TURNOVER E BIOMASSA DE RAÍZES FINAS E SUAS RELAÇÕES COM O PADRÃO DE CRESCIMENTO EM DIÂMETRO DE ÁRVORES EM UMA FLORESTA DE TERRA FIRME NA AMAZÔNIA CENTRAL

Abstract

The plants roots are one of the main ways to access the resources of the soil, and the fine roots (diameter <2 mm) primarily responsible for absorbing water and nutrients. Although little contribution to the stock of carbon, production is one of the main components of net primary production and cycling of organic matter, this process is of fundamental importance for the maintenance and production of tropical forests. However, despite the central role in the ecosystem, its operation is poorly understood, especially in tropical regions. Upon this, the objective of this study was to evaluate the effect of turnover and the fine root biomass in diameter growth of trees on the plateau and “baixio” and their relations with precipitation and water content in the soil (CVA) in a forest in central Amazonia. The research was conducted from December 2011 to June 2014, at the Experimental Station of the National Institute for Research in the Amazon (INPA), using the methods: dendrometer bands, soil core, auger, ingrowth core and scanner. As in other regions covered with tropical rainforests, the fine roots are concentrated in the first 20 cm of the soil. Its operation is influenced by soil type, topography and seasonal, where the standard of higher biomass, length (CR), surface area (ASR) and turnover was found in “baixio” and live roots. Regarding seasonality, it appears that the highest standard in living roots occurs in the dry season and the dead, in the rainy season. The average biomass of fine roots (live + dead and plateau + “baixio”), from all over the monitored period was 6.3 ± 0.40 Mg ha-1 (CI = 95%), and on the plateau 4.8 ± 0.35 Mg ha- 1 (CI = 95%) and on the “baixio” 7.9 ± 0.60 t ha-1 (CI = 95%), confirming that the contribution of the fine roots to the total forest biomass is approximately 2%. The estimated value of productivity total and 28%. The age ranged from 10-26 on the plateau and in the “baixio” between 8-20 years. These results demonstrate that the “baixio” roots are younger, resulting in higher turnover. It is noteworthy that the age increases with depth and that the roots of smaller diameter were younger than thick. In the relationship between the fine root variables with the increase, it appears that the highest rates were found in the “baixio”, indicating that this environment is more dependent on nutrient cycling. In the lower levels of rainfall, there is a greater investment of living fine roots (biomass, CR and ASR); with increasing amount of rain and CVA in decreased investment and at this time, larger diameter increment values are found. However, it is emphasized that this period is greater disappearance of roots and, consequently, increasing the decomposition rate which favors the diameter increment, proving the fundamental role of fine roots in nutrient cycling processes and forest productivity.