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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The coastal region of the São Paulo state (Southeastern Brazil) is marked by the presence of the Serra do Mar, a system of mountain ranges with altitude up to 1,000 m. Due to the difference of proximity of the mountain range to the coastline, the coastal plains have different width. As a consequence, the rivers that cross the plains also have different length, greater or less influence of marine waters and slope variation. We carried on an inventory of aquatic macrophyte species in order to assess the species and life form richness and latitudinal distribution in this region. Macrophytes were inventoried at 100 sampling sites in eight rivers (between 9 and 19 sites per river) in March 2017. General descriptions on taxonomic aspects, life forms and frequency of occurrence of the macrophytes were explored. We recorded 45 taxa of aquatic macrophytes belonging to 24 families. Three species are exotic, but they presented low frequencies of occurrence. The vast majority of the taxa have emergent life form. Floating and submerged macrophytes were found in only two rivers. The most frequent species were Crinum americanum L. (Asparagales, Amaryllidaceae), Spartina alterniflora Loisel. (Poales, Poaceae) and Schoenoplectus californicus (C. A. Mey.) Soják (Poales, Cyperaceae). Most taxa are rare in terms of occurrence. Only four species occurred along a large part of the north-south stretch sampled and these, possibly, have a wide tolerance to the variation in resource requirements and salinity. The north-south gradient of the taxa occurrence may be related to the diversity of environmental characteristics due to differences in the rivers length and coastal plains width.

1. The coastal rivers of the São Paulo State in SE Brazil have different lengths and seawater influence. We evaluated whether: (1) environmental heterogeneity (EH) is associated with the species and life-form richness of aquatic macrophytes; and (2) EH and geographical distance influence species composition in these coastal rivers. 2. We recorded the macrophyte species and life form occurrence and collected explanatory variables characterising the water, sediment, and river channel at 100 sampling sites over 8 rivers. We applied a principal component analysis to the explanatory variables and calculated the rivers' EH using the range of principal component 1 scores. We also determined the position of each river mouth along the coastline to measure the distance between the rivers. We used quasi-Poisson generalised linear models to evaluate the effects of EH on richness of species and life forms. To determine the effect of EH and geographical distance (Euclidean distance matrices) on the variation in species composition (Jaccard dissimilarity matrix) among the rivers, we applied multiple regressions on distance matrices. 3. The most heterogeneous river had heterogeneity score about five times greater than the least heterogeneous river. Sediment salinity, river width, total phosphorus concentration of water and distance from river mouth were the most important variables contributing to the rivers' EH. We found that EH did not explain variation in species richness; however, it had a significant positive relationship with life-form richness. The effect of EH was greater than that of the geographical distance on the variation in species composition among the rivers. The pairs of rivers with the most similar EH were the most similar in species composition, but not all of them were geographically close. 4. We conclude that EH influences life-form richness but does not influence species richness of aquatic macrophytes in the coastal rivers we studied; however, EH does influence species composition regardless of geographical distance among rivers. K E Y W O R D S aquatic plants, coastal plain, estuaries, macrophyte composition, river heterogeneity | 1895 NUNES Et al. 1 | INTRODUC TI ON Environmental heterogeneity (EH) has been reported as one of the main factors that explain species diversity (Reynolds, Hungate, Chapin, & D'Antonio, 1997), as it can promote high species richness