Element content and distribution has limited, tolerance metric dependent, impact on salinity tolerance in cultivated sunflower (Helianthus annuus)

Disruption of ion homeostasis is a major component of salinity stress's effect on crop yield. In cultivated sunflower prior work revealed a negative relationship between vigor and salinity tolerance. Here, we determined the association of elemental content/distribution traits with salinity tolerance, both with and without taking vigor (biomass in control treatment) into account. We grew seedlings of 12 Helianthus annuus genotypes in two treatments (0, 100 mM NaCl). Plants were measured for biomass (+allocation), and element content (Na, P, K, Ca, Mg, S, Fe, B, Mn, Cu, Zn) in leaves (young and mature), stem, and roots. Genotype tolerance was assessed as both proportional decline of biomass and as expectation deviation (deviation from the observed relationship between vigor and proportional decline in biomass). Genotype rankings on these metrics were not the same. Elemental content and allocation/distribution were highly correlated both at the plant and organ level. Suggestive associations between tolerance and elemental traits were fewer and weaker than expected and differed by tolerance metric. Given the highly correlated nature of elemental content, it remains difficult to pinpoint specific traits underpinning tolerance. Results do show that taking vigor into account is important when seeking to determining traits that can be targeted to increase tolerance independent of vigor, and that the multivariate nature of associated traits should additionally be considered.