Vortrag, Annual Meeting of the Britisch Ecological Society, Lancaster: 07.09.2004 - 09.09.2004
It is becoming increasingly apparent that the uptake of soil organic N can contribute substantially to plant nutrition in many ecosystems, including arctic and alpine tundra, boreal forest and subtropical rainforest . Most of the work, however, has been done in N-limited natural ecosystems, where the concentration of amino acids often exceeds that of inorganic N and therefore its potential uptake is considered especially important. Still, agricultural settings, e.g. grasslands, may also have high concentrations of soluble organic N in soil and considerable uptake of intact glycine has been shown to occur in these systems . Recent field studies revealed that more glycine is taken up by plants of low productivity grasslands where amino acids were the dominant soluble N form in soil than in fertilised grasslands where inorganic N dominates the plant available N pool . There are many amino acids present in the soil. However, most of the work focuses on the uptake of glycine being the smallest and simplest amino acid and also among the ones most commonly found. Still, amount and composition of total free amino acids in soil solution highly depends on soil characteristics such as pH and is liable to pronounced seasonal changes. Especially in unfertilized grasslands, more complex amino acids can show equal abundances in field soil solutions and amino acids like e.g. arginine built up as much as 17 % of the pool of TFAA. Uptake capacities of amino acids of varying complexity might therefore contribute to species abundances in differing grassland systems. To study this issue we assessed plant uptake of a range of amino acids in a temperate grassland system. Specifically, we investigated preferential uptake of dual-labelled (13C and 15N) glycine, serine, arginine and phenylalanine, as compared to inorganic N, by plants in a microcosm experiment with natural field soil. Five grass species were selected to represent those that occur along a fertility gradient ranging from improved, fertilised Lolium dominated grassland, through to unfertilised, less productive Agrostis-Festuca grassland.
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