No evidence that conifer biochar impacts soil functioning by serving as microbial refugia in boreal soils

It is well established that application of biochar to soils can promote soil fertility, which ultimately may enhance plant growth. While many mechanisms have been proposed to explain this, one specific mechanism, the “microbial refugia hypothesis” suggests that biochar may provide physical protection for soil microbe from soil micro-fauna that otherwise exert top-down control on microbial biomass and activity. We tested the microbial refugia hypothesis by incubating two boreal soils with and without biochar derived from a wood mixture of boreal tree species (Picea abies and Pinus sylvestris), and with and without soil nematodes. We measured phospholipid fatty acids (PLFA) as a relative measure of microbial biomass, and several variables indicative of microbial activity, including extractable nutrient concentrations (NH4+, NO3-, and PO4-), heterotrophic N2-fixation, and soil respiration. Contrary to our expectations, we found that biochar by itself did not stimulate microbial biomass or ...现有研究已证实，向土壤中施加生物炭（biochar）可提升土壤肥力，进而促进植物生长。尽管学界已提出多种机制解释该现象，但其中特定的微生物避难所假说（microbial refugia hypothesis）指出，生物炭可对土壤微生物提供物理保护，使其免受土壤微型动物的自上而下调控——这类微型动物通常会抑制微生物的生物量与活性。本研究通过温育两份北方森林土壤，设置是否添加生物炭、是否添加土壤线虫的双因素处理以验证该假说。所用生物炭由北方树种（挪威云杉*Picea abies*与欧洲赤松*Pinus sylvestris*）的混合木材制成。我们以磷脂脂肪酸（PLFA）作为微生物生物量的相对表征指标，并测定了多项反映微生物活性的变量，包括可提取态营养盐浓度（NH4+、NO3-与PO43-）、异养固氮作用以及土壤呼吸速率。与我们的预期相悖的是，单独施加生物炭并未显著提升微生物生物量或……