Susceptibility to photoinhibition of three deciduous broadleaf tree species with different successional traits raised under various light regimes

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.