Aluminum-tolerant bacteria improve the plant growth and phosphorus content in ryegrass grown in a volcanic soil amended with cattle dung manure

In Chilean volcanic soil, crop production often is limited by a combination of the low available P and high concentration of toxic aluminum (Al). In this study we aimed to isolate Al-tolerant plant-growth-promoting bacteria from the rhizosphere and the endosphere of ryegrass grown in acidic Chilean volcanic soil in order to characterize a bacterial consortium capable of contributing to alleviation of Al³⁺ toxicity and supporting plant growth in Andisol. Five strains, i.e. Klebsiella sp. RC3, Stenotrophomonas sp. RC5, Klebsiella sp. RCJ4, Serratia sp. RCJ6 and Enterobacter sp. RJAL6, were selected based on their capacity to tolerate high Al concentration (10 mM) and to exhibit multiple plant-growth-promoting traits (P solubilization, indole acetic acid production, 1-aminocyclopropane-1-carboxylate deaminase activity, and exudation of organic acid anions and siderophores). Based on the results, we can suggest that selected bacteria could alleviate Al stress by forming Al³⁺-siderophore complexes. The plant-growth-promoting potential of the bacterial consortium was confirmed in an assay with ryegrass plants. In the treatment with cattle dung manure, the consortium promoted plant growth and the phosphatase activity in the rhizosphere soil. Increased phosphatase activity coincided with elevated P concentration in shoots. Our results suggest that a combination of native Al-tolerant bacteria and cattle dung manure is effective in decreasing Al toxicity and promoting plant growth in Andisols of southern Chile.