Foliar-applied lanthanum chloride increases growth and phosphorus acquisition in phosphorus-limited adzuki bean seedlings

Abstract

Lanthanum, a rare earth element, is used in agriculture and forestry to promote plant growth and productivity. We aimed to investigate its role in altering the roots and alleviating P deficiency in the adzuki bean Vigna angularis. The adzuki bean variety “Jin No. 5” was pre-cultivated in sand. Fourteen-day-old seedlings were sprayed twice with 0.4 mM LaCl3 solution. Next, we treated the seedlings with half-strength Hoagland solution containing P reduced to 1% of its original concentration (P-deficient); P reduced to 5% of the original (P-marginal); and unadjusted solution (P-sufficient). We measured plant growth, root structure, root hydraulic conductivity, P content, gas exchange, and photosynthetic pigment levels in all groups. LaCl3 application significantly increased leaf P concentration, effectively improving the P uptake efficiency of roots, shoots, and leaves under severe P stress. Root morphology and acid phosphatase (APase) activity varied significantly in response to LaCl3 under low-P stress. A greater leaf area, gas exchange ability, chlorophyll content, and carotenoid content were observed in the presence of LaCl3 under P-marginal stress. The application of LaCl3 can promote growth and P acquisition in adzuki beans under P limitation by inducing changes in root morphology, APase activity, and hydraulic conductivity.