| Fulvic acid is widely used as a biological stimulant in agricultural production,but its molecular weight varies greatly from several hundred to tens of thousands of daltons.For a long time,little attention has been paid to whether there are differences in the effect of fulvic acid with different molecular weight.In order to provide a theoretical basis for the scientific and rational application of fulvic acid in agricultural production,the effect of fulvic acid with different molecular weight on wheat growth in two kinds of fluvo aquic soil and its possible mechanism were studied.In this study,pot experiments were conducted to study the effects of fulvic acid on wheat biomass,yield,nutrient uptake and soil available nutrients in two types of fluvo aquic soil,and to explore the mechanism through transcriptome analysis and soil microbial diversity analysis.Two kinds of fluvo aquic soil,sandy fluvo aquic soil(S)and loamy fluvo aquic soil(R),were used in the experiment.The molecular weight of fulvic acid was divided into three grades: less than 3000 Da(W1),more than 3000 Da and less than 10000 Da(W2),above 10000 Da(W3).The application concentration of fulvic acid was 0,10,25 and 50 ppm,which were marked as C1,C2,C3 and C4.In order to explore the physiological and molecular mechanism of fulvic acid promoting wheat growth,the wheat flag leaves with the best application of fulvic acid and the control were selected for transcriptome analysis and key enzyme activities of carbon and nitrogen metabolism.1.The results of elemental analysis show that with the increase of molecular weight,the relative content of carbon elements in fulvic acid increases,while the relative content of oxygen decreases,the ratio of C/H and C/O increases,which indicates that the smaller the molecular weight,the smaller the aromaticity,the more developed the side chain,the more oxygen functional groups.The results of infrared spectrum show that the position and intensity of absorption peaks of W1 and W2 are similar,and the positions and intensity of absorption peaks of W3 are different from those of W1 and W2.It shows that the structure and functional group content of fulvic acid with relative molecular weight of 10000 Da are not different.13 C NMR showed that with the increase of molecular weight of fulvic acid,the relative content of carbon atoms and carbonyl atoms of saturated hydrocarbons decreased gradually,and the relative content of carbon atoms of unsaturated hydrocarbons increased gradually.2.The main effect and interaction effect of molecular weight and concentration of fulvic acid on wheat yield reached significant level in the two fluvo aquic soils,and molecular weight of fulvic acid had significant effect on wheat biomass at flowering and maturity stages.Application of fulvic acid with different molecular weight could increase wheat yield(8.82% ～ 51.36%),flowering biomass(2.37% ～ 26.65%)and mature biomass(3.29% ～ 24.94%)significantly,and the effect of low molecular weight fulvic acid was the best.SW1C2 was the best in sandy fluvo aquic soil;RW1C3 was the best treatment for loamy fluvo aquic soil.3.The main and interactive effects of fulvic acid molecular weight and concentration on the nitrogen accumulation of wheat plants in flowering and mature stage and grain nitrogen accumulation reached significant level in two fluvo-aquic soils.The nitrogen accumulation of wheat plants in flowering stage(0.67% ～ 26.37%),nitrogen accumulation in mature stage(3.84% ～ 22.40%)and grain nitrogen accumulation(8.96% ～ 40.58%)were increased by applying different molecular weight fulvic acid significantly.4.The interaction effect of fulvic acid molecular weight and concentration on the iron concentration and iron accumulation in wheat grain reached a significant level in two fluvo-aquic soils.The application of different molecular weight fulvic acid increased the iron concentration(22.83% ～ 106.68%)and the iron accumulation(41.16% ～ 205.65%)in wheat significantly.5.In sandy fluvo-aquic soil,the total dry matter accumulation of wheat plants after flowering(8.13% ～ 74.36%),the nitrogen transport capacity of pre flower nutrient organs(24.30% ～ 40.27%),nitrogen transport capacity of pre flower nutrient organs(20.29% ～ 52.34%),and N transport efficiency of post flower nutrition organ(8.43% ～ 21.80%)were increased significantly,and SW1C2 treatment was the best.In loamy fluvo-aquic soil,the dry matter transport capacity of the nutrient organs before anthesis(12.38% ～ 75.95%)was increased by different molecular weight fulvic acid significantly,among which RW1C3 was the best.6.The activities of carbon and nitrogen metabolism related enzymes in flag leaves of wheat at flower stage treated with SW1C2 and RW1C3 and control were analyzed.The results showed that SW1C2 significantly increased the activity of 12.31%,glutamine synthetase(9.09%),and phosphoenol pyruvate carboxylase(15.21%).RW1C3 treatment significantly increased the activities of nitrate reductase(17.31%),glutamate dehydrogenase(8.75%),glutamate synthetase(18.18%)and phosphoenol pyruvate carboxylase(12.08%).7.The diversity of soil microbial communities in SW1C2 and RW1C3 and control treatment were analyzed.The results showed that Shannon index of soil bacteria was higher than that of control significantly,which increased by 6.74% and 16.64% respectively.The ace and Chao1 index of soil fungi were higher than that of the control significantly,and the ace index increased by 12.13%,58.81% and 15.53% and 50.21% respectively.8.The results showed that 3557 genes were induced by SW1C2 and RW1C3 treatment and control treatment in flowering stage.The results showed that 3557 genes were induced by SW1C2 treatment in sandy fluvo-aquic soil,of which 2443 genes were up regulated,and 1114 were down regulated significantly.In the soil moisture soil,RW1C3 treatment induced 1578 genes in flag leaves of wheat,946 genes were up regulated and 632 were down regulated significantly.The up regulated genes are mainly enriched in the processes of carbon metabolism,nitrogen metabolism,sugar metabolism and amino acid metabolism in sandy fluvo-aquic soil.The up regulated genes in the soil are mainly enriched in the process of hormone signal transduction,sugar metabolism and amino acid metabolism.The results showed that the biomass,yield,nitrogen accumulation,key enzyme activity of carbon and nitrogen metabolism,expression of genes related to carbon and nitrogen metabolism and soil microbial diversity were increased by different molecular weight fulvic acid treatment significantly.The results showed that SW1C2 treatment was the best in sandy fluvo-aquic soil.With the increase of fulvic acid application,the effect of W2 application increased,and the effect of W3 application increased first and then decreased;treatment the effect of RW1C3 is the best in soil moisture soil,and the effect of fulvic acid with different molecular weight increases first and then decreases with the increase of application amount. |
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