Arbuscular mycorrhizal fungi prevent mercury toxicity in Lactuca sativa (L.) seed germination

Mercury pollution is an issue of global concern. In Colombia, the use of contaminated water for food crop irrigation and artisanal mining contribute to mercury pollution in soil, affecting food production and restoration of perturbed areas. Mycorrhizal fungi are plant symbionts that provide benefits to plants, including resistance to heavy metals, but fungal effects on germination remain to be fully described. In this study, it was tested the effect of mercury and mycorrhizal fungi onLactuca sativaseed germination. A 2x5 completely randomized factorial experiment was performed to assess the effect of five HgCl2polluted treatments, two mycorrhizal treatments (i.e., with inoculum, without inoculum), and the interaction of both factors on seed germination, seedling root colonization, pH, and final water content. Without mercury, mycorrhizal fungi had an inhibitory effect on seed germination. Testing the effect of mercury on seed germination showed a significantly inhibitory effect of mercury on germination. However, in pots inoculated with arbuscular mycorrhizal fungi showed constant germination probabilities, independently of mercury concentration. According to the best model determined for the data, a key step in the mitigation of mercury toxicity in seed germination is to prevent substrate pH changes. The environmental conditions of the experiment contributed to activating a densely populated biomass of inoculum, promoting root invasion from various points. Overall, the presence of mycorrhizal fungi in seedbeds could lead to a reduced number of plant individuals. However, the use of a fungal inoculum in polluted environments highly contributes to plant stablishment.

汞污染是全球广受关注的环境议题。在哥伦比亚，受污染水体用于粮食作物灌溉以及手工采矿活动，共同加剧了土壤汞污染，进而威胁粮食生产并阻碍受干扰区域的生态修复。菌根真菌（mycorrhizal fungi）是一类植物共生微生物，可为宿主植物提供包括重金属抗性在内的多种有益性状，但目前真菌对种子萌发的调控效应尚未得到全面阐释。本研究以生菜（Lactuca sativa）为试验材料，探究汞与菌根真菌对其种子萌发的影响。本研究采用2×5完全随机析因试验设计，设置5组氯化汞（HgCl₂）污染处理梯度、2组菌根处理（分别为接种菌剂与不接种菌剂），并分析二者及其交互作用对种子萌发、幼苗根系定殖、基质pH值及最终含水量的影响。在无汞污染的对照组中，菌根真菌对种子萌发表现出抑制作用。单独探究汞对种子萌发的影响时发现，汞会显著抑制种子萌发进程。但在接种丛枝菌根真菌（arbuscular mycorrhizal fungi）的盆栽体系中，无论汞浓度高低，种子萌发概率均保持稳定。基于本研究数据筛选得到的最优模型可知，缓解汞对种子萌发毒性的关键举措是维持基质pH值稳定。本试验的环境条件有助于激活接种剂的高密度生物量，促进真菌从多个位点侵入植物根系。总体而言，苗床中存在菌根真菌可能会降低植株的最终定植数量，但在污染环境中施用真菌菌剂，可有效促进植物定植。