Characteristics and correlation of soil low-molecular-weight organic acids and nutrients in four plantations in red soil area of south China

Poor phosphorus availability is the key factor limiting yield in plantations in South China. Low-molecular-weight organic acids (LMWOAs) have a good effect on activating insoluble phosphorus in soil. In this study, the type, content, and distribution of LMWOAs in the soil of four monoculture afforestation plantations, each planted with different species: Phoebe bournei, Schima superba, Cunninghamia lanceolata, and Michelia macclurei, in the red soil area of South China and their correlation with nutrient element content were determined to inform soil management of the plantations. The results showed that linolenic acid only exists in the P. bournei forest. Eight LMWOAs exist in the soil across the four plantations. Across all four plantations and soil layers, the total content of the eight LMWOAs were ranked as follows: oxalic acid>fumaric acid>lactic acid>malonic acid>citric acid>palmitic acid>stearic acid>cinnamic acid. According to total LMWOAs content in the soil, the plantations were ranked as follows: P. bournei plantation>S. superba plantation>C. lanceolata plantation>M. macclurei plantation. The contents of oxalic, lactic, fumaric, and malonic acid in soil were highly significantly positively correlated with the available potassium content and highly significantly negatively correlated with the available phosphorus content. The oxalic acid contents in soil were highly significantly positively correlated with the ammonium nitrogen content. The contents of cinnamic acid and malic acid in soil were highly significantly positively correlated with nitrate content.