| There is a close relationship between wetlands and migratory birds.Wetlands are the home of migratory birds,and migratory birds are an important part of the wetlands.Global wetland degradation has brought about a reduction in the habitat of migratory birds,which has caused migratory birds to gather in some habitats.The Poyang Lake wetlands is the largest wintering site for migratory birds in Asia.In recent years,the number of migratory birds overwintering in the Poyang Lake wetlands has shown an increasing trend.The increase in the number of migratory birds will bring more feces input,but what kind of ecological impact this will bring to the soils of the Poyang Lake wetlands is still unknown.On the other hand,due to global warming and food shortages on migratory routes,part of the species of overwintering migratory birds has changed from migratory birds to resident birds,which has caused the species and number of resident birds in the wetlands of Poyang Lake to continue to increase.However,at present,we are not clear about the difference in the impact of migratory bird and resident bird feces on wetland soil,so we cannot assess what impact the conversion of migratory birds to resident birds will have on the Poyang Lake wetlands.Thus,this study carried out the following two parts of research in the Duchang Migratory Bird Provincial Nature Reserve during2019-2020: 1)field observation experiments,sampling and analysis of soil and feces were carried out before the arrival of winter migratory birds,during the peak of migration,and after their departure,to explore the impact of migratory bird feces input on wetland soil physicochemical indicators and microbial communities;2)Through indoor simulation experiments,to explore the difference in the impact of migratory bird and resident bird feces input on wetland soils.In this study,the physicochemical properties of the samples were analyzed by environmental chemistry methods,and the soil microbial community structure was analyzed by 16 S r RNA gene sequencing technology.Through the statistical analysis of these two parts of data,the following research results were obtained:1.Our field experiments showed that the input of migratory bird feces significantly increased soil nutrients,increased the ecological risk of soil heavy metal pollution,and significantly changed the soil bacterial community structure,reduced the niche differentiation and species interaction of the bacterial community,and decreased the stability of the bacterial community.The specific results were as follows:(1)After the entire overwintering period of migratory birds,the total organic carbon(TOC),total nitrogen(TN)and cadmium(Cd)content in the wetland soils increased significantly,reaching 25.74 g/kg,3.24 g/kg,and 5.02 mg/kg,respectively.The diversity and ecological functions of the bacterial community did not change significantly,but the species composition changed significantly(p < 0.05),which was mainly reflected in the significant reduction of the relative abundance of Gammaproteobacteria and Bacteroidia.(2)The impact of migratory bird feces input on wetland soil was closely related to the number and duration of migratory birds.This impact was most significant during the peak period of migratory bird migration,and the impact gradually weakened after the migratory birds leave.The large amount of fecal input from migratory birds during the peak period significantly increased the diversity of the bacterial community in the wetland soil(p < 0.05),increased in the relative abundance of the Deltaproteobacteria and Bacteroidia,but the relative abundance of Alphaproteobacteria and Actinobacteria was reduced.In addition,the results indicate that the dominant species in the feces of migratory birds,such as Firmicutes,have not been enriched in wetland soils.2.Compared to migratory birds,the input of resident bird feces increased the carbon content of wetland soil while depleting phosphorus and reduced the activity of phosphatase.The dominant species in resident bird feces werenot only enriched in soils,but also resident bird feces input increased the niche differentiation and species interaction of the bacterial community and improved the stability of the bacterial community.The specific results were as follows:(1)After 45 days of fecal impact,compared to migratory birds,the content of microbial biomass carbon(9.41 mg/kg)in soils affected by resident bird feces was significantly increased,but the activity of Phos was significantly reduced(29.66nmol/h/g).The dominant components in the feces of resident birds,Firmicutes was enriched in the soil.(2)The impact of feces input on the soil changed over time.The impact on the physicochemical properties of the soil and the composition of bacterial communities were the largest on day 7,but the impact on the microbial activity was the largest on day 15.From the overall perspective of the entire experimental cycle,compared to migratory birds,the fecal input of resident birds brought higher accumulation of MBC,reaching 12.63 mg/kg,but it would also brought the decrease of TP content and Phos activity,which were 0.20 g/kg and 25.10 nmol/h/g respectively.The input of feces from migratory birds increased the diversity of soil bacterial communities in the short term,while the input of feces from resident birds had no significant impact on the diversity of bacterial communities.Compared to migratory birds,the relative abundance of Proteobacteria and Gammaproteobacteria in soils affected by bird feces increased significantly,while the relative abundances of Chloroflexi and Acidobacteriota decreased significantly.The input of resident bird feces reduced the relative abundance of functions such as Energy metabolism,Metabolism of cofactors and vitamins in the wetland soil.The input of resident bird feces led to the reduction of the material metabolism level of the soil bacterial community,which might be related to the reduction of phosphorus in the soil to form phosphorus restriction.The input of resident bird feces increased the niche differentiation of the bacterial community and the ability to resist external disturbances,and increased the stability of the bacterial community,while migratory birds did the opposite.At the same time,our study also found that differences in bird species and feeding habits could significantly affect the effect of bird feces on soil,which was more significant than differences in bird residence types.In conclusion,this study scientifically assessed the effects of fecal input of wintering migratory birds and the transition of migratory birds to resident birds on wetland soils.The research results indicate that the increasing input of migratory bird feces is of great significance to alleviate the degradation of wetland soil fertility and biodiversity,and that the input of resident bird feces plays an important role in increasing the stability of the soil bacterial community in wetlands.Therefore,the research results will help us to understand the interaction between wintering migratory birds and wetland soils more comprehensively and provide technical supports and theoretical bases for better protection of migratory birds and wetlands. |
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