The Dynamic Of Free Amino Acid Content And Its Measurement Methods In Temperate Forest Soil

Free amino acid was one of the important nitrogen sources, and significant in plant nitrogen nutrition, it played a critical role in soil-N cycling in nitrogen cycling in forests and forest soils, became more and more important in evaluating nitrogen nutrition in soils, so it was of great significant to study free amino acid in forest soils. In this paper we studied content and seasonal dynamic of free amino acid, correlation between free amino acid and other N forms in soil and soil property, fate of free amino acid, net amino acid N production, net soluble organic N production, net N mineralization and net nitrification, gross proteolysis, and facts of impacting free amino acid, soluble organic nitrogen and gross proteolysis experiment analysis in Dark Brown Soil in primitive korean pine forest and its secondary broadleaved forest in northeast China, which were typical forests in temperate mixed forest.The main results were as follows:(1) The free amino acids content range was respectively78.44-151.66μgN-g-1and7.61-56.15μgN-g-1in primitive korean pine forest and white birch secondary forest soil; the size order of free amino acids content of every soil layer is rhizosphere soil>soil Al layer in July, fermentation litter layer> rhizosphere soil>soil Al layer in August and Fermentation litter layer>Fresh litter layer> rhizosphere soil>soil Al layer in October in primitive korean pine forest and white birch secondary forest soil. Correlation analysis showed that free amino acid content was correlation with pH, total nitrogen content and alkali-hydrolyzable content in soil Al layer and rhizosphere soil, and the free amino acid of litter layer was correlation with pH and total nitrogen content.(2) The net free amino acids production rate range was respectively-3.97μgN·(g·d)-1～3.25μgN·(g·d)-1and-0.54μgN·(g·d)-1～1.93μgN·(g·d)-1in primitive korean pine forest and white birch secondary forest soil; the free amino acids content varied with the depth of soil layer, was shown as:Fermentation litter layer>rhizosphere soil>soil Al layer; the free amino acids content in the two forests were generally shown as primitive korean pine forest>white birch secondary forest(except fermentation litter layer in October).(3) The native proteolysis range was respectively73.78～158.53μmolAA·g-1·5h-1and63.60-114.13μmolAA·g-1·5h-1in primitive korean pine forest and white birch secondary forest soil; and the potential proteolysis range was respectively96.80～222.05μmolAA·g-1·5h-1�'�92.20～233.57μmolAA·g-1·5h-1; the native proteolysis and potential proteolysis varied with the depth of soil layer, were both shown as:Fermentation litter layer>rhizosphere soil>soil Al layer; native potential was manifested as primitive korean pine forest>white birch secondary forest. (4) The free amino acids content that was extracted with KCl solution significantly greater than that extracted with distilled water in mineral soil, but the effect of extracting agent on the free amino content had not obvious rule in litter layer. The free amino acid content of soil that determined with three treatments that were added toluene and TCA separately and simultaneously were all increased, but that was only significant on that extracted with distilled water. The free amino acids content increased with oscillation time within thirty minutes, and it was no significant increase after thirty minutes. The order of soluble organic nitrogen content extracted from soil with different soil extractant was shown as potassium sulfate>distilled water>potassium chloride, and the difference was significant in three treatments with three soil extractants in mineral soil layer, but it is complex in litter layer, and the difference was not significant in three treatments with three soil extractants.(5) The impact of three buffer solution on soil proteolysis was shown as treatment1(buffer solution prepared with distilled water)> treatment2(mixed solution by buffer solution and KCl solution)> treatment3(buffer solution prepared with KCl solution); the impact of oscillation time on soil proteolysis was shown as5h>lh, and the soil proteolysis size order was treatment2(mixed solution by buffer solution and KCl solution)> treatment3(buffer solution prepared with KCl solution)>treatment1(buffer solution prepared with distilled water); the impact of TCA action time on soil native proteolysis and potential proteolysis was shown as1h>5min, and the size order of soil native proteolysis was treatment2(mixed solution by buffer solution and KCl solution)> treatment3(buffer solution prepared with KCl solution)>treatment1(buffer solution prepared with distilled water), potential proteolysis was not significant except treatment1(buffer solution prepared with distilled water).The soil gross proteolysis decreased with the concentration of adding TCA, and the decrease of soil gross proteolysis stoped when the concentration of TCA was0.55mol·L-1.