Soil amino acid composition across a boreal forest successional sequence

Soil amino acids are important sources of organic nitrogen for plant nutrition, yet few studies have examined which amino acids are most prevalent in the soil. In this study, we examined the composition, concentration, and seasonal patterns of soil amino acids across a primary successional sequence encompassing a natural gradient of plant productivity and soil physicochemical characteristics. Soil was collected from five stages (willow, alder, balsam poplar, white spruce, and black spruce) of the floodplain successional sequence on the Tanana River in interior Alaska. Water-extractable amino acid composition and concentration were determined by HPLC. Irrespective of successional stage, the amino acid pool was dominated by glutamic acid, glutamine, aspartic acid, asparagine, alanine, and histidine. These six amino acids accounted for approximately 80% of the total amino acid pool. Amino acid concentrations were an order of magnitude higher in coniferous-dominated late successional stages than in early deciduous-dominated stages. The composition and concentration of amino acids were generally constant throughout the growing season. The similar amino acid composition across the successional sequence suggests that amino acids originate from a common source or through similar biochemical processes. These results demonstrate that amino acids are important components of the biogeochemical diversity of nitrogen forms in boreal forests. (C) 2009 Elsevier Ltd. All rights reserved.