Elevated carbon dioxide effects on nitrogen dynamics in grasses, with emphasis on rhizosphere processes
Three perennial grass species, perennial ryegrass (Lolium perenne L.), colonial bentgrass (Agrostis capillaris L.), and sheep fescue (Festuca ovina L.), were grown at two CO{sub 2} concentrations (350 and 700 {micro}L L{sup {minus}1}) and under two N regimes: one with a minor addition of 8 kg N ha{sup {minus}1} and one with an addition of {approximately}278 kg N ha{sup {minus}1}, both labeled with {sup 15}N. The effects of elevated CO{sub 2} on {sup 15}N and N uptake and dynamics in the plant-soil systems were determined after 32 and 55 d, with close attention to the rhizosphere. Total N uptake by the plants was not affected by elevated CO{sub 2}, compared with ambient CO{sub 2}, independent on N treatment and grass species. A clear decrease from 1.77 at ambient CO{sub 2} to 1.25 at elevated CO{sub 2} was observed in the shoot/root (S/R) ratio of N, resulting from a significant decrease of the N concentration in shoots, and an unchanged root N concentration. At 700 {micro}L L{sup {minus}1} CO{sub 2}, N concentration in the shoots decreased from 12.9 to 9.9 g kg{sup {minus}1}, even at the low N supply, whereas the slight decrease in root N concentration for plants grown at elevated CO{sub 2} was not significantly different. The relative increase of {sup 15}N found in the rhizosphere soil microbial biomass (SMB) and the rhizosphere soil residue under elevated CO{sub 2} was too small to affect plant growth, even in the low N treatment. The total amount of {sup 15}N recovered in the plants was not affected by the CO{sub 2} treatment. Although at the second harvest slightly more {sup 15}N was found in the plants than at the first harvest, probably due to turnover of the SMB, no interaction with CO{sub 2} was observed. This shows that the fertilizer {sup 15}N had not been immobilized to a larger extent or for a longer time by the SMB at elevated CO{sub 2} than under ambient CO{sub 2}, even independent of N level and grass species. No evidence was found that under elevated CO{sub 2} substantial amounts of N had been immobilized by the SMB, nor than mineralization of native soil organic matter (SOM) had been stimulated by an increased supply of substrate to the SMB. The authors conclude that elevated CO{sub 2} has the potential to induce significant changes in plant N nutrition, modifying N allocation and tissue quality within perennial grasses, but that these effects appear to be independent of the SMB.
- Research Organization:
- Research Inst. for Agrobiology and Soil Fertility, Wageningen (NL)
- OSTI ID:
- 20062563
- Journal Information:
- Soil Science Society of America Journal, Vol. 63, Issue 6; Other Information: PBD: Nov-Dec 1999; ISSN 0361-5995
- Country of Publication:
- United States
- Language:
- English
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