Complex soil contamination severely impacts seed-sown crop viability in Australia

Abstract

Food security is a critical issue for many global communities. Heavy metal contamination in soils present a major and ongoing ecological risk associated with human activities which may impact the viability and safety of seed-sown crops. To better understand the impacts of soil contamination by heavy metals on seed-sown crop viability, we examined germination responses of eight commercially-important fruit and vegetable crop species to copper, zinc, and lead contamination at levels likely to be found in contaminated regions in Australia. We compared the germination attributes of days to first germination, germination period, and total proportion of seeds germinated under concentration limits of heavy metals detected at degraded sites and current Australian National Environment Protection Measure thresholds for domestic soils (i.e., copper 6,000 mg kg-1, zinc 4,700 mg kg-1, lead 300 mg kg-1). The combined heavy metal treatment (i.e. all three metals) significantly inhibited germination for all edible crop species with only carrots able to germinate under complex, multi-metal-contaminated conditions. Seed viability was significantly decreased in mulberry (M. alba var. tatarica, M. nigra, and M. rubra) and lettuce (L. sativa), with lowered seed germination in all metals compared to carrot (D. carota), radish (R. sativus), tomato (S. lycopersicum) and common bean (P. vulgaris). These results indicate heavy metal contamination is a notable risk to seed-sown crop species, with multi-metal contamination events likely to be severely damaging to lettuce, tomato, radish, common bean, and mulberry crops