Photosynthesis of alfalfa (Medicago sativa) in response to landfill leachate contamination
Introduction
Landfill leachate is a vital pollution source resulting from municipal landfill especially for unlined landfills and open dumpsites due to high content of nitrogen, organic pollutants, salty ions et al. (Renou et al., 2008, Huang et al., 2009). Unlined landfills and open dumpsites have put great threat on the security of soil and ground water due to leachate leakage (Ahmed and Sulaiman, 2001). Therefore the leaching characteristics of leachate contaminated soils are of great importance for pollutant migration. Phytoremediation is widely utilized in various kinds of contaminated soils based on excellent adaptation (Fu et al., 2012) and capacity of rhizosphere extraction (Belouchrani et al., 2016). Alfalfa was applied for soil phytoremediation of both inorganic and organic pollution, such as heavy metals (Zaefarian et al., 2013), benzo[a]pyrene (Fu et al., 2012), salts (Cao et al., 2012) and so on. It could be deduced that alfalfa is potential for complex contaminations like landfill leachate. Although several plants were employed to remove the complicated pollutants in landfill leachate according to previous studies (Pazoki et al., 2014, Lavagnolo et al., 2016), alfalfa was rarely applied on the phytoremediation of leachate contaminated soils.
It is worth mentioning that the toxicity of landfill leachate has been frequently reported. The investigation for the effects of leachate on the physiological features of alfalfa is desirable before the phytoremediation application. Photosynthesis is one of the most important processes of plant metabolism, and widely used as response characteristics to various pollution (Aristilde et al., 2010, Pan et al., 2011, Han et al., 2016). Among the parameters of photosynthesis, Fv/Fm and Pn were the most frequently applied in the variations of photosynthesis (Cambrollé et al., 2014). In this study, the response of photosynthesis to various leachate dosages were investigated and the correlation between leaching parameters (pH, EC, ammonium and COD) and photosynthesis parameters (Fv/Fm and Pn) were studied based on lab-scale experiments. The results are beneficial for the application of alfalfa on the phytoremediation of leachate polluted soils in the future.
Section snippets
Soil, leachate and alfalfa
Soil samples up to 20 cm below ground were collected from Maanshan Forest Park (Wuhan, China) on June 28th, 2016. The soil samples were air dried for 2 d and passed through 2 mm sieve before the application in pot experiments. The soil samples were oven dried at 35 °C to remove moisture prior to pot experiments. Background physiochemical prosperities of the tested soil before contamination were measured from three samples and listed in Table 1. Landfill leachate was collected from Changshankou
Effects of leachate contamination on soil leaching characteristics
The variations of leaching parameters with various leachate levels are presented in Fig. 1. It was obvious that soil pH of high-dose-leachate samples (40 ml and 60 ml leachate) presented a slight decline, while leaching COD, ammonium and EC increased with the increasing dosage of landfill leachate. The decrease of pH could be attributed to original acidic pH or organic matter degradation from leachate. Similar results were observed in many other studies (Yang et al., 2013, Yang et al., 2014,
Conclusions
Based on the present work, the effects of landfill leachate on alfalfa photosynthesis mainly depended on dosages and incubation time. Both of Fv/Fm and Pn were slightly facilitated in 20 ml and 40 ml dosage groups, while they were inhibited in the high-dosage group. Furthermore, the inhibition influence only occurred in the initial period and then disappeared in the end of the incubation process. It could be concluded that alfalfa was of great tolerance to landfill leachate. The differences
Acknowledgement
This work was supported by National Natural Science Foundation of China (No.51508430 and No.51278212) and the Open Research Fund of Hubei Key Laboratory of Mine Environmental Pollution Control & Remediation (No.2016101).
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