Seasonal and long-term effects of nutrient additions and liming on the nifH gene in cerrado soils under native vegetation.

Biological nitrogen fixation (BNF) represents the main input source of N in tropical savannas. BNF could be particularly important for Brazilian savannas (known as Cerrado) that show a highly conservative N cycle. We evaluated the effects of seasonal precipitation and nutrient additions on the nifH gene abundance in soils from a long-term fertilization experiment in a Cerrado's native area. The experiment consists of five treatments: (1) control, (2) liming, (3) nitrogen (N), (4) nitrogen + phosphorus (NP), and (5) phosphorus (P) additions. The nifH gene sequence was related to Bradyrhizobium members. Seasonal effects on N-fixing potential were observed by a decrease in the nifH relative abundance from rainy to dry season in control, N, and NP treatments. A significant reduction in nifH abundance was found in the liming treatment in both seasons. The findings evidenced the multiple factors controlling the potential N-fixing by free-living diazotrophs in these nutrient-limited and seasonally dry ecosystems.

Biogeomorphic succession in a fluvial-lacustrine delta of the Middle Paraná River (Argentina): Feedbacks between vegetation and morphodynamics.

The Leyes' Delta lies at the Middle Paraná River, the second-largest fluvial system in South America, and it is being quickly formed into the Setúbal fluvial lake, Argentina. In the context of the Fluvial Biogeomorphic Succession theory, our aim was to better understand interactions between physical and biotic processes contributing to the formation of the Leyes' Delta. We studied the genesis, morphologic development, and vegetation in three groups of its deltaic islands with contrasting formation ages. Different methodologies were applied. Genesis and morphologic development were interpreted from time-series of satellite images and aerial photography obtained from 1974 to 2014. Then landforms and vegetation communities were mapped on the most current images, and they were corroborated and characterized during fieldwork. Our results evidence that the three island groups (Channel crevasse splay islands, Delta bar-plain islands, and Delta front islands) were formed via two different geomorphic processes, determining differences in the initial vegetation colonization. Eight fluvial-lacustrine landforms and eight vegetation communities, both differently represented among the island groups, currently characterize these islands. The species richness accumulation curves and beta diversity showed that the morphodynamic activity can be as important in the floristic composition of the deltaic islands as formation ages. The floristic composition differed statistically among island groups. After identifying three of the four phases of the FBS, we concluded that even though the morphodynamic activity under which islands were formed determined differences in the initial vegetation colonization, under similar subsequent levels of morphodynamics the resulting vegetation heterogeneity tends to be similar even under contrasting genesis. Among the vegetation types, Lotic prairies would play a key role in the morphologic evolution of the deltaic islands, therefore, their distribution and interactions with flow and sediments should be considered during the studies of social ecological systems as the Leyes' Delta, in Santa Fe, Argentina.

Cryptic phenology in plants: Case studies, implications, and recommendations.

Plant phenology-the timing of cyclic or recurrent biological events in plants-offers insight into the ecology, evolution, and seasonality of plant-mediated ecosystem processes. Traditionally studied phenologies are readily apparent, such as flowering events, germination timing, and season-initiating budbreak. However, a broad range of phenologies that are fundamental to the ecology and evolution of plants, and to global biogeochemical cycles and climate change predictions, have been neglected because they are "cryptic"-that is, hidden from view (e.g., root production) or difficult to distinguish and interpret based on common measurements at typical scales of examination (e.g., leaf turnover in evergreen forests). We illustrate how capturing cryptic phenology can advance scientific understanding with two case studies: wood phenology in a deciduous forest of the northeastern USA and leaf phenology in tropical evergreen forests of Amazonia. Drawing on these case studies and other literature, we argue that conceptualizing and characterizing cryptic plant phenology is needed for understanding and accurate prediction at many scales from organisms to ecosystems. We recommend avenues of empirical and modeling research to accelerate discovery of cryptic phenological patterns, to understand their causes and consequences, and to represent these processes in terrestrial biosphere models.

Response of aquatic macrophyte biomass to limnological changes under water level fluctuation in tropical reservoirs / Resposta da biomassa de macrófitas aquáticas às mudanças limnológicas consequentes da variação do nível da água em reservatórios tropicais

Abstract We evaluated the response of the biomass of aquatic macrophytes under limnological changes after water level fluctuation (WLF) of two tropical reservoirs (R1 and R2), located in northeastern Brazil. Initially we tested the hypothesis that post-WLF limnological conditions and biomass of macrophytes increase or decrease, depending on the variable or species. We monitored a 4 × 50 m permanent plot, in four expeditions per period (pre- or post-WLF), assessing species biomass and 10 limnological variables. We utilized 0.25 × 0.25 m quadrats for biomass. Once the effect of WLF in limnological variables and species biomass was confirmed, we utilized Canonical Correspondence Analysis to understand the relationship between limnological variables and species biomass. The abundant and/or dominant species in pre-WLF of R1 ( Pistia stratiotes, Eichhornia crassipes and Salvinia auriculata) and R2 (Paspalidium geminatum and S. auriculata) reduced their biomass post-WLF and were correlated with temperature, total phosphorous and nitrate. The reduced biomass of P. stratiotes, E. crassipes and S. auriculata in post-WLF widened resource availability, allowing coexistence of species. Therefore, we suggest that the change of limnological conditions in post-WLF in artificial lakes acts only as a moderator factor of the interspecific interaction (especially coexistence), without direct relation between these conditions and species biomass.

Resumo Avaliamos a resposta da biomassa de macrófitas aquáticas às alterações ambientais após flutuação do nível de água (WLF) de dois reservatórios tropicais (R1 e R2), localizados no Nordeste do Brasil. Inicialmente, testamos a hipótese de que após uma WLF as condições limnológicas e a biomassa das macrófitas aumentam ou diminuem, dependendo da variável ou espécie. Por isso, monitoramos uma parcela permanente de 4 × 50 m, em quatro amostragens por período (pré ou pós-WLF), avaliando a biomassa de espécies e 10 variáveis ​​limnológicas. Utilizamos quadrados de 0,25 × 0,25 m na amostragem da biomassa. Uma vez que o efeito do WLF em variáveis limnológicas e biomassa das espécies foi confirmado, utilizamos a Análise de Correspondência Canônica para compreender a relação das variáveis ​​limnológicas com a biomassa de espécies. As espécies abundantes e/ou dominantes no pré-WLF de R1 (Pistia stratiotes, Eichhornia crassipes e Salvinia auriculata ) e R2 (Paspalidium geminatum e S. auriculata ) reduziram sua biomassa pós-WLF, correlacionando-se diretamente com temperatura, fósforo total e nitrato. A redução da biomassa de P. stratiotes , E. crassipes e S. auriculata em pós-WLF ampliou a disponibilidade de recursos, permitindo a coexistência de espécies. Portanto, sugerimos que a mudança das condições limnológicas no pós-WLF em lagos artificiais atua apenas como um fator moderador da interação interespecífica (em especial a coexistência), sem relação direta entre essas condições e a biomassa das espécies.

Response of aquatic macrophyte biomass to limnological changes under water level fluctuation in tropical reservoirs / Resposta da biomassa de macrófitas aquáticas às mudanças limnológicas consequentes da variação do nível da água em reservatórios tropicais

We evaluated the response of the biomass of aquatic macrophytes under limnological changes after water level fluctuation (WLF) of two tropical reservoirs (R1 and R2), located in northeastern Brazil. Initially we tested the hypothesis that post-WLF limnological conditions and biomass of macrophytes increase or decrease, depending on the variable or species. We monitored a 4 × 50 m permanent plot, in four expeditions per period (pre- or post-WLF), assessing species biomass and 10 limnological variables. We utilized 0.25 × 0.25 m quadrats for biomass. Once the effect of WLF in limnological variables and species biomass was confirmed, we utilized Canonical Correspondence Analysis to understand the relationship between limnological variables and species biomass. The abundant and/or dominant species in pre-WLF of R1 ( Pistia stratiotes, Eichhornia crassipes and Salvinia auriculata) and R2 (Paspalidium geminatum and S. auriculata) reduced their biomass post-WLF and were correlated with temperature, total phosphorous and nitrate. The reduced biomass of P. stratiotes, E. crassipes and S. auriculata in post-WLF widened resource availability, allowing coexistence of species. Therefore, we suggest that the change of limnological conditions in post-WLF in artificial lakes acts only as a moderator factor of the interspecific interaction (especially coexistence), without direct relation between these conditions and species biomass.(AU)

Avaliamos a resposta da biomassa de macrófitas aquáticas às alterações ambientais após flutuação do nível de água (WLF) de dois reservatórios tropicais (R1 e R2), localizados no Nordeste do Brasil. Inicialmente, testamos a hipótese de que após uma WLF as condições limnológicas e a biomassa das macrófitas aumentam ou diminuem, dependendo da variável ou espécie. Por isso, monitoramos uma parcela permanente de 4 × 50 m, em quatro amostragens por período (pré ou pós-WLF), avaliando a biomassa de espécies e 10 variáveis limnológicas. Utilizamos quadrados de 0,25 × 0,25 m na amostragem da biomassa. Uma vez que o efeito do WLF em variáveis limnológicas e biomassa das espécies foi confirmado, utilizamos a Análise de Correspondência Canônica para compreender a relação das variáveis limnológicas com a biomassa de espécies. As espécies abundantes e/ou dominantes no pré-WLF de R1 (Pistia stratiotes, Eichhornia crassipes e Salvinia auriculata ) e R2 (Paspalidium geminatum e S. auriculata ) reduziram sua biomassa pós-WLF, correlacionando-se diretamente com temperatura, fósforo total e nitrato. A redução da biomassa de P. stratiotes , E. crassipes e S. auriculata em pós-WLF ampliou a disponibilidade de recursos, permitindo a coexistência de espécies. Portanto, sugerimos que a mudança das condições limnológicas no pós-WLF em lagos artificiais atua apenas como um fator moderador da interação interespecífica (em especial a coexistência), sem relação direta entre essas condições e a biomassa das espécies.(AU)

Response of aquatic macrophyte biomass to limnological changes under water level fluctuation in tropical reservoirs

Abstract We evaluated the response of the biomass of aquatic macrophytes under limnological changes after water level fluctuation (WLF) of two tropical reservoirs (R1 and R2), located in northeastern Brazil. Initially we tested the hypothesis that post-WLF limnological conditions and biomass of macrophytes increase or decrease, depending on the variable or species. We monitored a 4 × 50 m permanent plot, in four expeditions per period (pre- or post-WLF), assessing species biomass and 10 limnological variables. We utilized 0.25 × 0.25 m quadrats for biomass. Once the effect of WLF in limnological variables and species biomass was confirmed, we utilized Canonical Correspondence Analysis to understand the relationship between limnological variables and species biomass. The abundant and/or dominant species in pre-WLF of R1 ( Pistia stratiotes, Eichhornia crassipes and Salvinia auriculata) and R2 (Paspalidium geminatum and S. auriculata) reduced their biomass post-WLF and were correlated with temperature, total phosphorous and nitrate. The reduced biomass of P. stratiotes, E. crassipes and S. auriculata in post-WLF widened resource availability, allowing coexistence of species. Therefore, we suggest that the change of limnological conditions in post-WLF in artificial lakes acts only as a moderator factor of the interspecific interaction (especially coexistence), without direct relation between these conditions and species biomass.

Resumo Avaliamos a resposta da biomassa de macrófitas aquáticas às alterações ambientais após flutuação do nível de água (WLF) de dois reservatórios tropicais (R1 e R2), localizados no Nordeste do Brasil. Inicialmente, testamos a hipótese de que após uma WLF as condições limnológicas e a biomassa das macrófitas aumentam ou diminuem, dependendo da variável ou espécie. Por isso, monitoramos uma parcela permanente de 4 × 50 m, em quatro amostragens por período (pré ou pós-WLF), avaliando a biomassa de espécies e 10 variáveis limnológicas. Utilizamos quadrados de 0,25 × 0,25 m na amostragem da biomassa. Uma vez que o efeito do WLF em variáveis limnológicas e biomassa das espécies foi confirmado, utilizamos a Análise de Correspondência Canônica para compreender a relação das variáveis limnológicas com a biomassa de espécies. As espécies abundantes e/ou dominantes no pré-WLF de R1 (Pistia stratiotes, Eichhornia crassipes e Salvinia auriculata ) e R2 (Paspalidium geminatum e S. auriculata ) reduziram sua biomassa pós-WLF, correlacionando-se diretamente com temperatura, fósforo total e nitrato. A redução da biomassa de P. stratiotes , E. crassipes e S. auriculata em pós-WLF ampliou a disponibilidade de recursos, permitindo a coexistência de espécies. Portanto, sugerimos que a mudança das condições limnológicas no pós-WLF em lagos artificiais atua apenas como um fator moderador da interação interespecífica (em especial a coexistência), sem relação direta entre essas condições e a biomassa das espécies.

Response of aquatic macrophyte biomass to limnological changes under water level fluctuation in tropical reservoirs

Abstract We evaluated the response of the biomass of aquatic macrophytes under limnological changes after water level fluctuation (WLF) of two tropical reservoirs (R1 and R2), located in northeastern Brazil. Initially we tested the hypothesis that post-WLF limnological conditions and biomass of macrophytes increase or decrease, depending on the variable or species. We monitored a 4 × 50 m permanent plot, in four expeditions per period (pre- or post-WLF), assessing species biomass and 10 limnological variables. We utilized 0.25 × 0.25 m quadrats for biomass. Once the effect of WLF in limnological variables and species biomass was confirmed, we utilized Canonical Correspondence Analysis to understand the relationship between limnological variables and species biomass. The abundant and/or dominant species in pre-WLF of R1 ( Pistia stratiotes, Eichhornia crassipes and Salvinia auriculata) and R2 (Paspalidium geminatum and S. auriculata) reduced their biomass post-WLF and were correlated with temperature, total phosphorous and nitrate. The reduced biomass of P. stratiotes, E. crassipes and S. auriculata in post-WLF widened resource availability, allowing coexistence of species. Therefore, we suggest that the change of limnological conditions in post-WLF in artificial lakes acts only as a moderator factor of the interspecific interaction (especially coexistence), without direct relation between these conditions and species biomass.

Resumo Avaliamos a resposta da biomassa de macrófitas aquáticas às alterações ambientais após flutuação do nível de água (WLF) de dois reservatórios tropicais (R1 e R2), localizados no Nordeste do Brasil. Inicialmente, testamos a hipótese de que após uma WLF as condições limnológicas e a biomassa das macrófitas aumentam ou diminuem, dependendo da variável ou espécie. Por isso, monitoramos uma parcela permanente de 4 × 50 m, em quatro amostragens por período (pré ou pós-WLF), avaliando a biomassa de espécies e 10 variáveis limnológicas. Utilizamos quadrados de 0,25 × 0,25 m na amostragem da biomassa. Uma vez que o efeito do WLF em variáveis limnológicas e biomassa das espécies foi confirmado, utilizamos a Análise de Correspondência Canônica para compreender a relação das variáveis limnológicas com a biomassa de espécies. As espécies abundantes e/ou dominantes no pré-WLF de R1 (Pistia stratiotes, Eichhornia crassipes e Salvinia auriculata ) e R2 (Paspalidium geminatum e S. auriculata ) reduziram sua biomassa pós-WLF, correlacionando-se diretamente com temperatura, fósforo total e nitrato. A redução da biomassa de P. stratiotes , E. crassipes e S. auriculata em pós-WLF ampliou a disponibilidade de recursos, permitindo a coexistência de espécies. Portanto, sugerimos que a mudança das condições limnológicas no pós-WLF em lagos artificiais atua apenas como um fator moderador da interação interespecífica (em especial a coexistência), sem relação direta entre essas condições e a biomassa das espécies.

Diaspore bank of aquatic macrophytes maintaining species diversity in a Neotropical pond / Banco de diásporos de macrófitas aquáticas para a manutenção da diversidade das espécies em uma lagoa Neotropical

The diaspore bank is an important component of biological diversity acting mainly as storage and source of diaspores, which also indicate dynamics and patterns of maintenance of plant diversity. We tested the hypothesis that the diaspore bank would be the responsible factor for the maintenance of the aquatic plant species, used two techniques to evaluate the diaspore bank: seedling emergence and direct counting of field samples. Density and richness of the diaspore bank were correlated with plant cover of the aquatic macrophyte communities and also with the euphotic zone radiation in different phases of the hydrological cycle. The diaspore bank is a key factor in maintenance of aquatic macrophyte assemblages in this pond. Nymphaea amazonum was one of the dominant species in the pond and presented temporally peaks of plant cover. Furthermore, depth allowed induction of germination of stored diaspores. Therefore, the diaspore bank may predict which species colonizes a site when environmental characteristics are favorable and allows inferring which processes are linked to changes in structure of aquatic macrophyte assemblages. These mechanisms are the means for recovery of macrophyte species under natural disturbances, represented by water level oscillations in floodplains.

O banco de diásporos é um componente importante da diversidade biológica atuando principalmente como armazenamento e fonte de diásporos, que também indicam a dinâmica e os padrões de manutenção da diversidade vegetal. Testamos a hipótese de que o banco de diásporos seria o fator responsável pela manutenção das espécies de plantas aquáticas, utilizando duas técnicas para avaliar o banco diásporo: emergência das plântulas e contagem direta de amostras de campo. Densidade e riqueza do banco de diásporos foram correlacionadas com cobertura vegetal das comunidades de macrófitas aquáticas e também com a radiação da zona eufótica em diferentes fases do ciclo hidrológico. O banco de diásporos é um fator chave na manutenção das assembleias de macrófitas aquáticas nesta lagoa. Nymphaea amazonum foi uma das espécies dominantes na lagoa temporalmente, apresentou picos de cobertura vegetal. Além disso, a profundidade permitiu a indução da germinação de diásporos armazenados. Portanto, o banco de diásporo é um preditor de quais espécies colonizarão um local quando as características ambientais são favoráveis e permite inferir que os processos estão ligados a mudanças na estrutura das assembleias de macrófitas aquáticas. Estes mecanismos são os meios para a recuperação de espécies de macrófitas sob as perturbações naturais, representados por oscilações do nível de água nas planícies aluviais.

Leaf mechanical resistance in plant trait databases: comparing the results of two common measurement methods.

BACKGROUND AND AIMS: The influence of leaf mechanical properties on local ecosystem processes, such as trophic transfer, decomposition and nutrient cycling, has resulted in a growing interest in including leaf mechanical resistance in large-scale databases of plant functional traits. 'Specific work to shear' and 'force to tear' are two properties commonly used to describe mechanical resistance (toughness or strength) of leaves. Two methodologies have been widely used to measure them across large datasets. This study aimed to assess correlations and standardization between the two methods, as measured by two widely used apparatuses, in order to inter-convert existing data in those global datasets. METHODS: Specific work to shear (W(SS)) and force to tear (FT) were measured in leaves of 72 species from south-eastern Australia. The measurements were made including and excluding midribs. Relationships between the variables were tested by Spearman correlations and ordinary least square regressions. KEY RESULTS: A positive and significant correlation was found between the methods, but coefficients varied according to the inclusion or exclusion of the midrib in the measurements. Equations for prediction varied according to leaf venation pattern. A positive and significant (r = 0·90, P < 0·0001) correlation was also found between W(SS) values for fresh and rehydrated leaves, which is considered to be of practical relevance. CONCLUSIONS: In the context of broad-scale ecological hypotheses and used within the constraints recommended here, leaf mechanical resistance data obtained with both methodologies could be pooled together into a single coarser variable, using the equations provided in this paper. However, more detailed datasets of FT cannot be safely filled in with estimations based on W(SS), or vice versa. In addition, W(SS) values of green leaves can be predicted with good accuracy from W(SS) of rehydrated leaves of the same species.

Diaspore bank of aquatic macrophytes maintaining species diversity in a Neotropical pond / Banco de diásporos de macrófitas aquáticas para a manutenção da diversidade das espécies em uma lagoa Neotropical

The diaspore bank is an important component of biological diversity acting mainly as storage and source of diaspores, which also indicate dynamics and patterns of maintenance of plant diversity. We tested the hypothesis that the diaspore bank would be the responsible factor for the maintenance of the aquatic plant species, used two techniques to evaluate the diaspore bank: seedling emergence and direct counting of field samples. Density and richness of the diaspore bank were correlated with plant cover of the aquatic macrophyte communities and also with the euphotic zone radiation in different phases of the hydrological cycle. The diaspore bank is a key factor in maintenance of aquatic macrophyte assemblages in this pond. Nymphaea amazonum was one of the dominant species in the pond and presented temporally peaks of plant cover. Furthermore, depth allowed induction of germination of stored diaspores. Therefore, the diaspore bank may predict which species colonizes a site when environmental characteristics are favorable and allows inferring which processes are linked to changes in structure of aquatic macrophyte assemblages. These mechanisms are the means for recovery of macrophyte species under natural disturbances, represented by water level oscillations in floodplains.(AU)

O banco de diásporos é um componente importante da diversidade biológica atuando principalmente como armazenamento e fonte de diásporos, que também indicam a dinâmica e os padrões de manutenção da diversidade vegetal. Testamos a hipótese de que o banco de diásporos seria o fator responsável pela manutenção das espécies de plantas aquáticas, utilizando duas técnicas para avaliar o banco diásporo: emergência das plântulas e contagem direta de amostras de campo. Densidade e riqueza do banco de diásporos foram correlacionadas com cobertura vegetal das comunidades de macrófitas aquáticas e também com a radiação da zona eufótica em diferentes fases do ciclo hidrológico. O banco de diásporos é um fator chave na manutenção das assembleias de macrófitas aquáticas nesta lagoa. Nymphaea amazonum foi uma das espécies dominantes na lagoa temporalmente, apresentou picos de cobertura vegetal. Além disso, a profundidade permitiu a indução da germinação de diásporos armazenados. Portanto, o banco de diásporo é um preditor de quais espécies colonizarão um local quando as características ambientais são favoráveis e permite inferir que os processos estão ligados a mudanças na estrutura das assembleias de macrófitas aquáticas. Estes mecanismos são os meios para a recuperação de espécies de macrófitas sob as perturbações naturais, representados por oscilações do nível de água nas planícies aluviais.(AU)