Measurements of CO2 exchange over a woodland savanna (Cerrado Sensu stricto) in southeast Brasil

The technique of eddy correlation was used to measure the net ecosystem exchange over a woodland savanna (Cerrado Sensu stricto) site (Gleba Pé de Gigante) in southeast Brazil. The data set included measurements of climatological variables and soil respiration using static soil chambers. Data were collected during the period from 10 October 2000 to 30 March 2002. Measured soil respiration showed average values of 4.8 molCO2 m-2s-1 year round. Its seasonal differences varied from 2 to 8 molCO2 m-2s-1 (Q10 = 4.9) during the dry (April to August) and wet season, respectively, and was concurrent with soil temperature and moisture variability. The net ecosystem CO2 flux (NEE) variability is controlled by solar radiation, temperature and air humidity on diel course. Seasonally, soil moisture plays a strong role by inducing litterfall, reducing canopy photosynthetic activity and soil respiration. The net sign of NEE is negative (sink) in the wet season and early dry season, with rates around -25 kgC ha-1day-1, and values as low as 40 kgC ha-1day-1. NEE was positive (source) during most of the dry season, and changed into negative at the onset of rainy season. At critical times of soil moisture stress during the late dry season, the ecosystem experienced photosynthesis during daytime, although the net sign is positive (emission). Concurrent with dry season, the values appeared progressively positive from 5 to as much as 50 kgC ha-1day-1. The annual NEE sum appeared to be nearly in balance, or more exactly a small sink, equal to 0.1 0.3 tC ha-1yr-1, which we regard possibly as a realistic one, giving the constraining conditions imposed to the turbulent flux calculation, and favourable hypothesis of succession stages, climatic variability and CO2 fertilization

Alguns efeitos do fluometuron sobre o crescimento inicial de Bidens pilosa L. Some effects of fluometuron on early growth of Bidens pilosa L.

Sementes de picão-preto (Bidens pilosa L.) foram germinadas em placas de petri sobre papel de filtro molhado com diferentes concentrações de fluometuron (0, 5, 25, 125 e 625 ppm). O ensaio foi conduzido em condições de laboratório, com variação de temperatura entre 24°C e 28°C e intensidade luminosa máxima de 600 lux e foi encerrado após sete dias (168 horas). O fluometuron diminuiu a germinabilidade e o comprimento da radídula e do hipocótilo, afetou o formato dos cotilédones e, nas concentrações mais elevadas, impediu a rejeição do pericarpo. Os efeitos observados não são atribuíveis a lesões bioquímicas do processo fotossintético.Seeds of Bidens pilosa L. (Compositae) were germinated in Petri dishes on filter paper wetted with aqueous suspensions of fluometuron at different concentrations (0, 5, 25, 125 and 625 ppm). The experiment was conducted during 7 days, under room conditions; the temperature range was 24°C - 28°C and the maximum light intensity was 600 lux. Fluometuron reduced germination percentage, radicle and hypocotyl lenght, affected cotyledon shape and, at the higher concentrations, prevented the pericarp rejection. The observed effects can not be attributed to biochemical lesions of the photosynthetic process

Alguns efeitos do fluometuron sobre o crescimento inicial de Bidens pilosa L.

Sementes de picão-preto (Bidens pilosa L.) foram germinadas em placas de petri sobre papel de filtro molhado com diferentes concentrações de fluometuron (0, 5, 25, 125 e 625 ppm). O ensaio foi conduzido em condições de laboratório, com variação de temperatura entre 24°C e 28°C e intensidade luminosa máxima de 600 lux e foi encerrado após sete dias (168 horas). O fluometuron diminuiu a germinabilidade e o comprimento da radídula e do hipocótilo, afetou o formato dos cotilédones e, nas concentrações mais elevadas, impediu a rejeição do pericarpo. Os efeitos observados não são atribuíveis a lesões bioquímicas do processo fotossintético.Seeds of Bidens pilosa L. (Compositae) were germinated in Petri dishes on filter paper wetted with aqueous suspensions of fluometuron at different concentrations (0, 5, 25, 125 and 625 ppm). The experiment was conducted during 7 days, under room conditions; the temperature range was 24°C - 28°C and the maximum light intensity was 600 lux. Fluometuron reduced germination percentage, radicle and hypocotyl lenght, affected cotyledon shape and, at the higher concentrations, prevented the pericarp rejection. The observed effects can not be attributed to biochemical lesions of the photosynthetic process

Produção de serapilheira e ciclagem de nutrientes de uma floresta estacional semidecidual em zona ripária Litter production and nutrient cycling of a semideciduous mesophytic forest in a riparian zone

O presente trabalho foi realizado em uma zona ripária no período de outubro de 2000 a setembro de 2001, em uma parcela representativa de mata ciliar com vegetação do tipo "Floresta Estacional Semidecidual", localizada no centro-sul do Estado de São Paulo. A produção total de serapilheira foi de 10.646,0 kg.ha-1.a-1. A maior deposição de serapilheira e nutrientes ocorreu no fim da estação seca. A transferência total de macronutrientes foi de 217,76 kg.ha-1 de N, 11,55 kg.ha-1 de P, 52,79 kg.ha-1 de K, 199,80 kg.ha-1 de Ca e 38,70 kg.ha-1 de Mg. A serapilheira acumulada foi estimada em 6.227,25 kg.ha-1, a estimativa da taxa instantânea de decomposição (K), de 1,71; e o tempo necessário para o desaparecimento de 50 e 95% da serapilheira produzida, 150 e 639 dias, respectivamente.<br>This work was carried out in a riparian zone from October 2000 to September 2001, within a representative plot of a riparian forest with semideciduous mesophytic forest vegetation, located in the center southern region of São Paulo state. The total litter production was 10.646 kg.ha-1.y-1. The season of highest litter and nutrient deposition was the late dry season. The total macronutrient transfer was 217.76 kg.ha-1 N; 11.55 kg.ha-1 P; 52.79 kg.ha-1 K; 199.80 kg.ha-1 Ca and 38.70 kg.ha-1 Mg. The accumulated litter was estimated as 6.227 kg.ha-1, instantaneous decomposition rate (K) 1.71 and time needed time for 50% and 95% litter disappearance was 150 and 639 days, respectively