The Effects Of Rhizobium Inoculation On Growth And Phosphorus Acquisition Of Soybean/maize In Different Soils

Low phosphorus(P)availability of soil is one of the main factors limiting the crop yield.How to improve the ability of crops to acquire and utilize the accumulated P in soils has attracted more and more attention.The previous studies have shown that rhizobium inoculation can not only promote the nitrogen uptake,but also P uptake by soybean in calcareous soils,but the mechanism is not clear.In addition,it is also not clear whether rhizobium inoculation can promote the P uptake by soybean in acid soils.In this experiment,a pot experiment with monoculture and intercropping of soybean and maize was conducted in both acid and calcareous soils in order to quantify the contribution of rhizobium inoculation to P uptake,and explore the possible mechanism on it.The main results are as follows:1.Rhizobium inoculation significantly increased the number of root nodules and promoted the formation of root nodules on the taproots in two kinds of soils.The number of root nodules was higher in calcareous soils than that in acid soils regardless of rhizobium inoculation or not,indicating that the calcareous soils was more beneficial to nodulation and nitrogen fixation of soybean than the acid soils with low P availability.The optimized P application(OP)not only increased the root nodule number and dry weight of soybean plants in acid soils,but also improved the root nodule dry weight of soybean plants inoculated with rhizobium in calcareous soils.In acid soils,the arbuscular mycorrhizal colonization of soybean and maize was between 25%-70%,while that of soybean and maize was between 25%-50% in calcareous soils.Rhizobium inoculation had little effect on arbuscular mycorrhizal colonization of soybean and maize.Low P(LP)increased the arbuscular mycorrhizal colonization of soybean and maize in acid soil.In calcareous soils,LP enhanced the arbuscular mycorrhizal colonization of monoculture soybean,but had no effect on that of intercropped soybean and maize.2.P application significantly increased the P content of soybean and maize in both kinds of soils.In acid soil,P application obviously enhanced the biomass and nitrogen content of soybean and maize,but only improved the biomass of monocropped soybean and the nitrogen content of soybean inoculated with rhizobium in calcareous soils.Rhizobium inoculation enhanced the biomass of intercropped soybean in calcareous soils,but had no effect in acid soils.Rhizobium inoculation significantly increased the nitrogen content of soybean in both kinds of soils at OP treatments,and reduced the P content of intercropped maize in acid soils,but increased the P content of soybean and intercropped maize at OP treatments in calcareous soils.These results indicate that rhizobial inoculation is beneficial to the growth and the P uptake of the intercropped soybean and the intercropped maize in calcareous soils.Futhermore,intercropping significantly increased the biomass,the nitrogen and P contents of maize at OP treatment,but had less effect on soybean in acid soils.In contrast,in calcareous soils,intercropping obviously improved the biomass,the nitrogen and P contents of maize,but significantly reduced the biomass,the nitrogen and P contents of soybean at both OP and LP treatments,indicating that the intercropping advantage of soybean and maize is more obvious in calcareous soils.3.P application significantly increased the total root length and root surface area of soybean and maize in acid soils,but had little effect in calcareous soils.In calcareous soils,rhizobium inoculation significantly increased the total root length of intercropped maize at OP treatments,and intercropping enlarged the total root length and root surface area of maize inoculated with rhizobium compared to monoculture.At the same time,rhizobium inoculation significantly reduced the rhizosphere p H of intercropped soybean at OP treatments in calcareous soils.In summary,rhizobium inoculation in both kinds of soils can enhance the number of root nodules.In acid soils,rhizobium inoculation significantly increased the nitrogen content of soybean,but had no effect on the biomass and P uptake of soybean and intercropped maize at OP treatments.In calcareous soils,rhizobium inoculation increased the biomass,nitrogen and P contents of soybean,and also improved the P content of intercropped maize at OP treatments.In terms of the rhizosphere p H value and root growth,the promotion effect of rhizobium inoculation on P activation and absorption may be attributed to the rhizosphere acidification of soybean and the stimulation of root growth in calcareous soils.