Micronutrients are essential for healthy development, survival, and reproduction of all organisms. Accordingly, micronutrient availability and intake are tightly linked to organismal performance across ecosystems and form fundamental components of eco-evolutionary dynamics. As the sixth most abundant element in the Earth’s crust, sodium plays an essential role in eco-evolutionary dynamics and trophic level interactions. Even though it is understood that sodium effects on plants tend to be detrimental, we still have ways to go to understand how adaptations to environmental sodium affect fitness and sodium accumulation reaction norms across plant family taxa. A systematic review performed on 107 populations in 69 species across 20 families were used to classify plants biomass growth and sodium accumulation phenotype into six and seven reaction norms, respectively. We designed models that represented hypothesized reaction norms that reflected possible plant responses to environmental sodium. Models were selected based on BIC.
Results/Conclusions
Results showed that the phenotypes for biomass fall into the following categories: hump-shaped 14.0%; linear decrease 37.40%; linear increase 2.80%; non-linear decrease, convex upward 33.64%; concave upward 9.35%, and zero slopes 2.80%. Most plant taxa grew less as sodium increased in the substrate; only hump-shaped, linear increase, non-linear decline, concave upward, and zero slopes tolerated NaCl additions. Only plants with hump-shaped or linear increase biomass reaction norms grew at 250 mM of NaCl treatments. All populations grew poorly at NaCl concentrations >500 mM.
Also, we classified sodium accumulation reaction norms as follows: asymptotic increase 20.56%, exponential increase 12.15%, hump-shaped 11.21%, linear increase 32.71%, non-linear increase 6.54%, sigmoidal increase 15.89% and zero slope 0.935%. All populations’ reaction norms included an increase in sodium accumulation in total plant tissues as NaCl increased in the substrate. Above- and belowground tissues differed in their sodium accumulation responses across biomass growth phenotypes. However, only hump-shape differ significantly in sodium accumulation between above and belowground tissues (Wilcoxon test: n=68, Z=3.824, p>0.001, r=0.464).
Biomass growth reaction norms did not segregate with respect to sodium accumulation reaction norms. Even so, irrespective of biomass growth reaction norm, tissue concentrations of sodium for most taxa (77%) increased as sodium concentrations in the substrate increased. These results show that overall patterns of biomass growth adaptations do not correspond to sodium accumulation phenotypes in plants across taxa. However, some plant biomass growth adaptations benefit more from environmental sodium than others, mainly halophytes.