Effects of organic acid on organic phosphorus and mineralization of typical temperate forest soils

The effects of different concentrations (10,25,50 and 100 mmol/L) of oxalic acid, citric acid and acetic acid on soil organic phosphorus and mineralization in different stand types (natural birch secondary forest, Pinus koriensis plantation, larch plantation and virgin Betula costata-P. koriensis forest) of typical temperate forest were studied by using 120-day indoor incubation methods. The results showed that inorganic phosphorus was dominant in A layer soil in P. koriensis plantation, but organic phosphorus was dominant in the other 3 stands and accounted for more than 50% of total phosphorus. Three types of acids significantly changed the proportion of organic phosphorus in the larch plantation soil. The mineralization rate of organic phosphorus was the maximum after 0-30 days incubation, amount of organic phosphate mineralization(AM) and mineralization rate (MR) were significantly increased under the organic acid treatment(P 0.05). When organic acid concentration was 10 mmol/L, AM and MR were the highest in birch natural secondary forest soil under the citric acid treatment,in P. koriensis plantation soil under the oxalic acid treatment, in larch plantation and virgin B. costata-P. koriensis forest under the acetic acid treatment, respectively; when organic acid concentration was higher than 10 mmol/L, AM and MR were the highest in all forest soil under the acetic acid treatment, particularly its priming effect on the mineralization of soil organic phosphorus was strongest in P. koriensis plantation, increased MR by 60.84%. With the acid concentration increasing, AM and MR increased, but organic phosphorus decreased. During 30-120 days of incubation, with the acid concentration increasing, the difference in AM and MR between the acid types and between their concentrations would decrease, CMR would increase during the whole incubation period, the acid concentration was not the major factor limiting the change of soil organic phosphorus, and the acidification and the number of hydroxyl and carboxyl groups of organic acid only had weak influence on the organic phosphorus mineralization.