The Effects Of Nutrients Input And Enclosure Treatment On Soil Nematode Community In Degraded Grassland

Nematodes are the most abundant and diverse invertebrate metazoans in terrestrial ecosystems.They occupy multiple trophic levels in the soil detritus food web and play important role in energy flow and nutrient cycling.The community structure and diversity of soil nematodes can reflect changes of ecosystem functioning.In the past decades,large-scale grassland in China has been degraded to varying degrees due to unreasonable development and utilization,such as overgrazing.Exogenous nutrient input and grazing enclosure are important management strategies to maintain the nutrient balance of grassland ecosystem and restore its ecological and productive functions.Both nutrient inputs and grazing enclosure can affect soil nematode community by changing plant community composition and soil physical and chemical characters.While there is mounting evidence showing the effects of fertilization and grazing enclosure on the soil nematode community in mature and/or undisturbed grassland of China,few studies have focused on the soil nematode community in degraded grassland,although degraded grassland ecosystems are widespread.In this study,I first examined the effects of nitrogen input on soil nematode abundance,trophic group composition,and community structure in different seasons in degraded grassland ecosystem based on a controlling experimental setup located in Xilin Gol of Inner Mongolia.Further,I revealed whether such impacts of N inputs on soil nematode community would be dependent on the changes of phosphorus availability.Last,I examined the interactive effects of nutrient inputs and grassland management strategies in driving the changes of soil nematode community.The main results are as follows:(1)The dominant genera of soil nematodes in degraded steppe of Xilin Gol:Chiloplacus,Acrobeles,Cervidellus,Tylencholaimus,Aphelenchoides,Thonus,and Scutylenchus.(2)The effects of nitrogen input on nematode community abundance significantly varied among different months(P = 0.019).Nitrogen input significantly increased the maturity index of free living soil nematode(P < 0.001),indicating that nitrogen input improved soil health and increased the stability and complexity of soil nematode community.(3)Nitrogen input and phosphorus input significantly interacted to affect the total abundance of soil nematodes in this degraded grassland(P = 0.011),which showed that nitrogen input inhibited the positive effects of phosphorus input on the total abundance of soil nematodes.The results showed that the effects of different types of nutrients on soil nematode abundance were not additive.Both the main and interactive effects of nitrogen input and phosphorus input on soil nematode diversity were not statistically significant.Neither nitrogen input nor phosphorus input changed the decomposition pathway of the soil as indicated by the stable soil nematode community composition,with bacterial decomposition as the dominant pathway.With the presence of livestock grazing,nitrogen input significantly increased the maturity index of soil nematode community(P = 0.009),reduced the plant parasitic index(P <0.001),and weakened the positive effect of phosphorus input on plant parasitic index(P = 0.002),indicating that nitrogen input can reduce negative external disturbances such as livestock grazing,improve soil health,and promote the complexity of soil nematode community and below-ground food web in this degraded grassland.(4)The effects of nutrients input on soil nematode community was significantly dependent on different grassland management strategies.Nutrients input and grazing enclosure significantly interacted to affect the total abundance of nematodes,in that the positive effect of grazing enclosure on soil nematode abundance only presented in the absence of nutrients input.Nutrients input and grazing enclosure did not affect soil nematodes diversity in this degraded grassland,but they significantly interacted to affect maturity index(P = 0.003)and plant parasitic index(P = 0.005)of soil nematode community.Under the treatments with nutrients input,grazing enclosure weakened the negative effect of nutrient inputs on maturity index and its positive effect on plant parasitic index.Grazing enclosure alleviated the disturbance of nutrients to the soil environment,improved the stability and complexity of below-ground food web,and promoted the positive succession of underground community.In summary,nitrogen input significantly affected the abundance and community structure of soil nematodes,the effect of nitrogen input on soil nematode community was regulated by the state of phosphorus in soil.Nitrogen input inhibited the positive effect of phosphorus input on nematode abundance,but also alleviated the negative effect of phosphorus on the stability of soil nematode community.The effect of nutrient input on nematode community was regulated by grassland managementmeasures.Enclosure treatment could alleviate the negative effect of nutrient input on soil environment and nematode community and promote the positive succession of subterranean community.