Background and aims

Plants living on gypsum are adapted to uptake nutrients in extremely poor alkaline soils. Under such extreme conditions, processes affecting the chemical conditions of the rhizosphere may be crucial for plant survival and growth. Rhizosphere acidification in plants living on gypsum soils has never been reported before and the effect of root exudation and microbes on the rhizosphere pH remains undescribed.

Methods

In this study we cultivated seeds of the gypsum specialist Ononis tridentata in rhizoboxes with natural gypsum soil and with gypsum soil with reduced microbiota, and monitored changes in the rhizosphere pH with planar optodes coupled to a calibrated image recording system. Soil microbial life was estimated with PLFAs analyses and root exudation was characterised.

Results

The reduced microbiota treatment decreased both fungal and microbial presence. Plants grown in natural soil, with unaltered presence of soil microbiota, had lower rhizosphere pH. However, in the microbial-reduced treatment we found higher root exudation of several organic acids and alcohols such as malonic and isocitric acids and sorbitol-mannitol. Interestingly, plant biomass was not significantly altered by treatments.

Conclusion

The natural soil microbiota contributed to acidify alkaline gypsum soils, likely improving nutrient availability. However, O. tridentata seedlings grown in microbial-reduced soils seemed to compensate the effects of microbes through increased root exudation, attaining similar growth both in natural and microbial-reduced soils. These seedlings seemed to be adapted to soil where microbial abundance fluctuates.

中文翻译：

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土壤微生物群的变化改变了石膏特有的 Ononis tridentata L 的根系分泌物和根际 pH 值。

背景和目标

以石膏为生的植物适应在极贫碱性土壤中吸收养分。在这种极端条件下，影响根际化学条件的过程可能对植物的生存和生长至关重要。以前从未报道过生活在石膏土壤上的植物的根际酸化，并且根系分泌物和微生物对根际 pH 值的影响仍未被描述。

方法

在这项研究中，我们在含有天然石膏土壤和微生物群减少的石膏土壤的根箱中培育了石膏专家Ononis tridentata的种子，并通过与校准图像记录系统耦合的平面光极监测根际 pH 值的变化。通过 PLFA 分析估算土壤微生物寿命，并表征根系分泌物。

结果

减少微生物群的处理减少了真菌和微生物的存在。在天然土壤中生长的植物，土壤微生物群未改变，根际 pH 值较低。然而，在减少微生物的处理中，我们发现几种有机酸和醇（例如丙二酸、异柠檬酸以及山梨醇-甘露醇）的根部分泌物较多。有趣的是，植物生物量并没有因处理而显着改变。

结论

天然土壤微生物群有助于酸化碱性石膏土壤，可能提高养分利用率。然而，在微生物减少的土壤中生长的三齿稻幼苗似乎通过增加根系分泌物来补偿微生物的影响，在自然土壤和微生物减少的土壤中都获得了相似的生长。这些幼苗似乎适应了微生物丰度波动的土壤。