Uptake of organic nitrogen by eight dominant plant species in Kobresia meadows

Abstract

N-15-labelled glycine experiments were carried out in both a Kobresia pygmaea meadow and a Kobresia humilis meadow to investigate whether alpine plants can take up organic nitrogen directly from the soil and whether different plant species differ in this respect. Eight plant species were selected in the two meadows, five in the Kobresia humilis meadow and four in the Kobresia pygmaea meadow, with one common species. After 4 h following N-15 injection, atom% excess N-15 in the aboveground parts of Ptilagrostis concinna was about 0.012, higher than in the aboveground parts of the other three species in the Kobresia pygmaea meadow, while that in the aboveground parts of Festuca ovina was higher than in the aboveground parts of the other four species in the Kobresia humilis meadow. After 1 day all the values for atom% excess N-15 were substantially higher, except in the aboveground parts of Gentiana straminea in the Kobresia pygmaea meadow and in the aboveground parts of Festuca ovina and Gentiana aristata in the Kobresia humilis meadow. One day after N-15 injection, atom% excess 15N in the roots was higher than that in any of the aboveground parts. In the first 4 h, uptake rates of organic nitrogen by the four species in the Kobresia pygmaea meadow were in the range of 0-0.83 mumol g(-1) h(-1), with a value of 1.43 mumol g(-1) h(-1) for the roots. In contrast, those of five species and the roots in the Kobresia humilis meadows varied between 1.34-8.08 mumol g(-1) h(-1). Key species such as Kobresia pygmaea and Kobresia humilis showed a greater capacity to take up organic nitrogen than non-key species over a 5-day period. This implies that alpine plants can take up organic nitrogen from the soil, but uptake capacity varies widely among different species, and for the same species from different Kobresia meadows.