Characteristics Of Biochar Of Spartina Alterniflora And Phragmites Communis And Their Improvement Effect On Saline-alkali Soil

The problem of soil salinization in coastal wetlands and continuous degradation of the ecological environment is becoming more and more serious.Biochar is a soil improvement material that has attracted much attention in recent years due to its wide range of raw materials,rich nutrient content,excellent adsorption performance,and stable properties.In this study,the Yellow River Delta coastal wetland was used as the research area,and the intertidal saline-alkali soil in the area was used as the research object.Spartina alterniflora and Phragmites communis which are typical local plant resources were used as raw materials to make biochar at different temperatures,to explore the effects of different raw materials and preparation temperatures on the characteristics of biochar.The improvement experiment of saline-alkali soil was carried out according to different add scale of biochar.through the changes of soil physical and chemical properties,enzyme activity and microbial community structure and diversity,the effect and mechanism of biochar on saline-alkali soil were explored.Finally,through the calculation of membership function and factor weights,various physical and chemical properties and biological characteristics of the soil are quantified as soil quality index,and the effect of biochar in improving soil is evaluated.The research results can provide theoretical guidance and data support for the rational development and utilization of coastal wetland plant resources and the improvement of saline-alkaline soil,and provide new ideas for the evaluation of the improvement effect of saline-alkaline soil in coastal areas.The main results of the study are as follows:(1)Spartina alterniflora biochar has higher pH and base ion content than Phragmites communis biochar;Phragmites communis biochar contained higher contents of C,H,N and oxygen-containing functional groups such as-COOH,-COH and-OH.With the increase of preparation temperature,the pH of the two kinds of biochar increased,the content of C decreased,the content of H increased,and the content of N increased at first and then decreased.The amount of oxygen-containing functional groups decreased.(2)The addition of Spartina alterniflora and Phragmites communis biochar significantly increased the cation exchange capacity and salt content of saline-alkali soil,and reduced the exchange sodium percentage of the soil.When the amount of carbon application is low,the soil pH decreases,but with the increase of the amount of carbon application,the soil cation exchange capacity and salt content increase,the exchange sodium percentage decreases,and the soil pH presents an increasing trend.When the preparation temperature of biochar increases,the pH of biochhar increases,the amount of surface functional groups decreases,the salt content increases,and the effect of improving soil cation exchange capacity,exchange sodium percentage,pH and salt content is also weakened.The nutrient content of TC,TN,TP,SOM and AP,potassium,calcium,sodium,magnesium and other nutrients in the soil increases with the addition of biochar,and the adsorption capacity of fast-acting nutrients such as nitrate nitrogen and ammonium nitrogen increases.As the amount of carbon added and the preparation temperature increase,the content of nitrate nitrogen and ammonium nitrogen decreases instead.(3)The addition of Spartina alterniflora biochar and Phragmites communis biochar significantly promotes the activity of soil sucrase(SUC),and the promotion effect of Spartina alterniflora biochar is significantly higher than the latter;both have an effect on urease(URE).There is a certain inhibitory effect,and there is no obvious difference.For the alkaline phosphatase(ALP)activity,the Phragmites communis biochar has an inhibitory effect,and the Spartina alterniflora biochar has a promoting effect.The increase of TC and TN nutrient content promotes the activity of sucrase in saline-alkali soil,but inhibits the activity of urease and alkaline phosphatase.Compared with sucrase,urease and alkaline phosphatase were more affected by salinity,pH and CEC.(4)Through the changes of microbial community diversity and structure after adding biochar,it was found that the dominant phyla of bacteria in the intertidal bare beach soil of the Yellow River Delta coastal wetland were Proteobacteria and Bacteroidetes,and the dominant genera were marine bacteria with salt tolerance.The addition of biochar reduced Shannon diversity index and increased Simpson diversity index.Biochar application could significantly increase the abundance of nutrient and salt tolerant microbial communities in saline alkali soil,but there was no significant difference at the species level.(5)By comparing the changes of soil quality index of two kinds of biochar under different application schemes,the improvement of saline soil by biochar is mainly reflected in increasing nutrient content,reducing alkalization degree,promoting nutrient cycle and so on.After comparative analysis,it was found that Spartina alterniflora biochar had better soil improvement effects than Phragmites communis biochar,and that Spartina alterniflora biochar prepared at 550°C had the best effect.And with the increase of biochar application rate,the soil quality index increased.