Aims

Facilitation is common among plants, but our understanding of indirect belowground facilitative mechanisms is limited. We followed up on previous research showing that Pinus sylvestris had strong facilitative effects on co-occurring Amorpha fruticosa shrubs by testing the effects of root exudates of the Pinus on various components of the N cycle in the soil around Amorpha roots.

Methods

We applied different concentrations of Pinus root exudates (0, 1x, and 4x) to soils, and measured the responses of the soil metabolome, microbial functional groups and the biomass of Amorpha.

Results

A 1x concentration of Pinus root exudates promoted microbial metabolism and plant secondary metabolite biosynthesis. The same concentration increased the abundance of specific microbial genera in the rhizosphere involved in nitrification and nitrogen (N) fixation. These root exudates also increased the abundance of microbial taxa and genes involved in ammonification and nitrification, but inhibited microbial denitrification. In addition, pathway analysis indicated that Pinus root exudates indirectly facilitate Amorpha biomass by regulating its rhizosphere N-cycle. Together, these results indicate that 1x concentrations of Pinus root exudates promote the efficient conversion of ammonium to nitrate and the absorption and utilisation of organic N, while reducing gaseous N losses, thereby promoting the overall N uptake, and potentially growth, of Amorpha.

Conclusions

Our results point to the importance of root exudates as an indirect facilitative mechanism, operating through effects on microbes involved in the N cycle, but their ecological relevance should be further validated in the field.

中文翻译：

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樟子松根分泌物通过改变氮循环间接促进紫穗槐的生长性能

目标

促进作用在植物中很常见，但我们对间接地下促进机制的理解有限。我们跟进了之前的研究，通过测试松树根系分泌物对紫穗槐根部周围土壤中氮循环各个组成部分的影响，表明樟子松对共生紫穗槐灌木具有很强的促进作用。

方法

我们将不同浓度的松树根分泌物（0、1x和4x）施用于土壤，并测量土壤代谢组、微生物功能群和紫穗槐生物量的响应。

结果

1x浓度的松树根分泌物促进微生物代谢和植物次生代谢产物生物合成。相同的浓度增加了根际中参与硝化和固氮（N）的特定微生物属的丰度。这些根分泌物还增加了参与氨化和硝化作用的微生物类群和基因的丰度，但抑制了微生物反硝化作用。此外，路径分析表明，松根分泌物通过调节根际氮循环间接促进紫穗槐生物量。总之，这些结果表明，1x浓度的松树根分泌物促进铵有效转化为硝酸盐以及有机氮的吸收和利用，同时减少气态氮损失，从而促进紫穗槐的总体氮吸收和潜在生长。

结论

我们的结果表明根系分泌物作为一种间接促进机制的重要性，通过对参与氮循环的微生物的影响来发挥作用，但其生态相关性应在现场进一步验证。