Anthropogenic soil acidification severely imperils microbial diversity and functionality

Soil acidification, a pervasive yet often underestimated issue in the Anthropocene, poses a critical threat to ecosystem health. Although microorganisms are the cornerstone of soil health, the impact of anthropogenic soil acidification on microbial communities remains unresolved. Here, we leverage 455 experimental studies to disentangle how soil acidification affects microbial traits in different scenarios (anthropogenic acidification versus natural pH gradients), based on ‘Mill's causal inference’. Anthropogenic soil acidification caused by nitrogen and acid addition significantly decreases microbial diversity, biomass, and functionality; in stark contrast, natural pH gradients exert only minimal effects on these microbial traits. Notably, nitrogen-induced acidification significantly reduces microbial richness, Shannon index, biomass, and functionality by 5.1%, 3.1%, 4.1%, and 5.1%, respectively. Meanwhile, acid addition decreases microbial biomass and functionality by 9.4% and 15%, respectively. Disturbingly, croplands experience more severe acidification (by 10.0%) compared to natural ecosystems (by 6.5%), leading to markedly steeper declines in microbial traits. Reductions in microbial biomass, rather than diversity loss, primarily drive the decline of soil functionality. These findings underscore the imperative to mitigate anthropogenic soil acidification to sustain soil health, particularly in intensively managed croplands.

土壤酸化是人类世（Anthropocene）中一种普遍却常被低估的问题，对生态系统健康构成严重威胁。尽管微生物是土壤健康的基石，但人为土壤酸化对微生物群落的影响仍未明确。本研究依托455项实验研究，基于“米尔因果推断（Mill's causal inference）”，厘清了不同场景下（人为酸化与自然pH梯度）土壤酸化对微生物性状的影响机制。由氮添加与酸输入引发的人为土壤酸化，会显著降低微生物多样性、生物量与功能；与之形成鲜明对比的是，自然pH梯度仅对这些微生物性状产生极微弱的影响。值得注意的是，氮诱导的酸化会使微生物丰富度、香农指数（Shannon index）、生物量及功能分别显著下降5.1%、3.1%、4.1%与5.1%。与此同时，酸添加会使微生物生物量与功能分别下降9.4%与15%。令人担忧的是，农田系统的酸化程度（10.0%）较自然生态系统（6.5%）更为严重，由此导致微生物性状的下降幅度也显著更大。微生物生物量的减少而非多样性丧失，是土壤功能下降的主要驱动因素。这些研究结果凸显了缓解人为土壤酸化以维持土壤健康的必要性，在集约化管理的农田中尤为如此。