M. Kitao et al., Susceptibility to photoinhibition of three deciduous broadleaf tree species with different successional traits raised under various light regimes, PL CELL ENV, 23(1), 2000, pp. 81-89
The susceptibility to photoinhibition of tree species from three different
successional stages were examined using chlorophyll fluorescence and gas ex
change techniques. The three deciduous broadleaf tree species were Betula p
latyphylla var. japonica, pioneer and early successional, Quercus mongolica
, intermediate shade-tolerant and mid-successional, and Acer mono, shade-to
lerant and late successional. Tree seedlings were raised under three light
regimes: full sunlight (open), 10% full sun, and 5% full sun. Susceptibilit
y to photoinhibition was assessed on the basis of the recovery kinetics of
the ratio of vaviable to maximum fluorescence (F-v/F-m) of detached leaf di
scs exposed to about 2000 mu mol m(-1) s(-1) photon flux density (PFD) for
2 h under controlled conditions (25 to 28 degrees C, fully hydrated). Diffe
rences in susceptibility to photodamage among species were not significant
in the open and 10% full sun treatments. But in 5% full sun, B. platyphylla
sustained a significantly greater photodamage than other species, probably
associated with having the lowest photosynthetic capacity indicated by lig
ht-saturated photosynthetic rate (B. platyphylla, 9.87, 5.85 and 2.82; Q. m
ongolica, 8.05, 6.28 and 4.41; A. mono, 7.93, 6.11 and 5.08 mu mol CO2 m(-1
) s(-1) for open, 10% and 5% full sun, respectively). To simulate a gap for
mation and assess its complex effects including high temperature and water
stress in addition to strong light on the susceptibility to photoinhibition
, we examined photoinhibition in the field by means of monitoring Delta F/F
'(m) on the first day of transfer to natural daylight. Compared with Delta
F/F'(m) in AM, the lower Delta F/F'(m) in PM responding to lower PFD follow
ing high PFD around noon indicated that photoinhibition occurred in plants
grown in 10 and 5% full sun. The diurnal changes of Delta F/F'(m) showed th
at Q. mongolica grown in 5% full sun was less susceptible to photoinhibitio
n than A. mono although they showed little differences both in photosynthet
ic capacity in intact leaves and susceptibility to photoinhibition based on
leaf disc measurements. These results suggest that shade-grown Q. mongolic
a had a higher tolerance for additional stresses such as high temperature a
nd water stress in the field, possibly due to their lower plasticity in lea
f anatomy to low light environment.