Aims

Aluminium toxicity in acidic soils adversely affects wheat growth. Foliar-applied magnesium (Mg) contributes to mitigating soil acidity stress in wheat, but the mechanisms are unknown. This study explored the mechanism of foliar-Mg mediated enhancement of wheat growth in acidic soil.

Methods

Two contrasting near-isogenic wheat (Triticum aestivum L.) genotypes differing in Al resistance (Al-sensitive ES8 and Al-resistant ET8) were grown to the vegetative stage (Zadoks 24) in a reconstituted acidic soil (pH_{0.1 M CaCl2} 4.0) profile with three rates of foliar Mg (0, 200 and 500 mg Mg L^− 1 using MgSO₄.7H₂O). Magnesium was applied to the foliage twice [14 and 28 days after sowing (DAS)], and plant growth and root exuded carboxylates were measured up to 42 DAS.

Results

Applying 200 mg Mg L^− 1 to the foliage increased organic acid anion exudation from wheat roots by ~ 2-fold compared to 0 foliar Mg treated plants. The Al-resistant wheat genotype exuded 1.3-fold more malate and citrate from roots than the Al-sensitive genotype in the absence of foliar Mg. Malate exudation was delayed relative to citrate following foliar Mg application. The foliar-applied Mg increased shoot and root dry weight (by ~ 38 %), total root length (by ~ 33 %) and intrinsic water-use efficiency (by ~ 80 %) compared to plants treated with no Mg. Applying foliar Mg decreased soil acidity stress (as shown by a significant increase in chlorophyll fluorescence Fv/Fm ratio) in wheat compared to 0 foliar Mg.

Conclusions

Increased malate and citrate exudation is the underlying mechanism of enhanced wheat growth following foliar Mg application under acidic soil conditions.

中文翻译：

---

通过刺激苹果酸和柠檬酸的渗出，施用叶面镁可促进酸性土壤中小麦的生长

目的

酸性土壤中的铝毒性会对小麦生长产生不利影响。叶面施用的镁（Mg）有助于缓解小麦的土壤酸度胁迫，但机理尚不清楚。这项研究探讨了叶面镁介导的在酸性土壤中促进小麦生长的机制。

方法

在重构的酸性土壤（pH _{0.1 M CaCl2} 4.0）中，将两种不同的抗铝性不同的近等基因小麦（Triticum aestivum L.）基因型（铝敏感的ES8和铝抗性的ET8）生长到营养阶段（Zadoks 24）。三种叶面镁含量（使用MgSO ₄ .7H ₂ O分别为0、200和500 mg Mg L ^-1）的曲线。两次[在播种后14和28天（DAS）]将镁施用于叶片，并测量了植物生长和根系分泌的羧酸盐，最高达到42 DAS。

结果

与0叶面Mg处理过的植物相比，向叶面施用200 mg Mg L ^-1可使小麦根部有机酸阴离子渗出增加约2倍。在没有叶面镁的情况下，耐铝基因型的小麦根部分泌的苹果酸和柠檬酸含量比耐铝基因型高1.3倍。施用叶面镁后，苹果酸盐的分泌相对于柠檬酸盐有所延迟。与未施用镁的植物相比，叶面施用的镁增加了枝条和根的干重（增加约38％），总根长（增加约33％）和内在水分利用效率（增加了约80％）。与0叶量的镁相比，施用叶面Mg可以降低小麦的土壤酸度胁迫（如叶绿素荧光Fv / Fm比的显着增加所示）。

结论

苹果酸和柠檬酸盐的渗出增加是在酸性土壤条件下施用叶面镁后小麦生长增强的潜在机理。