Effects Of Nitrogen And Phosphorus Levels On The Horizontal Distribution Of Tomato Root Intercropped With Soybean And Potential Capability Of Rhizosphere Mobilization

Plant roots play an important role in perception of soil context and alter morphology to respond nutrients and neighbors,but it is not clear whether neighboring plants alter their root distribution by altering the availability of nitrogen and phosphorus nutrient resources.In our study,we first screened tomato,cucumber,rocket,garland chrysanthemum,soybean,hairy vetch and wheat that take effect on to tomato root horizontal symmetry in different tomato-neighbor interactions,then verified the function of nitrogen(0、100、200 mg N kg^-1 sand soil)and phosphorus(0、100、200 mg P₂O₅ kg^-1 sand soil)in the intercropping system,and finally tested the tomato nutrient uptake and rhizosphere mobilization,which revealed the physiological mechanism of the altered root horizontal distribution of tomatoes through intercropped with soybean and provided a theoretical basis for intercropping and nutrient management in agricultural production.Main results of this paper were as following:（1）Intercropped with soybean had an effect on tomato root phenotypic plasticity,other intercropping plants had no effect.Intercropped with soybean caused horizontal asymmetry in tomato roots-the root dry weight and total root length of tomato seedlings in the intercropping region were significantly higher than those in the non-intercropping region.In addition,tomato,cucumber,rocket,garland chrysanthemum,soybean,hairy vetch and wheat were competitive with tomato,with less competition between soybean and tomato,and with less inhibition on tomato.（2）Phosphorus levels,rather than nitrogen levels,significantly affected the phenotypic plasticity of tomato roots in soybean intercropping systems.In the absence of phosphorus supply,tomato roots grew towards soybean roots（more roots in the intercropping than the non-intercropping region）.In the presence of phosphorus addition,tomato roots were evenly distributed in intercropping and non-intercropping regions.With the phosphorus concentration increase,the tomato dry weight increased.In the presence of phosphorus addition,compared with monoculture,the dry weight of focal tomato intercropped tomato was significantly decreased,there was no significant difference among other treatments.In the presence of phosphorus addition,there was no significant difference among the treatments（3）In the absence of phosphorus supply,intercropped with soybean significantly increased the phosphorus absorption of focal plants.Compared with intercropped with tomato,intercropped with soybean significantly increased the phosphorus concentration and content of tomato plants by 16.99%and 21.82%,respectively,and the phosphorus content in the tomato rhizosphere and bulk soil increased by over 20.00%.（4）Soybean root exudates had potential capability of rhizosphere phosphorus mobilization.With the phosphorus concentration increase,more protons,acid phosphatase and organic acids in the tomato and soybean rhizosphere activated phosphorus in the soil.In the absence of phosphorus supply,compared with tomato,cucumber,rocket,garland chrysanthemum,hairy vetch and wheat,more protons,acid phosphatase and organic acids in the soybean rhizosphere.In summary,intercropped with soybean changed tomato root horizontal distribution,tomato roots grew towards the soybean under low phosphorus condition.This is related to the soybean rhizosphere mobilization.