WATER RELATIONS, GAS-EXCHANGE, AND GROWTH OF RESPROUTS AND MATURE PLANT SHOOTS OF ARBUTUS-UNEDO L AND QUERCUS-ILEX L

Resprout and mature plant shoot growth, leaf water status and gas exch ange behavior, tissue nutrient content, flowering, and production were studied for co-occurring shallow-rooted (Arbutus unedo L.) and deep-r ooted (Quercus ilex L.) Mediterranean tree species at the Collserola N atural Park in Northeast Spain. Resprouts showed higher growth rates t han mature plant shoots. During fall, no differences in eco-physiologi cal performance of leaves were found, but mobilization of carbohydrate s from burls strongly stimulated growth of fall resprouts compared to spring resprouts, despite low exposed leaf area of the fall shoots. Du ring summer drought, resprouts exhibited improved water status and car bon fixation compared to mature plant shoots. Shoot growth of Q. ilex was apparently extended due to deep rooting so that initial slower gro wth during spring and early summer as compared to A. unedo was compens ated. Tissue nutrient contents varied only slightly and are postulated to be of minor importance in controlling rate of shoot growth, perhap s due to the relatively fertile soil of the site. Fall flowering appea red to inhibit fall shoot growth in A. unedo, but did not occur in Q. ilex. The results demonstrate that comparative examinations utilizing vegetation elements with differing morphological and physiological ada ptations can be used to analyze relatively complex phenomena related t o resprouting behavior. The studies provide an important multi-dimensi onal background framework for further studies of resprouting in the Eu ropean Mediterranean region.