Morphophysiological plasticity and dynamics of biomass partitioning of Mentha arvensis under light intensity gradient

Abstract

Light intensity is a key ecophysiological factor in in vitro systems, directly modulating growth, biomass partitioning, and photoprotective mechanisms. This study investigated the morphophysiological and photo-oxidative responses of Mentha arvensis to a light gradient (28–130 µmol m ² s ¹) under a completely randomized design with five irradiance levels. Total biomass production exhibited a significant quadratic response (P < 0.001; adjusted R² = 0.50), with an optimum at 103.3 µmol m ² s ¹. Leaf biomass followed a similar pattern (adjusted R² = 0.60), indicating prioritization of the photosynthetic apparatus under intermediate irradiance. Shoot length displayed an inverted quadratic curve (adjusted R² = 0.397), with pronounced etiolation under low light and more robust morphology at intermediate intensities. Root biomass showed a positive linear response up to 97 µmol m ² s ¹. High irradiance (130 µmol m ² s ¹) induced biomass decline and activation of photo-oxidative defense mechanisms, likely involving antioxidant enzymes. Maximum light-use efficiency (1.157 mg µmol ¹ photon) occurred at 51 µmol ⁻ m ² s ¹, and the critical threshold for photoinhibition was identified at 94 µmol m ² s ¹. These results highlight the high phenotypic plasticity of M. arvensis in response to light and provide precise ecophysiological parameters for optimizing micropropagation protocols and cultivation strategies aimed at maximizing productivity and secondary metabolite quality.