Patrícia Anjos Bittencourt Barreto

Atividade microbiana, carbono e nitrogênio da biomassa microbiana em plantações de eucalipto, em seqüência de idades

SUMMARY : ACTIVITY, CARBON AND NITROGEN OF MICROBIAL BIOMASSIN EUCALYPT PLANTATIONS IN AN AGE SEQUENCE Microbial activity is highly relevant for nutrient cycling and soil fertility in forestplantations. Due to the long growth cycles, continuous litter production and dead rootscontribute to storage and increase of soil organic matter. Changes in soil and litter microbialbiomass and activity under 1, 3, 5 and 13-year-old eucalypt plantations were evaluated.Soil and climate conditions were the same at the sites. Microbial biomass C and N werehigher in litter than in soil. Then, litter could be an important sink of microbial C and N ineucalypt plantation. No increase or drop in microbial biomass and activity was observedas plantations grew older, probably because the soil and litter samples were from reformedplantations. Litter quality had a direct influence on litter microbial activity and microbialbiomass C and N. Organic carbon and N content were the most reliable indicators to showchanges in the soil under eucalypt plantations, while in the litter it were the microbialattributes and cellulose, lignin, and N content.Index terms: organic matter, nutrient cycling, forest soils.

DECOMPOSIÇÃO DA SERAPILHEIRA FOLIAR DE FLORESTA NATIVA E PLANTIOS DE Pterogyne nitens E Eucalyptus urophylla NO SUDOESTE DA BAHIA

The decomposition process regulates the accumulation of litter and nutrient cycling in forest ecosystems, being central to its maintenance. The objective of this study was to evaluate the dynamics of leaf litter decomposition in three forest ecosystems (semideciduous forest Montana and homogeneous stands of Pterogyne nitens Tul. and Eucalyptus urophylla ST Blake), located in Vitoria da Conquista, Bahia, Brazil. To evaluate the decomposition, newly fallen leaves on the ground of trees and shrubs in each of the studied toppings were collected. The sheets were dried at 65 °C, and thereafter, 10 g portions were weighed and placed in litter bags, which were randomly distributed on the surface of the forest floor in each of the areas studied. Five litter bags at random were collected after 30, 60, 90, 120, 150 and 180 days of installation. After collection, the material contained in each litter bag was subjected to drying in an oven at 65 °C and weighed. Based on the obtained masses were estimated the percentage of the remaining mass, the rate of decomposition ( k ) and half-life time of the litter ( t 1 /2 ). For chemical characterization three subsamples were separated from the dried leaf litter, which were ground and analyzed by determination of the total nitrogen, carbon, polyphenols, lignin and cellulose. The decomposition was related to environmental variables (precipitation, temperature and humidity) and the microenvironment (temperature and soil moisture).The total accumulated litter varied significantly between the settlements studied, the highest value was observed in the area of Eucalyptus urophylla (12,7 Mg ha -1 ), followed by native forest (6,9 Mg ha -1 ) and Pterogyne nitens (1,1 Mg ha -1 ). At the end of the six months of the experiment, Eucalyptus urophylla showed the greatest remaining mass (73,6%), followed by native forest (67,8%) and Pterogyne nitens (46,3%). The decomposition constant ( k ) was higher in litter of Pterogyne nitens (0,0054 g g -1 day), with lower values for native forest (0,0016 g g -1 day) and Eucalyptus urophylla (0,0015 g g -1 day). The rate of decomposition of leaf litter of the peopling of Pterogyne nitens is in a superior position in relation to rates of native forest and stand of Eucalyptus urophylla , which provides the largest species ability to recycle organic matter and nutrients. The decomposition process in the studied ecosystems is influenced not only by the quality of the litter but also by the quality of their microenvironment.