Evidence for non-additive effects of successive heat stress events as a consequence of stress response amplification or the priming effect
Most measured variables illustrated the non-additive effects of the successive events, meaning that the cumulative impact of the respective effects of each SES (e.g. mod2, mod3, SEScml) differed from the effect of CES (mod1). When a mismatch was observed, the effect of the CES was either (i) higher than the effects of the SEScml or (ii) lower than the effects of the SEScml. Under HS, the CES effects (absolute value) on total yield, seed conductivity, the ABA:GA3 ratio and seed N concentration were higher than the SEScml effects, whereas the CES effects were lower for the [raffinose+stachyose]:sucrose ratio and the FA concentration (Table 4), but to a lesser extent for the FAs. Similar mismatches were observed under LS for seed conductivity, the ABA:GA3 ratio (higher CES effects than SEScml effects), FA concentration (lower CES effects than SEScml effects) but not for total yield, the [raffinose+stachyose]:sucrose ratio, for which the CES effects were lower than (or equal to) the SEScml effects. Therefore, this analysis highlights that S availability determines the magnitude (value and direction of variation) of the mismatches between the SEScml and CES effects.