Effects of Gamma Amino Butyric Acid (GABA) on Nutrient Uptake of Loquat [<i>Eriobotrya japonica</i> (Thunb.) Lindl.] Seedlings

Gamma amino butyric acid (GABA), an important free amino acid in plant tissues, plays an essential role in all stages of plant growth and development. In this study, we aimed to explore the effects of GABA on the nutrient absorption of loquat [Eriobotrya japonica (Thunb.) Lindl.] seedlings. The effects of applying exogenous GABA in different concentrations (0.0, 0.5, 1.0, 1.5, and 2 g L−1) on the nutrient uptake of loquat seedlings were studied. GABA increased the biomass (dry weight) and contents of photosynthetic pigments in loquat seedlings to a certain extent. GABA concentration exhibited a quadratic polynomial regression relationship with the biomass. Exogenous GABA in different concentrations increased the total nitrogen (N) and phosphorus (P) contents in loquat seedlings, whereas only 0.5 and 1.0 g L−1 of GABA increased the potassium (K) content. Similarly, GABA concentration also had a polynomial regression relationship with the total N, P, and K contents. Compared to the control, 0.5, 1.0, 1.5, and 2.0 g L−1 of GABA increased the shoot total N content by 27.30, 32.99, 15.41, and 12.93%, respectively, and also increased the shoot total P content by 26.12, 37.52, 21.99, and 9.61%, respectively. Furthermore, correlation and grey relational analyses showed that the carotenoid content, root biomass, and soil alkali-hydrolyzable N concentration were the indicators most closely associated with the uptakes of N, P, and K in shoots. This study shows that exogenous GABA can promote the growth and nutrient uptake of loquat seedlings at an optimum concentration of 1.0 g L−1