 |
| Titel |
Contrasting effects of long term vs short term N addition on foliar CO2 exchange parameters of two common Arctic peat land plant species |
| VerfasserIn |
Martine Janet Van de Weg, Gaius Shaver, Verity Salmon |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046502
|
|
|
|
|
|
| Zusammenfassung |
| The productivity of Arctic peatlands is generally limited by cold temperatures, short growing
seasons and low nitrogen (N) supply. However, due to increased deposition rates as a
consequence of anthropogenic activity, as well as through higher mineralization
rates following climate warming, the N availability in the Arctic ecosystems is
expected to increase. In fertilizer experiments, higher N availability is known to
increase primary production as well as the leaf area index. Furthermore, N addition
changes species composition: shrub cover typically increases while bryophyte cover
decreases. Less is known, however, about the effects of N addition on the leaf CO2
exchange parameters. Previous N addition experiments in Arctic peat lands (lasting 1-4
years) showed some increases in the leaf level net C-uptake, though this response
was inconsistent among species. It is also unclear whether this response can be
extrapolated to a prolonged period of elevated N supply (> 20 years). Moreover, less is
known about whether and how the investment of N in different components of the
photosynthetic apparatus changes following short or long term N addition. The latter
is of particular interest, since in many vegetation models or upscaling exercises
the parameters determining leaf level C-uptake are scaled by the amount of foliar
N.
The aims of our study were (1) to investigate the effects of short and long term N addition
on the foliar CO2exchange parameters of Arctic peat land species, and (2) to determine
relative N investment in different parts of the photosynthetic apparatus after short
and long term N addition. We compared the carboxylation efficiency of Rubisco
(Vcmax), electron transport capacity (Jmax), dark respiration (Rd), chlorophyll content
and total foliar N of sun lit leaves from two species after short term (6 weeks),
and longer term (4 years and 21 years) N (and P) addition. The species included
were Betula nana and Eriophorum vaginatum and the experiments were carried
out in moist acidic tussock tundra in Northern Alaska, near the Toolik Lake field
station.
(1) For both B. nana and E. vaginatum no significant differences in Vcmaxand Jmax were
observed after short and long term N addition. In contrast, Rd was significantly higher in both
species after 24 years of N addition, but not in the shorter term treatments. (2) For E.
vaginatum, the N content did not change greatly after short or long term N addition, and
hence no significant differences in partitioning of N to the photosynthetic parameters
were found. For B. nana, however, the foliar N was increased by 20 to 50% as a
consequence of 6 weeks to 24 years of N addition, respectively. In other words, for B.
nana the photosynthetic N use efficiency decreased with increasing N availability.
The amount of chlorophyll increased only for B. nana in the 6 weeks N addition
treatment.
Overall, these results show that the effects of N addition on plot level productivity
observed in other studies are not a consequence of changes in the photosynthetic capacity per
unit leaf area. It also implies that species from N-limited areas like Arctic peatlands might
already optimize their photosynthetic capacity and that the photosynthetic capacity:
N ratio is flexible within one species. Finally, the Rd results showed that some
effects of increased N addition can only be observed after more than two decades of
fertilisation, which underlines the importance of long term ecological experiments. |
|
|
|
|
|
|