Effects Of Nitrogen Deposition On Urban Green Space(Cynodon Dactylon)

Atmospheric nitrogen deposition was a highlight of global change research.With the conception and development of eco-city,people have pay more attention to the ecological significance?Biodiversity protection?and environmental value?Cooling and Humidification,Carbon-fixing and Oxygen-releasing,Anti-pollution,Noise Reduction?of urban green space.Therefore,nitrogen deposition may affectto urban green systems,which including plants,soil,and soil fauna and so on.However,there are limit studies so far on the impacts of nitrogen deposition on the increasing urban green spaces.To clarify such effects on the typical urban grasses?Cynodon dactylon?,soil physical and chemical properties and soil fauna,one control experiment was conducted for one year term,in which NH₄NO₃ was added as the external nitrogen sources with four treatments of nitrogen addition(0 g·m^-2·a^-1?N0?,5g·m^-2·a^-1?N1?,10 g·m^-2·a^-1?N2?and 15 g·m^-2·a^-1?N3?).The results showed that:?1?Appropriate amount of nitrogen deposition is beneficial to the growth and biomass accumulation of plant.The above and underground biomass and the density of the green grass reached maximum with the N1 treatment,while the plant height was maximum with the N2treatment.The ratio of root-shoot was decreased with the increasing nitrogen addition from N0 to N3.?2?Nitrogen deposition changes the available nutrient supply of grass.The N content of plants are increase with increasing nitrogen deposition.Nitrogen treatment doesn't effect on the total carbon content of plant.Low-nitrogen(5g·m^-2·a^-1)and medium-nitrogen(10 g·m^-2·a^-1)less the the total phosphorus content of plant while high-nitrogen(15 g·m^-2·a^-1)increase the the total phosphorus content of plant.Nitrogen deposition reduce the C:N and C:P ofplants.Low-nitrogen(5g·m^-2·a^-1)increase the N:P of plants,but with the increasing of nitrogen deposition,the N:P of plants is reduced.Greens grass growth is still limited by N.?3?Nitrogen deposition causes changes in soil chemical properties.The soil pH is decreased with the increasing nitrogen deposition.Low nitrogen deposition can neutralize the alkaline soil.With the increasing of nitrogen deposition,the available nitrogen content is increased.?4?The critical point for negative effects of nitrogen addition on soil fauna in this experiment is around 5 g·m^-2·a^-1.Treatment of medium-nitrogen(10 g·m^-2·a^-1)and high-nitrogen(15 g·m^-2·a^-1)inhibits soil fauna diversity.The effects of nitrogen deposition on soil fauna are mainly due to changing of soil environmental factors,which caused by nitrogen deposition,and pH is the main factor which affects soil fauna.Soil fauna can be one of the biological indicators respond nitrogen deposition on urban soil in the context of urbanization.?5?There is a threshold on the effects of nitrogen deposition on urban green space ecosystem.We should focus on the regional changes of nitrogen deposition in future studies,and find out the critical value of the negative effects that nitrogen deposition brings to the plant growth and environmental indices of urban green space.