| Phosphorus(P)is the second most essential nutrient for crop growth.However,for majority of the agricultural soil,total phosphorus content is high but the available phosphorus concentration is low,which far can’t meet the needs of the normal growth of plants.Meanwhile low phosphorus availability also seriously restricts the development of agriculture in China and even all over the world.Therefore,fully exploring and exploiting soils P pool as well as improving crop P use efficiency become urgent problems in the current agricultural production and practice.Maize(Zea mays L.)and alfalfa(Medicago sativa L.)are important grains and perennial legume herbage in the farming and pastoral area of northeast China,respectively.Their intercropping plays an important in the food security maintenance and ecological environment protection in this region.Recent studies about maize/alfalfa and P uptake have focused on a certain characteristic like root morphology,mycorrhizal colonization or root exudates,but whether rhizosphere characteristics are interaction of maize and alfalfa in an individual level and their contribution of rhizosphere characteristics in intercropping system have not been reported.In this study,maize/alfalfa was used in the pot cultural experiment under greenhouse conditions.There were two P application levels:no P application(P0)and P application(P1).Two inoculation levels:inoculate 200 g of sterilizing inoculum(F0)and inoculate 200g of non-sterilizing inoculum(F1);4 root separation ways:PS plastic film separation,5μm nylon mesh separation(NN5),30μm nylon mesh separation(NN30),not separation(NS);there are 5 replicates in each treatment.Under different phosphorus levels,different inoculation treatments and root separation conditions,the growth status and phosphorus acquisition characteristics of maize and alfalfa,as well as the root morphology,root mycorrhizal colonization and root exudates changes were studied.Major results were presented as follows:(1)Under conditions of complete isolation(simulated single planting),the total phosphorus uptake of maize and alfalfa were significantly increased by 32.30%to184.49%at different phosphorus levels after AM inoculation.The frequency of mycorrhizal infection and total root length were significantly increased by AM inoculation,but the concentration of citric acid and total organic acid in rhizosphere were significantly decreased,and the ratio of fine root surface area was significantly decreased by 39.76%and 15.45%.AM inoculation treatment significantly increased the frequency of alfalfa mycorrhizal infection,but significantly reduced the ratio of root surface area by 53.35%and 26.67%.The content of citric acid and total organic acid in rhizosphere was significantly increased under the P0 condition,and significantly decreased under the P1 condition.The root morphology and root exudates of maize and alfalfa were regulated by AM inoculation.(2)The interaction between phosphorus level and root separation ways on the total biomass of maize was significant.Compared with the no AM inoculation treatment,the total biomass of maize was significantly increased by 42.86%with AM inoculation.Compared with no P application,P application significantly increased the total biomass of maize by 224.23%to 299.74%.Irrespective the phosphorus application level,no separating treatment significantly increased maize biomass when compared with separating treatment.The interaction between phosphorus level and root separation ways on the total biomass of alfalfa was significant.The total biomass of alfalfa was significantly increased by 19.14%after AM inoculation.Phosphorus application had no significant effect on the total biomass of alfalfa under unseparated treatment,but the total biomass of alfalfa was significantly increased by 39.42%and 70.54%with 5μm and 30μm nylon mesh separation ways.Regardless of phosphorus application level,the total biomass of alfalfa was significantly reduced with the completely separated treatment.The decrease of alfalfa biomass(18.78%and 42.31%,respectively)was effectively compensated by the increase of maize biomass(111.93%and 62.33%,respectively).(3)There was significant interaction between phosphorus level and AM inoculation treatment on total phosphorus uptake of maize.Compared with no AM inoculation treatment,AM inoculation was significantly increased total phosphorus uptake of maize by 58.61%and 26.64%irrespective the phosphorus application level.Compared with no P application,P application significantly increased the total P uptake of maize by 44.62%and 67.17%with and without AM inoculation,respectively.Compared with the completely separated treatment,no separation treatment significantly increased the phosphorus uptake of maize by 61.88%.The total phosphorus uptake of alfalfa was significantly increased by 23.86%after AM inoculation.Irrespective the phosphorus application level,5μm,30μm nylon mesh separation had no significant effect on the total phosphorus uptake of alfalfa,but under the condition of phosphorus application,the total phosphorus uptake of alfalfa was reduced by 51.76%under no separation treatment.(4)Soil equivalent ratio(LER_P)of P uptake by maize/alfalfa intercropping was significantly greater than 1 regardless of P application and AM inoculation,and their intercropping showed an advantage in P uptake.LER_P was significantly reduced by P application,but was significantly increased by 25.96%with AM inoculation.Under no phosphorus application condition,5μm nylon mesh separation,30μm nylon mesh separation and non-separation treatment increased the land equivalent ratio of phosphorus uptake by 18.81%,38.61%and 51.49%,respectively.Under P application conditions,30μm nylon mesh separation treatment and non-separation treatment significantly increased LER_P by 14.85%and 26.73%,respectively.(5)Under different phosphorus levels,the contribution of rhizosphere characteristics in P efficient uptake and utilization is different.Under no AM inoculation condition,the efficient utilization of intercropping phosphorus is mainly caused by root interaction.Regardless of P application,the root interaction contribution is greater than the root exudates interaction contribution(64%,73%>>36%,27%);With AM inoculation treatment,the mutual contributions of roots,mycorrhizal fungi and root exudates interaction were 37%,37%,26%,52%,29%,and 19%,respectively.Under P application condition,the contribution of root interaction improved while mycorrhizal fungi’s and root exudates’contribution decreased in the efficient utilization of phosphorus.To sum up,in the maize and alfalfa phosphorus uptake process,AM inoculation regulated root morphology and root exudates,changed belowground carbon distribution,and promoted phosphorus uptake and utilization.Maize/alfalfa intercropping promoted the efficient utilization of phosphorus,and the relative contribution of rhizosphere characteristics to the equivalent ratio of phosphorus absorption under phosphorus application conditions:root interaction>symbiotic mycorrhizal network interaction>root exudates interaction. |
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