TY - JOUR
T1 - Seasonal variation in ammonia compensation point and nitrogen pools in beech leaves (Fagus sylvatica)
AU - Wang, Liang
AU - Xu, Yingchun
AU - Schjørring, Jan Kofod
PY - 2011/6
Y1 - 2011/6
N2 - 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, χNH3, was measured by both a twig cuvette and bioassay techniques involving measurements of pH and ammonium (NH4+) concentration in the leaf apoplastic solution. The χNH3 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 χNH3 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, χNH3 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 χNH3 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 NH4+ 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.
AB - 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, χNH3, was measured by both a twig cuvette and bioassay techniques involving measurements of pH and ammonium (NH4+) concentration in the leaf apoplastic solution. The χNH3 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 χNH3 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, χNH3 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 χNH3 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 NH4+ 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.
U2 - 10.1007/s11104-010-0693-7
DO - 10.1007/s11104-010-0693-7
M3 - Journal article
SN - 0032-079X
VL - 343
SP - 51
EP - 66
JO - Plant and Soil
JF - Plant and Soil
IS - 1-2
ER -