such as high temperature and water stress in the field, possibly due to their lower plasticity in leaf anatomy to low light environment.Key-words: chlorophyll fluorescence; photodamage; photoprotection; photosynthesis; successional types. INTRODUCTIONphotoinhibition, which is defined as the slow reversible decline of photosynthetic efficiency, occurs when absorbed light is in excess of that required for carbon assimilation (Powles 1984; Demmig-Adams & Adams 1992; Long, Humphries & Falkowski 1994). It is well known that leaves developed in shade are more vulnerable to photoinhibition than those developed in full sun because shade leaves have a higher light-capturing capacity as a result of larger antenna size of photosystem (PS) II and lower rates of light saturated photosynthesis due to lower amounts of photosynthetic enzymes such as Rubisco (Björkman 1981;Anderson & Osmond 1987;Osmond 1994). Tree seedlings grown in the forest understory are prone to experience photoinhibition under an increased light level through formation of a gap. The significance of photoinhibition in forest succession is reflected in the number of recent studies in this area (Mulkey & Pearcy 1992;Pearcy 1994;Naidu & DeLucia 1997; Lovelock et al. 1998). Effects of photoinhibition could be alleviated after a period of acclimation (Naidu & DeLucia 1997) or by producing new leaves adapted to the new light environment (Mulkey & Pearcy 1992). However, given the competitive environment for light and spaces within forest gaps (Canham & Marks 1985), tree seedlings capable of minimizing photoinhibition and reducing the time lag for acclimation may gain a substantial advantage in growth and regeneration.Species vary considerably in shade tolerance and in their response to the increased light after a gap creation. Some have suggested a trade-off between shade tolerance and gap response (Canham 1989;Bazzaz 1996). In the deciduous broadleaf forests of northern Japan, Quercus mongolica var. crispula Blume is a gap-dependent species. Gap formation is essential to the growth and regeneration of Q. ABSTRACTThe susceptibility to photoinhibition of tree species from three different successional stages were examined using chlorophyll fluorescence and gas exchange techniques. The three deciduous broadleaf tree species were Betula platyphylla var. japonica, pioneer and early successional, Van't.) Hara is a typical shadetolerant species in northern Japan. This species is relatively more shade-tolerant than Q. mongolica as indicated by its higher survival rates in intact forest understory (Higo 1994) and its more effective low-light photosynthesis (Koike 1986; Koike 1988). Therefore, we hypothesized that the intermediate shade-tolerant Q. mongolica is less susceptible to photoinhibition than the shade-tolerant A. mono. In addition, as the endpoint of shade-intolerant species, we also examined the relationship between shade-acclimation and susceptibility to photoinhibition for a pioneer species, Betula platyphylla Sukatchev var. japonica (Miq.) Hara (Koike & ...

Photosynthetic acclimation of deciduous broad-leaved tree species was studied along a vertical gradient within the canopy of a multi-species deciduous forest in northern Japan. We investigated variations in (1) local light regime and CO2 concentration ([CO2]), and (2) morphological (area, thickness and area per mass), biochemical (nitrogen and chlorophyll concentrations) and physiological (light-saturated photosynthetic rate) attributes of leaves of seven major species on three occasions (June, August and October). We studied early successional species, alder (Alnus hirsuta (Spach) Rupr.) and birch (Betula platyphylla var. japonica (Miq.) Hara); gap phase species, walnut (Juglans ailanthifolia Carrière) and ash (Fraxinus mandshurica var. japonica Rupr.); mid-successional species, basswood (Tilia japonica (Miq.) Simonk.) and elm (Ulmus davidiana var. japonica (Rehd.) Nakai); and the late-successional species, maple (Acer mono Bunge). All but maple initiated leaf unfolding from the lower part of the crown. The [CO2] within the vertical profile ranged from 320-350 ppm in the upper canopy to 405-560 ppm near the ground. The lowest and highest ambient [CO2] occurred during the day and during the night, respectively. This trend was observed consistently during the summer, but not when trees were leafless. Chlorophyll concentration was positively related to maximum photosynthetic rate within, but not among, species. Leaf senescence started from the inner part of the crown in alder and birch, but started either in the outer or top portion of the canopy of ash, basswood and maple. Chlorophyll (Chl) to nitrogen ratio in leaves increased with decreasing photon flux density. However, Chl b concentration in all species remained stable until the beginning of leaf senescence. Maximum photosynthetic rates observed in sun leaves of early successional species, gap phase or mid-successional species, and late successional species were 12.5-14.8 micromol m(-2) s(-1), 4.1-7.8 micromol m(-2) s(-1) and 3.1 micromol m(-2) s(-1), respectively.

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Ground-level ozone (O(3)) has gained awareness as an agent of climate change. In this respect, key results are comprehended from a unique 8-year free-air O(3)-fumigation experiment, conducted on adult beech (Fagus sylvatica) at Kranzberg Forest (Germany). A novel canopy O(3) exposure methodology was employed that allowed whole-tree assessment in situ under twice-ambient O(3) levels. Elevated O(3) significantly weakened the C sink strength of the tree-soil system as evidenced by lowered photosynthesis and 44% reduction in whole-stem growth, but increased soil respiration. Associated effects in leaves and roots at the gene, cell and organ level varied from year to year, with drought being a crucial determinant of O(3) responsiveness. Regarding adult individuals of a late-successional tree species, empirical proof is provided first time in relation to recent modelling predictions that enhanced ground-level O(3) can substantially mitigate the C sequestration of forests in view of climate change.

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