Productivity and biological humus activities in forest soils

In forest soils the mineralization and humification processes are not disturbed by intense management practices, and they are controlled by the type of mineral substrate, by the climate, water availability, vegetation cover, and by the activity of the soil organisms. In order to investigate the interaction between productivity and biological humus activities in forest soils, three undisturbed forest soils, located in a unique climatic area under different vegetal covers (Abies alba, Fagus sylvatica and Abies + Fagus) were classified, and their yielding capacities were assessed. The presence of the two species combined induced the best basal annual increments, litter production, and protein litter content compared to the average overall data obtained from the monospecific cover. Furthermore, the lowest C/N ratio, the best humic matter content, the percentage distribution in the Sephadex fractions and low molecular size (HEf) fraction content confirm that the best evolution of mineralization and humification processes were in the Abies + Fagus site. We also demonstrated that the HEf humic fraction activities varied according to the soil cover and to the collection horizon. Moreover, in this case, the HEf fraction extracted from the Abies + Fagus site was endowed with the highest hormone-like activities. The high molecular size (HSp) fraction as well as the original humic extracts showed only negligible hormone-like activities. The efficiency of nitrate uptake was induced only by the HEf humic fractions, while the HSp and the original humic extracts were not effective.