No Escape: The Influence of Substrate Sodium on Plant Growth and Tissue
Sodium Responses
Abstract
As an essential micronutrient for many organisms, sodium plays an
important role in ecological and evolutionary dynamics. Although plants
mediate trophic fluxes of sodium, from substrates to higher trophic
levels, we know relatively little about plants’ comparative growth and
sodium accumulation responses to variation in substrate sodium. We
carried out a systematic review to examine how plants respond to
variation in substrate sodium concentrations. We compared growth and
tissue-sodium responses among 107 populations (67 species in 20 plant
families), broadly expanding beyond the agricultural and model taxa for
which several generalizations previously have been made. We hypothesized
a priori response models for each population’s growth and sodium
accumulation responses as a function of increasing substrate NaCl. We
used BIC to choose the best model. Additionally, using a phylogenetic
signal analysis, we tested for phylogenetic patterning of growth and
sodium accumulation responses across plant taxa. The influence of
substrate sodium on growth differed across taxa, with most populations
experiencing detrimental effects at high concentrations. Irrespective of
growth response, tissue concentrations of sodium for most taxa increased
as sodium concentrations in the substrate increased. We found no strong
associations between growth and types of sodium accumulation responses
across taxa. Our phylogenetic signal analyses found that evolutionary
history helps predict the distribution of total plant growth responses
across the phylogeny, but not sodium accumulation responses. Our study
suggests that saltier plants in saltier soils may prove to be a broadly
general pattern for sodium across plant taxa. Regardless of growth
responses, sodium accumulation mostly followed an increasing trend and
did not have any evident association with growth responses as substrate
sodium levels increased. Finally, plant adaptations to substrate sodium
vary with a degree of phylogenetic conservatism.