| The pressure of climate change is increasing by the growing world's population and greenhouse gas emissions,which will affect the agriculture production capacity worldwide.The negative impact of chemical agriculture(soil degradation including:soil acidification,organic matter loss and soil compaction)on soil and environment resultd in the decrease of soil resource productivity and ecosystem services function,which further exacerbated severe challenges for the sustainable development of agriculture.On the other hand,especially in China,rapid urbanization and industrialization resulted in gradually weak of agriculture and countryside,following imcomplete treatment of biomass wastes of agriculture and life.And byproduct of crop production-straw was abandoned even open burning,which led to the increasing environmental effects by agricultural greenhouse gas emissions and air pollution.All these had become the social criticism.But if we treat crop straw with pyrolysis,turn it to biochar and return biochar into farmland soil,the problem of straw treatment will be partly solved,while the soil carbon sequestration will be enhanced to achieve the purpose of improving soil quality.However,the recent studies of biochar are mostly about short-term effects,while the laboratory or greenhouse pot experiment accounts for a large proportion.Therefore,we urgently need the results of long-term field experiments,so as to scientifically evaluate the agricultural application value of straw biochar.Two field experiment pots were chosen,which locate at the typical area of rice cultivation:Tai Lake Plain(YX,Yixing county,Jiangsu province)and Chengdu Plain(SC,Guanghan county,Sichuan Province).One-time application of wheat straw biochar(20 t ha1)(BA)with the control of no biochar application(NB)was done in 2009(YX)and 2010(SC)before rice transplanting,while the field management followed the local custom without biochar application in the following years.After the harvest of rice in 2015,the topsoil(0-15 cm)was collected for analysis with the bulk density measured in situ.Soil physical and chemical properties,nutrient content and microbial biomass carbon and nitrogen were measured.Soil aggregation was detected by separating soil water stable aggregates,while MUB-linked method was done for soil extracellular enzymes.The total DNA and RNA of soil were extracted at the same time,then the abundance and community structure of microorganisms and active microorganisms were determined by real-time fluorescence quantitative PCR and second-generation sequencing.All these were done to find out the sustainable effects of one-time application of biochar on paddy soil.Furthermore,soil aggregate samples(YX)were determined,with carbon and nitrogen content,extracellular enzyme activity,microbial community abundance and structure,to explore the mechanism of soil function in rice field from the perspective of soil aggregates.The main results were as follows:1.The sustainable effects of biochar on soil aggregate structure,fertility and extracellular enzyme activities of rice paddy(1)Compared to NB,BA changed the mass distribution of differernt particle fractions of soil aggregates at YX,6 years after one-time amendment with biochar.The proportion of soil macroaggregates(2000-250 ?m)and microaggregates(250-53 ?m)was increased,while that of coarse(53-20 ?m)and fine(20-2 ?m)silt fractions was decreased and no change in clay particle fractions with the mean weight diameter(MWD)was increased by 25.4%,under BA over NB.Furthermore,the biochar particles was found embedded inside macroaggregates through SEM experiment,which indicated that biochar was involved in soil aggregation.However,no change was found in the mass distribution and MWD of soil aggregates between treatments at SC,so did the SEM results.(2)One-time application of biochar still increased the content of soil organic carbon,total nitrogen and available nitrogen by 45.6%,34.8%and 14.0%at YX 6 years after treatment,so did the microbial biomass carbon(10.4%)and nitrogen(30.4%).But the bulk density decreased by 0.08 g cm-3 under BA over NB with no change in pH.However,no change was found in the index,expect the soil organic carbon and pH was increased by 16.7%and 0.26 units with biochar amendment.(3)Soil extracellular enzyme activities(EEAs)were still influenced by biochar treatment except phosphatase activity 6 years after application at YX.Under BA over NB,the activity of ?-cellobiosidase,N-Acetyl-glucosaminidase and sulfatase was shown elevated by 55%,50%and 53%while that of ?-glucosidase,?-glucosidase and ?-xylosidase by 32%,28%and 34%.Comparatively,that of phenol oxidase and peroxidase was moderately enhanced respectively by 17%and 16%under BA over NB.Overall,the normalized enzyme activity(NEA)was higher by 33%under BA than under NB.However,all these were not found at SC.2.The sustainable effects of biochar on soil bacterial and fungal communities of rice paddy(1)One-time biochar amendment still increased soil bacterial abundance by 32%of DNA level over NB at YX 6 years after treatment,while no change of RNA level.And no difference was found between treatments for fungal abundance of DNA and RNA level.However,soil bacterial and fungal abundance of SC at both level was not influenced by biochar.(2)The metrics(observed_species,Chao 1,Shannon index)of soil bacterial and fungal diversity(?-diversity)at both DNA and RNA level were shown no difference between treatments at YX and SC.But the changes of soil bacterial and fungal community structure(?-diversity)were different at the two sites.At YX,bacterial community structure shifted with biochar treatment at both DNA and RNA level,while there was difference of fungal community structure between treatments of DNA level,but not RNA.However,at SC,the only difference between treatments was found at RNA level for fungal community structure.(3)For bacterial functional traits,at RNA level,the abundance of 'Metabolism of Other Amino Acids','Amino Acid Metabolism' and 'Xenobiotics Biodegradation and Metabolism'were decreased under BA over NB,while that of 'Translation' and 'Transcription' were increased;but no change was found at DNA level at YX.And no difference was found between treatments at SC,for both DNA and RNA level.For fungal functional taxa,'Pathotrophic','Saprotrophic' and 'Symbiostrophic' were found.The relative abundance of pathotrophic fungi were decreased under BA over NB,at DNA level of YX,which were identified as 'Bryophyte Parasite' and 'Plant Pathogen';but no change was found for RNA level.However,at DNA level of SC,there was no difference.But the abundance of'Undefined Saprotroph' classified as saprotrophic fungi was decreased under BA over NB at RNA level.3.Change of biological characters in aggregate level at YX(1)Content of organic carbon(OC)and total nitrogen(TN)with carbon nitrogen ratio(C/N)were increased under BA over NB,in different particle fractions of soil aggregates,except no change of TN in microaggregates.OC and TN followed the trend:microaggregates>macroaggregates>clay particle fraction>coarse silt fraction>fine silt fraction;and C/N was increased with the rasied mean diameter of different particle fractions.Compared to NB,BA soil increased NEA by 37%and 33%,respectively in coarse and fine silt fraction,while no change in other fractions.And the NEA followed the trend:macroaggregates>microaggregates>fine silt fraction>clay particle fraction>coarse silt fraction.(2)Bacterial abundance was increased in microaggregates and coarse silt fraction,under BA over NB,while no change in other fractions.And there was no change for fungal abundance between treatments in each fraction.For all the fractions,bacterial anundance was found highest in clay particle fraction,following macroaggregates and microaggregates,and lower in silt fractions,especially in coarse silt fraction;while fungal abundance was highest in microaggregates and macroaggregates,and lower in coarse silt,fine silt and clay particle fractions,especially in clay particle fraction.Compared to NB,BA increased the Shannon index of bacterial community diversity in coarse silt,fine silt and clay particle fractions with no change in macroaggregate and microaggregate,while there was no difference between treatments for fungal community diversity in each fraction.For different particle fraction,bacterial Shannon index was highest in macroaggregate,reduced with the decreased mean diameter of different particle fractions,which was lowest in clay particle fraction;while fungal Shannon index was highest in macroaggregate,following microaggregate,but there was no difference between them,and lower in silt and clay fractions.Based on the PCoA(weighted UniFrac),bacterial community structure of each fraction was separated from each other,and biochar also influenced the bacterial community structure in each fraction,as PC3.While fungal community structure of macroaggregate and clay particle fraction was separated from it of the other fractions,with the influence of biochar(PC3)in macroaggregates,microaggregates and coarse silt fractions.However,based on the unweighted one,biochar as PC2,significantly influenced bacterial and fungal community composition.(3)The relative abundance of functional trait 'Energy metabolism' of bacterial communities was increased under BA over NB in microaggregates,while no change of functional traits between treatments in other fractions.And classified to KO tier 3,the relative abundance of 'Carbon fixation pathways in prokaryotes','Methane metabolism','Carbon fixation in photo synthetic organisms' were increased under BA over NB,which belonged to'Energy metabolism'.The bacterial networks were highly modular and equally complex in all the fractions of soil aggregates under NB and BA.The diameter of network increased under BA over NB in coarse silt fraction,so did the average shortest path length.The negative correlations of bacterial networks were under 50%in all the fractions of soil aggregates,and it increased from 40.4%(NB)to 49.05%(BA)in macroaggregates.In conclude,the effects of biochar on paddy soil were significantly different between two soil types.The biochar effect in glutinous ferric oxide-rich paddy soil was still significant after 6 years of one-time biochar amendment,and the amplitude of variation was still large in abiotic and biological character.However,the possible lack of effective interaction of biochar and soil in sandy ferric oxide-poor paddy might lead to instability and loss with water of biochar.But the residual amount of biochar in soil was not compared in this research.The research of soil aggregates at YX indicated that microbial community distribution of soil aggregates was mainly affected by particle size,and there were significant interactions between biochar and particle size.Although biochar affected the carbon and nitrogen content,enzyme activities,microbial community with its function and network of soil aggregates,the changes of bacteria were more significant than those of fungi.And the changes of enzyme activity and bacterial diversity were more obvious in the aggregates with smaller particle size,while the changes of bacterial function and network were more obvious in the aggregates with larger size.Therefore,the microbial effect was shown weaker than abiotic effect after biochar application for several years.This was the issue of sustainability of biochar amendment to soil health,which needed more experimental observation.In brief,biochar still had a significant positive effect in the soil with active soil processes after many years following application,which provided enlightenment for straw biochar service for sustainable agriculture. |
PDF Full Text Request