Contrasting Physiological Responses of Noni Seedlings to Acidic and Alkaline Soils and Their Differential Response to Biochar Amendment

Abstract

The rapid expansion of Morinda citrifolia L. (noni) cultivation in tropical regions is driven by its recognized medicinal value, yet little is known about its agronomic and physiological responses to different soil environments. In particular, the effects of soil acidity on noni seedling performance and product safety remain poorly understood. This study investigated the growth and photosynthetic responses of noni seedlings in two contrasting soils—alkaline cambisols and acidic ferralsols—and evaluated the role of biochar in soil amendment. Seedlings performed better in alkaline cambisols than in acidic ferralsols, where higher aluminum and manganese concentrations were detected in aboveground tissues. Interestingly, although leaf photosynthetic rates were higher in acidic soil, seedlings exhibited a broader range of light adaptation under alkaline conditions, indicating distinct physiological responses to soil environments. Biochar application significantly enhanced seedling biomass in acidic soil but had detrimental effects in alkaline soil. These findings reveal a strong soil-dependent physiological response of noni seedlings and demonstrate that biochar amendment must be tailored to the soil type. The study provides new agronomic insight into noni cultivation and highlights the importance of soil-specific management for the sustainable production of this medicinal crop.