EFFECTS OF CO2 CONCENTRATION AND NUTRIENT STATUS ON GROWTH, GROWTH RHYTHM AND BIOMASS PARTITIONING IN A WILLOW, SALIX-PHYLICIFOLIA

Cuttings of the willow Salix phylicifolia were grown in pots containin g moist organic-rich soil for four months in closed chambers at 4 CO2 concentrations (300). 500, 700, 1000 ppm) and 4 nutrient levels (ferti lization of 0, 100, 500, 1000 kg ha-1 monthly). The plants received na tural light, but the average temperature was 3-6-degrees-C higher than out of doors. Both CO2 concentration and fertilization affected bioma ss production. the average increase caused by CO2 enhancement being ap prox. 100%. Nutrient level had a considerable effect on the increased biomass production achieved by CO2 enhancement, since the increase was minimal at lower nutrient levels. At the same time the effect of fert ilization was dependent on the CO2 concentration, the production incre ase caused by fertilization being much less at 300 ppm than at the oth er CO2 concentrations. CO2 concentration and fertilization had the opp osite effects on biomass partitioning, a higher nutrient level increas ing the proportion of the biomass located in the stems and a higher CO 2 concentration that in the roots. Both fertilization and CO2 concentr ation affected the growth rhythm, a high CO2/nutrient ratio leading to a shorter growing season and a low ratio to a longer one.