Citywide tree planting in urban cities is occurring rapidly because of the benefits urban vegetation provide to the environment. Nutrient cycling in tropical urban ecosystems is relatively unknown. Nitrogen utilisation in urban and rural conditions can vary substantially hence foliar N characteristics of two common tree species grown in the tropics was compared between urban roads and parkland sites. The study was carried out in the tropical island state of Singapore situated 1° north of the equator. Foliar sampling of nitrate reductase, %C, %N, δ¹³C and δ¹³N in two tree species grown along urban roads and parklands were evaluated. Foliage sampled along roads were depleted of δ¹⁵N compared to parkland foliage. Significantly higher levels of δ¹³C, nitrate reductase activity (NRA), %C and %N were found in the northern and southern Parklands. Samanea saman, and Khaya senegalensis showed significantly greater ability to assimilate nitrate at the park sites, measured through NRA. There were no significant differences in foliar N and C characteristics between tree species. Significant variation in foliar N and C concentrations were only observed between regions and at park and road sites. The isotopic and %N data suggested greater N availability and higher available nitrate at park sites as a result of variable site histories. These previous land use, land cover change may have accumulated organic matter in the rhizosphere primarily in the stable form of humus alongside that of biological nitrogen fixation. N cycling in urban systems and associated physiological changes in vegetation is critical as these may have implications for carbon sequestration, while N retention or export can impact on water quality in urban environments.

中文翻译：

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城市道路和公园地带两种热带树木的叶氮特征

由于城市植被为环境带来的好处，城市中的全市植树活动正在迅速开展。热带城市生态系统中的养分循环相对未知。城乡条件下的氮利用差异很大，因此在城市道路和绿地之间比较了热带地区两种常见树种的叶片氮素特性。这项研究是在赤道以北1°的热带岛屿国家新加坡进行的。硝酸还原酶，％C，％N，叶面采样δ ¹³ C和δ ¹³ N的沿城市道路和公园中生长2个树种进行了评价。叶子沿着道路采样被耗尽的δ ¹⁵ N进行比较，以草木叶子。显著较高水平δ的¹³C，硝酸盐还原酶活性（NRA），％C和％N在帕克兰北部和南部发现。Samanea saman和塞内加尔海牙通过NRA测得的结果表明，在公园场所吸收硝酸盐的能力明显增强。树种之间的叶片氮和碳特征无显着差异。仅在区域之间以及公园和道路站点观察到了叶面氮和碳浓度的显着变化。同位素和％N数据表明，由于地点历史的变化，公园地点的N利用率更高，硝酸盐含量更高。这些先前的土地利用，土地覆被变化可能已经以稳定的腐殖质形式以及生物固氮的形式在根际中积累了有机质。城市系统中的N循环以及相关的植被生理变化至关重要，因为它们可能会对碳固存产生影响，