Effects of intercropping on phosphorus transformability and phosphobacteria community structure in the rhizosphere of tomato and potato onion

Objectives Intercropping with potato onion can alleviate the soil sickness of tomato and thus enhance tomato plant nutrient uptake. In this study, effects of intercropping with potato onion on the activity and structure of phosphobacteria (P-bacteria) in the rhizosphere of tomato were studied to reveal the improvement of plant nutrition affected by P-bacteria in intercropping system.

Methods The soil used in the pot experiment was collected from a greenhouse in which solanaceae crops had been cultivated continuously for 8 years. The tomato cultivar of ‘Dongnong708’ and potato onion cultivar of ‘Wuchanghongqishe’ were used in this study. The experiment included four treatments: tomato and potato onion intercropping, tomato monoculture, potato onion monoculture, and no crop control. The dry weight and phosphorus concentration in the plant were measured at the 23rd, 30th and 37th days after transplanting. The rhizosphere soil was obtained by brushing off the tomato and potato onion roots, which was used to analyze the transformation intensity and abundance of P-bacteria community. The PCR-DGGE method was used to determine the structure of P-bacteria community.

Results 1) Compared with monocropping, the shoot and root dry weights of tomato plants under intercropping were increased, while those of potato onion were decreased, and the changes reached significant levels at the 37th day. 2) Both the number of inorganic phospher(P_i) and organophosphorus (P_o) bacteria in the rhizosphere of intercropping system were significantly higher than those in no crop control during the whole culture period. In the rhizosphere of intercropping tomato, the number of P_i and P_o bacteria were increased, and the increments all reached significant levels at the 23rd and 37th days. In the rhizosphere of intercropped potato onion, the number of P_i bacteria was decreased and the decrement reached significant level at the 23rd day, while the number of P_o bacteria kept increased and the increase reached significant level at the 37th day. At the 23rd day of intercropping, both the transformation intensity of P_i and P_o bacteria increased significantly in the rhizosphere of tomato, while those were on the contrary in the rhizosphere of potato onion. At the 37th day, the transformation intensity of P_i and P_o bacteria in rhizosphere of potato onion were increased significantly. 3) Intercropping significantly increased pH but decreased EC of tomato and potato onion rhizosphere soils, and soil pH of the three treatments was higher than that of no crop control. The available P content of intercropped tomato rhizosphere was significantly higher than that in the monocropping at the 30rd day, while significantly reduced soil available P content at the 37th day. There was no significant difference in available P content in rhizosphere of potato onion between monocropping and intercropping systems during all the sampling time. However, soil available P content of tomato rhizosphere was lower, while this soil nutrient content of potato onion was higher than that in no crop control. Intercropping significantly increased plant P concentration and uptake of tomato, but only distinctly increased plant P concentration of potato onion. The number of bands, Shannon index and evenness index of P_i bacteria in rhizosphere of intercropped tomato were significantly higher than those in monocropping system, but those of intercropped potato onion were significantly lower than in monocropping system. The number of bands, Shannon diversity index and evenness index of P_o bacteria in rhizosphere of intercropped tomato were significantly higher than those in monocropping system at the early stage and significantly lower than those in monocropping at the later stage. There was no significant difference for potato onion between monocropping and intercropping systems.

Conclusions Intercropping will change the number and structure of P-bacteria community in the rhizosphere of tomato, improve the transformation intensity of P-bacteria, and increase soil available phosphorus content and plant P concentration and uptake of tomato and thus improve plant phosphorus nutrition.