The Amazonian wetlands cover a vast area subject to a monomodal flood pulse with an annual amplitude averaging 10 m, which defines an aquatic phase and a terrestrial phase of great biological importance. According to the geological origin and the catchment areas, the physical and chemical properties of the wetland will vary, being defined two major groups, the várzeas and the igapós. Although aquatic herbaceous plants do occur in the two types, higher species richness and densities are typical of the várzeas where aquatic herbaceous species, particularly C 4 plants may exhibit high biomass values and net primary production -NPP about three times these of the floodplain forest. The aquatic herbaceous plants are very important in the carbon and nutrient budgets of the várzea, since through their decomposition they promote the enrichment of the aquatic system and associated floodplains, both during the aquatic and terrestrial phases of the hydrologic cycle. The major threats to herbaceous aquatic plants are related to the modification and contamination of the habitats owing to their use in economic activities as cattle and buffalo ranching and agriculture. Degradation improves the susceptibility of these systems to fire especially during the terrestrial phase, resulting in economic losses and further degradation of floodplains. Recently oil spills linked to the petroliferous activities in the region are of major concern demanding further and urgent evaluation.

The Amazonian wetlands cover a vast area subject to a monomodal flood pulse with an annual amplitude averaging 10 m, which defines an aquatic phase and a terrestrial phase of great biological importance. According to the geological origin and the catchment areas, the physical and chemical properties of the wetland will vary, being defined two major groups, the várzeas and the igapós. Although aquatic herbaceous plants do occur in the two types, higher species richness and densities are typical of the várzeas where aquatic herbaceous species, particularly C 4 plants may exhibit high biomass values and net primary production-NPP about three times these of the floodplain forest. The aquatic herbaceous plants are very important in the carbon and nutrient budgets of the várzea, since through their decomposition they promote the enrichment of the aquatic system and associated floodplains, both during the aquatic and terrestrial phases of the hydrologic cycle. The major threats to herbaceous aquatic plants are related to the modification and contamination of the habitats owing to their use in economic activities as cattle and buffalo ranching and agriculture. Degradation improves the susceptibility of these systems to fire especially during the terrestrial phase, resulting in economic losses and further degradation of floodplains. Recently oil spills linked to the petroliferous activities in the region are of major concern demanding further and urgent evaluation.

RESUMO -(Tolerância deHimatanthus sucuuba Wood. (Apocynaceae) ao alagamento na Amazônia Central). Himatanthus sucuuba é uma espécie arbórea de reputado valor fitoterápico, que coloniza regiões de várzea e de terra firme na Amazônia Central. Objetivou-se verificar durante quatro meses, em casa de vegetação, a germinação e o desenvolvimento inicial de plântulas da espécie, oriundas de sementes dos dois diferentes ecossistemas. Não houve diferença significativa em relação ao peso de matéria seca de sementes da várzea e da terra firme. Entretanto, a taxa de germinação da espécie variou de acordo com o substrato e o local de procedência das sementes. No substrato areia+serragem (não-alagado) a germinação da espécie foi alta, independente do ambiente (várzea 94% e terra firme 91%). No substrato constituído apenas por água (alagado), as sementes provenientes da várzea tiveram a maior taxa de germinação (96%) e de formação de plântulas (84%), quando relacionadas às da terra firme, que apresentaram taxa de germinação de 64%, e nenhuma das sementes germinadas formou plântulas. Neste tratamento foi verificado o apodrecimento da radícula poucos dias após sua emissão, indicando que as sementes oriundas da várzea apresentam características adaptativas ao ambiente inundado em relação às da mesma espécie oriundas da terra firme. Palavras-chave: anoxia, hipoxia, dispersão hidrocórica, estabelecimento de plântulas ABSTRACT -(Tolerance of Himatanthus sucuuba Wood. (Apocynaceae) to the flooding regime in the Central Amazonian).Himatanthus sucuuba is a tree species with known phytotherapic value which colonizes both white-water floodplains (várzea) and upland forests (terra firme) in Central Amazonian. The objective of this study was to compare germination and initial seedling development from seeds collected in both the ecosystems. There was no significant difference between dry seed mass, but in a four month period in a glasshouse in Manaus, Brazil, germination rate differed according to the substrate and origin of the seeds. In the substrate sand + sawdust (nonflooded) germination rate was high, independent of seed origin (várzea 94% and terra firme 91%). In the substrate constituted only by water (flooded), the seeds originating from várzea had a higher germination rate (96%) and seedling formation (84%) than those originating from terra firme which had a germination rate of 64% and none of the seeds formed seedlings. In this treatment, the radicles rot few days after their emission, indicating that the seeds originating from várzea present adaptive characteristics to the floodplain environment which are not present in seeds from terra firme.

ResumoA paisagem da várzea modifica-se todos os anos nas chamadas fases terrestre e aquática, em conformidade com a dinâmica fluvial, a qual é responsável pela destruição de parte das margens dos rios, o que geralmente conduz à destruição de grandes áreas de vegetação. Abstract Study of herbaceous vegetation of the floodplain in CentralAmazonia. The floodplain landscape changes each year from the aquatic to the terrestrial phase according to the river dynamic which is responsible for the destruction of part of the riverbank that leads to the destruction of large extent of vegetation. On the other hand, the sediment deposition makes at the same time a new habitat. Echinochloa polystachya (Kunth) Hitchc. herbaceous vegetation at Marchantaria Island, Amazonas state was studied. Biomass data were colected and it was found a biomass increasing of 6. INTRODUÇÃOA região amazônica compreende uma larga faixa que se estende ao longo das fronteiras norte, onde é banhada pelo oceano Atlântico, passando pelas Guianas. Seguindo para o oeste, em direção ao oceano Pacífico, alcança a Cordilheira dos Andes. Abrange nove países da América do Sul e nove estados no território brasileiro, sendo uma região de notável riqueza étnica, cultural, florística e faunística. Nessa grande extensão ainda verde, destacam-se dois ecossistemas, a saber, a terra firme e as áreas inundáveis.Poucas áreas no planeta permanecem inundadas de sete até quinze metros acima da cota do nível do mar da localidade durante cerca de seis meses por ano. Esse fenômeno acontece no sudoeste da Ásia, no oeste do continente africano e ao longo dos rios da Amazônia (AYRES et al., 1998).A vegetação inundável que coloniza esses ambientes está inserida em um gradiente de diferentes níveis de alagamento, que definem hábitats desde permanentemente aquáticos até totalmente terrestres. A amplitude de inundação nessas áreas varia entre 10 m e 15 m acima da cota do nível do mar da localidade, e o tempo de inundação, de 50 até 270 dias, todos os anos, conforme a altura de relevo considerada na planície de inundação (JUNK, 1989;FERREIRA, 1997).A área total da planície inundável da Amazônia é de 1.350,000 km 2 , e cerca de dois terços desse total, são áreas de várzea (JUNK, 1993). Por abranger tão larga extensão, volta-se para esse ecossistema grande interesse pela sua potencialidade para agricultura e bovinocultura, sendo esses ambientes