Seasonal variation in ammonia compensation point and nitrogen pools in beech leaves (Fagus sylvatica) |
| |
Authors: | Liang Wang Yingchun Xu Jan Kofod Schjoerring |
| |
Institution: | 1. Plant and Soil Science Section, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Copenhagen, Denmark
|
| |
Abstract: | Ammonia (NH3) fluxes between beech leaves (Fagus sylvatica) and the atmosphere were investigated in a 90-year-old forest canopy and related to leaf nitrogen (N) pools and glutamine synthetase (GS) activities. The stomatal ammonia compensation point, ?? NH3, was measured by both a twig cuvette and bioassay techniques involving measurements of pH and ammonium (NH 4 + ) concentration in the leaf apoplastic solution. The ?? NH3 determined on the basis of the gas exchange measurements followed a seasonal variation with early-season peaks during leaf expansion (9.6 nmol NH3 mol?1 air) and late-season peaks during leaf senescence (7.3 nmol NH3 mol?1 air). In the mid-season, the ?? NH3 of mature green leaves was much lower (around 3 nmol NH3 mol?1 air) and dropped below the NH3 concentration in the ambient atmosphere. For comparison, ?? NH3 obtained by the apoplastic bioassay were 7.0, 3.7 and 6.4 nmol NH3 mol?1 air in early-, mid-, and late -season, thus agreeing reasonably well with ?? NH3 values derived from the gas exchange measurements. Potential NH3 emission fluxes during early and late season were 1.31 and 0.51 nmol m?2 leaf surface area s?1, respectively, while leaves were a sink for NH3 during mid-season. During leaf establishment and senescence, both apoplastic and bulk tissue NH 4 + concentrations were relatively high coinciding with low activities of glutamine synthetase, which is a key enzyme in leaf N metabolism. In conclusion, the exchange of NH3 between beech leaves and the atmosphere followed a seasonal variation with NH3 emission peaks being related to N mobilization during early leaf establishment and remobilization during late leaf senescence. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|