Few long-term fertilization experiments have been performed in forests, even though the effects of nitrogen (N) addition on soil microbial biomass are a cause for concern. Our objective was to examine the effects of repeated fertilization for 36 years on soil microbial biomass in two forest stands. We measured soil chemical properties and microbial biomass carbon (C) and N in soils in fertilized and non-fertilized plots in a birch stand (Betula maximowicziana Regel) and a fir stand (Abies sachalinensis Fr. Schmidt). We also performed lime amendments and a 21-day laboratory incubation, and measured microbial biomass to clarify the effects of acidification due to fertilization. Soil pH was significantly lower in fertilized plots in both stands, and soil microbial biomass C and N were lower (significantly so in the fir stand) in the fertilized plots after 36 years of repeated fertilization. In the laboratory incubation, lime amendment did not significantly affect the microbial biomass C, N, or C:N ratio, despite an increase of about 1 unit in soil pH. Our results therefore indicate that factors other than soil pH also have important effects on soil microbial biomass in repeatedly fertilized forest stands.

中文翻译：

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反复施肥和石灰浸种对桦木和冷杉冷杉土壤微生物生物量的影响。施密特站在日本

尽管添加氮（N）对土壤微生物生物量的影响值得关注，但很少在森林中进行长期的施肥实验。我们的目的是研究36年重复施肥对两个林分土壤微生物生物量的影响。我们在桦木林分（Betula maximowicziana Regel）和冷杉林分（Abies sachalinensis）的施肥区和非施肥区中测量了土壤的化学性质以及微生物生物量碳（C）和氮神父 施密特）。我们还进行了石灰改良和21天实验室培养，并测量了微生物生物量，以阐明由于施肥引起的酸化作用。在重复施肥36年后，两个林地中施肥地的土壤pH值均显着降低，施肥地中土壤微生物生物量碳和氮含量较低（在冷杉林中显着降低）。在实验室温育中，尽管土壤pH值增加了约1个单位，但石灰改良剂并未显着影响微生物生物量的C，N或C：N比。因此，我们的结果表明，土壤pH以外的其他因素也对反复施肥的林分土壤微生物生物量具有重要影响。