Sustained growth and phosphorus efficiency under iron excess in Paspalum densum, a C4 grass for mining site revegetation

Abstract

Iron (Fe) is a strong phosphorus (P) chelator in Fe-rich environments. In Fe mining sites, the P deficiency might limit plant development. This study aims to understand how the interaction between the Fe excess and P deficit affects the P-use efficiency and photosynthesis in Paspalum densum, a C4 tropical native grass indicated for use in revegetation of iron mining areas. The plants were exposed to four treatments in Hoagland's nutrient solution: standard (100 % P and 0.019 mM Fe); Fe excess (100 % P and 7 mM Fe); P deficit (1 % P and 0.019 mM Fe); and the combination of P deficit and Fe excess (1 % P and 7 mM Fe). The interaction between Fe excess and P deficiency changed the P allocation in the root and root apoplast. In roots, P deficit caused a higher Fe concentration, and, in the leaf, lower levels of P were found in plants exposed to the Fe excess. The stomatal limitation was the main cause of net photosynthesis decline due to Fe excess in both P doses, however without affecting plant biomass or promoting oxidative damage. The iron excess increased the P-use efficiency (PUE) at the leaf level in P-deficient plants. The photosynthetic PUE and whole biomass PUE were higher due to P deficiency. Therefore, in an environment of Fe toxicity and P deficit, as in areas impacted by Fe mining, the adjustments in P allocation and use efficiency coupled with photosynthetic responses contribute to the P. densum performance during revegetation.