Effects Of Soybean Stover-derived Biochar On Sulfur Transformations And Microbial Community In Loess

Sulfur is an essential macro-element required for plant growth and overall soil health.Recently,however,sulfur deficiencies in China's Loess Plateau,as well as numerous other areas around the world,have become an increasing issue for local farmers and large-scale agricultural producers.Soils require adequate amounts of sulfur in order to support the biota and microbiota that live and thrive within the pedosphere.Without sufficient amounts of available sulfur,legumes are unable to fix N₂ at optimal levels and crops,at large,observe reduced yields.An increase in sulfur deficient soils has led to a growing number of studies regarding potential soil amendments and techniques and their role in maintaining soil sulfur levels.Biochar,a material produced from heating various types of biomass in the absence of oxygen?i.e.pyrolysis?,has been used as a soil amendment in a variety of different remediation and improvement techniques.Biochar amendments have been shown to change the physicochemical properties of soil,which in turn can lead to healthier soils depending on site specific factors.Studies have verified that biochar impacts soil organic matter?SOM?,soil pH,soil electrical conductivity?EC?,as well as many other soil properties.Due to its large surface area and porous structure,biochar shows promise in increasing soil microbial abundance and improving sulfur depleted soils.Two biochars were produced by pyrolyzing soybean stover at temperatures of 300°C and600°C?referred to as BC300 and BC600,respectively?and were applied to 100 g samples of loess at rates of 1%,3%,and 5%?w/w?.These treatments will be referred to as BC300-1,BC300-3,BC300-5,BC600-1,BC600-3,and BC600-5.The physicochemical properties,enzyme activity,and sulfur content of the treated soils,and a control containing no biochar,were tested initially and then again after 3,6,9,12 and 15weeks of incubation.After week 15,DNA extraction and PCR amplification were used to identify sulfur-oxidizing bacteria and to determine the changes in microbial community.The main results of this study are as follows:?1?A higher pyrolysis temperature caused both physical and chemical changes in soybean stover-derived biochar.As pyrolysis temperature increased from 300°C to 600°C the pH increased from 7.87 to 8.42,ash content increased from 13.5%to 15.5%,and the BET surface area increased from 2.00 to 13.84 m²·g^-1.?2?When added to loess,biochar treatments caused significant differences in soil physicochemical properties and soil enzyme activity.After fifteen weeks of incubation,the soil pH of BC300 treatments were 3.1%,3.4%,and 5.3%higher than the control for 1%,3%,and 5%application rates,respectively.BC600 treatments were 2.9%,4.5%,and 5.9%higher than the control for 1%,3%,and 5%application rates,respectively.EC saw trends similar to pH,but they were more pronounced with 5%application rates causing 25.6%and 36.6%increases from the control for BC300 and BC600,respectively.Biochar treatments initially caused slight increases in SOM,however after week nine they began to drop lower than the control.After fifteen weeks of incubation,urease activity was 8.1%to 10.2%higher than the control with the addition of BC300 and 2.5%to 8.6%lower than the control with the addition of BC600.Variations in catalase activity appeared to be more arbitrary,and did not follow any specific trends with relation to pyrolysis temperature or application rate.?3?Biochar affected sulfur transformations in a variety of ways.Significant changes were seen in total sulfur,water-soluble sulfur,and organic sulfur content,but changes in adsorbed sulfur and HCl-soluble sulfur were less pronounced.The most notable changes were in water-soluble and organic sulfur content.All of the biochar amendments caused significant increases in water-soluble sulfur after the first three weeks of incubation and were all much higher when compared to the control.Comparing data from week 15 showed that organic sulfur in biochar treatments tended to be lower than or much lower than the control.?4?BC600 samples contained the highest relative abundance of sulfur-oxidizing bacteria and bacteria from the genus Lysobacter.Relative abundance of Lysobacter in BC600treatments ranged from 2.84%to 4.19%,whereas BC300 treatments and the control only ranged from 1.24%to 2.38%.All of the samples were mainly associated with the bacteria phyla Proteobacteria,Gemmatimonadetes,Actinobacteria,Bacteroidetes,and Chloroflexi.The majority of biochar treatments showed an increase in the relative abundance of Proteobacteria from the control?27.3%?with BC300-5 and BC600-5 being the highest at34.2%and 35.2%,respectively.The relative abundance of Gemmatimonadetes increased significantly in all biochar treatments where BC300-1 and BC600-3 were the most notably different than the control?14.6%?at 22.0%and 23.6%,respectively.Biochar caused reductions in the relative abundance of Actinobacteria and Chloroflexi,but Bacteroidetes and Acidobacteria saw little to no change.This study shows that soybean stover-derived biochar not only caused significant changes in the sulfur transformations and physicochemical properties of loess,but also led to shifts in its microbial community.Based on the results,soybean stover-derived biochar should be considered as a soil amendment due to its beneficial effects on microbial community and sulfur mineralization.