| Soil acidification is a representative type of soil degradation,which can severely decrease soil quality,cause nutrient loss and threaten crop yield.At present,the acidified soils are widely distributed in China and the acidification is becoming more and more serious.Soil acidification can greatly affect agricultural sustainable development.Biochar is an emerging soil amendment that can be utilized to correct soil acidity,increase soil fertility and change soil microbial living environment due to its unique properties.To get a better understanding of the effects of biochar on the chemical and biochemical characteristics of acidified soil,we conducted a series of experiments to explore how biochar acts as an effective soil amendment.We characterized the property of biochars pyrolyzed at different temperatures and derived from different feedstocks,and evaluated their application value in agricutural production.Then,we added typical biochars into four types of acidified soils for incubation,and observed biochar effects on soil acidity correction and soil fertility improvement.Furthermore,we obeserved biochar effects on acidified soil microbial abundance and diversity,and inverstigated the underlying mechanisms.We also explored the microbial community structure,dominant microbial phylum and functional genes responsible for C and N metabolism that located within biochars.These results provide a theoretical reference and technical guidance for people to use biochar for acidified soil amendment.The main results are listed as follows:(1)Via preparation and characterization of biochars derived from single feedstock,we observed the relationship between biochar physicochemical properties and found the trend how pyrolysis temperature and feedstock affect biochar properties.We collected nine types of feedstock to produce biochars at two pyrolysis temperatures of 300℃ and 500℃,and characterized their physicochemical property.Results showed that the property of biochar was determined by pyrolysis temperature and feedstock type.The aromaticity,pH,ash,surface area,total C,total P,base cations increased with increasing pyrolysis temperature,whereas the total H,total O and yield rate decreased.Manure biochar is recommended to correct soil acidity and increase soil fertility as it has higher pH,ash content,total P and total base cations,while straw biochar is recommended to enhance soil carbon sequestration or act as adsorption material as it has higher carbon content and surface area,respectively.(2)Via preparation and characterization of biochars derived from mixed feedstocks,we evaluated the roles of resulting biochar in environment and agriculture areas.We produced biochars by pyrolyzed the mixtures of rice straw and swine manure with different mass proportions.Then,we characterized their physicochemical property and evaluated the application value in agricultural production.As the straw proportion increased,the pH,total C and surface area in biochars increased,whereas the ash content and yield rate decreased.Elemental composition analysis,XRD,FTIR and SEM spectra showed that the elemental composition,mineral crystal structure,surface functional groups and morphology structure were altered with straw feedstock addition.Biochars derived from mixed feedstocks was considered as an effective and comprehensive potential soil amendment as they had the advantages from both straw biochar and manure biochar.We suggest that high proportion straw biochars can be used to increase soil organic carbon or used as adsorption materials,while the low proportion straw biochars can increase soil mineral nutrients.(3)By investigating biochar effects on soil acidity and fertility,we selected the most effective amendment and the most appropriate soil for biochar correction.We conducted incubation experiment to investigate the effects of four biochars(swine manure biochar,reed straw biochar,rape straw biochar and pineapple peel biochar)on the chemical properties of three acidified soils(Psammaquent,Plinthudult,and Paleudalf soils).We found that biochars increased soil pH,organic C,base cations and pH buffering capacity,and alleviated Al toxicity.The mechanisms of soil pH increases following biochar addition had two aspects:biochar alkalinity increased soil pH immediately(within 3 days)and nitrification decreased soil pH during the early periods(within 30 days).As biochar alkalinity had a greater effect on soil pH change than nitrification,biochars finally increased soil pH to a great extent.With respect to low pH soil,biochars mainly contributed to soil acidity correction.With respect to relatively high pH soil,biochars can not only contribute to acidity correction,but also affect soil nutrient cycling(especially for nitrogen cycling).Swine manure biochar was the best soil amendment among four biochars and the Psammaquent with low pH and nutrient content was the most appropriate soil type to be amended.(4)By investigating biochar effects on microbial community in acidified soil,we demonstrated the differences in microbial community between rhizosphere soil and bulk soil,and between bacteria and fungi.We conducted a rice pot experiment to investigate biochar effects on soil microbial community structures in both bulk soil and rhizosphere soil.Results revealed that biochar significantly changed microbial living environment by decreasing soil acidity and increasing soil fertility,and consequently altered microbial community structure.In addition,biochar stimulated root growth.Biochar also increased the relative abundance of soil copiotroph,e.g.Bacteroidetes,and decreased the relative abundance of soil oligotroph,e.g.Acidobacteria.Moreover,bacterial Alpha diversity was significantly changed by biochar addition,whereas the fungal Alpha diversity was not much changed.Multivariate statistical analyses showed that biochar-corrected acidity parameter and nutrient parameter co-determined bacterial community structure,while the nutrient parameter was more important in determining fungal community structure than acidity parameter.On the other hand,the increased root development enhanced rhizodeposition,i.e.secreting more carbon exudates,which can greatly influence microbial community structure.Simultaneously,biochar can adsorb and retain carbon exudates,preventing them moving into surrounding soils and make the carbon exudates more accessible to microbes in rhizosphere soil.Thus,based on the importance of carbon nurtient for microbial growth,the microbial community in rhizosphere soil was more sensitive to biochar addtion than in bulk soils.(5)By examining the microbial species,community structure and functional genes within biochar,we found the underlying mechanisms of differential microbial colonization in different biochars.We added biochars pyrolyzed at 300℃ and 700℃into a nutrient sufficient-soil and a nutrient-deficient soil for incubation.Then,the biochars were extracted from soils and Illumina Miseq sequencing was applied to examine the microbial species,community structure and functional genes responsible for C and N metabolisms located wthin biochars.Results showed that the microbial activity and biomass(e.g.respiration rate,DOC and DNA concentrations)in biochar300 were higher than in biochar 700,while the microbial diversity(e.g.OTU richness,Chao 1 and Shannon index)was higher in biochar 700 than in biochar 300.The dominant phylum that colonized in biochar was Actinobacteria,and the dominant genes responsible for carbon and nitrogen metabolisms were carbohydrate metabolism genes,denitrification genes and assimilation and dissimilation nitrate reduction genes.Given that biochar300 had more aliphatic C that can be readily utilized by microbes for growth and metabolism than biochar700,the microbial abundance in biochar 300 was higher than in biochar700.Given that biochar700 had unique physicochemical properties,which can attract a variety of bacteria with different physiological characteristics and lifestyles,the diversity in biochar700 was higher in biochar300.However,due to the limited C substrates,the whole bacterial abundance and activity was inhibited in biochar700. |
