School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, WA, 6009, Australia.
Grupo de Estudios Ambientales, IMASL-CONICET & Universidad Nacional de San Luis, Av. Ejercito de los Andes 950, 5700, San Luis, Argentina.
Oecologia. 2020 Aug;193(4):843-855. doi: 10.1007/s00442-020-04733-6. Epub 2020 Aug 20.
Plants that produce specialised cluster roots, which mobilise large quantities of poorly available nutrients such as phosphorus (P), can provide a benefit to neighbouring plants that produce roots in the cluster rhizosphere, as demonstrated previously in pot studies. To be effective, such roots must be present within the short time of peak cluster activity. We tested if this requirement is met, and quantified potential P benefits, in a hyperdiverse Mediterranean woodland of southwest Australia where cluster-rooted species are prominent. Using minirhizotrons, we monitored root dynamics during the wet season in the natural habitat. We found non-cluster roots intermingling with all 57 of the observed cluster roots of the studied tree species, Banksia attenuata. Almost all (95%) of these cases were observed in a high-moisture treatment simulating the 45-year average, but not present when we intercepted some of the rainfall. We estimate that cluster-root activity can increase P availability to intermingling roots to a theoretical maximum of 80% of total P in the studied soil. Due to their high P-remobilisation efficiency (89%), which results from P rapidly being relocated from cluster roots within the plant, senesced Banksia cluster roots are a negligible P source for other roots. We conclude that, rather than serving as a P source, it is the cluster-root activity, particularly the exudation of carboxylates, that may improve the coexistence of interacting species that are capable of root intermingling, thus potentially promoting species diversity in nutrient-poor habitats, and that this mechanism will be less effective in a drying climate.
产生专门丛生根的植物可以将大量难以获得的养分（如磷）转移到土壤中，这对在丛生根根际产生根的邻近植物有益，这在之前的盆栽研究中已经得到证实。为了发挥作用，这些根必须在丛生根活动高峰期的短时间内存在。我们测试了在澳大利亚西南部的一个超多样化的地中海林地中是否满足了这一要求，并量化了潜在的磷素益处，该林地以丛生根物种为主要特征。我们使用小型根箱在自然栖息地的雨季监测根的动态。我们发现，非丛生根与所研究的树种——细叶瓶干树的 57 个观察到的丛生根中的所有根都交织在一起。几乎所有（95%）这些情况都出现在模拟 45 年平均水平的高湿度处理中，但当我们拦截部分降雨时则没有出现。我们估计，丛生根活动可以将土壤中总磷的 80%增加到与交织根共生的磷的理论最大值。由于其高磷再利用效率（89%），磷迅速从植物内的丛生根中重新定位，因此衰老的瓶干树丛生根对其他根来说是微不足道的磷源。我们得出结论，不是作为磷源，而是丛生根的活动，特别是羧酸的分泌，可能会改善能够根交织的相互作用物种的共存，从而有可能促进营养贫瘠栖息地的物种多样性，并且这种机制在干燥气候下的效果会降低。
