Acetic and formic acids increased in concentration with decomposition of wood chips during a mycoremediation process [48]. Low meanwhile molecular weight organic acids are thought to be responsible for minimizing crop damage by the root-knot nematode Meloidogyne incognita (Kofoid and White (Chitwood)) [49]. Production of gluconic acid by rhizosphere soil bacteria presents an efficient strategy to avoid protozoan grazing. Gluconic acid was shown to cause encystment or death of protozoa [9]. Succinic acid decreased the growth and conidial germination of Fusarium oxysporum f. sp. niveum [50], while propionic, acetic, lactic, malic, and citric acids were all demonstrated to have significant antibacterial effects [51].
Organic acids were found to increase the activity of acid phosphomonoesterase in soil at low concentrations (<1��mol/g), whereas higher concentrations (>5��mol/g) of citric, oxalic, malic, and tartaric acid inhibited this activity [52]. Organic acids also act as adsorbents of acid phosphomonoesterase [4] from minerals and colloids (desorption by up to ca. 60%). This indicates the changes in behaviour of acid phosphomonoesterase in the rhizosphere, where organic acids are released from plant roots, compared to bulk soil. Organic acids in soil are produced by plant root exudation and by activity of soil microorganisms. Phosphate-solubilizing bacteria (Bacillus, Rhodococcus, Arthrobacter, Serratia, Chryseobacterium, Delftia, Gordonia, and Phyllobacterium) which increase P-uptake by plants were reported to produce aliphatic organic acids such as citric, gluconic, lactic, propionic, and succinic acids [53].
Average respiration rates of organic acids (oxalate, citrate) were reported to be around 209nmol/g soil/d, and respiration of organic acids increased with soil depth [6, 39]. Van Hees et al. [21] and Str?m et al. [54] reported rapid degradation of citric, malic, and oxalic acid in most soils. In some cases, organic acid degradation may be inhibited by complexation with Ca (oxalate in calcareous soils); degradation of individual organic acids may also differ between rhizosphere and bulk soil [39, 54]. Forest soils differ in their abilities to anaerobically consume organic acids such as oxalate. The addition of electron donors (acetate, glucose, vanillate, or hydrogen) or acceptors (nitrate or sulphate) did not affect anaerobic consumption of oxalate, whereas CO2 or bicarbonate totally repressed it [55].
There is a paucity of literature on organic acid enantiomers, but what does exist points to the need for urgent study. Liao GSK-3 et al. [25] identified D-tartaric acid in concentrations up to 6��g/g in the rhizosphere of Lactuca sativa L., which, along with L-citric acid, formed the dominant organic acid. A recent review has highlighted the potential importance of future research in this area [56].2.1.1.