher than those in the P-inefficient genotype, respectively.

Conclusion In the low organic P supply levels, good root morphology in the P-efficient wild barley genotypes was beneficial to expand attaching space of water and nutrition, which provided a good basis for growth and P uptake. Meanwhile, the increases in the activities of acid phosphatase and phytase excreted by roots in the P-efficient genotypes in the low organic P condition improved the bioavailability of P and accelerated to assimilate and utilize organic P, which should be one of the mechanisms contributing to efficiently absorb and utilize P in the P-efficient wild barley genotypes.