Human footprints in urban forests: implication of nitrogen deposition for nitrogen and carbon storage

Abstract

Purpose Rising levels of nitrogen (N) deposition are influencing urban forest carbon (C) and N dynamics due to greater human disturbance compared to those in rural areas. N deposition in combination with increased atmospheric carbon dioxide (CO 2 ) and water limitation may alter C and N storage in urban forests. This review aimed to provide a better understanding of N and C storage under N deposition scenarios in urban forests. Results and discussion Globally, fuel combustion and biomass burning contribute in approximately 70 and 16 % of the NO x emission respectively. It is also estimated that NH y and NO x are two to four times higher in urban forests compared to rural areas. However, higher N deposition may not always result in increased N and C storage in urban forests. In fact, urban forests may even show early symptoms of N and C losses under climate change. For example, urban forests in fire-prone areas require higher frequency of burning to reduce the threat of wildfires, leading to an acceleration of C and N loss. Additionally, chronic N deposition may result in an early N loss in urban forests due to faster N saturation and soil acidification in urban forests compared to rural forests. Studies of N deposition on urban forests using N isotope composition (δ 15 N) also showed that N loss from urban forests can occur through the direct leaching of the deposited NO 3 − -N.We also noted that using different 15 N signal of soil and plant in combination of tree ring δ 15 N may provide a better understanding of N movement in urban forests.Conclusions Although urban forests may become a source of C and N faster than rural forests, N-limited urban forests may benefit from N deposition to retain both N and C stocks longer than non-N-limited urban forests. Appropriate management practices may also help to delay such symptoms; however, the main source of emission still needs to be managed to reduce both N deposition and rising atmospheric CO 2 in urban forests. Otherwise, the N and C stocks in urban forests may further decline when prolonged drought conditions under global climate change increase the frequency of fires and reduce plant photosynthesis.

Application of manures to mitigate the harmful effects of electrokinetic remediation of heavy metals on soil microbial properties in polluted soils

“…Furthermore, organic treatments increase soil organic C and nutrients due to high organic content (Darby et al 2016;Nguyen et al 2017). Soil organic C is the primary source of C for soil microorganisms and has been reported to influence soil microbial activities (Bardgett 2005;Darby et al 2016;Flessa et al 2000;Hosseini Bai et al 2015). The negative effects of increasing the toxicity of heavy metals by EK might have been offset by the stimulation effects of CME and PME on soil microbial biomass, activity and abundance.…”

Nitrogen cycling and urban afforestation success inNew York City

“…These losses are a concern in forest ecosystems, as they reduce availability of a limiting nutrient and can cause eutrophication in receiving waters (Galloway et al, 2004). High nitrification is often associated with site disturbance (Bormann & Likens, 1979;Vitousek et al, 1979) and urban forests are subject to a wide range of stressors inherent to cities that can disrupt soilplant-microbial interactions and stimulate nitrification (Bai et al, 2015;Bednova et al, 2018;Bulbovas et al, 2020). N losses can also occur through denitrification, the microbial process that converts NO 3 À to gaseous forms (NO, N 2 O, and N 2 ; Robertson & Groffman, 2015).…”