ABSTRACT Plant responses to environmental conditions are commonly assessed through experiments employing discrete treatment levels. However, such experimental approach may mask nonlinear responses and interaction regimes among the studied factors. To overcome these limitations, we examine Arabidopsis thaliana plants cultivated under continuous irradiance-temperature gradients and use generalized additive models to quantify light-temperature regulation of growth, carbon status and phenolics metabolism. The patterns of estimated traits revealed by gradient-based experiments and generalized additive modelling are broadly consistent with conclusions derived from experiments at discrete irradiances and temperatures. However, this approach resolves, nonlinearities and interaction regimes that remain largely inaccessible to conventional factorial experiments. Across broad ranges of irradiance and, in particular, temperature, responses of most measured traits were non-linear, frequently exhibiting shifts between synergistic and antagonistic interactions. Phenolic compounds increased with rising irradiance and decreasing temperature, except at temperatures above 40°C, where their accumulation increased again. Irradiance is the dominant factor influencing the absolute size of the carbon pool, strongly enhancing biomass production, non-structural carbohydrate accumulation, and total phenolic content, while temperature is an important cue for carbon allocation between growth and defence. Microscopic analyses confirmed that whole-leaf phenolic patterns were accompanied by marked shifts in tissue-level flavonoid distribution, consistent with photoprotective and antioxidant functions. In contrast to this clear environmental response, phenolic compound accumulation increased with non-structural carbohydrates only up to a certain point, after which further increases in phenolics were strongly associated with the C/N ratio, indicating regulation by integrated carbon–nutrient status rather than carbon surplus alone.
Pleva et al. (Mon,) studied this question.