Foliar nitrogen characteristics of two tropical tree species along urban roads and parklands
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Foliar nitrogen characteristics of two tropical tree species along urban roads and parklands Lai Fern Ow 1 & Subhadip Ghosh 1 & Mohd Lokman Yusof 1
# Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract 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. Keywords Foliar nitrogen . Nitrate reductase . Parklands . Stable isotopes . Urban roads
Introduction Nitrogen (N) is an essential nutrient required by plants (Resh et al. 2002; Forrester et al. 2006). However, urbanization alters ecosystem functioning (Miller and Small 2003) and can lead to habitat destruction through land use change (e.g. soil alterations), and extreme atmospheric conditions (Nowak 2000; Baxter et al. 2002; Li et al. 2013). Therefore, soil is often found to be of poorer quality in urban areas as compared to rural sites (Nowak et al. 2006; Jiang et al. 2009). One key concern of urbanization is the change in N cycling and availability. Changes in N cycle can have significant effects on ecosystem function and species composition (Schlesinger 2009; Butler et al. 2012).
* Lai Fern Ow [email protected] 1
Centre for Urban Greenery and Ecology, National Parks Board, Singapore Botanic Gardens, 1 Cluny Road, Singapore 259569, Singapore
In urban areas, N deposition from anthropogenic emissions has increased N availability (Aber et al. 1998) by 3– 5 tim
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