Citric Acid Promotes the Mobilization of Phosphorus under the Lower Concentration of Low Molecular Weight Organic Acids in Acidic Forest Soil

Abstract

Low molecular weight organic acids (LMWOAs) secreted by plant roots enhanced the release of inorganic P (Pi) and organic P (Po) into the soil solution and thereby increased plant-available Pi in soils. Not the effect of LMWOAs on inducing organic P (Po) released into soil solution through soil microorganisms at different temperatures was poorly understood, but the transform mechanism for P fraction was also not well explained. This study used three experiments to determine the release of P and the transformation mechanism of P fractions induced by oxalic acid, citric acid, and malic acid in acidic forest soils. The results showed that LMWOAs, as carbon sources for microorganisms, mobilize Po more effectively than glucose. Inorganic P and organic P were released by LMWOAs followed by oxalic acid > citric acid > malic acid if the substrates of P and LMWOAs were enough. There may be a critical threshold for the concentration of citric acid and oxalic acid between 10 mM and 25 mM to require for the solution of adsorbed and precipitated P, respectively. In all, LMWOAs increased the concentration of labile P by decreasing the concentration of stable P. The results indicated that LMWOAs can significantly promote P availability in acidic forests soils, and the effect of microorganisms on soil available P was more inclined to use LMWOAs than glucose.

Organic acid mediated phosphorus mobilization from phytin and glycerophosphate

“…When more than one carboxyl groups are present the intramolecular H-bonding will be more and due to dimer formation the affinity of organic acid deceases to react with metal, which ultimately helps to release the P. The higher release of P in citric than malic acid may be related to the fact that citric acid has three carboxyl groups while malic has only two. Therefore, intra-molecular H-bonding was more in malic acid while one carboxyl group was always free in case of citric acid to react and release P. Zhu et al [26] reported significant P mobilization in subalpine forest soil due to citric acid through desorption and ligand exchange process rather than the acidification and lowering of the soil pH. Jones and Darrah [25] also reported that malic acid is poor comparison to citric acid for mobilizing micronutrients and P from all the test soils.…”

“…Low molecular weight organic acids released Po rapidly in a short time, and then the release rate slowed down with the increase of time ( Fig- 1 and Fig- 2). Zhu et al [26] suggested that inorganic P and organic P were released by low molecular weight organic acids if the substrates of P and organic acid concentration were enough.…”

Improving Upland Acid Soil Properties And Increasing Maize Yield By Phosphate Rock Application With Organic Acids

“…OAs were able to increase metal cations such as Al and Fe so that they had nutrients, especially P, that became available. OAs passed through groups that bind ions such as Al and Fe in soil solution so that the phosphate chelated by Al and Fe would function and become available P. As reported by Park et al [33], Ch'ng et al [3], and Xie et al [44], the addition of OAs will increase the available P. Furthermore, Zhu et al [38] reported an increase in P inorganic and P organic soils with the addition of OAs followed by oxalic acid > citric acid > malic acid. According to Zhu et al [38], oxalic acid and malic acid more efectively and least efectively released Pi than citric acid, respectively.…”

“…Inorganic P and organic P were released by LMWOAs, followed by oxalic acid > citric acid > malic acid if the substrates of P and LMWOAs were enough. LMWOAs can signifcantly promote P availability in acidic soils [34,[36][37][38]. Te P removal efciency was worst afected by citric acid in the optimal pH range of 9.0-10.5, followed by succinic acid and acetic acid [37].…”