Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden; Slovak Environment Agency, Tajovského 28, 975 90 Banská Bystrica, Slovakia.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden; Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, SE-230 53 Alnarp, Sweden.
Sci Total Environ. 2022 Sep 10;838(Pt 3):156327. doi: 10.1016/j.scitotenv.2022.156327. Epub 2022 May 28.
Nutrient enrichment can alleviate productivity limitations and thus substantially increase carbon (C) uptake in northern coniferous forests. Yet, factors controlling stand-to-stand variation of forest ecosystem responses to nutrient enrichment remain unclear. We used five long-term (13 years) nutrient-enrichment experiments across Sweden, where nitrogen (N), phosphorus, and potassium were applied annually to young Norway spruce forests that varied in their baseline ecosystem properties. We measured tree biomass and soil C and N stocks, litterfall C inputs, soil CO efflux, and shifts in composition and biomass of soil microbial communities to understand the links between above and belowground responses to nutrient enrichment. We found that the strongest responses in tree biomass occurred when baseline site productivity was lowest. High increases in tree biomass C stocks were generally balanced by weaker responses in organic soil C stocks. The average ecosystem C-N response rate was 35 kg C kg N added, with a nearly five-fold greater response rate in tree biomass than in soil. The positive nutrient enrichment effects on ecosystem C sinks were driven by a 95% increase in tree biomass C stocks, 150% increase in litter production, 67% increase in organic layer C stocks, and a 46% reduction in soil CO efflux accompanied by compositional changes in soil microbial communities. Our results show that ecosystem C uptake in spruce forests in northern Europe can be substantially enhanced by nutrient enrichment; however, the strength of the responses and whether the enhancement occurs mainly in tree biomass or soils are dependent on baseline forest productivity.
养分富集可以缓解生产力的限制，从而大大增加北方针叶林的碳（C）吸收。然而，控制森林生态系统对养分富集响应的个体间变异的因素仍不清楚。我们使用了瑞典的五个长期（13 年）养分富集实验，其中每年向不同基本生态系统特性的年轻挪威云杉林施加氮（N）、磷和钾。我们测量了树木生物量和土壤 C 和 N 储量、凋落物 C 输入、土壤 CO 通量以及土壤微生物群落组成和生物量的变化，以了解养分富集对地上和地下响应之间的联系。我们发现，当基线站点生产力最低时，树木生物量的响应最强。树木生物量 C 储量的大幅增加通常与有机土壤 C 储量的较弱响应相平衡。平均生态系统 C-N 响应速率为 35 kg C kg N 添加，树木生物量的响应速率几乎是土壤的五倍。生态系统 C 汇的正养分富集效应是由树木生物量 C 储量增加 95%、凋落物产量增加 150%、有机层 C 储量增加 67%以及土壤 CO 通量减少 46%所驱动的，同时土壤微生物群落的组成也发生了变化。我们的结果表明，北欧云杉林的生态系统 C 吸收可以通过养分富集得到显著增强；然而，响应的强度以及增强是否主要发生在树木生物量还是土壤中，取决于基线森林生产力。
