ROOT RESPIRATION AND ITS IMPORTANCE FOR THE CARBON BALANCE OF BEECH SAPLINGS (FAGUS-SYLVATICA L) IN A MONTANE BEECH FOREST

Root respiration of 10-year-old beech saplings (Fagus sylvatica L.) grown in the understorey (UND) and in a natural gap (GAP) of a mature beech forest in the Selling mountains, FRG, was investigated from April until December, 1990. Respiration rates of fine, medium and coarse roots were measured in situ by a PC-controlled cuvette system. Fine root respiration rates were in the range of 0.5 - 9.8 nmol CO2 gDW(-1) s(-1) at both sites, but respiration rates of UND saplings were higher, compared to those of GAP saplings. The dependence of respiratory activity on soil temperature proved to be highly significant (p < 0.001) for both plots, following a quasi-Arrhenius type curve. Fine root respiration rates of UND saplings were highly significantly, negatively correlated with the water content of the attached organic material, whereas respiration rates of GAP saplings did not show such a correlation. Further, a significant correlation (p < 0.01) between mycorrhizal biomass and respiration rate was detected at the UND site, but not at the GAP site. Medium and coarse root respiration rates were very similar and no significant differences between the two sites were detected. Maximum respiration rates of 3.1 nmol CO2 gDW(-1) s(-1) were reached in the middle of July. Due to low light intensities in the under storey, daily net CO2 assimilation rates of UND saplings were much smaller than those of GAP saplings. At both sites, net CO2 assimilation rates varied more than respiration rates and thus the carbon balance of beech saplings was more affected by the rate of carbon fixation than by the rate of respiratory carbon loss.