Effects Of Chamaecrista Rotundifolia On Dynamic Changes Of Soil Soluble Nitrogen And Bacterial Communities In Orchard Red Earth

In order to better understand the effects of legume on soil soluble nitrogen,soil bacterial communities,structure and function in southern red soil hilly region of south China,the conventional analysis methods and microbial high-throughput sequencing methods were used in laboratory experiments and field experiments in this study.All soil samples divided into 3 treatments which were control?CK,no adding legume?,P treatment?adding P.americanum×P.purpureum to soil?,and J treatment?adding Chamaecrista rotundifolia to soil?and were incubated in 15??marked 1?and 25??marked 2?for 180d.Soil soluble nitrogen,soil bacteria numbers,composition and structure were studied for 9 times in laboratory experiments.Simultaneously,in the field experiment,soil soluble nitrogen,soil physical and chemical properties,soil bacteria numbers,composition and structure were studied after mulching C.rotundifolia in orchard for 20 years.Our aim is to reveal the biological response mechanism of soil bacteria to the application of C.rotundifolia,and provide a theoretical basis for the application of C.rotundifolia.The main results were shown as follow:1.The total soil nitrogen?TSN?,soil organic Nitrogen?SON?and soil inorganic nitrogen?SIN?contents in the soil sampled from orchard of Red soil hilly region were significantly effected by C.rotundifolia under two constant temperature and humidity incubation conditions.The soil was incubated for 10?40d,TSN?SIN and SON content were decreased,and the significant difference for SIN content was observed between different treatments.When the soil incubated for 40d or 60d to 180d,TSN?SIN and SON content was significantly increased.TSN,SIN and SON contents in soil adding with C.rotundifolia were significantly increased compared with the soil adding P.americanum×P.purpureum.Soil TSN,SIN and SON content were higher in soil incubated at 25? than at 15?.2.The addition of C.rotundifolia significantly affected the numbers of soil bacteria?phylum,class,order,family and genus?at 15? and 25? incubation,but the difference between the C.rotundifolia and P.americanum×P.purpureum was less than that between C.rotundifolia and control.At 15? incubation,the change of soil bacteria numbers caused by adding C.rotundifolia were observed during 10?180d,while the same performance of C.rotundifolia was only occurred in 10?60d?phylum?,10?80d?class,order,family and genus?at 25? incubation respectively,and there was no significant difference in the relative abundance of bacteria between the three treatments in 180d.The incubation temperature also had a significant effect on the population of bacteria at different levels of the orchard red soil.3.The addition of C.rotundifolia to the red soil which incubated at 15? and 25? significantly changed numbers of soil bacteria at phylum and genus level.The relative abundances of Proteobacteria and Bacteroides were significantly increased by the application of C.rotundifolia,and the enhancement performance was gradually declined in continuous incubation.Meanwhile the application of C.rotundifolia to red soil significantly increased the relative abundances of Rhizomicrobium,Phenylobacterium,Bradyrhizobium,Mesorhizobium,Devosia,Massilia,Bur kholderia-Paraburkholderia,Haliangium,Acidibacter,Candidatus_Koriba cter,Mucilaginibacter and Niastella.The relative abundances of Actinobacteria,Acidobacteria,Firmicutes,Chloroflexi,Verrucomicrobia and 7 genues?Sphingomona,Variibacter,Pseudolabrys,Lysobacter,Candidatus_Solibacter,Bryobacter and Acidothermus?were reduced by the application of C.rotundifolia,and inhibition performances on Acidobacteriaand Actinobacteria were gradually declined in continuous incubation.4.The results showed that the application of C.rotundifolia had changed soil bacteria composition and diversity.Adding C.rotundifolia to red soil significantly decreased the soil bacteria Simpson index and Shannon index at 15? and 25? incubation.ACE index and Chao1 index of the red soil were significantly increased by C.rotundifolia incubated at 25?.Compared with the soil adding P.americanum×P.purpureum,simpson index and Shannon index in soil adding with C.rotundifolia were significantly increased.simpson index and Shannon index were higher in soil incubated at 25? than at 15? for 10?30d,but the opposite performance were observed for 100?180d.The application of C.rotundifolia had changed soil bacteria structure,the factors affecting soil bacterial community structure were green manure addition,incubation time and green manure species.And the factors affecting soil bacterial community structure were incubation time,adding green manure and green manure varieties.5.High-throughput sequencing data were deeply analyzed to evaluate the effect of application of C.rotundifolia on soil bacteria community function,The application of C.rotundifolia significantly increased the proportion of amino acid metabolism gene and aetabolism of other amino acids gene at 15?and 25?incubation,decreased the proportion of energy metabolism gene,global and overview maps gene and carbohydrate metabolism gene,but there were little difference among the soil samples with different incubation time and between C.rotundifolia and P.americanum×P.purpureum treatments.There was significant relationship between SIN and Proteobacteria and Nitrospirae,which indicated that both Proteobacteria and Nitrospirae are key phyla to produce SIN,and there was significant relationship between SON and fivephyla,includingProteobacteria,Acidobacteria,Chloroflexi,Gemmatimonadetes and Planctomycetes,which showed that they are key phyla to produce SON.The further taxonomic analyses revealed that there was significant relationship between SIN and 5 genus,including Sphingomonas,Bradyrhizobium,Acidibacter,Candidatus Solibacter and Bryobacter,which indicated that they are key phyla to produce SIN.Meanwhile,there was significant relationship between SON and eight phyla,including Sphingomonas,Rhizomicrobium,Bradyrhizobium,Phenylobacterium,Acidibacter,Candidatus Solibacter,Mesorhizobium and Bryobacter,which indicated that they are key phyla to produce SON in orchard red earth after Chamaecristarotundifolia application.6.The high content of TSN,SIN and SON were observed in spring and summer,while low content of TSN and SON were observed in and autumn and winter.The highest content of TSN and SON were observed in June and August at 0-20cm and 20-40cm soil layers,respectively;and the lowest content were observed in February and December.At 0-20cm and 20-40cm soil layers,Significant differences for TSN and SON content were observed between two groups,which are TPC Vs TPN treatment,in February,April and June.However,SON content were decrease in TPC treatment compared with TPN treatment in August at0-20cm soil layers,and opposite demonstration were observed at20-40cm soil layers.Meanwhile,we described the bacterial community in the 0-20 cm soil profile under long-term?approximate 20 years?C.rotundifolia mulching in subtropical and tropical China.The results showed that the soil chemical properties had been significantly altered by long-term C.rotundifolia mulching,demonstrating a significant increase in the concentrations of TN,TP,AN,NO₃^--N,and OM in TPC treatment.The Illumina-based sequencing showed that soil bacterial community membership and structure were significantly altered by C.rotundifolia mulching?TPC?,and the change in soil bacteria dominant communities was demonstrated as a reduction in the Simpson,Shannon,Chao1 and ACE indices.Proteobacteria and Nitrospira were enriched in TPC treatments,while Firmicutes,Chloroflexi,WPS-2 and Planctomycetes were enriched in TPN.Cluster analysis showed that the three repetitions of TPC were divided into one class,and the three repetitions of TPN were divided into one class,and TPC and TPN were separated on PCA1 and PCA2.Therefore,our results indicate that long-term interplanting of green manure Cassia in orchard has changed the number,composition and structure of soil bacterial communities.Our results indicate that long-term C.rotundifolia mulching had significantly influenced the soil chemical properties and bacterial communities in the orchard in subtropical and tropical China.