Biochar application is perceived as a promising agricultural technology, but risk evaluation on the soil ecosystem has focused exclusively on soil microbes, whether microfood-web is likewise influenced by biochar remains unclear. We carried out a pot experiment planted with rapeseed for 2 years to test how biochar application (0, 20, 60 t ha −1 ), with or without nitrogen (N) fertilizer (0, 60, 120 t ha −1 ), affected soil microbes and microfauna (protists and nematodes). We observed that a high amount of biochar (60 t ha −1 ) increased crop productivity, microbial activity, and biomass carbon (C) and N, as well as the abundance of flagellates (protists), but decreased the abundances of bacterivorous, fungivorous, and herbivorous nematodes as well as the abundance of amoebae (protists). High biochar addition rates also shifted nematode community composition toward a fungivore dominance, and favored herbivores by decreasing the ratio of microbivorous to herbivorous nematodes. However, N fertilizer and its interaction with biochar generally had no effect on microbial activity and biomass as well as the abundance of protist and nematode. A structural equation model revealed that the effects of biochar on soil biota were largely direct, which might depend on biochar properties (e.g., pore size and alkalinity), whereas indirect effects, mediated by crop, soil pH, soil moisture, and polycyclic aromatic hydrocarbon (PAH) concentration, generally had no effect on soil biota. We conclude that biochar is a suitable soil amendment for increasing crop growth, but its detrimental effect on multitrophic levels of soil fauna calls for an identification of the optimal application rate and size fraction that could minimize potential negative effects on certain soil communities.

中文翻译：

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生物炭对栽培酸性土壤中多个营养水平的土壤动物产生负面影响

生物炭的应用被认为是一种很有前途的农业技术，但对土壤生态系统的风险评估主要集中在土壤微生物上，微食物网是否同样受到生物炭的影响尚不清楚。我们进行了一项种植油菜籽 2 年的盆栽试验，以测试生物炭施用（0、20、60 吨公顷 -1 ）、有或没有氮 (N) 肥料（0、60、120 吨公顷 -1 ）如何影响土壤微生物和微型动物（原生生物和线虫）。我们观察到，大量的生物炭（60 t ha -1 ）提高了作物生产力、微生物活性和生物量碳（C）和氮，以及鞭毛虫（原生生物）的丰度，但降低了食细菌、食真菌的丰度。和食草线虫以及大量的变形虫（原生生物）。高生物炭添加率也将线虫群落组成转向食真菌动物的优势，并通过降低食微生物线虫与食草线虫的比例来偏爱食草动物。然而，氮肥及其与生物炭的相互作用通常对微生物活性和生物量以及原生生物和线虫的丰度没有影响。结构方程模型表明，生物炭对土壤生物群的影响在很大程度上是直接的，这可能取决于生物炭的特性（例如，孔径和碱度），而间接影响则由作物、土壤 pH 值、土壤水分和多环芳烃介导(PAH) 浓度，一般对土壤生物群没有影响。我们得出结论，生物炭是一种适合促进作物生长的土壤改良剂，