Effect of combined copper, salt and plant growth promoting rhizobacteria inoculation on the growth, photosynthesis and ion accumulation in the halophyte Salicornia ramosissima: a phytoremediation perspective

Salicornia ramosissima is a C3 halophyte native to salt marshes of southwestern Spain, where it naturally thrives under salinity and heavy metal pollution. Despite its ecological and agricultural significance, its potential for phytoremediation has been understudied. This work explores the effect of salinity (0, 10 and 60 g L^-1 NaCl), copper (0 and 1000 ppm Cu) and bacterial bioaugmentation (four different consortia) on the growth, photosynthesis and ion accumulation capacity of S. ramosissima under greenhouse conditions. High salinity resulted in negative effects for S. ramosissima growth (40% decrease in dry weight) and photosynthesis (decline of 40% net photosynthetic rate and 50% stomatal conductante), thriving best under low to moderate salinity. The addition of 1000 ppm Cu to the substrate exacerbated growth inhibition (up to 77%) under non and high salinity, but not under moderate salinity. Also, S. ramosissima was an effective accumulator of both Na and Cu, accumulating twice the Na in shoots than in roots while retaining the majority of Cu in roots. Another key finding was that Plant Growth Promoting Rhizobacteria (PGPR) bioaugmentation in Cu-contaminated substrate led to a x4.5 increase in plant growth, a notable recovery in photosynthetic parameters (especially iWUE, up to 1000%) and promoted up to a 3x greater accumulation of Cu in the roots. Each inoculum showed different effects in plants and survival rate. Combining S. ramosissima with PGPR could be a sustainable tool for the phytostabilization of Cu and the phytoextraction of Na, allowing to use S. ramosissima in bioremediation and agriculture.