Soil amino acid utilization among species of the Cyperaceae: Plant and soil processes

Amino acids are released during the decomposition of soil organic matter an d have been shown to be utilized as a nitrogen source by some non-mycorrhiz al species in the family Cyperaceae (the sedge family). Twelve out of 13 Cy peraceae species examined in the current study were capable of absorbing so il amino acids in the non-mycorrhizal state. With two exceptions (two speci es in the genus Kobresia), species from subalpine or alpine habitats exhibi ted lower rates of total nitrogen uptake compared to species from more temp erate habitats, which is possibly explained by lower growth rates in the al pine and subalpine species and a lower overall demand for soil nitrogen. Th e alpine and subalpine species exhibited higher rates of glycine uptake rel ative to NH4+ and NO3 uptake, compared to species from the more temperate h abitats. This may reflect specialization toward the uptake of organic N in the alpine and subalpine species. In three ecosystems where sedges commonly occur, amino acids were present i n the soil pore water, but in highly variable amounts. Seasonal maximum ami no acid concentrations in alpine soil pore water ranged from 13 to 158 mu m ol/L in four dry meadow sites. The most common amino acid in these alpine s oils was glycine. In a subalpine fen habitat, aspartate was the most common ly observed amino acid, and total amino acid concentrations were 15-20 mu m ol/L. In a shortgrass steppe habitat, glutamate was the most abundant amino acid, and total amino acid concentrations were 25-45 mu mol/L. Soil protease activities correlated positively with soil protein content wh en all three ecosystems (alpine, subalpine fen, and shortgrass steppe) were considered together. The addition of protein (as casein) significantly inc reased soil protease activity, indicating that soil protein content contrib utes to the capacity to generate soil amino acids. Soil protein contents co rrelated positively with total soil N content when the alpine and shortgras s steppe sites were considered together. The retention of NH4+ and amino ac ids on the alpine soil was high compared to soils of lower organic matter c ontent that have been investigated in past studies. We conclude that (1) th e potential to take up amino acids in non-mycorrhizal roots of the family C yperaceae is widespread among species native to a variety of different habi tats, (2) amino acids are available for uptake (though most abundant in the alpine), (3) the potential to generate soil amino acids is proportional to soil protein concentration, and (4) soil amino acids can be retained in th e soil at high levels, leading to the conclusion that the soil binding affi nity of amino acids may constrain uptake by plant roots and microorganisms.