| As an effective way to improve soil quality,biochar might prevent red soil from degradation.Previous studies focused on the effect of biochar on crop growth,soil physial and chemical properties as well as microbiological properties,however,little attention has been paid to its effect on soil fauna,especially micro-fauna.This study investigated the effect of different doses of biochar and nitrogen fertilization on soil physicochemical properties,microbial properties,soil microfauna assemblage via integrating field and greenhouse experiment approach.A long-term field trial was conducted in red soil region to investigate the influences of different doses of biochar(0,10,20,30,40t hm-2)and nitrogen fertilization(60,90,120 kg N hm-2)on soil properties and nematode assemblage during drought and wet period in sweet potato growth stage.The main results were as follows:(1)Biochar significantly affected soil moisture(SM)and pH(P<0,05)regardless of drought or wet period.With the increasing of biochar amount,soil pH significantly increased,while soil moisture increased first and then decreased.(2)Soil microbial properties(microbial biomass C,N,C/N ratio,basal respiration)were significantly affected by biochar and nitrogen fertilization.Lower doses of biochar stimulated microbial activity,while higher doses posed a reverse effect.For example,averaged across different N amount,biochar amendment less than 30 t hm-2 could increase microbial activity in the drought and wet period.When the biochar dose was higher than 30 t hm-2,microbial biomass carbon(MBC)was significantly higher in the drought period than the control without biochar,but no differences were observed in the wet period.But microbial biomass nitrogen(MBN)showed reverse pattern.(3)Dissolved organic matter(DOC,DON)and mineral N(Min-N)were significantly affected by biochar and nitrogen fertilization(P<0.01)in the drought period,however,they were only affected by nitrogen fertilization instead of biochar in the wet period.(4)There was a significant interaction between biochar and nitrogen fertilization on soil nematode abundance and nematode trophic composition independent of wet or drought period.Combined biochar and nitrogen fertilization at high doses promoted nematode abundance.Moreover,the biochar increased the proportion of fungivores especially in the drought period,suggesting biochar stimulated fungal energy channel of soil ecosystem.(5)Redundancy analysis(RDA)revealed significant correlations among soil microbial properties,soil nutrients and nematode assemblage The relationship between DOC,DON,Min-N,SM,pH,basal respiration(BR)and nematodes was more close in the drought than wet period.In contrast,DOC,DON,Min-N,MBN and microbial biomass C/N have a larger impact on nematodes in the wet period.Based on the field experiment,a greenhouse experiment was conducted to further assess the doses of biochar(0,20,60 t hm-2)and nitrogen fertilization(0,60,120 kg N hm-2)on soil properties,microbial properties,enzyme activities and soil microfauna during rape(Brassica napus)growing stage.The main results were as follows:(1)Biochar and nitrogen fertilization significantly affected SM and pH(P<0.05).Biochar application increased pH significantly but decreased SM.Sampling time also affected SM and pH significantly.(2)DOC,DON,Min-N and available phosphorus(AP)were affected by biochar and nitrogen fertilization(P<0.01).With the increasing of biochar doses,DOC and DON decreased,while AP increased during rape flowering and ripening stage.Compared to flowering stage,DOC,DON,Min-N were higher in treatement with biochar and N fertilization,and AP lower at ripening stage.(3)Biochar but not N fertilization significantly affected MBC.Nitrogen and their interaction with biochar significantly affected BR.With the increasing doses of biochar,MBC and MBN significantly increased first and then decreased independent of growth stage.Applying biochar could increase microbial activity at flowering stage,but not at ripening stage.(4)There was a significant interaction between biochar and N fertilization on protozoa,nematode abundance and the trophic structure of nematode assemblage.At flowering stage,biochar increased the flagellate abundance,but reduced amoeba and nematode abundance.With the increased doses of biochar,the protozoa and nematode abundance declined at ripening stage.Compared to flowering stage,the proportion of the bacterivourous nematodes decreased,while other trophic groups increased at ripening stage.Biochar increased the proportion of fungivorous nematodes,suggesting biochar perfered to the fungal energy pathway,similar to the results derived from field experiment.(5)Non-metric multidimensional scaling(nMDS)ordination revealed that the soil nematode assemblage was affected by sampling time,while no clear effects by biochars or N fertilization.DOC,DON,SM,AP,pH and BR correlated with the nematode assemblage.(6)Biochar and nitrogen fertilization significantly affected soil enzyme activities involved in C,N and P cycling.Low doses of biochar stimulated them,while high doses depressed them.Specific enzyme activities and overall enzyme activities were significantly and positively correlated with SM,AP,Min-N and BR,but negatively with DOC and DON.(7)Biochar and nitrogen fertilization and their interaction significantly affected rape biomass.Biochar and nitrogen fertilization have a synergistic interaction on rape biomass at flowering and ripening stage.Rape productivity was significantly affected by biochar.With the increasing of biochar application,rape yield significantly increased.Rape biomass and rape yield had a positive relation with soil pH(P<0.05),but a significantly negative relationship with SM and Min-N(P<0.01).In summary,soil microbial properties,protozoa and nematode assemblage were affected by biochar and nitrogen fertilization.Soil nematode assemblage analysis provides complementary information of soil ecosystem state,facilitating a comprehensive understanding soil ecosystems under different agricultural managements. |
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