Study On Correlations Between Biochar And Microbes Associated With N-cycling In The Soil Of Vegetable Fields

In the nitrogen cycling of the soil of vegetable fields,N-fixing bacteria and ammonia-oxidizing microorganisms are of great importance to increase nitrogen content,change nitrogen forms and enhance plant nitrogen use efficiency.Adding biochar can increase nutrition,water content,O₂ and pH,thus the microbial?bacterial,fungi,archael?communities shift after adding biochar.The effect of biochar on the microbial community associated with the N-cycling is unclear and worth of study.The field sampling and laboratory soil incubation test were conducted to study the effect of different cultivation systems on the abundance of ammonia oxidizing bacteria?AOB?,ammonia-oxidizing archaea?AOA?,and nitrogen-fixing bacteria in soil,the correlations of soil parameters and these abundance were found.The influence of biochar on above-mentioned abundance and nitrogen form was further studied.We also discussed the effect of selected biochar as carrier of Azotobacter chroococcum on the survival of inoculants in soil incubation test.qPCR based on amoA genes and T-RFLP were used.The results as below:?1?This study aimed to investigate effect of two different cultivation systems,soil and substrate systems on the rhizosphere bacterial community of lettuce?Lactuca sativa?.Real-time PCR and PCR-DGGE were implied to analyze the characteristics of rhizosphere bacterial communities.Real-Time PCR detection showed that the population of rhizosphere bacteria in substrate system was significantly higher than that of soil system?P<0.05?.PCR-DGGE profiles revealed that the diversity of substrate system was significantly higher than that of soil system.RDA revealed that soil and substrate systems had different bacterial communities,and pH and nitrate were two main factors that determined the community structure,followed by water content.These factors possibly influenced the correlations between biochar and N-cycling associated microbes.?2?Based on soil parameters,the clustering result showed that the organic cultivation and conventional cultivation were different:organic cultivation possessed higher EC,total carbon,total nitrogen,ammonium,nitrate,available phosphorus,available potassium content than conventional cultivation significantly?P<0.05?;pH and carbon nitrogen ratio of conventional cultivation were significantly higher than that of organic cultivation?P<0.05?.The way of organic or conventional cultivation significantly influenced the abundance of AOA and AOB?P<0.05?,AOA was inclinded to organic cultivation and AOB was inclined to conventional cultivation.The abundance of AOA was positively correlated with ammonium?R=0.76,P<0.05?,available potassium?R=0.64,P<0.05?,available phosphorus?R=0.60,P<0.05?;the abundance of AOB was positively correlated with carbon nitrogen ratio?R=0.86,P<0.001?and pH?R=0.89,P<0.001?,and negatively correlated with ammonium?R=-0.79,P<0.01?.The nifH abundance of conventional open field was highest,that of organic open field was lowest;this was consistent with the content of ammonium,the ammonium content played more important role in determining the abundance of nifH.?3?The incubation time,organic fertilizer significantly increased nitrate content?P<0.001?and nitrification,while biochar weakened the nitrification by inhibiting the mineralization approved by the lower content of nitrate and total soluble nitrogen of treatments with biochar compared with treatments without biochar?P<0.05?.Treatments with biochar had the higher copy numbers of AOB and AOA amoA genes.AOA was more abundant than AOB and the dynamic nitrate content indicating AOA was the main driver of ammonium oxidization.T-RFLP analysis of the amoA gene fragments showed that AOA community changed immediately by adding organic fertilizer,while biochar weakened this priming effect.AOB community also changed by organic fertilizer,leading to the distinct between treatments with organic fertilizer and treatments without organic fertilizer in the end of the test.Biochar played a more important role in AOA rather than AOB.Biochar also mitigated the decrease of nifH genes.The result of the incubation test showed that incubation time significantly decreased the abundance of inoculants?P<0.05?,while biochar didn't influence the abundance significantly?P>0.05?,however,biochar inoculated with Azotobacter chroococcum firstly was obviously better than directly mixed with inoculants.In sum,biochar increased abundance of AOA,AOB and nitrogen-fixing bacteria,while inhibited mineralization and weakened the prompting effect of organic fertilizer on mineralization and nitrification.The effect of biochar as inoculant's carrier remained to be further discussed.