Ecological Adaptation And Mechanism Of Three Cold-season Turfgrasses To Nitrogen Deposition Under Different Nutrient Environments

Human activities have accelerated the global nitrogen cycle,and China is one of the regions with the most serious nitrogen deposition in the world.Excessive nitrogen deposition can affect the productivity,species diversity and soil microbial characteristics of various ecosystems.Nitrogen deposition will lead to the enrichment of nitrogen in the soil.When nitrogen exceeds the soil capacity,it will cause irreversible damage to the local ecosystem.At present,there is no unified conclusion and law on the impact of nitrogen deposition,which depends not only on the degree of nitrogen deposition,but also on different ecological and environmental factors,such as ecological type,soil nutrient level and climatic conditions.The soil nutrient levels in urban lawn grass planting areas are different,and their responses to nitrogen deposition are also different.The systematic study on the response of turfgrass to nitrogen deposition in different nutrient environments is helpful to better understand the effect of nitrogen deposition on turfgrass ecosystem and its mechanism.This is conducive to guiding the restoration and protection of urban ecological environment,and taking corresponding management measures to reduce the negative impact of nitrogen deposition on the ecosystem and promote the sustainable development of urban ecological environment.In this study,Lolium perenne L.,Trifolium repens L.and Medicago sativa L.,which are common cold-season turfgrasses in Yantai City,were selected as the research objects.Pot experiments were conducted to set up soils with different nutrient levels,simulate different nitrogen deposition intensities,and detect plant growth indexes,soil physical and chemical properties,soil microbial community diversity,structure and ecological functions,especially soil microbial nitrogen cycle related functions.To reveal the effects of soil nutrient levels on the adaptation strategies of different plants to nitrogen deposition under the background of nitrogen deposition.The main results are as follows:(1)Nitrogen deposition and different nutrient levels had significant effects on the biomass of three turfgrasses,especially aboveground biomass.When the nutrient content is low,nitrogen deposition can promote its growth;when the nutrient content is high,nitrogen deposition will inhibit its growth.The biomass of Lolium perenne L.was less affected by different soil nutrient levels than that of white clover and Medicago sativa L.,indicating that Lolium perenne L.has a higher ability to adapt to nitrogen deposition.(2)Taking Lolium perenne L.planting soil as an example,according to the results of relative quantitative sequencing analysis of soil bacterial community amplicons,with the increase of nitrogen deposition,Latescibacterota showed a trend of decreasing first and then increasing,Actinobacteriota showed a gradual downward trend,and Nitrospirota showed a gradual upward trend.With the increase of soil nutrient levels,Nitrospirota showed a gradual upward trend,Acidobacteriota and Myxococcota showed a gradual downward trend.(3)With the increase of soil nutrient levels,the abundance of nitrogen metabolism related genes amoA,amoB,amoC,Hao,narG,narH,narI,napB,nirK and norC increased,and the abundance of nifD and nifK decreased.With the increase of nitrogen deposition,in the low nitrogen deposition treatment,the abundance of amoB,amoC,nifK,nifD,nifH,norC,nosZ,nirB,nirD and nrfH increased,and the abundance of nasA and nasB decreased.In high nitrogen deposition treatment,the abundance of amoB,amoC,nirD,nrfH and norC increased,while nasA,nasB,nir B,nifD,nifK,nifH and nosZ decreased.Nitrogen deposition was always proportional to soil available nitrogen,and soil nutrient level was only correlated with soil available nitrogen in high nitrogen deposition treatment.Soil nutrient levels mainly affect the nitrification,denitrification and nitrogen fixation processes in the soil,and high nutrient levels may increase nitrogen emissions;the nitrogen deposition level suitable for soil nutrient level can promote nitrogen metabolism.High nitrogen deposition slows down nitrogen fixation,accumulates soil nitrate,and damages soil environment.In summary,under different soil nutrient levels,the three cold-season turfgrasses have different strategies to cope with nitrogen deposition.In comparison,Lolium perenne L.has stronger nitrogen adaptability under different soil nutrient levels,and the nitrification process and denitrification process in the soil are accelerated.Among them,the nitrogen cycle related genes in the Lolium perenne L.planting soil are closely related to its aboveground biomass and soil physical and chemical properties.Its strong nitrogen deposition adaptability is to accelerate the nitrogen cycle by increasing the abundance of functional genes in the nitrification and denitrification processes of the soil microorganisms,and to ensure that its biomass is improved at low soil nutrient levels,thereby maintaining the stability of the system lawn grass productivity and also accelerating the nitrogen cycle,revealing the ecological adaptation and mechanism of Lolium perenne L.to nitrogen deposition from the gene level.This study found that soil nutrients have an important impact on the nitrogen deposition adaptation mechanism of lawn grass,which provides a new theoretical basis for further understanding participation of soil microorganisms in biogeochemical cycles and urban ecological environment.