大气氮沉降是近年来全球变化研究的焦点问题之一,大量而持续的氮沉降对陆地生态系统造成了广泛的影响,但关于氮沉降对城市绿地生态系统的影响及其机制仍然缺少足够的研究.通过模拟氮沉降控制试验,以 NH4NO3作为外加氮源,设置了N0、N1、N2和N3(分别相当于氮沉降0、5、10、15 g·m-2·a-1)4个不同处理,历时12个月,探讨不同程度氮沉降增加对典型城市绿化物种果岭草(Cynodon dactylon)生长状况及土壤化学性质的影响.研究结果表明:(1)氮沉降量为5 g·m-2·a-1时,果岭草地上、地下生物量以及植株密度最大;氮沉降量为10 g·m-2·a-1时,株高最高;根冠比随着施氮量的增加呈减小趋势;适量氮沉降处理有利于植株的生长以及生物量的积累;同时,降水的季节变化可能影响植物对氮的吸收利用;(2)城市绿地土壤pH值随施氮量的增加呈减少趋势,低度适量的氮沉降作用于城市碱性土壤可以中和土壤酸碱度,调节土壤pH值;(3)施氮处理使得城市绿地土壤中的有效氮含量和城市绿地生产力得到一定程度提高.本研究结果证明氮沉降将对城市绿地植物及土壤理化性质产生持续的影响,同时一定程度的氮沉降对城市绿地植物生产力的提高具有促进作用.%Atmospheric nitrogen deposition was a highlight of global change research. There were limited 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)and the soil chemical properties,one control experiment was conducted for one year term,in which NH4NO3was added as the external nitrogen sources with four treatments of nitrogen addition (0 g·m-2·a-1(N0), 5 g·m-2·a-1(N1), 10 g·m-2·a-1(N2) and 15 g·m-2·a-1(N3)). Results showed that: (1) 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 N2 treatment. The ratio of root-shoot was decreased with the increasing nitrogen addition from N0 to N3. Appropriate amount of nitrogen deposition is beneficial to the growth and biomass accumulation of plant. However, seasonal variation of precipitation may affect the nitrogen absorption and utilization of plant. (2) The soil pH was decreased with the increasing nitrogen deposition. Low nitrogen deposition could neutralize the alkaline soil. (3) With the increase of nitrogen deposition, the available nitrogen content was increased. The increasing of nitrate nitrogen and ammonium nitrogen would increase the productivity of urban green spaces. These results showed that nitrogen deposition will have a sustained impact on urban green space (UGS). To some extent nitrogen deposition would increase the productivity of urban green spaces.
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