Aims

Non-mycorrhizal species such as Banksia (Proteaceae) that depend on root exudates to acquire phosphorus (P) are prominent in south-western Australia, a biodiversity hotspot on severely P-impoverished soils. We investigated the consequences of an exudate-releasing P-mobilising strategy related to control of iron (Fe) acquisition in two Banksia species, B. attenuata R.Br. and B. laricina C. Gardner, that differ greatly in their geographical distribution and rarity.

Methods

We undertook solution culture experiments to measure root-mediated Fe reduction (FeR) in non-cluster and cluster roots at four stages of cluster-root development, and whole root systems for plants grown at 2 to 300 μM Fe (as Fe-EDTA). As a positive control, we used Pisum sativum (cv. Dunn) to validate the FeR assay.

Results

Unlike typical Strategy I species, both Banksia species showed no significant variation in FeR, for either cluster or non-cluster roots, when grown at a wide range of Fe supply. For roots of different developmental stages, we measured a range for B. attenuata cluster roots of 0.13 ± 0.03 to 1.29 ± 0.14 μmol Fe³⁺ reduced g⁻¹ FW h⁻¹ and 0.56 ± 0.11 to 1.10 ± 0.24 μmol Fe³⁺ reduced g⁻¹ FW h⁻¹ in non-cluster roots. Similarly, for B. laricina cluster-roots, FeR ranged from 0.22 ± 0.07 to 1.21 ± 0.37 μmol Fe³⁺ reduced g⁻¹ FW h⁻¹, and in non-cluster roots from 0.56 ± 0.11 to 0.71 ± 0.08 μmol Fe³⁺ reduced g⁻¹ FW h⁻¹. We also observed only minor differences for whole-root system FeR, and even though B. attenuata showed signs of leaf Fe deficiency in the 2 μM Fe treatment, its FeR was the lowest of both species across all treatments at 0.079 ± 0.009 μmol Fe³⁺ reduced g⁻¹ FW h⁻¹, compared with the fastest rate of 0.20 ± 0.014 μmol Fe³⁺ reduced g⁻¹ FW h⁻¹ for B. laricina in the 28 μM Fe treatment. Taking plants through a pulse from low to high Fe, then back to low Fe supply did not elucidate any significant response in FeR.

Conclusions

Although Fe acquisition is tightly controlled in the investigated Banksia species, such control is not based on regulation of FeR, which challenges the model that is commonly accepted for Strategy I species.

中文翻译：

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没有证据表明两种策略I簇生的班克西亚种（Proteaceae）对根介铁还原的调控

目的

非根腐类物种，例如山龙眼（Proteaceae），依靠根系分泌物来获取磷（P），在澳大利亚西南部（这是严重磷贫瘠的土壤上的生物多样性热点）非常突出。我们调查了与两个Banksia物种B.衰减a R.Br中的铁（Fe）采集控制有关的渗出物释放P动员策略的后果。和B. laricina C. Gardner，在地理分布和稀有性上有很大的不同。

方法

我们进行了溶液培养实验，以测量簇生根发育的四个阶段以及非簇生根和簇生根的根介铁还原（FeR），以及生长2至300μMFe的植物的整个根系（以Fe-EDTA表示） 。作为阳性对照，我们使用了豌豆（Pisum sativum，cv。Dunn）来验证FeR分析。

结果

与典型的策略I物种不同，当以大量的Fe供应时，无论是簇生根还是非簇生根，两种Banksia物种的FeR均无明显变化。对于不同的发育阶段的根，我们测量的范围B. attenuata 0.13±0.03簇根1.29±0.14微摩尔的Fe ³⁺还原克^-1 FWħ ^-1和0.56±0.11至1.10±0.24微摩尔的Fe ³⁺还原g ^-1 FW h ^-1在非集群根中。类似地，对于B. laricina簇根，FeR为0.22±0.07至1.21±0.37μmolFe ³⁺还原的g ^-1 FW h ^-1Fe ³⁺从0.56±0.11到0.71±0.08μmolFe ³⁺减少了g ^-1 FW h ^-1。我们还观察到全根系FeR的细微差别，即使弱毒双歧杆菌在2μMFe处理中显示出叶片铁缺乏的迹象，但其FeR在所有处理中均为最低，为0.079±0.009μmolFe ^{3 +}降低了g ^-1 FW h ^-1，而最快的速率为0.20± 0.014μmolFe ³⁺降低了B. laricina的g ^-1 FW h ^-1在28μM铁处理中 使植物经历从低铁到高铁的脉冲，然后再回到低铁供应，这并未阐明铁的显着响应。

结论

虽然收购铁在调查严格控制班克西亚物种，这种控制不是基于FER，其挑战是常用的策略I物种接受模型的调控。