Evidence that arbuscular mycorrhizal and phosphate-solubilizing fungi alleviate NaCl stress in the halophyte Kosteletzkya virginica: nutrient uptake and ion distribution within root tissues.

The effects of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae, and a phosphate-solubilizing microorganism (PSM), Mortierella sp., and their interactions, on nutrient (N, P and K) uptake and the ionic composition of different root tissues of the halophyte Kosteletzkya virginica (L.), cultured with or without NaCl, were evaluated. Plant biomass, AM colonization and PSM populations were also assessed. Salt stress adversely affected plant nutrient acquisition, especially root P and K, resulting in an important reduction in shoot dry biomass. Inoculation of the AM fungus or/and PSM strongly promoted AM colonization, PSM populations, plant dry biomass, root/shoot dry weight ratio and nutrient uptake by K. virginica, regardless of salinity level. Ion accumulation in root tissues was inhibited by salt stress. However, dual inoculation of the AM fungus and PSM significantly enhanced ion (e.g., Na(+), Cl(-), K(+), Ca(2+), Mg(2+)) accumulation in different root tissues, and maintained lower Na(+)/K(+) and Ca(2+)/Mg(2+) ratios and a higher Na(+)/Ca(2+) ratio, compared to non-inoculated plants under 100 mM NaCl conditions. Correlation coefficient analysis demonstrated that plant (shoot or root) dry biomass correlated positively with plant nutrient uptake and ion (e.g., Na(+), K(+), Mg(2+) and Cl(-)) concentrations of different root tissues, and correlated negatively with Na(+)/K(+) ratios in the epidermis and cortex. Simultaneously, root/shoot dry weight ratio correlated positively with Na(+)/Ca(2+) ratios in most root tissues. These findings suggest that combined AM fungus and PSM inoculation alleviates the deleterious effects of salt on plant growth by enabling greater nutrient (e.g., P, N and K) absorption, higher accumulation of Na(+), K(+), Mg(2+) and Cl(-) in different root tissues, and maintenance of lower root Na(+)/K(+) and higher Na(+)/Ca(2+) ratios when salinity is within acceptable limits.