Short CommunicationSoil algae pipe assay: ex situ method for the evaluation of soil quality based on soil algae and its application to the pot test
Introduction
Soil quality reflects not only soil pollution but also soil functions and ecosystem services (Bünemann et al., 2018). Therefore, new biological indicators and methods are necessary to improve soil quality assessment. The development of biological assays using soil algae to assess soil quality has been a focus of ecotoxicological research (Chae et al., 2018, Hammel et al., 1998, Kwak et al., 2017, Kwak et al., 2018, Kim et al., 2018, Kim et al., 2019, Nam and An, 2015, Nam and An, 2016, Nam and An, 2017, Nam et al., 2017, Nam et al., 2018a, Nam et al., 2018b). Hammel et al. (1998) first quantified the chlorophyll absorbance of Chlorococcum infusionum exposed to antimony-polluted soils in a Petri dish. Thereafter, soil algal assays have been developed using test tubes (Nam and An, 2015), microplates containing paper-disc soil (Nam and An, 2016, Nam et al., 2018a), and multi-well microplates (Nam and An, 2017). Using these approaches, the growth (based on chlorophyll fluorescence or growth zone), photosynthetic activity, cell morphology, enzyme activity, cell membrane permeability, and oxidative stress of Chlorococcum infusionum, Chlamydomonas reinhardtii, and Pseudokirchneriella subcapitata have been quantified. Furthermore, Nam et al. (2017) developed an algae-soaked disc seeding assay, where a paper disc is used to collect algae grown on soil. However, these methods do not consider the direct exposure of soil algae in situ because it is difficult to collect intact algae grown on surface soil or subsoil. In this study, a soil algae pipe assay to assess soil quality ex situ was developed and validated. An ex situ evaluation was performed in a greenhouse and the chlorophyll-a content in the green alga C. reinhardtii was determined.
Section snippets
Methodology
Chlamydomonas reinhardtii (UTEX No. 2244), purchased from the University of Texas at Austin (USA), was incubated in Tris-acetate-phosphate medium at 24 ± 2 °C, with shaking at 100 rpm, a light:dark cycle of 16:8 h, and a light intensity of 54 μmol photons/m2s. Algal suspensions (OD660 2.0) were inoculated in the exponential growth phase. Five soils (Soils 1, reference soil; Soils 2–5, heavy metal-contaminated soils) were used to validate the soil algae pipe assay. The initial physicochemical
Results and discussion
The chlorophyll-a content in soil algae was lower in the contaminated soils (Soils 2–5) than in the reference soil (Soil 1) (Fig. 2A and B). In addition, algal growth on soil surface after inoculation in the pipe was observed by macroscopy seven days after the pot test (Fig. 2C). We observed green algae on the surface of Soils 1–3 (Fig. 2C); however, we did not observe green algae growth on the surface of Soils 4 and 5. Generally, the growth of soil algae depends on nitrogen and phosphorus (
Acknowledgments
This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (2016R1A2B3010445, 2016M3A6A7945504). This work was also supported by Korea Environment Industry & Technology Institute (KEITI) through “The Chemical Accident Prevention Technology Development Project”, funded by Korea Ministry of Environment (MOE) (No.2016001970001). We thank Mr. Jongmin Moon and Dr. Shin Woong Kim for providing pot setup, and the Korea
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