COLD-INDUCED PHOTOINHIBITION AND GROWTH OF SEEDLING SNOW GUM (EUCALYPTUS-PAUCIFLORA) UNDER DIFFERING TEMPERATURE AND RADIATION REGIMES IN FRAGMENTED FORESTS

Fluorescence characteristics and growth of seedling snow gum (Eucalypt us pauciflora Sieb, ex Spreng,) during autumn and winter were related to variation in radiation and temperature regime in a fragmented fores t. Seedlings were planted in four treatments along transects perpendic ular to tree island edges to characterize plant responses to microclim ates ranging from those of cleared areas to those beneath forest canop ies, Three-dimensional mapping of seedling leaf display, in combinatio n with information retrieved from hemispherical photographs about shad ing from overstory canopies, were used to calculate the intercepted am ounts of direct radiation energy for unit area of leaves on clear days (IDRE), IDRE was highest on the outside, most variable at the edges a nd lowest well inside the tree islands. Minimum temperature decreased with increasing view of the sky. Photoinhibition, measured as decrease in F-v/F-m, was correlated with spatial and seasonal differences in w eekly minimum temperature and IDRE, Seedlings in the open and under th e most canopy cover, with low variability in IDRE in a scale of weeks, exhibited less variability in photoinhibition than those growing alon g forest edges. Seedlings in the open tended to be most photoinhibited and grew the most. The combination of increased IDRE with reduced min imum temperatures resulted in persistent and strong photoinhibition as the season progressed. Results are discussed in relation to the poten tial for seedling establishment following forest fragmentation.