which indicated that rates were usually limited by J [5].
Reasons
why the results presented here for soybean concerning the nature
of the limitation to A at elevated CO2 at high PPFD differ from those
for soybean in the SoyFACE system [6] are not known, but might
be related to the fact that in that study, responses of A to Ci were
measured in the laboratory on excised leaves collected as much as
two days after the field measurements [6], rather than responses
of A to Ci measured in situ. This could also account for their conclusion
that leaves at ambient CO2 were mostly also limited by J
rather than VCmax even at midday, which is highly unusual [1]. The
appearance of J limitation could occur in this type of analysis if, for
example, photosynthesis in plants in the field were reduced at the