 |
| Titel |
Vertical structure and diurnal variability of ammonia exchange potential within an intensively managed grass canopy |
| VerfasserIn |
B. Herrmann, M. Mattsson, S. K. Jones, P. Cellier, C. Milford, M. A. Sutton, J. K. Schjoerring, A. Neftel |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 1 ; Nr. 6, no. 1 (2009-01-06), S.15-23 |
| Datensatznummer |
250003311
|
| Publikation (Nr.) |
 copernicus.org/bg-6-15-2009.pdf |
|
|
|
|
|
| Zusammenfassung |
Stomatal ammonia compensation points (χs) of grass species on a mixed
fertilized grassland were determined by measurements of apoplastic
[NH4+] and [H>+] in the field. Calculated χs values were
compared with in-canopy atmospheric NH3 concentration (χa)
measurements.
Leaf apoplastic [NH4+] increased by a factor of two from the
lowest level in the canopy to the top level. Bulk leaf [NH4+] and
especially [NO3−] slightly increased at the bottom of the canopy
and these concentrations were very high in senescent plant litter.
Calculated χs values were below atmospheric χs at
all canopy levels measured, indicating that the grassland was characterized
by NH3 deposition before cutting. This was confirmed by the χa
profile, showing the lowest χa close to the ground (15 cm above soil
surface) and an increase in χa with canopy height. Neither χs
nor χa could be measured close to the soil surface, however, the
[NH4+] in the litter material indicated a high potential for
NH3 emission.
A diurnal course in apoplastic [NH4+] was seen in the regrowing
grass growing after cutting, with highest concentration around noon. Both
apoplastic and tissue [NH4+] increased in young grass compared to
tall grass. Following cutting, in-canopy gradients of atmospheric χa
showed NH3 emission but since calculated χs values of the cut
grass were still lower than atmospheric NH3 concentrations, the
emissions could not entirely be explained by stomatal NH3 loss. High
tissue [NH4+] in the senescent plant material indicated that this
fraction constituted an NH3 source. After fertilization,
[NH4+] increased both in apoplast and leaf tissue with the most
pronounced increase in the former compared to the latter. The diurnal
pattern in apoplastic [NH4+] was even more pronounced after
fertilization and calculated χs values were generally higher, but
remained below atmospheric [NH3]. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|