School of Emergency Management, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, PR China.
Faculty of Natural Resources Management, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada.
Sci Total Environ. 2024 Apr 15;921:171246. doi: 10.1016/j.scitotenv.2024.171246. Epub 2024 Feb 23.
Soil respiration (R) indicates below-ground biological activities. Previous studies have suggested that higher nitrogen (N) deposition due to human activities exerts an increasingly negative effect on R. However, the mechanisms underlying this negative effect remain highly uncertain on a global scale. Using a global dataset of 262 N addition experiments, here we show the overall N addition effects on R changed from positive to negative with increasing N addition rate and duration. By constructing a structural equation model (SEM) that explained 41 % variation in the responses of R to N addition, we revealed that R under increasing N addition was simultaneously associated with decreases in soil pH, root biomass and microbial biomass, with the strongest influence by root biomass. Decreasing soil pH had cascading effects on root and microbial biomass, while N-addition-induced root biomass reduction further manifested a decrease in microbial biomass. Across global variations in the environment, lower background soil pH amplified the negative impacts of N addition on root and microbial biomass, which consequently exhilarated the negative impact of high N on R. Our results highlight that predicting the response of belowground biological activities to global changes is complex with the essence of integrative understanding for the multivariate pathways through soil physical properties, plants and microorganisms.
土壤呼吸（R）表明了地下生物活动。先前的研究表明，由于人类活动导致的氮（N）沉降增加对 R 产生了越来越负面的影响。然而，这种负面影响的机制在全球范围内仍然高度不确定。利用全球 262 个 N 添加实验数据集，我们表明，随着 N 添加率和持续时间的增加，N 添加对 R 的总体影响从正变为负。通过构建一个结构方程模型（SEM），解释了 R 对 N 添加的响应变化的 41%，我们揭示了在不断增加的 N 添加下，土壤 pH 值、根系生物量和微生物生物量同时减少，其中根系生物量的影响最大。不断下降的土壤 pH 值对根和微生物生物量产生级联效应，而 N 添加引起的根系生物量减少进一步表现为微生物生物量的减少。在全球环境变化下，较低的背景土壤 pH 值放大了 N 添加对根和微生物生物量的负面影响，从而加剧了高 N 对 R 的负面影响。我们的研究结果强调，预测地下生物活动对全球变化的反应是复杂的，需要综合理解土壤物理特性、植物和微生物的多变量途径。
