The greater bioavailability of nitrogen (N), phosphorus (P) and potassium (K) in the Anthropocene has strongly impacted terrestrial plant communities. In northwest Europe, because high N deposition is considered the main driver of plant diversity loss, European Union (EU) legislation to reduce N deposition is expected to promote plant species recovery. However, this expectation is simplistic: it ignores the role of other macronutrients. Analysing the relationship between plant species pools and species stoichiometric niches along nutrient gradients across northern Eurasia’s herbaceous ecosystems, we found that both absolute and relative P availability are more critical than N or K availability. This result is consistent with stoichiometric niche theory, and with findings from studies of hyperdiverse forests and shrublands at lower latitudes. We show that ecosystems with low absolute and relative P availability harbour a unique set of threatened species that have narrower nutrient-based niche widths than non-threatened species. Such ecosystems represent a conservation priority, but may be further threatened by latent effects of relative P enrichment arising from reduction of N availability without simultaneous reduction of P. The narrow focus of EU legislation on reducing N, but not P, may therefore inadvertently increase the threat to many of Europe’s already threatened plant species. An EU Phosphate Directive is needed.

人类世中氮 (N)、磷 (P) 和钾 (K) 的更高生物利用度对陆地植物群落产生了强烈影响。在西北欧，由于高氮沉降被认为是植物多样性丧失的主要驱动因素，欧盟（EU）减少氮沉降的立法有望促进植物物种恢复。然而，这种期望很简单：它忽略了其他常量营养素的作用。沿着欧亚大陆北部草本生态系统的营养梯度分析植物物种库和物种化学计量生态位之间的关系，我们发现绝对和相对 P 可用性都比 N 或 K 可用性更重要。这一结果与化学计量生态位理论以及对低纬度高度多样化森林和灌木地的研究结果一致。我们表明，绝对和相对 P 可用性较低的生态系统拥有一组独特的受威胁物种，其基于营养的生态位宽度比未受威胁的物种窄。这样的生态系统代表了保护的优先事项，但可能会进一步受到由减少 N 可用性而不同时减少 P 引起的相对 P 富集的潜在影响的威胁。因此，欧盟立法对减少 N 而不是 P 的狭隘关注可能会无意中增加对欧洲许多已经受到威胁的植物物种构成威胁。需要欧盟磷酸盐指令。但可能会进一步受到由减少 N 可用性而不同时减少 P 引起的相对 P 富集的潜在影响的威胁。植物品种。需要欧盟磷酸盐指令。但可能会进一步受到由减少 N 可用性而不同时减少 P 引起的相对 P 富集的潜在影响的威胁。植物品种。需要欧盟磷酸盐指令。