Inter-specific variability in organic nitrogen uptake of three temperate grassland species.

We tested the inter-specific variability in the ability of three dominant grasses of temperate grasslands to take up organic nitrogen (N) in the form of amino acids in soils of differing fertility. Amino acid uptake was determined by injecting dual labeled glycine-2-13C-15N into the soil, and then measuring the enrichment of both 13C and 15N in plant tissue after 50 hours. We found enrichment of both 13C and 15N in root and shoot material of all species in both soils, providing first evidence for direct uptake of glycine. We show that there was considerable inter-specific variability in amino acid uptake in the low fertility soil. Here, direct uptake of amino acid was greater in the grass Agrostis capillaris, which typically dominates low fertility grassland, than Lolium perenne, which inhabits more fertile sites. Direct uptake of amino acid for Holcus lanatus. was intermediate between the above two species. Unlike in the low fertility soil, there was no difference in uptake of either 13C or 15N by grasses in the high fertility soil, where uptake of mineral N is thought to be the major mechanism of N uptake of these grasses. Overall, our findings may contribute to our understanding of differences in competitive interactions between grasses in soils of different fertility status