O papel de espécies arbóreas e fatores edáficos na variação espacial do sistema serapilheira em uma floresta de terra firme na Amazônia: conhecimento e perspectivas para a conservação

Abstract

The dense ombrophilous forest, also known as tropical rain forest, is a formation that presents great complexity in the composition, distribution and density of species and occupies a good part of the Brazilian Amazon. In the region, the differences between plant communities and animals form a mosaic divided into eight areas or centers of endemism, separated by the main rivers, with their own biota and evolutionary relationships, three of which (Belém, Xingu and Tapajós) are entirely Brazilian. The Belém endemism center is the most threatened by deforestation and small-scale local investigations are essential to understand the effects of this disturbance on the functioning of the forest. The decomposition of litter is one of the key factors of this functioning and occurs in a hierarchical sequence of interaction processes mediated by climatic factors (temperature and humidity), physical properties of the soil, chemical limitations related to the sources of resources and biological regulation (micro and macroorganisms). In this research, it was discovered that sensitive changes in the structure of a primary forest threatened by urban growth, caused by the intensity of the natural succession dynamics, altered the humus system, since the organisms' competition for nutrients depleted the soil during the regeneration of areas affected by falling trees. Thus, the physical-chemical conditions of the forest soil became a selective filter of tree species and the major factors in the decomposition hierarchy, since temperature and humidity had little variation in the system. Then, leaves of specific tree species of the humus system, which formed a finer structure, determined the diversity of saprotrophic fungi positively related to the better quality of these leaves and the soil. Conversely, where the litter morphology was thicker and more structured, there was an increase in the diversity of litter transforming macrofauna, to the detriment of earthworm populations, which preferred higher quality leaves and soil. Soilplant-decomposer interactions are indicators of decomposition speed in humus systems, with consequent formation of mosaics of litter spots with different decomposition dynamics. Thus, places where humus function was classified as Mesomull or Oligomull were characterized by soils with a high available carbon content and good cation exchange capacity. Mull type humus systems are sensitive to variations in soil quality and earthworm activity. This explained the change to the Dysmull humus system in areas with large leaves, characterized by low nutrient availability, as confirmed in the soils of these places, although a slow functioning may indicate a conservative state of organic matter. The methodology proved to be favorable to predict changes at different scales that may affect the forest restoration.