Effects of magnesium supply level on growth, nutrient element absorption and distribution, and quality of Panax quinquefolium

Abstract

This study aims to investigate the effects of different magnesium supply levels on the growth, nutrient absorption and distribution, and quality of Panax quinquefolium, and to determine the optimum content of exchangeable magnesium in soil. Three-year-old plants of P. quinquefolium were used in this study, and eight magnesium supply gradients(CK, Mg1-Mg7) were designed for indoor pot experiment(cultivation in soil). The plant growth indexes, nutrient element content in soil and plant, and root saponin content were determined at the end of the growth period. The correlation analysis of nutrient element content in aboveground and underground parts of P. quinquefolium showed significantly negative correlations of magnesium-calcium, magnesium-potassium, and magne-sium-manganese. With the increase in magnesium supply level, the biological absorption coefficient of magnesium increased, while that of total nitrogen, potassium, iron, and manganese decreased; the biological transfer coefficient of magnesium decreased, while that of nitrogen, phosphorus, calcium, iron, and manganese increased. The saponin content was analyzed by principal component analysis, which showed the comprehensive score in the order of Mg4(2.537), Mg2(1.001), Mg3(0.600), Mg1(0), Mg7(-0.765), CK(-0.825), Mg6(-0.922), and Mg5(-1.663). The partial least squares-path modeling(PLS-PM) showed that the correlation coefficients of exchangeable magnesium and pH with quality were-0.748 and-0.755, respectively, which were significant. Magnesium-calcium, magnesium-potassium, and magnesium-manganese showed antagonism in the nutritional physiology of P. quinquefolium. Excessive application of magnesium can lead to the imbalance of nutrient elements in P. quinquefolium. The content of exchangeable magnesium in soil suitable for the quality formation of P. quinquefolium was 193.34-293.34 mg·kg~(-1). In addition to exchangeable magnesium, pH was also important to the quality formation of P. quinquefolium. Therefore, exchangeable magnesium and pH could be regarded as monitoring factors for the quality formation of P. quinquefolium.