Effects of Wildfire on the Adsorption-Desorption of Soil Free Amino Acids in a Dahurian Larch Forest in Northeast China

The objective of this study was to evaluate the effects of wildfire on the adsorption-desorption of soil free amino acids in a Dahurian larch forest in Northeast China. The study examined the adsorption and desorption of glutamic acid (Glu), glycine (Gly), and lysine (Lys) using the batch equilibrium method in two soil depths-surface soil (0–5 cm) and subsurface soil (5–10 cm)-under unburned (UB) and heavily burned (HB) conditions. Regardless of wildfire occurrence, the adsorption and desorption curves at the same exogenous concentration were determined by the types of the amino acid. Adsorption decreased in the order Lys > Gly > Glu, and desorption decreased in the order Lys > Glu > Gly. Five years after the wildfire, the adsorption of the three amino acids increased, but surface Lys adsorption decreased. An increase in the amount of clay was beneficial for the adsorption of Glu and Lys, and an increase in the amount of free iron oxide (Fe_d) promoted the adsorption of Gly. Wildfire also promoted the desorption of Gly caused by decreased soil organic matter (SOM) and inhibited the desorption of Lys and subsurface Glu, which were the combined results of these three changes in Fe_d, amorphous iron oxides (Fe_ox) and free aluminum oxide (Al_d). Overall, 5 years after the wildfire, the fixation and re-release of the three free amino acids were still affected by fire disturbance in the cold temperate coniferous forest of the Daxing’an Mountains.