Produção de raízes finas em uma floresta secundária da Amazônia oriental.

Abstract

The fine root production may contribute to the biogeochemistry cycling in forest ecosystems, especially in emission of gases important to climatic change. Despite the importance of fine roots, few studies have been conducted in this part of the plant mainly due to the difficulty of measuring their production. The objective of this work were (1) to assess the water and nutrients availability through irrigation and litter removal on the fine root production, and (2) to assess the fine root production dynamic of a forest regrowth at different ages. The study was carried out in an forest regrowth, located in Castanhal, in the state of Pará, Brazil. The fine root production (≤ 2 mm) was monitored using the Ingrowth Core method, removed every two months, between July 2005 and July 2007. To assess the water and nutrients availability one area of forest regrowth of 18 years was divided into four blocks; three 20m x 20m plots were set up randomly within each block, one plot was irrigated (IRR), the litter was removed from one plot (REM) and one plot was the control (CTL). The irrigation (5mm of water per day per plot) occurred only in the dry season. The litter removal was manual, every 15 days. The average of live root biomass production showed a significant interaction between treatment and period of collection, with greater production in the dry season (CTL: dry = 17.915g/m²/month, rainy = 10.761g/m²/month; IRR: dry = 19.48 g/m²/month, rainy = 11.263g/m²/month; REM: dry = 10.58 g/m²/month, rainy = 5.90 g/m²/month). The average of dead root biomass production showed a seasonality, and is also greater in dry season (CTL: dry = 0.377g/m²/month, rainy = 0.181g/m²/month; IRR: dry = 0.65g/m²/month, rainy = 0.231g/m²/month; REM: dry = 0.66g/m²/ month, rainy = 0.30g/m²/month). The dynamics of fine root length production (m/m²/year) was similar to biomass dynamics. The root specific length was similar between treatments (CTL = 52.74m/g; = IRR 61.42 m/g REM = 50.73m/g), e between the collection period. To assess the dynamics of fine root production in forest regrowth at different ages were chosen one 18 – year-old site (FS18) and one 10 year-old site (FS10). In the FS10 the average of live and dead fine root biomass production was 88.386 and 2.235 g/m²/year, respectively. In the FS18 the average of live and dead fine root biomass production was 86.030 and 1.673 g/m²/year, respectively. The monthly biomass production of live roots was similar between sites, but presented a seasonality and was significantly greater in the dry season (FS10: dry = 17.523 g/m²/month, rainy = 11.939 g/m²/month; FS18: dry = 17.915 g/m²/month, rainy = 10.761 g/m²/month). The average of dead root biomass production showed a significant interaction between treatment and collection period, the values were greater in FS10 during the dry season (FS10: dry = 0.373 g/m²/month, rainy = 0.373 g/m²/month; FS18: dry = 0.377 g/m²/month, rainy = 0.181 g/m²/month). The dynamics of fine root length production (m/m²/year) also was similar to biomass dynamics. The root specific length was significantly different between sites, with greater production in FS10 during the wet season (FS10: dry = 64.57m/g, rainy = 66.74m/g; FS18: dry = 47.23m/g, rainy = 57.72m/g).