Record ID No. |
1802 |
Author(s) |
Clemmensen, K.E., Sorensen, P.L., Michelsen, A., Jonasson, S., Strom, L , 2008 |
Affiliation |
Univ Copenhagen, Inst Biol, Dept Terr Ecol, Oster Farimagsgade 2D, DK-1353 Copenhagen K, DENMARK |
Title |
Site-dependent N uptake from N-form mixtures by arctic plants, soil microbes and ectomycorrhizal fungi |
Source. Vol.(no):Page |
Oecologia.155(4):771-783p. |
Categories |
Ectomycorrhiza |
Subjects |
Biochemistry |
Sub-subjects |
Miscellaneous |
Organism |
n.a. |
Country |
DENMARK,Europe |
Abstracts |
Soil microbes constitute an important control on nitrogen (N) turnover and
retention in arctic ecosystems where N availability is the main constraint on primary production.
Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific N pools
available in various arctic ecosystems. We report here our study on the N uptake patterns of
coexisting plants and microbes at two tundra sites with contrasting dominance of the circumpolar
ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH4+-N and NO3--N, with one N
form labelled with N-15 at a time, and in the case of glycine, also labelled with C-13, either
directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6,
7.7 and 9.1% (heath tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH4+- and
NO3--N-15, respectively, recovered in the plant-soil system, and the major part of N-15 in the
soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days,
microbial N turnover transferred about half of the immobilized N-15 to the non-extractable soil
organic N pool, demonstrating that soil microbes played a major role in N turnover and retention
in both tundra types. The ECM mycelial communities at the two tundras differed in N-form
preferences, with a higher contribution of glycine to total N uptake at the heath tundra;
however, the ECM mycelial communities at both sites strongly discriminated against NO3-. Betula
nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants
is modulated by the N uptake patterns of both fungal and plant components of the symbiosis and by
competitive interactions in the soil. Our field study furthermore showed that intact free amino
acids are potentially important N sources for arctic ECM fungi and plants as well as for soil
microorganisms. |