Aims

Microorganisms play a dichotomous role in the soil nitrogen cycle through mineralization and immobilization. We aimed to understand how nitrogen availability modifies the effect of microorganisms on plant growth. We hypothesized that soil microorganisms would increase plant biomass following amendment with a substrate rich in organic nitrogen (net mineralization), be neutral when adding inorganic nitrogen, and decrease biomass when adding organic nitrogen-limited substrate (nitrogen competition).

Method

Barley (Hordeum vulgare L., cv. Evergreen) was exposed to either i) limited, organically bound nitrogen, ii) organically bound nitrogen or iii) inorganic nitrogen. In these amendments, we assessed the differences in plant biomass and physiology between plants with or without soil microbiome addition.

Results

The soil microbiome reduced shoot biomass equally (12%) across all nitrogen amendments. However, nitrogen availability did modulate the effect of the soil microbiome on plant physiological parameters associated with nitrogen deficiency.

Conclusions

The results indicate that the net negative effect of complex microbiomes on shoot biomass is independent of nitrogen availability. Thus, microbiome addition was deleterious to biomass even in a nutrient-stress-free environment. We suggest that strategies for improving plant growth through manipulation of microorganisms should not exclusively focus on beneficial and pathogenic microorganisms, but also include minimizing plant metabolic costs of microbiome interactions.

中文翻译：

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在不同的氮素利用率下，土壤微生物均匀减少大麦生物量

目的

微生物通过矿化和固定化作用在土壤氮循环中起二分作用。我们旨在了解氮素的利用如何改变微生物对植物生长的影响。我们假设土壤微生物会在富含有机氮的基质（净矿化）作用下增加植物生物量，在添加无机氮时呈中性，而在添加有机氮受限的基质时（氮竞争）降低生物量。

方法

将大麦（Hordeum vulgare L.，cv.Evergreen）暴露于i）有限的，有机结合的氮，ii）有机结合的氮或iii）无机的氮。在这些修订中，我们评估了添加或不添加土壤微生物组的植物之间植物生物量和生理的差异。

结果

在所有氮素改良剂中，土壤微生物组平均减少了枝条生物量（12％）。但是，氮的利用确实可以调节土壤微生物组对与氮缺乏相关的植物生理参数的影响。

结论

结果表明，复杂的微生物组对苗生物量的净负效应与氮的有效性无关。因此，即使在无营养胁迫的环境中，添加微生物组对生物质也是有害的。我们建议通过操纵微生物来改善植物生长的策略不应只集中在有益和致病的微生物上，而应包括使微生物组相互作用的植物代谢成本降至最低。