Environmental gradients and competition influence aquatic macrophyte distribution in estuaries. The competition-to-stress hypothesis states that some species are excluded from lower estuaries (high salinity) due to abiotic stress and others from upper estuaries (low salinity) by competition. The growth of Crinum americanum L. and Spartina alterniflora Loisel. in monoculture (10:0/0:10) and mixed culture (5:5) under different salinity levels (4/12/26) was analysed by a laboratory experiment (3 cultures 9 3 sediment types 9 3 replicate) to understand the role of competition and salinity on the distribution of these species in a tropical estuary as well as to verify whether the competition-to-stress hypothesis explains their zonation. We tested the hypothesis that S. alterniflora is not established in the upper estuary due to the effect of competition with C. americanum, whereas the latter presents restrictions to high salinity and has greater competitive ability in the upper estuary. Our data confirm the competition-to-stress hypothesis but not as proposed originally. We conclude that abiotic stress (low nutrient availability) is responsible for the absence of S. alterniflora in the upper estuary and that the competition between the two species is responsible for the absence of C. americanum in the lower estuary.

Esta pesquisa foi desenvolvida com o objetivo de comparar 3 modelos matemáticos (Page, Cavalcanti Mata e Fick com 3 termos da série) na secagem do caju sem epiderme, desidratados osmoticamente em xarope com concentrações de 50ºBrix, para elaboração de passas de caju. A secagem foi realizada em secador de bandejas em três temperaturas (50, 60 e 70ºC). As equações propostas por Fick com 1, 2 e 3 termos da série, Cavalcanti Mata e Page foram usadas para ajuste dos dados de secagem O programa computacional Statistic 5.0 foi utilizado para as análises dos modelos por meio da aplicação do método numérico de Rosenbrock Quasi Newton e Quase Newton. O melhor ajuste para os dados experimentais da secagem do caju, com prétratamento osmótico, foi obtido com a equação proposta por Cavalcanti Mata, com R 2 =99,93% em média.

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Aim: Non-destructive methods for estimating aquatic macrophytes biomass may be employed by using indirect measurements, especially in experimental studies, thus enabling the conservation of plant samples. It is possible to estimate macrophyte biomass by developing mathematical equations that relate the plants' dry mass to their morphological variables. The aim of this study was to evaluate the relationship between different morphological variables and biomass in order to determine which variable is easier to be obtained for the emergent aquatic macrophytes Crinum americanum and Spartina alterniflora. Methods: We obtained the aboveground area and height of individuals of both species, with different sizes and distinct developmental stages. The samples were collected in the Itanhaém River Estuary (SP, Brazil). The plants were dried in a laboratory oven and weighed so as to obtain their dry mass. Simple linear regression analyses were applied to the morphological variables and the individual dry mass to obtain equations. Results: For the both species, the relationship between area and biomass, and the relationship between individual height and biomass presented significant coefficients of determination (p < 0.0001). For the elaboration of models involving the individual height, we used only one morphological measure for each individual, whereas for models involving the individual area it was necessary to obtain more than one hundred morphological measurements per individual. Conclusions: The morphological variables chosen are good attributes for estimating the aboveground biomass of C. americanum and S. alterniflora. Considering the models' adjustment and the consumed time to obtain the measurements, we conclude that the individual height measurement is better for biomass estimation for both species.Keywords: dry mass; plant traits; morphological variables; Crinum americanum; Spartina alterniflora.Resumo: Objetivo: Métodos não destrutivos para avaliação da biomassa de macrófitas aquáticas podem ser empregados usando-se medidas indiretas, especialmente em estudos experimentais, permitindo a conservação das amostras vegetais. Pode-se estimar a biomassa vegetal através da elaboração de equações matemáticas que relacionem a massa seca com as variáveis morfológicas dos vegetais. O objetivo deste estudo foi avaliar a relação entre diferentes variáveis morfológicas e biomassa para determinar qual variável é mais fácil de ser obtida para as macrófitas aquáticas This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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