THE RESPONSE OF EUROPEAN BEECH (FAGUS-SYLVATICA L) SEEDLINGS FROM 2 ITALIAN POPULATIONS TO DROUGHT AND RECOVERY

The response of gas exchange, leaf chlorophyll content, relative fluor escence to decreasing water potential and recovery was followed in Eur opean beech seedlings from two Italian populations, differing in their native precipitation amounts. A population from Sicily (southern Ital y) was selected as representative of a xeric population while a popula tion from central Italy, Abetone, represented a mesic one. Dry-matter partitioning, leaf area, hydraulic sufficiency and xylem embolism were evaluated in both well-watered control plants as well as in plants su bjected to drought. With the onset of water stress, values of water po tential, leaf relative water content, net photosynthesis, leaf conduct ance and leaf chlorophyll concentration de creased concurrently while relative fluorescence remained unchanged. The population from Sicily s howed a delay in effects of the imposed drought. Within 5 days of rewa tering, leaf conductance was not fully recovered while all of the othe r parameters recovered to control levels, in both populations. Total, shoot, stem and root dry weight tended to be higher in seedlings from Abetone, even though both populations had similar photosynthetic rates . The population from Sicily exhibited about 3% greater (even if not s ignificant) allocation to roots than the population from Abetone. Seed lings from Abetone had higher, but not significant, leaf specific cond uctivity and per cent loss in hydraulic conductivity than seedlings fr om Sicily. Drought resulted in a reduction of hydraulic conductivity a nd hydraulic sufficiency in seedlings from both populations, Photosynt hesis of water stressed plants from both populations appeared to be re duced primarily by carbon dioxide diffusion through stomata and perhap s secondarily by changes in chlorophyll concentration rather than by e fficiency of photosystem II. The effect of hydraulic factors on gas ex change during drought and recovery was not clearly evident.