Influenza della siccità estiva sull'accrescimento primaverile in Juglans regia L.

Ejji:ct ojlate swnmer drought on spring growth in Juglans regia L The effect of a drought peri od, imposed towards the end of the exponential phase of growth in 1998, was studied o n walmzt plants (Juglans regia L). Photosynthesis, growth and storagc carbohydrate accumulation were strongly affccted by watcr stress. The reduced photosyntheszs m drought~ stressed plants caused an almost immediate inhibition of stem collar diametri ca l growth and a strong reduction zn total storage carbohydrate content. Carbon isotope discrimination analysis indicated a strong contribution of photosynthetic products synthesised during the drought peri od t o star<.:.h accumulateci in the latera! roots a t the end of the season During spring !999, early shoot growth was supported by carbohydrates assimilateci during the drought period and was strongly affected by water stress suffered in the previous season. Indeed, plants that were subjected to drought in 1998, were characterzsed by earlier bue! break, recluced shoot an d stem collar spring growth rate an d reduced leaf area, compared to contro! plants. l n conclusion, although during the season 1999 ali plants were maintained at field capacity, those subjected to drought in the prcvious year showed a clear residua! effect of watcr stress that Iasted for all the season.