Shading Impairs Mycorrhizal Benefits on Plant Growth, Leaf Gas Exchange, and Active Ingredients in Polygonum cuspidatum

Abstract

Polygonum cuspidatum, an important medicinal plant, often experiences shading from surrounding vegetation during its growth phase, raising questions about the impact of such conditions on the functionality of arbuscular mycorrhizal fungi. This study investigated the effects of an arbuscular mycorrhizal fungus (Funneliformis mosseae) on the growth, leaf gas exchange, and concentrations of active ingredient concentrations in leaves and roots of P. cuspidatum under shading (with a 72% shading rate) conditions. A nine-week shading intervention significantly suppressed root colonization by F. mosseae and the formation of soil mycorrhizal mycelium. Shading significantly inhibited the above-ground growth performance, biomass production, leaf photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO2 concentration, while F. mosseae significantly increased these variables in the absence of shading. Plant height, leaf biomass, stem biomass, leaf photosynthetic rate, transpiration rate, and stomatal conductance were all decreased by F. mosseae when the plants were shaded. The shading treatment also significantly diminished the concentrations of active components measured in both leaves and roots. Under no-shading conditions, F. mosseae significantly boosted the concentrations of polydatin, resveratrol, aloe-emodin, emodin, chrysophanol, and physcion in roots, as well as the concentrations of polydatin and chrysophanol in leaves. Conversely, in the presence of shading, F. mosseae distinctly reduced these active ingredient levels in roots, followed by an increase in leaf polydatin and chrysophanol concentrations. In summary, shading substantially impaired the mycorrhizal benefits on plant growth, leaf gas exchange, and root active ingredients in P. cuspidatum, highlighting the importance of sufficient light to maximize mycorrhizal contributions.