| Due to its negative effects on microbial activity and soil nutrient availability, soil salinity poses a major threat to soil productivity in coastal saline soil, and salinization has become a worldwide problem restricting global crop production and food quality, especially in the Yellow River Delta-the biggest estuary wetland in China, the situation is so serious that we should take effective measures to establish comprehensive technologies in order to solve this environmental problem.Biochar is a carbon-rich material produced via pyrolysis of biomass with limited oxygen. Biochar used as a soil amendment has been widely shown its beneficial role in increasing crop yield due to its effects on bulk density, water-holding capacities, and microbial diversity.With biochar, beneficial biophysical effects could be expected on the availability of nutrient within the root zone and in turn on the germination and survival of plants. However, most research studying the benefits of biochar application to soils has been conducted in soils that are usually low in salinity, alkalinity and have a neutral to acid soil pH values. Addition of biochar amendments to coastal saline soil has received much less attention.The objective of this research was to investigate the potential benefits of biochar addition to a coastal saline soil with the hypothesis that it would increase plant biomass by improving nutrient (N, P) availability and changing microbial community structure in rhizosphere soil. To prove that, a series of experiments were set:Firstly, according to the specific properties of coastal saline soils, the study tried to seek for a suitable and economical raw material and a production method which was fitted for improving soil fertility. Finally, peanut shell, due to its low-cost and plenty resource, was selected as the raw material to produce biochar. In production process, slow pyrolysis at low temprature make the biochar nutrient riched, can help to improve soil fertility.Two halophytes, sesbania (Sesbania cannabina) and seashore mallow (Kosteletz kyavirginica), were chosen as the tested plants for a 52 days pot experiment. By observing the paraments of plant growth, rhizosphere characteristics, and nutrients (N, P) absorbtion and use efficiency, the study explored the effect of using biochar on plant growth in different species, and selected the best treatment for improving plant biomass. It is showed that a low amount of biochar addition (e.g.,1.5%) applied to the coastal saline soil could significantly increase biomass and promote the root growth of Sesbania and seashore mallow, and biochar with fertilizers could reach the upmost biomass. In addition, low amount of biochar addition (e.g.,1.5%) can enhance N and P uptake capacity of plant. However, saline-alkali soil after applying biochar showed no significant influence on plant germination, plant height, stem diameter, leaf morphology, chlorophyll and utilization capacity of P in plants.Meanwhile, by analyzing soil organic matter (SOM), C/N, CEC and exchangeable sodium after adding biochar, and the differences in soil pH, salinity, ammonium, nitrate and available phosphorus between rhizosphere and non-rhizosphere soil, the study explore the mechenics that how biochar affected nutrient availability in rhizosphere soil and eventually increased the plant biomass. The result exhibited that low amount of biochar addition (e.g.,1.5%) applied to the coastal saline soil could decrease soil pH and salinity, improve SOM, C/N and CEC, but showed no significant differences in soil exchangeable sodium and alkalinity (ESP). For soil nutrient availability, with the regulation of microorganisms and plant rhizosphere:on the one hand, biochar increased ammonium nitrogen in rhizosphere soil; on the other hand, biochar promoted the absorption of nitrate nitrogen; thirdly, biochar increased the content of available phosphorus content in rhizosphere soil. Thereby, biochar increased the nutrient availability of rhizosphere soil. Rhizosphere regulation with biochar also reflected on the decline in rhizosphere soil pH and salinity after adding biochar to the soil, which were both lower than that of the non-rhizosphere soil, and when biochar applied together with urea biochar soil pH can be further reduced.Biolog technology was used to test the effect of biochar on microbial community structure in rhizosphere and non-rhizosphere soil, the result showed that low amount of biochar addition (e.g.,1.5%) applied to the coastal saline soil could significantly improve microbial metabolic activity and strength in rhizosphere soil, especially in the group of microorganisms that use multi-carbon sugars as carbon source. Biochar also increased microorganisms’ abandance, diversity and evenness in rhizosphere soil.In summary, adding biochar to coastal saline soil at low amount (e.g.,1.5%) can change microbial community structure in rhizosphere, with the regulation of microorganisms and plant rhizosphere, soil nutrient availability, soil physical and chemical properties improved, and finally increased plant biomass. |
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