Nitrogen inputs and losses in response to chronic CO<sub>2</sub> exposure in a subtropical oak woodland
Rising atmospheric CO<sub>2</sub> concentrations may alter the nitrogen (N) content of ecosystems by changing N inputs and N losses, but responses vary in field experiments, possibly because multiple mechanisms are at play. We measured N fixation and N losses in a subtropical oak woodlan...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-06-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/3323/2014/bg-11-3323-2014.pdf |
| Summary: | Rising atmospheric CO<sub>2</sub> concentrations may alter the nitrogen (N)
content of ecosystems by changing N inputs and N losses, but responses vary
in field experiments, possibly because multiple mechanisms are at play. We
measured N fixation and N losses in a subtropical oak woodland exposed to 11
years of elevated atmospheric CO<sub>2</sub> concentrations. We also explored the
role of herbivory, carbon limitation, and competition for light or nutrients in shaping the response of N fixation to elevated CO<sub>2</sub>.
Elevated CO<sub>2</sub> did not significantly alter gaseous N losses, but lower
recovery and deeper distribution in the soil of a long-term <sup>15</sup>N tracer
indicated that elevated CO<sub>2</sub> increased leaching losses. Elevated
CO<sub>2</sub> had no effect on nonsymbiotic N fixation, and had a transient effect
on symbiotic N fixation by the dominant legume. Elevated CO<sub>2</sub> tended to
reduce soil and plant concentrations of iron, molybdenum, phosphorus, and
vanadium, nutrients essential for N fixation. Competition for nutrients and
herbivory likely contributed to the declining response of N fixation to
elevated CO<sub>2</sub>. These results indicate that positive responses of N
fixation to elevated CO<sub>2</sub> may be transient and that chronic exposure to
elevated CO<sub>2</sub> can increase N leaching. Models that assume increased
fixation or reduced N losses with elevated CO<sub>2</sub> may overestimate future
N accumulation in the biosphere. |
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| ISSN: | 1726-4170 1726-4189 |