Response of microbial communities to biochar-amended soils:a critical review

Application of biochar to soils changes soil physicochemical properties and stimulates the activities of soil microorganisms that influence soil quality and plant performance.Studying the response of soil microbial communities to biochar amendments is important for better understanding interactions of biochar with soil,as well as plants.However,the effect of biochar on soil microorganisms has received less attention than its influences on soil physicochemical properties.In this review,the following key questions are discussed:(i)how does biochar affect soil microbial activities,in particular soil carbon(C)mineralization,nutrient cycling,and enzyme activities?(ii)how do microorganisms respond to biochar amendment in contaminated soils?and(iii)what is the role of biochar as a growth promoter for soil microorganisms?Many studies have demonstrated that biochar-soil application enhances the soil microbial biomass with substantial changes in microbial community composition.Biochar amendment changes microbial habitats,directly or indirectly affects microbial metabolic activities,and modifies the soil microbial community in terms of their diversity and abundance.However,chemical properties of biochar,(especially pH and nutrient content),and physical properties such as pore size,pore volume,and specific surface area play significant roles in determining the efficacy of biochar on microbial performance as biochar provides suitable habitats for microorgan-isms.The mode of action of biochar leading to stimulation of microbial activities is complex and is influenced by the nature of biochar as well as soil conditions.

Arsenic removal from water and soils using pristine and modified biochars

Arsenic(As)is recognized as a persistent and toxic contaminant in the environment that is harmful to humans.Biochar,a porous carbonaceous material with tunable functionality,has been used widely as an adsorbent for remediating As-contaminated water and soils.Several types of pristine and modified biochar are available,and significant efforts have been made toward modifying the surface of biochars to increase their adsorption capacity for As.Adsorption capacity is influenced by multiple factors,including biomass pyrolysis temperature,pH,the presence of dissolved organic carbon,surface charge,and the presence of phosphate,silicate,sulfate,and microbial activity.Improved As adsorption in modified biochars is attributed to several mechanisms including surface complexation/precipitation,ion exchange,oxidation,reduction,electrostatic interactions,and surface functional groups that have a relatively higher affinity for As.Modified biochars show promise for As adsorption;however,further research is required to improve the performance of these materials.For example,modified biochars must be eco-friendly,cost-effective,reliable,efficient,and sustainable to ensure their widespread application for immobilizing As in contaminated water and soils.Conducting relevant research to address these issues relies on a thorough understanding of biochar modifications to date.This study presents an in-depth review of pristine and modified biochars,including their production,physicochemical properties,and As adsorption mechanisms.Furthermore,a comprehensive evaluation of biochar applications is provided in As-contaminated environments as a guide for selecting suitable biochars for As removal in the field.