Influencing Mechanism Of Long-term Fertilization On Microbial Communities In Wheat Field Of Lime Concretion Black Soil

Lime concretion black soil is an ancient cultivated soil widely distributed in the Huanghuaihai Plain of China,which is mainly distributed in northern Anhui.However,its tillage traits are not good.At present,the key measures for the sustainable development of the agricultural ecosystem in the area of lime concretion black soil are "forest management" and "fertilization management".At present,a complete shelter-forest network for fields has been constructed in northern Anhui.At the same time,a long-term fertilization experiment station has been set up,and it is found that long-term fertilization have a significant impact on the soil microbial community.In agroecosystems,crop roots divide the lime concretion black soil into three different habitats: bulk soil(BS),rhizosphere(RS)and root endosphere(ES).The communities of microorganisms living in these three microhabitats are similar but also significantly different from one another.In particular,microorganisms living in the rhizosphere and root endosphere play an extremely important role in crop growth,physiology and health due to their closer interactions with crop plant.However,there is still a lack of research on detailed comparative studies of microbial communities in these three microhabitats.Therefore,a comprehensive study of soil and root microbial communities should take into account the potential problems that soil and crops may face under different fertilization regimes,and can provide a scientific basis for the sustainable development of agricultural production.In this study,based on an experimental system of long-term fertilization in lime concretion black soils in Mengcheng,Anhui province,using modern molecular biology techniques,we systematically compared the influencing mechanism of long-term fertilization on different habitats in wheat field of lime concretion black soil.The main results of this study are as follows:(1)Long-term different fertilization managements had a significant impact on the agricultural productivity in lime concretion black soils.Long-term NPK treatment could significantly improve soil fertility and root nutrient contents,but at the same time,it could lead to a significant decrease of soil p H,and a large accumulation of root manganese.The combined application of organic materials could further increase the nutrient contents of soil and root,and reduce the stoichiometric ratio between nutrients such as carbon,nitrogen and phosphorus.However,the supplement of straw could not alleviate the decline of soil p H in BS and RS,and the excessive manganese content of root;while the supplement of manure,especially cow manure,could significantly increase the p H of BS and RS,and significantly reduce the manganese content of roots.Among all fertilization treatments,NPKM had the highest yield-increase rate with 26.3 % relative to NPK treatment.(2)Both habitat and fertilization had significant effects on bacterial diversity,community structure and functional composition.The bacterial diversity in ES was the lowest.The relative abundance of Proteobacteria,Bacteroidetes and Firmicutes increased significantly in ES,and Fusobacteria was also increased in ES.NPK addition significantly decreased the bacterial richness in three habitats;but the addition of manure significantly restored the bacterial richness only in BS.CPA analysis showed that a gradually weakened effect of fertilization on bacterial community composition from BS to RS to ES,with the explanation rate of fertilization to the three habitats were 49 %,44 % and 38 %,respectively.The relative abundance of r-strategy bacterial groups such as Firmicutes decreased significantly,while the relative abundance of k-strategy bacterial groups such as Acidobacteria increased significantly under long-term fertilization regimes.However,the addition of manure significantly promoted the growth of r-strategist bacterial groups.The change in bacterial community composition in BS and RS was mainly driven by p H,which the independent interpretation rates of the bacterial community changes in BS and RS were up to 48 % and 38 %,respectively.The change of bacterial community composition in ES was mainly related to the root TP and C/P ratio,which the total interpretation rate could reach 33 %.In addition,it was found that the influence of fertilization on the functional structure of bacterial community predicted by Tax4 Fun was similar to that of bacterial community structure.(3)Habitat had a significant impact on the fungal diversity and community structure.The fungal diversity in ES was lowest,but it had the highest proportion of special fungal OTUs.Ascomycota,Basidiomycota and Mortierellomycota were the dominant fungal phyla in the three compartments,but in terms of community composition of the three habitats were significantly different from one another.There was no significant effects of fertilization on fungal diversity,but the treatment of NPKP significantly reduced the diversity in BS and RS,which was due to the significant increase of P and Zn caused by pig manure added.However,different fertilizer treatments had significant effects on the fungal community structure in the three habitats,and the explanatory rates in BS,RS and ES were 55.2 %,51.9 % and 37.1 %,respectively.Mantel test showed that the changes of fungal community composition in BS,RS and ES were mainly related to AP,TP and root C/P ratio,respectively.In addition,the prediction of fungal functional groups by FUNGuild revealed that there were more pathogenic fungi in RS and ES than in BS.Further analysis of indicator species showed that there were relatively abundant beneficial fungi such as Pseudaleuria and Mortierella in the treatment of NPKP,suggesting that the addition of pig manure might reduce the existence of pathogenic fungi through the existence of competitive beneficial fungi.And the addition of cow manure might reduce the pathogenicity by promoting the presence of fungi with anti-fungal activity.(4)Both habitat and fertilization had significant effects on arbuscular mycorrhizal fungal(AMF)diversity,community structure and co-occurrence network.The diversity of AMF in ES was significantly lowest.The community in BS,RS and ES was dominated by Glomeraceae,Claroideoglomeraceae,and Paraglomeraceae,respectively.And the network analysis showed that the co-occurrence network of AMF community in ES was the most complex and stable.The responses of the AMF community in ES was completely different from that in RS or BS.The results of correlation analysis showed that the increases of AMF diversity and relative abundance of Paraglomeraceae in ES were mostly correlated with root manganese.The main factors affecting the composition of AMF communities in BS,RS and ES were soil p H(correlation coefficient 0.62),available phosphorus(correlation coefficient 0.55)and root C:P ratio(correlation coefficient 0.66),respectively.In addition,the richness of AMF was the most important factor affecting the co-occurrence network of AMF both in RS and ES,and the explanatory rates of the changes RS and ES networks are 75 % and 39 %,respectively.(5)Network patterns of the microbial communities(bacteria,fungi and AMF)were significantly different between RS and ES.Compared with RS,the microbial co-occurrence network in ES had lower nodes and edges,but higher connectance,connectedness and transitivity,indicating the network in ES was more complex,cohesive and stable.And the network in ES contained a higher proportion of AMF species(18.0 %).We also found that the competitive relationships of the co-occurrence network in RS mainly existed among bacterial species,while competitive relationships of the co-occurrence network in ES mainly existed among fungal species.In addition,fertilizer treatments had no significant effect on the microbial co-occurrence network in ES,however,had a significant effect on that in RS.The effects was mainly caused by the influence of p H,and its explanatory rate could reach about 50.3 %.In addition,it was found that five fungal keystones of the network in RS,and three AMF keystones of the network in ES though netwrok analysis.Module analysis found module 3 of the network in RS and module 1 of the network in ES were significantly correlated with crop yield,suggesting that the species in the two modules and their interaction might play an important role in the potential process of crop yield promotion by fertilization.