UWA School of Biological Sciences, The University of Western Australia, Crawley (Perth), Western Australia, Australia.
Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Crawley (Perth), Western Australia, Australia.
Physiol Plant. 2021 Jul;172(3):1724-1738. doi: 10.1111/ppl.13384. Epub 2021 Mar 19.
The calcifuge habit of plants is commonly explained in terms of high soil pH and its effects on nutrient availability, particularly that of phosphorus (P). However, most Proteaceae that occur on nutrient-impoverished soils in south-western Australia are calcifuge, despite their ability to produce cluster-roots, which effectively mobilize soil P and micronutrients. We hypothesize that the mechanism explaining the calcifuge habit in Proteaceae is their sensitivity to P and calcium (Ca), and that soil-indifferent species are less sensitive to the interaction of these nutrients. In this study, we analyzed growth, gas-exchange rate, and chlorophyll fluorescence of two soil-indifferent and four calcifuge Hakea and Banksia (Proteaceae) species from south-western Australia, across a range of P and Ca concentrations in hydroponic solution. We observed Ca-enhanced P toxicity in all analyzed species, but to different extents depending on distribution type and genus. Increasing P supply enhanced plant growth, leaf biomass, and photosynthetic rates of soil-indifferent species in a pattern largely independent of Ca supply. In contrast, positive physiological responses to increasing [P] in calcifuges were either absent or limited to low Ca supply, indicating that calcifuges were far more sensitive to Ca-enhanced P toxicity. In calcifuge Hakeas, we attributed this to higher leaf [P], and in calcifuge Banksias to lower leaf zinc concentration. These differences help to explain these species' contrasting sensitivity to Ca-enhanced P toxicity and account for the exclusion of most Proteaceae from calcareous habitats. We surmise that Ca-enhanced P toxicity is a major factor explaining the calcifuge habit of Proteaceae, and, possibly, other P-sensitive plants.
植物的喜钙习性通常可以用高土壤 pH 值及其对养分可用性的影响来解释，特别是对磷（P）的影响。然而，在澳大利亚西南部营养贫瘠的土壤中，大多数山龙眼科植物都是喜钙的，尽管它们能够产生簇根，有效地动员土壤中的 P 和微量元素。我们假设，解释山龙眼科植物喜钙习性的机制是它们对 P 和钙（Ca）的敏感性，以及土壤不敏感物种对这些养分相互作用的敏感性较低。在这项研究中，我们分析了来自澳大利亚西南部的两种土壤不敏感和四种喜钙的 Hakea 和 Banksia（山龙眼科）物种的生长、气体交换率和叶绿素荧光，这些物种在水培溶液中跨越了一系列 P 和 Ca 浓度。我们观察到所有分析的物种都存在 Ca 增强的 P 毒性，但程度因分布类型和属而异。增加 P 供应在很大程度上独立于 Ca 供应，增强了土壤不敏感物种的植物生长、叶片生物量和光合作用速率。相比之下，对增加 [P]的正向生理响应在喜钙植物中要么不存在，要么仅限于低 Ca 供应，表明喜钙植物对 Ca 增强的 P 毒性更为敏感。在喜钙的 Hakea 中，我们将其归因于更高的叶片 [P]，而在喜钙的 Banksia 中，我们将其归因于更低的叶片锌浓度。这些差异有助于解释这些物种对 Ca 增强的 P 毒性的不同敏感性，并解释了大多数山龙眼科植物被排除在钙质生境之外的原因。我们推测，Ca 增强的 P 毒性是解释山龙眼科植物喜钙习性的一个主要因素，可能也是其他对 P 敏感的植物的一个主要因素。
