EFFECT OF LOPPING ON WATER POTENTIAL, TRANSPIRATION, REGROWTH, C-14 PHOTOSYNTHATE DISTRIBUTION AND BIOMASS PRODUCTION IN ALNUS-GLUTINOSA

The effects of light, moderate and heavy branch pruning or lopping tre atments (resulting in removal of 28-31, 56-60 and 80-82% of the foliag e, respectively, unlopped control = 0%) were studied in 3-year-old bla ck alder (Alnus glutinosa L. Gaertn.) plants. Within 24 h of lopping, transpiration rates decreased and water potentials increased. The effe cts of lopping continued for 48 days. The improved water status of the lopped plants enhanced water-use efficiency during the first 30 days. Regrowth was related to a combination of enhanced net assimilation ra tes during the first 30 days after lopping, use of current photoassimi lates and stored carbohydrates in the roots (particularly in medium an d heavily lopped plants) for the production of new leaf area, and dela yed leaf senescence. The lightly and moderately lopped plants develope d 62 and 57% more leaf area, respectively, than the unlopped plants, b ut total leaf area development was slower in the heavily lopped plants . Lightly lopped plants produced total biomass equivalent to that of u nlopped plants, but the moderately and heavily lopped plants produced less biomass than the unlopped plants. During the first 30 days after lopping, there was a net loss of nodule dry matter and recovery to con trol values did not occur during the period of study. Immediately (24 h) after lopping, more C-14-photosynthate was translocated to the root s of lopped plants than to the roots of unlopped plants. When a branch near the base of the main stem was fed (CO2)-C-14, C-14-photosynthate translocation to the shoot increased with increasing intensity of lop ping, at 50 days after lopping.