Soil amino composition across a boreal forest successional sequence

Abstract

I examined the landscape, temporal, and vertical patterns of soil amino acid composition 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 Tanana River successional sequence in interior Alaska in June, August, and September 2001; water-extractable amino acid composition and concentration were determined by HPLC. I also assessed differences among the forest floor (Oe/Oa), buried organic horizons (BOHs), and mineral horizons in balsam poplar and white spruce soils. Irrespective of successional stage, month, or horizon, the dominant amino acids were alanine, asparagine, aspartic acid, glutamic acid, glutamine, and histidine, accounting for roughly 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. Amino acid composition and concentration were generally constant throughout the growing season. Amino acid concentrations were highest in the Oe/Oa horizon and rapidly decreased with depth. BOHs generally had greater amino acid concentrations than the surrounding mineral horizons. These results further demonstrate that amino acids are important components of the biogeochemical diversity of nitrogen forms in boreal forests.