Comparison of the responses between maize and faba bean to
low phosphorus stress in the field

【Objectives】 In response to limited P availability, plants have evolved a wide adaptive mechanisms.Thers is a hypothesis that maize responds to P deficiency by modifying root morphological structure rather than by changing physiological processes. Comparision between the root morphological and physiological variations of maize and faba bean under low P condition was performed in the field to prove this hypothesis. 【Methods】 The experiments were conducted in the field of long-term P-fertilizer with two P levels (0 and 100 kg/hm2) at the Shangzhuang Experimental Station of the China Agricultural University, Beijing in 2012 and 2013. Maize and faba bean were planted by monoculture with three replicates. Samples from the treatments in two years were taken at elongation and bell stage for maize and at initial and full bloom stage for faba bean in an interval of 10-12 days .Plant growth, P uptake, root distribution within the 0-40 cm soil profile, and rhizospheric pH and acid phosphatase activity of both plant species were incestigated. 【Results】 Data showed that the dry weight (DW) and P content of maize were significantly higher than those of faba bean. At the first harvest in two years, DW ratio in root versus shoot of faba bean was significantly higher than that of maize, and DW ratios of root versus shoot from both plant species under P0 were higher than that under P100. The total roots distribution of maize plant in the 0-10 cm soil layer were higher than those of faba bean at both harvests in two years, and faba bean has higher the specific root length than maize; While the amount of P taken up per unit in roots of faba bean was less than that of maize, regardless of the harvest time and P supply. The acid phosphatase activity on the root surface of faba bean was significantly higher than that of maize at both harvests, but the root surface of maize grown under P0 and P100 exhibited different activities, while that of faba bean under P0 was higher than that under P100. The value of pH in rhizosphere of faba bean grown under P0 was significantly lower than that grown under P100. However, there was no difference in rhizosphere pH of maize grown both at P0 and P100 levels.【Conclusions】 The DW ratios of root versus shoot of maize and faba bean grown under P0 were significantly higher than those under P100. Maize plants took up more P per unit of root length, and exhibited more roots distribution in the top soil layer riching available P relative to faba bean. However, P deficient maize did not increase the release of proton and acid phosphatase in the rhizosphere soil, indicating that maize responds to P deficiency by mainly modifying root morphology. In comparison, faba bean responds to P deficiency by root morphological and physiological variations.