Microbial strategies in non-target invasive Spartina densiflora for heavy metal clean up in polluted saltmarshes.
Rhizoremediation is the use of microorganisms from the rhizosphere to assist plant phytoremediation. Optimistic results have been obtained these years for this biotool, but its effects in non-target cohabiting species has never been studied. This concern, in principle pointless, gains importance when the non-target species is an invasive plant. It is the case of highly polluted saltmarshes in SW Spain, where the native cordgrass Spartina maritima, proposed for heavy metal rhizoremediation, cohabitates with the invasive Spartina densiflora. In this work, we designed a greenhouse experiment where S. densiflora was placed in pots with natural metal polluted soil from Tinto marsh and inoculated with a bacterial consortium designed for rhizoremediation purposes with S. maritima. After 30 days of treatment, our data revealed that inoculated S. densiflora showed better fitness and metal accumulation capacity than non-inoculated control plants. This enhancement was demonstrated by increased S. densiflora biomass (58% for belowground tissues), amelioration of photosynthetic parameters (i.e., 48% for net photosynthetic rate (AN) and stomatal conductance (gs) and 17% for intrinsic water-use efficiency (iWUE)), and finally by an increase of inoculated S. densiflora root metal uptake, reaching around 40% in case of cadmium and lead. Within this scenario, the rhizoremediation strategy proposed using S. maritima should be managed cautiously, and if would be entitled to determine to which extent its practical implementation may boost invasive capability of S. densiflora.