Effects of Zn²⁺ on nodulation and growth of a South American actinorhizal plant, Discaria americana (Rhamnaceae)
2007
Cusato, M. S | Tortosa, R. D | Valiente, L | Barneix, A. J | Puelles, M. M
Discaria americana is a xerophytic shrub which lives in symbiosis with an actinomycete of the genus Frankia. The objective of this paper was to investigate the effects of high soil Zn²⁺ concentrations on growth and nodulation on the association Discaria americana-Frankia with the aim of determining if this association is suitable for improving contaminated soils. Two experiments were performed in 1 dm³ pots containing soil and different Zn additions, from 0 to 2,000 mg Zn²⁺ kg-¹ dry soil, with or without N fertilization. Zn additions strongly delayed shoot and root growth, but once growth was initiated, the biomass production of the plants supplied with moderate Zn amounts did not differ from the control plants. Zn reduced the final nodule number, but not the total nodule biomass. At the end of the experiment only the highest Zn treatments showed a lower nodule weight than the control plants, while N addition completely inhibited nodulation. It is concluded than Zn reduces the number of Frankia infections, but once the actinomycete is inside the roots, nodules can continue growing according to plant demand for N, compensating the reduced nodule number with more biomass. On the other hand, there is a toxic effect of Zn itself on plants when present in very high concentrations.
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