Phosphorus Shortage Induces an Increase in Root Exudation in Fifteen Eucalypts Species

Abstract

A significant proportion of the carbon fixed by plants is transported to the roots and exuded to the rhizosphere. Exudates may have important roles in the rhizosphere, such as desorbing labile phosphorus (P) or mobilizing manganese (Mn) and other metal cations. This study evaluated the root exudation profiles of seedlings of 15 eucalypt species in response to a P shortage and if the ability to exude organic compounds was related to P and Mn accumulation in the shoots. The plants were grown on sand and were irrigated with nutrient solutions containing either sufficient P (500 µM) or low P (25 µM). Organic acids (OA), amino acids/polyamines, and phenolics were analyzed in the root exudates by UPLC-MS/MS. Plants with a low P level had low leaf P contents and growth reduction. A P shortage induced the exudation of the three groups of metabolites analyzed at higher levels than sufficient P availability. Despite that, the composition pattern of root exudates was similar among species under low or sufficient P concentrations. Citric and isocitric acids were the major OAs found in the exudates, followed by oxalic, malic, and succinic acids. Among the amino acids/polyamines identified, putrescine was the most abundant in all species, followed by glycine. Cinnamic acid was the predominant phenolic in the root exudates. Our results indicate that P limitation induces a conserved response genetic mechanism in eucalypts. Such results can be further investigated to adapt commercial clones to soils with low P availability.