Banco de sementes de uma floresta secundária amazônica dominada por Vismia

The floristic compostion of a secondary forest dominated by Vismia in central Amazonia was studied and compared to the composition of the seed bank in the soil. The area contained 20 tree species, with Vismia being the dominant genus in importance value, relative density, and basal area. The seed bank collected from the area exhibited 17 species that germinated, all pioneers, of which half were herbaceous and half were woody. In general, the composition of the seed bank was characteristic of successional stages with a strong influence from the abandoned pasture, the presence of pioneer species, and a large number of herbs and grasses. Two genera, Goupia and Laetia, were absent from the bank, although adult individuals were in the canopy. The three genera over-represented in the seed bank, relative to the canopy, were Cecropia, Bellucia and Trema, whose seeds probably arrived after the development of the canopy of Vismia. In field plots where the canopy was removed, germination mirrored the composition of the established vegetation in the area without the presence of new species exclusive to the seed bank. Thus, the return to primary forest will be delayed and depend on the proximity of seed sources as well as the presence of dispersers to contribute a diverse seed rain.

A composição florística de uma floresta secundária dominada por Vismia na Amazônia central foi estudada e comparada de acordo com sua composição ao banco de sementes no solo. A área apresentou um total de 20 espécies arbóreas, sendo Vismia o gênero dominante em indíce de valor de importância, densidade relativa e área basal. O banco de sementes coletado na área apresentou germinação de apenas 17 espécies, todas pioneiras, entre as quais metade foi de herbáceas e a outra metade de lenhosas. A composição do banco de sementes foi em geral característica de estágios sucessionais, com forte influência do histórico de pastagem, presença de espécies pioneiras e um elevado número de herbáceas e gramíneas. Os gêneros Goupia e Laetia estiveram ausentes no banco mesmo com indivíduos adultos representados no dossel. Os três gêneros com maior representação no banco de sementes em relação ao dossel foram Cecropia, Bellucia e Trema, os quais provavelmente germinaram de sementes chegadas depois do desenvolvimento do dossel de Vismia. As parcelas que tiveram o dossel removido refletiram muito bem a composição da vegetação estabelecida na área, onde sementes de espécies da floresta mais madura não germinaram. Desta forma, o retorno à floresta primária deverá ser um processo lento e dependente de fontes de sementes próximas, além da presença de dispersores capazes de contribuir com a chuva de sementes.

Allelopathic potential of menthofuran monoterpenes fromCalamintha ashei.

A reversed-phase HPLC analysis was used to separate and quantify five menthofuran monoterpenes inCalamintha ashei leaf soaks and washes. (+)-Evodone and desacetylcalaminthone were the major constituents of both soaks and washes. Concentrations of (+)-evodone and desacetylcalaminthone were as high as 0.66 and 0.74 mM, respectively, in leaf soaks. The highest concentration of monoterpenes in leaf washes obtained by misting was 0.021 mM. Aqueous solubilities of the menthofurans were determined to exceed concentrations required for growth inhibition. Bioassays of individualCalamintha monoterpenes demonstrated effects on germination as low as 0.05 mM for (+)-evodone. An equimolar mixture of desacetylcalaminthone and (+)-evodone reducedRudbeckia hirta germination by 17% at a combined concentration of 0.025 mM forLeptochloa dubia. Confirmation of allelopathic effects byCalamintha ashei will require long-term bioassays ofCalamintha menthofurans on the growth of native sandhill species under conditions comparable to the harsh environment of the Florida scrub.

Bioassays for allelopathy: Measuring treatment responses with independent controls.

In bioassays for allelopathy, where responses to treatments are determined in conjunction with responses to independent controls, statistical comparisons among treatments require an index which measures each treatment response (T) in relation to its control response (C). The most commonly used index, the treatment-control ratio (T/C), exhibits two analytical problems. First, means ofT/C values are distorted upward when any of the individual values is greater than one, i.e., when stimulation occurs. Second, the distribution ofT/C values may not be normal and homoscedastic. We provide two alternative indices of response whose means do not exhibit the upward distortion ofT/C means. Then, the two indices are compared toT/C values in an empirical test for normality and homoscedasticity on a large bioassay data set. Results indicate that for this data set, one of the alternatives,RI, is clearly superior.RI is defined as 1 - (C/T) ifT≥C and asT/C - 1 ifT