| Nematodes play a critical role in soil micro-food web with feeding behaviors,life history strategies and the complex relationship between microbial diversity.Bacterial-feeding nematodes are one of the dominant vegetative groups in soil nematodes.The interaction between bacterial-feeding nematodes and bacteria plays an important role in soil nutrient mineralization and litter decomposition.Phragmites australis and Spartina alterniflora are two typical halophytes from coastal salt marshes in China,among which P.australis is the native species in China and S.alterniflora is the invasive species.Litter decomposition of the two halophytes is important for coastal nutrient dynamics,nutrient cycling,and is important for the maintenance and conservation of coastal fishery resources.For further studies the role of bacterial-feeding nematodes in the litter decomposition of two halophytes.In this study,1)a dominant species of bacterial-feeding nematode was isolated and cultured;2)The "buffet" plate culture method was used to compare the feeding preferences of the bacterial-feeding nematodes to the litter of the two species;3)The effects of types of litters and initial nematode densities on the population proliferation and litter decomposition of bacterial-feeding nematodes were compared;4)With high-throughput sequencing technology,analyzed microbial biomass,activity and bacterial community,and elucidated the internal mechanism of interaction between bacterial-feeding nematodes and bacteria.This study was of great significance to clarify the role of soil micro food web in litter decomposition process and enrich soil ecology theory.The main research results of this study are as followed:(1)According to the morphological characteristics of the nematodes,the dominant species of the P.australis litter was identified as Diplolaimella stagnosa;The results showed that the effect of passage and propagation fed on the nutrient culture medium was good;The eggs of this species were elliptic(long axis: 49.7 ± 4.7?m,short axis:27.7 ± 3.7?m);The adult larvae developed at 20 ? without light,The egg hatching process was taken 58 hours;The female length was 1039.7 ± 14.7?m and the male was 898.1 ± 6.0?m.(2)By "buffet" plate researched bacterial-feeding nematode feeding preferences,I found that The nematode number of P.australis leaf extracted within 24 h was significantly higher than that of the other three food sources(S.alterniflora,habitat water and distilled water).Illumina-Miseq high-throughput sequencing showed that the relative abundance of Proteobacteria in both species was higher than 50%.The abundance of Planctomycetes in S.alterniflora was significantly higher than P.australis.These results indicated that bacterial-feeding nematodes preferred to feed on bacteria in the extract of the native plant P.australis.The relatively low abundance of Planctomycetales might be the reason why it is more attractive to bacteria-feeding nematode.(3)The effects of halophyte leaves on the population growth of bacterial-feeding nematodes were studied by microcosm system.The results showed that: The litter type and decomposition time of initial nematode density had significant effects on nematode population proliferation;The initial nematode density,litter type and decomposition time had significant effects on nematode population proliferation;After adding 10 nematodes,the number of nematodes in P.australis leaves was significantly higher than that in S.alterniflora leaves and mixed leaves after 32 days;After the addition of 100 nematodes,the number of nematodes in P.australis leaves was significantly higher than that of S.alterniflora after the 16 th day;The leaf decomposition rate with nematode addition was higher than that without nematode addition at different sampling time;The type of litter and its interaction with the initial density of nematodes had significant effects on the C content and C/N ratio of the remaining litter.These results indicated that the litter of P.australis was more conducive to the proliferation of the bacteria-feeding nematode D.stagnosa than S.alterniflora.The initial number of nematode colonization had a certain effect on the population growth of nematode,and nematode could accelerate the decomposition rate of halophyte litter.(4)Comparison of two kinds of halophytes litter decomposition of microbial biomass and enzyme activity,the results showed that the decomposition of the 64 th day,add10 nematodes of P.australis leaves micro biomass carbon(MBC)and micro biomass nitrogen(MBN)were significantly lower than not add nematodes,add 100 nematodes,but the carbon cycle related enzymes ?G and the nitrogen cycle related enzymes NAG activity were significantly increased.In S.alterniflora litters,the effects of nematode initial density on MBC and MBN were inconsistent,and there was no significant effect on ?G and NAG activities.Comparison of bacterial communities in the litters of two halophytes by high-throughput sequencing showed that: In the leaves of P.australis,the relative abundance of Proteobacteria belonging to Gram-negative bacteria was significantly increased by adding a small amount of nematodes,which was mainly manifested as the relative abundance of Azospirillum.The addition of nematodes to S.alterniflora litter decreased the relative abundance of Bacteroidetes and Proteobacteria,but significantly increased the relative abundance of Firmicutes.Add nematodes of bacterial community structure of P.australis litter significant influence,S.alterniflora litter bacteria community structure effect was not obvious.The results showed that compared with the invasion of plants,a proper amount of food in native plant litter bacteria nematodes could reduce microbial biomass,but increased the decomposition enzyme enzyme activity,changed the bacterial community structure,nematodes and bacteria food bacteria interactions would promote indigenous litter decomposition process. |
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