Biochar and deactivated yeast as seed coatings for restoration: performance on alternative substrates

Seedling establishment is often a critical bottleneck to revegetation of mine tailings and similar substrates with a low capacity to retain water and plant nutrients. Biochar and deactivated yeast are potential sustainable, low-cost materials with high nutrient- and water-holding capacity that could be used in this context as seed coatings to aid in seedling establishment on challenging substrates. We conducted a greenhouse study to assess the effectiveness of biochar and deactivated yeast, applied alone in a factorial combination, as seed coatings, on the germination, establishment, and early growth of white clover (Trifolium repens) and purple prairie clover (Dalea purpurea). Coated seeds were applied to a mine tailing, a coarse granitic sand, and potting soil mix substates; seedling establishment and growth were monitored over 75 days. Results indicate strong interactive effects of seed coating type with effects of species and substrate. Biochar coatings enhanced germination of Trifolium, while yeast coatings did so for Dalea. In some cases, these effects persisted throughout the experiment. Biochar coatings resulted in a ~5-fold increase in Trifolium biomass at harvest for plants in the potting soil mix but had neutral effects on sand and tailings. Yeast seed coatings enhanced biomass at harvest on tailings for Dalea. Our results indicate that biochar- and yeast-based seed coatings can have lasting effects on plant growth well beyond germination, but also emphasize highly species-specific responses that highlight the need for further study of broader patterns and mechanisms.幼苗建成往往是尾矿及保水保肥能力低下的类似基质开展植被恢复的关键瓶颈。生物炭（biochar）与灭活酵母（deactivated yeast）是一类潜在的可持续、低成本材料，具备优异的保水保肥性能，可在该场景中用作种子包衣（seed coating），以助力逆境基质上的幼苗建成。本研究开展温室试验，评估单独施用及析因组合施用的生物炭与灭活酵母作为种子包衣剂，对白三叶（Trifolium repens）和紫色草原三叶草（Dalea purpurea）的萌发、建成及早期生长的影响。将包衣种子分别播植于尾矿、粗粒花岗岩砂及营养土混合基质中，并对幼苗建成与生长状况进行为期75天的监测。研究结果表明，种子包衣类型与物种、基质的效应间存在显著交互作用。生物炭包衣可提升白三叶的萌发率，而酵母包衣则对紫色草原三叶草的萌发具有促进效果。在部分试验条件下，此类促进效应可贯穿整个试验周期。在营养土混合基质中，生物炭包衣可使收获期白三叶的生物量提升约5倍，但对花岗岩砂及尾矿基质中的植株生物量无显著影响。酵母种子包衣则可提升尾矿基质中紫色草原三叶草收获期的生物量。本研究结果表明，基于生物炭与酵母的种子包衣剂对植物生长的促进效应可远不止于萌发阶段，但同时也凸显出极强的物种特异性响应，这提示未来需针对更广范围的规律与作用机制开展进一步研究。