Changes in nutrients and decay rate of Ginkgo biloba leaf litter exposed to elevated O3 concentration in urban area.

Wei Fu,Xingyuan He,Bo Li,Sheng Xu,Lili Su,Wei Chen,Yan Li,Qin Ping

doi:10.7717/peerj.4453

Wei Fu, Xingyuan He + Show 6 more

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https://doi.org/10.7717/peerj.4453

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Abstract

Ground-level ozone (O3) pollution has been widely concerned in the world, particularly in the cities of Asia, including China. Elevated O3 concentrations have potentially influenced growth and nutrient cycling of trees in urban forest. The decomposition characteristics of urban tree litters under O3 exposure are still poorly known. Ginkgo biloba is commonly planted in the cities of northern China and is one of the main tree species in the urban forest of Shenyang, where concentrations of ground-level O3 are very high in summer. Here, we hypothesized that O3 exposure at high concentrations would alter the decomposition rate of urban tree litter. In open-top chambers (OTCs), 5-year-old G. biloba saplings were planted to investigate the impact of elevated O3 concentration (120 ppb) on changes in nutrient contents and decomposition rate of leaf litters. The results showed that elevated O3 concentration significantly increased K content (6.31 ± 0.29 vs 17.93 ± 0.40, P < 0.01) in leaves of G. biloba, significantly decreased the contents of total phenols (2.82 ± 0.93 vs 1.60 ± 0.44, P < 0.05) and soluble sugars (86.51 ± 19.57 vs 53.76 ± 2.40, P < 0.05), but did not significantly alter the contents of C, N, P, lignin and condensed tannins, compared with that in ambient air. Furthermore, percent mass remaining in litterbags after 150 days under ambient air and elevated O3 concentration was 56.0% and 52.8%, respectively. No significant difference between treatments was observed in mass remaining at any sampling date during decomposition. The losses of the nutrients in leaf litters of G. biloba showed significant seasonal differences regardless of O3 treatment. However, we found that elevated O3 concentration slowed down the leaf litter decomposition only at the early decomposition stage, but slightly accelerated the litter decomposition at the late stage (after 120 days). This study provides our understanding of the ecological processes regulating biogeochemical cycles from deciduous tree species in high-O3 urban area.

Highlights

In recent decades, due to the large increases in the emission of O3 precursors including NOx and VOCs around the world, the ground-level O3 concentrations are constantly increasing, in Asia (Sitch et al, 2007; IPCC, 2013)
It is estimated that the O3 concentration in the troposphere will increase by 40% to 60% by 2100 (Akimotoa et al, How to cite this article Fu et al (2018), Changes in nutrients and decay rate of Ginkgo biloba leaf litter exposed to elevated O3 concentration in urban area
We found that elevated O3 showed no significant impact on chemical compositions and decay rates of G. biloba, it decreased the contents of C, P, C/N ratio, lignin, total phenols, condensed tannins, and soluble sugars in G. biloba leaves by the end of gas fumigation

Summary

Introduction

Due to the large increases in the emission of O3 precursors including NOx and VOCs around the world, the ground-level O3 concentrations are constantly increasing, in Asia (Sitch et al, 2007; IPCC, 2013). O3 effects on litter decomposition in urban forests have not yet been explored Filling such gap is important, as in urban ecosystems, where tropospheric O3 concentration can be very high due to photochemical air pollution; urban trees play a fundamental role in mitigating air pollution (Manes et al, 2012). Their leaf litter, if decaying faster when exposed to high O3 concentration, would improve soil chemical properties and promote nutrient cycles, affecting the sustainable development of urban areas (Nikula, Vapaavuori & Manninen, 2010; Xu et al, 2012)

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