I. Nijs et al., LEAF NITROGEN-CONTENT AS A PREDICTOR OF PHOTOSYNTHETIC CAPACITY IN AMBIENT AND GLOBAL CHANGE CONDITIONS, Journal of biogeography, 22(2-3), 1995, pp. 177-183
Leaf assimilation capacity in Lolium perenne, grown in elevated CO2 le
vel (700 mu mol mol(-1)) and/or increased air temperature (ambient + 4
degrees C) could be predicted from leaf N content expressed on an are
a basis, although the linear relationships between maximum carboxylati
on rate (Vc(max)) Or maximum electron transport rate (J(max)) and leaf
N depended on treatment. The model, based on Farquhar, Von Caemmerer
& Berry (1980) showed negative long-term effects of increased air temp
erature on Vc(max) and J(max) while longterm exposure to increased CO2
level affected only Vc(max). Acclimation responses to these global ch
anges therefore could not be explained by changes in N-content alone,
but also in terms of changes in photosynthetic nitrogen use efficiency
. Stimulation of photosynthesis by elevated CO2 was not affected by re
duction of leaf N in leaves developed in ambient air temperature, whil
e part of the CO2 benefit was lost in leaves developed in increased ai
r temperature. This suggests that N-deficient ecosystems maintain the
potential to respond to elevated CO2 concentration, unless other proce
sses than the primary carbon metabolism become limiting at low N suppl
y. Similar to nitrogen content, changes in photon flux density did not
change the CO2 benefit either, unless a transition occurred from one
limiting process to another (electron transport to carboxylation or vi
ce versa). Hypotheses on interaction between CO2 level, nitrogen statu
s of the leaf and light intensity are formulated to support these find
ings.