Photosynthetic induction responses to variable light under field conditions in three species grown in the gap and understory of a Fagus crenata forest.

摘要

Photosynthetic induction responses to abrupt increases in photon flux density (PFD) (to 800 and 1500μmol m-2 s-1 from either darkness or background 100μmol m-2 s-1) were examined in situ in the leaves of Fagus crenata, Daphniphyllum humile and Acer rufinerve growing in a canopy gap and in the understorey of an F. crenata forest at Naeba Mountain in Niigata Prefecture, Japan, during 1997. F. crenata exhibited the highest assimilation rate (A100), stomatal conductance at the background PFD and A100/Amax (Amax; maximum assimilation rate) in both the canopy gap and the understorey. Time required for full induction depended on both background PFD and maximum PFD. The induction period was 2- to 4-fold shorter at a background PFD than in darkness. Forthe 3 understorey species, the time required to full induction was 2- to 3-fold longer when irradiance was increased from darkness to 800μmol m-2 s-1 than when irradiance was increased from darkness to 1500μmol m-2 s-1. A. rufinerve exhibited higher initial stomatal conductance (gs0) and a shorter induction period in the understorey than in the canopy gap, F. crenata exhibited a similar gs0 and induction period in both habitats, while D. humile demonstrated lower gs0 and a longer induction period in the understorey than in the gap. It is concluded that initial stomatal conductance is closely correlated with the photosynthetic induction response and that the photosynthetic induction response is affected by the light conditions experienced by plants before the sudden increase in irradiance and by the extent of the increase in irradiance.