Effects Of Partial Substitution Of Chemical Fertilizer With Organic Amendments On Microbial Characteristics Of Soil Aggregates In Greenhouse Vegetable Production

As an intensive form of agriculture,the unique greenhouse vegetable production has been characterized as high agricultural inputs,high cropping indexes,and high temperature and humidity.The activity and diversity of soil microbes,which play a key role in the decomposition of soil organic matter and nutrient recycling,is affected by the unique greenhouse vegetable production.As the basic units of soil structure,soil aggregates provide spatially heterogeneous habitats for microorganisms,affecting the biochemical processes in the soil.However,knowledge of microbial communities and their activities within soil aggregates in greenhouse vegetable field is currently seldom reported for relatively comprehensive understanding of the effect of partial substitution of chemical fertilizer with manure and/or straw.Thus,it is necessary for a relatively deep understanding of how the activity and microbial community composition of soil responses to nutrient management measures in greenhouse vegetable production occurs.Based on the 6-year partial substitution of chemical fertilizer with manure and/or straw experiment in Dahe Experimental Station belonging to the Hebei Academy of Agriculture and Forestry Sciences,Hebei Province,the effects of different fertilization patterns on microbial biomass C and N,enzyme activity,microbial community structure and yield in greenhouse vegetable system were investigated.The field experiment comprised five treatments:4/4CN?CN,nitrogen in chemical fertilizer?,3/4CN+1/4MN?MN,nitrogen in pig manure?,2/4CN+2/4MN,2/4CN+1/4 MN+1/4 SN?SN,nitrogen in corn straw?and 2/4CN+2/4SN.The amounts of nitrogen?N?,phosphorus?P₂O₅?,and potassium?K₂O?were equal in the five treatments.The main findings obtained were summarized as follows:1.Effects of different partial substitution of chemical fertilizer with organic amendments on greenhouse vegetable yield.In the long run,chemical fertilizer substituted by organic amendments,especially substituted by corn straw,were effective in increasing the vegetable yield.The 4/4CN treatment had higher vegetable yield than treatments using organic amendment substitutions in the first three growing seasons for new-built greenhouse.Starting with the fourth growing season,the optimal yield was obtained from soil treated with straw.And from the fourth to ninth growing season,the vegetable yield increased in soils amended with straw?2/4CN+1/4MN+1/4SN,2/4CN+2/4SN?by 2.2%-15.6%compared with 4/4CN and 1.1%-9.6%compared with soils amended with pig manure?3/4CN+1/4MN,2/4CN+2/4MN?,with the average increases of 7.5%and 5.8%,respectively.2.Effects of different partial substitution of chemical fertilizer with organic amendments on microbial biomass C and N,enzyme activity,and microbial community structure in bulk soil.Different partial replacements of inorganic fertilizer by organic amendments,especially soils amended with straw,significantly increased the soil microbial biomass C and N,enzyme activities?involved in C,N and P cycle?,total PLFA content,and the relative abundances of bacteria,fungi and actinomycetes.Microbial biomass C and N,most enzyme activities and microbial community composition in bulk soil of greenhouse vegetable field were significantly and positively related to vegetable yields.As the main factor of affecting soil enzyme activity and microbial community,MBC could account for 89.5%and52.3%of the total enzyme activity and total community variability,respectively.3.Effects of different partial substitution of chemical fertilizer with organic amendments on the distribution of soil aggregates and the contents of nutrients and microbial biomass C,N across soil aggregates.The predominant size fractions in greenhouse vegetable soil were 250-1000?m fractions and>2000?m fractions,which accounted for 32.0%and 38.4%of the bulk soil on average by weight,respectively.Compared with 4/4CN treatment,organic amendments increased the proportion of>250?m fractions and soils amended with straw had a relatively large impact on the distribution of soil aggregates with a significantly improvement in soil aggregate stability.The MWD and GMD values in straw-treated soil were 6.1%and 11.2%higher than those in 4/4CN-treated soil,respectively.The organic carbon and total nitrogen in 250-1000?m fractions and>2000?m fractions were the main sources of the organic carbon and nitrogen in the soil,which accounted for 34.1%and 35.2%of the total organic carbon stocks,and 34.0%and 36.4%of the total nitrogen stocks,respectively.The content of soil nitrate nitrogen was higher in 250-1000?m fractions and 1000-2000?m fractions than in other aggregate fractions.Soil available potassium,microbial biomass C and N contents increased with the increasing soil aggregate-size,whereas soil available phosphorus decreased with the increasing soil aggregate-size.4.Effects of different partial substitution of chemical fertilizer with organic amendments on extracellular enzyme activities in soil aggregates.The activities of?-glucosidase,?-cellobiosidase,?-xylosidase,and?-glucosidase?involved in the C cycle?were increased in the organic-amended soil,mainly distributing in 250-1000?m fractions and>2000?m fractions.For enzymes related to the N cycle,the activity of urease increased with the decreasing soil aggregate-size,whereas the activities of N-acetyl-glucosaminidase and L-leucine aminopeptidase were higher in>2000?m fractions than in others.The activity of phosphatases decreased with the decreasing soil aggregate-size.Different fertilization treatments were the main factors affecting the extracellular enzyme activity of soil aggregates,followed by the effect of aggregate size and interaction,accounting for 61.4%,19.3%and 7.1%of the extracellular enzyme change,respectively.Mantel test showed that soil organic carbon and microbial biomass carbon and nitrogen affected by fertilization pattern were the main indicators of extracellular enzyme activity changes in soil aggregates.5.Effects of different partial substitution of chemical fertilizer with organic amendments on soil microbial community structures in soil aggregates.Significant differences were found in microbial community compositions among different aggregate-size.The total PLFA content and the relative abundance of bacteria were the highest in the 1000-2000?m fractions,followed by<250?m fractions and 250-1000?m fractions.The relative abundance of fungi increased with the decreasing soil aggregate-size.The relative abundance of actinomycetes and gram-positive bacteria were higher in250-1000?m fractions and 1000-2000?m fractions than in other fractions,whereas the relative abundance of gram-negative bacteria was higher in>2000?m fractions.Mantel test showed that soil organic carbon and total nitrogen affected by fertilization pattern were the main indicators affecting the change of microbial community structure in<2000?m fractions,whereas the corresponding indicators for>2000?m fractions were soil organic carbon,microbial biomass C and N,and available potassium.6.Effects of different partial substitution of chemical fertilizer with organic amendments on soil bacterial flora in soil aggregates.Compared with 4/4CN treatment,alpha diversity index of bacteria were significantly increased in 2/4CN+2/4MN treatment by 4.4%-7.9%,whereas there was no significant change in straw-treated soil.The relative abundance of dominant bacterial phyla,including Firmicutes,Nitrospirae,and Cyanobacteria,were decreased in organic-amended soil,but were increased for the relative abundance of dominant bacterial phyla,including Chloroflexi,Saccharibacteria,and Planctomycetes.With the increasing aggregate-size,the relative abundance of Actinobacteria tended to decrease,whereas the relative abundance of Nitrospirae tended to increase.The relative abundance of Firmicutes was significantly higher in>2000?m fractions than in others,however,the Gemmatimonadetes was significantly lower in<250?m fractions.PERMANOVA analysis showed that there were significantly differences in soil bacterial community structure among fertilization treatments,but only in>2000?m vs.<250?m fractions and 1000-2000?m vs.<250?m fractions for soil aggregates.The redundancy analysis showed that soil organic carbon was the main environmental factor affecting soil bacterial community structure changes,which could explain 19.2%of the change in bacterial community.In summary,organic amendments as substitutes increased organic carbon,total nitrogen,and microbial biomass C and N in soil aggregates.The change of soil organic carbon,total nitrogen,and microbial biomass C and N mediated by different partial substitution of chemical fertilizer with organic amendments changed the extracellular enzyme activities and microbial community structure compositions,and affected the yield of vegetables.Relatively comprehensively considering the effects of different partial manure and/or straw substitution on improving the microbial characteristics of soils and increasing vegetable yield,and the practical feasibility,combined application of chemical fertilizer,manure,and straw?2/4CN+1/4MN+1/4SN?can improve soil quality and maintain sustainable high yield in greenhouse vegetable production.