Effects Of Biochar On Soil Microorganisms In A Drip-irrigated Cotton Field

[Object] Biochar has a large specific surface and microporous structure, which can store water and nutrient.Soil amendment with biochar provides a habitat for microorganisms that can affects the soil microbial populations, community structure and physiological activity. Additionally, the effects of biochar on soil microorganisms may relate to its feedstock and production conditions, which together control the physico-chemical properties of the biochars. The objective of this study was to assess the effect of biochars derived from cotton straw, corn cob and chicken manure on soil microbial community composition and functional diversity in drrip-irrigated desert soil under cotton field. This may provide a basis for reasonable using biochar application in agricultural system.[Method] The two parts field experiment, including different application rate of biochar experiment and different types of biochar experiment, were carried out.(1) The different application rate of biochar experiment with five treatments: the control(CK), cotton straw 6(S1) and 12 t ha-1(S2), cotton straw biochar 2.25(B1) and 4.5 t ha-1(B2), cotton straw and its biochar was carried out with equal C amount in this experiment. The two nitrogen rates(0 and 300 kg ha-1, denoted as N0, and N300) were completely modular designed.(2) The different types of biochar experiment with five treatments: the control(CK),cotton straw 6 t ha-1(ST), cotton straw biochar 2.25 t ha-1(CS), corn cob biochar 2.25 t ha-1(CC) and chicken manure biochar 2.25 t ha-1(CM).[Result](1) The dry matter weights and nitrogen uptakes of cotton were increased significantly by the addition of cotton straw and its biochar. Under low N input(N0), the dry matter weights and nitrogen uptakes in the biochar with low dosage treatment(B1) was higher than the biochar(B2) and cotton straw(S2) with higher dosage treatments; under N300, the dry matter weights in biochar treatments(B1 and B2) was no significant differences with S2 treatment, but the nitrogen uptakes in biochar treatments(B1 and B2) was significantly higher than S2 treatment. The cotton yield has no significant difference among the B1, B2 and ST treatments, and significantly higher that in S1 and CK treatments. The nitrogen use efficiency was followed B2, B1 > S2 > S1, CK.(2) Application of cotton straw biochar increased soil enzyme activities related C cycling( b-glucosidase and cellobihydrolase). Compared with the control, the biochar with higher dosage(B2)increased arylamidase activity by 18.7% and L-glutaminase activity by 39%. The capacity of the C substrate utilization for soil microbial increased with the biochar application rate increased. The B2 treatment shifted the soil microbial community composition and increased the total PLFA of soil microbial by 27%. The total PLFA of Gram-negative bacteria, Gram-positive bacteria, AMF and actinomycetes all increased in B2 treatment.(3) The different types of biochar affected the AWCD values with cotton straw biochar(CS), corn con biochar(CC) > cotton straw(ST) > chicken manure biochar(CM) > the control(CK). Compared with the control, application of cotton straw biochar and corn cob biochar altered the functional metabolism of the microbial community significantly, but the cotton straw and chicken manure biochar had a little influence.(4) Application of cotton straw(ST) and three types of biochar(CS、CC and CM) shifted the soil microbial community composition, significantly increased the total PLFA of AMF, and decreased the total PLFA of saprophytic fungi. The microbial community composition had higher similarity in the soil with cotton straw biochar(CS) and corn cob biochar(CC), which increased the total PLFA of soil microbial,Gram-negative bacteria and actinomycetes.(5) Application of cotton straw and three types of biochar(cotton straw biochar, corn cob biochar and chicken manure biochar) increased the bacterial community diversity ACE index, which highest in chicken manure treatment. While has no significant differences in bacterial community diversity(including OUT richness, Chao, Shannon and Simpson indices).(6) The most abundant phyla in all sequence libraries were Proteobacteria, Actinobacteria and Acidobacteria. Application of cotton straw(ST) had large change with Proteobacteria, Acidobacteria,Actinobacteria and Bacteroidetes, while the three types of biochar(CS, CC and CM) had large change with the first three groups of bacteria. ST treatment had large changes in bacteria community composition, than CC and CM treatments, than CS treatment. In addition, Application of cotton straw(ST) and three types of biochar(CS, CC and CM) increased the relative abundance of some specific groups in genus level,especially, induced genera in cellulose degraders(Cellvibrio and Cellulomonas). Nitrifying bacteria including Nitrosospira and Nitrospira were increased in CC and CM treatments, decreased in CS and ST treatments. N fixation bacteria Rhizobacter and Rhizobium increased in biochar treatments(CS, CC and CM), Mesorhizobium increased in CC treatments. ST treatment increased the relative abundance of Rhizobium, Bradyrhizobium and Mesorhizobium.[Conclusion]Addition of biochar increased enzyme activity related to C and N transformation. and the capacity of C substrate utilization of the soil microbial, shifted the microbial community composition in the drip-irrigated desert soil, especially the biochar with higher application rate(cotton straw biochar 4.5 t ha-1).Application of cotton straw biochar, corn cob biochar and chicken manure biochar changed the microbial community functional metabolism and structure, increased the relative abundance of some specific groups including cellulose degraders, nitrifying bacteria and N fixation bacteria.