Physiological Response To Heterogeneous Distribution Of Salt And Nitrogen In Rhizosphere Of Suaeda Salsa

In this study,the root of Suaeda salsa L.was divided into two parts by the method of split-roots experiment,and treated with different concentrations of NaCl to study the influence of salt heterogeneous distribution on the growth of the species.Meanwhile,the effect of heterogeneous treatments of nitrogen(nitrate nitrogen)on the growth of the species was explored to study its nitrogen requirement,in order to provide guidance for nitrogen fertilizer management in S.salsa cultivation.The results are as follows:1.Physiological response of S.salsa to the heterogeneous distribution of salt in the root zoneThe salt concentration of optimal growth in S.salsa is 200 m M NaCl.Therefore,this experiment selected 50/50 m M NaCl as the low-salt homogeneous control.After the split-root treatment for 10 days,the shoot dry weight in the heterogeneous treatment with 50/350 m M NaCl tended to be increasedcompared to that in the 200/200 and 350/350 m M NaCl treatments.The same trend was found in the root dry weight on the side of 50 m M NaCl at 50/350 m M NaCl treatment,which may be due to the increase of root length,surface area and number of tips.Compared with 200/200 m M NaCl treatment,the Na⁺and K⁺contents in the leaves at 50/350m M NaCl treatment did not change,but Cl^-content increased.Compared with 350/350 m M NaCl treatment,the Na⁺and Cl^-contents in the leaves at 50/350 m M NaCl treatment decreased significantly,while the K⁺content increased significantly.The concentrations of Na⁺,Cl^-and K⁺in the roots of 50 m M side at 50/350 m M NaCl treatment were higher than those at 50/50 m M NaCl treatment,indicating that low-salt supply on one side of the root may reduce the Na⁺and Cl^-accumulation in the leaves,but increased of K⁺accumulation in the leaves,which will help plants to alleviate salt damage.At the same time,high-salt supply on one side of the roots can increase ion accumulation in low-salt side of the roots,which may help reduce water potential and promote water absorption in the low-salt side of the roots.One day after the salt heterogeneity treatment,the Na⁺efflux in the roots of the 50 m M side at 50/350 m M NaCl treatment was significantly higher than that of the 50/50 m M NaCl treatment.Combined with the result of leaf Na⁺content,it can be suggested that Na⁺efflux in the roots on the side of 50 m M NaCl can reduce leaf Na⁺accumulation and promote root K⁺absorption,thereby promoting plant growth at 50/350 m M NaCl treatment.In addition,ABA content in the roots on the side of 350m M NaCl was high at 50/350 m M NaCl treatment when seedlings were treated for 1 day,and the value in the roots on the side of 50 m M NaCl at 50/350 m M NaCl treatment increased compared to that at 50/50 m M NaCl treatment,which suggests salt heterogeneous treatment may promote salt-induced ABA accumulation,to play an important role in plant response to salinity in order to regulate seedling salt tolerance,which needs to be further investigated.2.Physiological response of S.salsa to heterogeneous distribution of NO₃^-in the root zoneUnder the condition of 200 m M NaCl,the shoot dry weight of S.salsa at 0.5/2 m M NO₃^--N treatment has no significant difference from the 2/2 m M NO₃^--N treatment.The same trend was found between the 0.5/3.5 and 3.5/3.5 m M NO₃^--N treatment,indicating that low nitrogen supply on one side of the roots did not affect the biomass accumulation in S.salsa.Compared with the2/2 m M NO₃^--N treatment,the 0.5/3.5 m M NO₃^--N heterogeneous treatment promoted shoot dry weight,indicating that root nitrogen heterogeneous treatment may increase shoot biomass and nitrogen utilization efficiency.The increased root dry weight at 0.5/2 m M NO₃^--N treatment may be related to the increase in the root number.Compared to 2/2 m M NO₃^--N treatment,0.5/3.5m M NO₃^--N heterogeneous treatment did not up-regulate Ss NRT1.1,while the Ss NRT2.1 was significantly up-regulated at 24 h.Compared with 2/2 m M NO₃^--N treatment,Ss NRT1.1 was significantly up-regulated in the roots on the side of 0.5 m M NO₃^--N,while Ss NRT2.1 was significantly up-regulated at 24 h at 0.5/2 m M NO₃^--N heterogeneous treatment.This indicates that the up-regulation of these genes may be related to nitrate uptake during nitrogen heterogeneous treatment,which may be beneficial to the uptake of NO₃^-by the roots,thus maintaining the normal growth of the shoots under the condition of lower nitrogen supply.In conclusion,based on the above results,it can be suggested that the supply of low nitrogen on one side of the roots in S.salsa may not affect the growth of the shoot,i.e.,seedlings can maintain stable shoot biomass even under partial low nitrogen supply.