Elsevier

Journal of Environmental Sciences

Volume 46, August 2016, Pages 147-155
Journal of Environmental Sciences

Effects of road dust on the growth characteristics of Sophora japonica L. seedlings

https://doi.org/10.1016/j.jes.2015.08.031Get rights and content

Abstract

Road dust is one of the most common pollutants and causes a series of negative effects on plant physiology. Dust's impacts on plants can be regarded as a combination of load, composition and grain size impacts on plants; however, there is a lack of integrated dust effect studies involving these three aspects. In our study, Sophora japonica seedlings were artificially dusted with road dust collected from the road surface of Beijing so that we could study the impacts of this dust on nitrogen/carbon allocation, biomass allocation and photosynthetic pigments from the three aspects of composition, load and grain size. The results showed that the growth characteristics of S. japonica seedlings were mostly influenced by dust composition and load. Leaf N, root–shoot ratio and chlorophyll a/b were significantly affected by dust composition and load; leaf C/N, shoot biomass, total chlorophyll and carotenoid were significantly affected by dust load; stem N and stem C/N were significantly affected by dust composition; while the dust grain size alone did not affect any of the growth characteristics. Road dust did influence the growth characteristics more extensively than loam. Therefore, a higher dust load could increase the differences between road dust and loam treatments. The elements in dust are well correlated to the shoot N, shoot C/N, and root–shoot ratio of S. japonica seedlings. This knowledge could benefit the management of urban green spaces.

Introduction

Road dust is one of the most common pollutants in cities and consists of particles from atmospheric and vehicular-related deposition, as well as materials produced by soil erosion and pavement abrasion (Tang et al., 2013). Road dust can cause a series of negative effects to plant physiology; for example, by reducing diffusive resistance (Thompson et al., 1984), blocking the stomata (Farmer, 1993), increasing the absorption of infrared radiation (Eller, 1977), lowering pigment contents (Prusty et al., 2005, Prajapati and Tripathi, 2008), and restraining photosynthesis (Chaturvedi et al., 2013). However, quantitative studies of the effects of road dust are fewer than qualitative ones on this subject.

Dust's impacts on plants can be regarded as a combination of dust load, composition, and grain size impacts on plants. Studies on the effects of dust loads outnumber those on dust composition and grain size. In previous artificial dusting studies, several dust load treatments were compared (Armbrust, 1986, Shukla et al., 1990, Charlesworth et al., 2003, Kuki et al., 2009), concerning loam, fly ash, iron dust, and cement dust. As for the dust composition's effects on plants, in the ore dust studies, ore element contents and plant characteristics were often linked (Kuki et al., 2008, Neves et al., 2009). However, comparison is lacking for the ways dusts of different compositions affect plants. Studies of grain size effects on plants are rare. The stomatal conductance of plants dusted by carbon black of different grain sizes has been studied (Hirano et al., 1995). When the dust grain size was larger than the plants' stomata openings, then the particles piled up on the pores. If the grains were even smaller, then they clogged the stomata and affected the gas exchange and the growth of the plants(Rai et al., 2010). What now is lacking are integrated studies of dust effects resulting from the dust load, composition and grain size.

In North China, Sophora japonica L. is a native and widely distributed tree species. It is also the dominant street tree species planted in Beijing as it accounts for 81% of the street trees in urban areas of Beijing (Zheng and Zhang, 2011). Its growth plays an important role in adjusting the air quality and keeping the urban ecosystem healthy. In our study, S. japonica seedlings were artificially dusted with road dust collected from the road surfaces of Beijing in order to study the impacts of the road dust on nitrogen/carbon allocation, biomass allocation and the photosynthetic pigments related to dust composition, dust load and grain size.

Road dust includes high concentrations of heavy metals, such as Cd, Cr, Cu, Pb, and Zn (Charlesworth et al., 2003, Tang et al., 2013), which are different in composition from natural dusts such as loam. To highlight the dust composition effects of road dust, we used loam from an unpolluted rural area for comparison. Loam is often used to study the physical effects of dust on plants (Armbrust, 1986, Hirano et al., 1995). Road dust and loam were the two dust composition treatments used in our study. To determine the dust loads' effects, dust loads on the street trees S. japonica in our previous study and an extremely high dust load situation were simulated. As for dust grain size, a dry sieving method was used to divide the dust and loam into fine and coarse grain sizes. We assumed that the effects of dust on the growth characteristics of S. japonica seedlings would be increased with higher dust loads as well as finer dust grain sizes. The purposes of our work were to detect (1) whether dust load, composition, and grain size all impact the trees' growth characteristics; if so, then which characteristics do they impact? (2) Are there differences between road dust and loam effects on plants' growth characteristics? Do the elements in dust relate to these growth characteristics?

Section snippets

Plant experimental materials

Seed germination was performed under greenhouse conditions at the Beijing Forestry University Forest Science Co., Ltd., in April 2012. S. japonica seedlings were obtained from the germination of seeds provided by a nursery in Qingyuan County in Hebei Province. The seeds were soaked in 85–90°C water for 24 hr and then germinated in nursery trays after the seeds swelled. If the seeds did not swell properly, we repeated the soaking once or twice. Then, 20 days after emergence, the seedlings were

Effects of dust composition, load and grain size on carbon and nitrogen allocation

Based on the Multivariate ANOVA results (Table 4), dust composition and load significantly affected leaf N. Dust composition significantly affected stem N and stem C/N ratio. Dust load significantly affected leaf C/N ratio. The interaction of dust composition and load affected root N. The interaction of all three dust attributes affected root N and root C/N. As shown in Fig. 1, leaf N of the A8 treatment was significantly lower than A0. Stem N of A2, A4, A5, and A6 were significantly lower than

Growth characteristics were affected by dust

In our study, most growth characteristics were influenced by the dust. Shoot biomass, root biomass, total biomass, leaf N, stem N, chlorophyll a/b, total chlorophyll, and carotenoid of S. japonica seedlings had a declining trend after dusting, while root–shoot ratio, leaf C/N, and stem C/N had an increasing trend. A higher root–shoot ratio and lower pigments in road dust treatments corresponded to lower shoot N and higher shoot C/N. Plants allocate relatively less biomass to leaves and more to

Conclusions

Most growth characteristics of S. japonica seedlings were influenced by dust composition and load. Leaf N, root–shoot ratio, and chlorophyll a/b were significantly affected by dust composition and load; leaf C/N, shoot biomass, total chlorophyll, and carotenoid were significantly affected by dust load; stem N and stem C/N were significantly affected by dust composition; and dust grain size alone did not affect any growth characteristics. Road dust influenced the growth characteristics more

Acknowledgments

This research was supported by the National Natural Science Foundation of China (Project 41430638 to KMM). The authors express their appreciation to the laboratory members, especially Mr. Guorui Xu for providing assistance in cultivation and measurements of materials.

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