Toxic effects of soil manganese on tropical trees
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Toxic effects of soil manganese on tropical trees Graham Zemunik & Klaus Winter & Benjamin L. Turner
Received: 8 March 2020 / Accepted: 11 June 2020 # Springer Nature Switzerland AG 2020
Abstract Aims Manganese (Mn) is toxic to plants at high concentrations with recent evidence indicating slowed tropicaltree growth by high soil Mn concentrations. However, little information exists about the physiological effects of high Mn on tropical trees. We investigated physiological responses and toxicity effects of Mn in several tropical tree species. Given potential physiological interactions between Mn and phosphorus (P), we also hypothesised that P could be used to detoxify Mn. Methods We conducted two controlled-growth experiments on seedlings of five tree species from Panama. The first experiment tested the effects of increasing concentrations of soil Mn; the second examined whether P availability mitigates Mn toxicity. Results Severe Mn toxicity occurred at 5 mM Mn, with toxicity symptoms in some species at 1.5 mM Mn. Responses to Mn toxicity were species-specific and depended on P supply. One species intolerant of high Mn responded by using P for detoxification; others either tolerated or detoxified Mn by another mechanism. Conclusions We conclude that Mn can be toxic to tropical tree species and Mn toxicity increases P demand in Responsible Editor: Antony Van der Ent Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11104-020-04603-3) contains supplementary material, which is available to authorized users. G. Zemunik (*) : K. Winter : B. L. Turner Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancón, Republic of Panama e-mail: [email protected]
some species. Other species are broadly tolerant of high Mn, suggesting that Mn tolerance might contribute to differences in species distributions and growth of tropical trees. Keywords Mycorrhizal symbioses . Phosphatase activity . Phosphorus . Relative growth rate
Introduction Manganese (Mn) is an essential micronutrient for plants, playing a key role in physiological processes such as photosynthesis, but it can become toxic at high concentrations (Foy et al. 1978; El-Jaoual and Cox 1998). Toxicity manifests in a variety of ways, including reduction in growth, leaf chlorosis and spots on leaves (ElJaoual and Cox 1998; Millaleo et al. 2010). Manganese availability is enhanced in acidic soils (Marschner 1995) and toxic concentrations of Mn occur widely in strongly weathered tropical soils, which are often acidic. Mn toxicity can be further exacerbated in soils developed on parent materials that are rich in Mn, such as Hawaiian basalts (e.g., Hue et al. 2001). In general, plants resist Mn toxicity by avoiding uptake of Mn or by employing mechanisms to tolerate it (limit its toxicity) if taken up in high quantities. Several tolerance mechanisms are known, including sequestration of Mn in the cell apoplast, complexation with organic acids, and export of excess Mn ions to the cell surface (Mill
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