Record ID No. |
1742 |
Author(s) |
Hobbie, EA; Colpaert, JV; White, MW; Ouimette, AP; Macko, SA. , 2008 |
Affiliation |
Hobbie EA, Univ New Hampshire, Complex Syst Res Ctr, Durham,NH 03824 USA |
Title |
Nitrogen form, availability, and mycorrhizal colonization affect biomass and nitrogen isotope patterns in Pinus sylvestris |
Source. Vol.(no):Page |
Plant and Soil, 310(1-2): 121-136 |
Categories |
Ectomycorrhiza |
Subjects |
Biochemistry |
Sub-subjects |
Miscellaneous |
Country |
USA, North America |
Abstracts |
Nitrogen (N) isotope patterns are useful for understanding carbon and nitrogen dynamics in mycorrhizal systems but questions remain about how different N forms, fungal symbionts, and N availabilities influence delta N-15 signatures. Here, we studied how biomass allocation and delta N-15 patterns in Pinus sylvestris L. Cultures were affected by nitrogen supply rate (3% per day or 4% per day relative to the nitrogen already present), nitrogen form (ammonium versus nitrate), and mycorrhizal colonization by fungi with a greater (Laccaria laccata) or lesser (Suillus bovinus) ability to assimilate nitrate. Mycorrhizal (fungal) biomass was greater with ammonium than with nitrate nutrition for Suillus cultures but similar for Laccaria cultures. Total biomass was less with nitrate nutrition than with ammonium nutrition for nonmycorrhizal cultures and was less in mycorrhizal cultures than in nonmycorrhizal cultures. The sequestration of available N by mycorrhizal fungi limited plant N supply. This limitation and the higher energetic cost of nitrate reduction than ammonium assimilation appeared to control plant biomass accumulation. Colonization decreased foliar delta N-15 by 0.5 to 2.2 parts per thousand (nitrate) or 1.7 to 3.5 parts per thousand (ammonium) and increased root tip delta N-15 by 0 to 1 parts per thousand (nitrate) or 0.6 to 2.3 parts per thousand (ammonium). Root tip delta N-15 and fungal biomass on root tips were positively correlated in ammonium treatments (r(2) = 0.52) but not in nitrate treatments (r(2) = 0.00). Fungal biomass on root tips was enriched in N-15 an estimated 6-8 parts per thousand relative to plant biomass in ammonium treatments. At high nitrate availability, Suillus colonization did not reduce plant delta N-15. We conclude that: (1) transfer of N-15-depleted N from mycorrhizal fungi to plants produces low plant delta N-15 signatures and high root tip and fungal delta N-15 signatures; (2) limited nitrate reduction in fungi restricted transfer of N-15-depleted N to plants when nitrate is supplied and may account for many field observations of high plant delta N-15 under such conditions; (3) plants could transfer assimilated nitrogen to fungi at high nitrate supply but such transfer was without N-15 fractionation. These factors probably control plant delta N-15 patterns across N availability gradients and were here incorporated into analytical equations for interpreting nitrogen isotope patterns in mycorrhizal fungi and plants. |