| The low nitrogen utilization efficiency in saline alkali soil can lead to a decrease in soil fertility and plant quality.Organic fertilizer combined with inorganic fertilizer can effectively improve the soil environment,but the mechanism of its impact on the transformation and absorption of nitrogen in soil and plants,as well as on soil nitrogen functional microorganisms,is not yet clear.Therefore,through the pot experiment of sorghum-sudangrass,this study uses the combination of high-throughput sequencing,gene chip determination,15N isotope tracing and other technologies to study the effect of different proportions of organic fertilizer combined with chemical fertilizer(T1:100%organic fertilizer;T2:70%organic fertilizer+30%inorganic fertilizer;T3:50%organic fertilizer +50%inorganic fertilizer;T4:30%organic fertilizer+ 70%inorganic fertilizer;T5:100%inorganic fertilizer)on nitrogen transformation in soil and absorption in plants,Through the structure of bacterial and fungal communities,as well as N functional prediction and N functional microorganisms,the inherent microbiological mechanisms of nitrogen transformation and absorption in soil and sorghum-sudangrass were revealed.The main conclusions are as follows:(1)The results of the 15N sorghum-sudangrass seedling pot experiment showed that the proportion of plant nitrogen from inorganic fertilizer(Ndff),soil nitrogen from inorganic fertilizer(Ndfs),soil nitrogen residue rate(NRF),and soil nitrogen loss rate(NLR)all increased with the increase of inorganic fertilizer application.But the nitrogen utilization efficiency(NUE)T3 is the highest,which is 10.29%-82.56%higher than other treatments.Pearson correlation analysis showed a significant positive correlation(P<0.05)between the nitrogen utilization efficiency of inorganic fertilizer 15N(NUE(15N)and plant growth physiological indicators such as dry weight,root length,plant height,and leaf area index.(2)The results of a pot experiment of sorghum-sudangrass throughout its entire growth period showed that the treatment with organic fertilizer application(T1,T2,T3,T4)significantly increased soil moisture content,salt absorption capacity,and the content of soil macroaggregates(>0.25 mm particle size fraction)(P<0.05).The ammonium nitrogen content in T3 soil decreased by 3.90%-46.8%compared to other treatments,while nitrate nitrogen increased by 4.41%66.70%,maintaining a relative dynamic balance of nitrogen transformation.The content of soil total nitrogen increased with the application of more organic fertilizers,and the total nitrogen content of T1 during the entire growth period increased by 10.58%-37.74%compared to other treatments.The content of available phosphorus and available potassium in soil is similar to that of total nitrogen.(3)The results of soil microbial community indicate that the Gemmatimonadota phylum of T3 has the highest relative abundance,which is beneficial for the transformation of nitrogen in the soil.The dominant genera of each treatment(Lactobacillus;Paenibacillus;Pseudorhizobium;Arthrobium;Brevundimonas)have mineralization,converting organic nitrogen in organic fertilizers into inorganic nitrogen.The results of soil nitrogen functional genes showed that the relative abundance of ammonia oxidation genes(amoA1,amoB),denitrification genes(nirS3,nasA),and nitrogen fixation genes(nifH)in T3 were the highest,which could efficiently carry out soil nitrogen cycling and transformation.The main nitrogen genes(nirS2,nirK1,nirK2 and narG)in T5 are all related to denitrification.(4)T3 significantly promoted plant growth(P<0.05),with plant height,root length,dry weight,and leaf area increased by 9.55%-51.01%compared to other treatments.The nitrogen utilization efficiency(NUE)of T3 was the highest,increased by 27.74%-72.22%compared to other treatments,while the nitrogen loss rate(NLR)in the soil was the lowest,decreased by 14.95%-25.81%compared to other treatments.The partial least squares path model(PLS-PM)results indicate that the combination of organic fertilizer and chemical fertilizer mainly promotes plant growth by altering the structure and function of soil microorganisms.Both T3 and T5 have a promoting effect on plant growth,but the nitrogen utilization efficiency of T3(path coefficient,0.609)is better than that of T5(path coefficient,-0.154).To sum up,the combined application of organic fertilizer can effectively alleviate soil salinization.50%organic fertilizer+50%inorganic fertilizer can change the soil microbial community structure,affect bacterial functional metabolism and N gene expression,improve the efficiency of nitrogen accumulation,transport and absorption in the ’soil-sorghum-sudangrass’system,and improve soil quality.This study provides a theoretical basis for alleviating soil salinization,improving soil micro-ecological environment and improving nitrogen use efficiency. |
