A common temperature dependence of nutritional demands in ectotherms.

In light of ongoing climate change, it is increasingly important to know how nutritional requirements of ectotherms are affected by changing temperatures. Here, we analyse the wide thermal response of phosphorus (P) requirements via elemental gross growth efficiencies of Carbon (C) and P, and the Threshold Elemental Ratios in different aquatic invertebrate ectotherms: the freshwater model species Daphnia magna, the marine copepod Acartia tonsa, the marine heterotrophic dinoflagellate Oxyrrhis marina, and larvae of two populations of the marine crab Carcinus maenas. We show that they all share a non-linear cubic thermal response of nutrient requirements. Phosphorus requirements decrease from low to intermediate temperatures, increase at higher temperatures and decrease again when temperature is excessive. This common thermal response of nutrient requirements is of great importance if we aim to understand or even predict how ectotherm communities will react to global warming and nutrient-driven eutrophication.

Substrate-Limited and -Unlimited Coastal Microbial Communities Show Different Metabolic Responses with Regard to Temperature.

Bacteria are the principal consumers of dissolved organic carbon (DOC) in the ocean and predation of bacteria makes organic carbon available to higher trophic levels. The efficiency with which bacteria convert the consumed carbon (C) into biomass (i.e., carbon growth efficiency, Y) determines their ecological as well as biogeochemical role in marine ecosystems. Yet, it is still unclear how changes in temperature will affect Y and, hence, the transfer of consumed C to higher trophic levels. Here, we experimentally investigated the effect of temperature on metabolic functions of coastal microbial communities inoculated in both nutrient-limited chemostats and nutrient-unlimited turbidostats. We inoculated chemostats and turbidostats with coastal microbial communities into seawater culture medium augmented with 20 and 100 µmol L-1 of glucose respectively and measured CO2 production, carbon biomass and cell abundance. Chemostats were cultured between 14 and 26°C and specific growth rates (µ) between 0.05 and 6.0 day-1, turbidostats were cultured between 10 and 26°C with specific growth rates ranging from 28 to 62 day-1. In chemostats under substrate limitation, which is common in the ocean, the specific respiration rate (r, day-1) showed no trend with temperature and was roughly proportional to µ, implying that carbon growth efficiency (Y) displayed no tendency with temperature. The response was very different in turbidostats under temperature-limited, nutrient-repleted growth, here µ increased with temperature but r decreased resulting in an increase of Y with temperature (Q10: 2.6). Comparison of our results with data from the literature on the respiration rate and cell weight of monospecific bacteria indicates that in general the literature data behaved similar to chemostat data, showing no trend in specific respiration with temperature. We conclude that respiration rates of nutrient-limited bacteria measured at a certain temperature cannot be adjusted to different temperatures with a temperature response function similar to Q10 or Arrhenius. However, the cellular respiration rate and carbon demand rate (both: mol C cell-1 day-1) show statistically significant relations with cellular carbon content (mol C cell-1) in chemostats, turbidostats, and the literature data.

Hydrological pulse regulating the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes.

We evaluated in situ rates of bacterial carbon processing in Amazonian floodplain lakes and mainstems, during both high water (HW) and low water (LW) phases (p < 0.05). Our results showed that bacterial production (BP) was lower and more variable than bacterial respiration, determined as total respiration. Bacterial carbon demand was mostly accounted by BR and presented the same pattern that BR in both water phases. Bacterial growth efficiency (BGE) showed a wide range (0.2-23%) and low mean value of 3 and 6%, (in HW and LW, respectively) suggesting that dissolved organic carbon was mostly allocated to catabolic metabolism. However, BGE was regulated by BP in LW phase. Consequently, changes in BGE showed the same pattern that BP. In addition, the hydrological pulse effects on mainstems and floodplains lakes connectivity were found for BP and BGE in LW. Multiple correlation analyses revealed that indexes of organic matter (OM) quality (chlorophyll-a, N stable isotopes and C/N ratios) were the strongest seasonal drivers of bacterial carbon metabolism. Our work indicated that: (i) the bacterial metabolism was mostly driven by respiration in Amazonian aquatic ecosystems resulting in low BGE in either high or LW phase; (ii) the hydrological pulse regulated the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes mostly driven by OM quality.

The effect of temperature and salinity on the physiological rates of the mussel Perna perna (Linnaeus 1758)

The aim of this work was to study the rates of respiration, clearance, excretion and absorption efficiency at different temperature and salinity under laboratory conditions for Perna perna. Results showed variations in physiological rates and in acclimatization capacity which, taken together, enabled to understand its behavior in the environment, as well as to estimate its scope for growth. All experiments were carried out in static conditions, in ten replicas with one mussel by flasks. Perna perna was capable of achieving acclimatization for both clearance and absorption efficiency (15 to 30 °C), but it achieved only partial acclimatization for respiration and excretion under chronic temperature conditions. The clearance and respiration rates increased twofold as the mussel was submitted to temperature shock, which signified a response to metabolism activity. Acclimatization to salinity was clearly the best developed capability (20 to 40 ‰). Net growth efficiency reduced as the temperature increased, but remained constant in the 20 to 35 ë salinity range.

O molusco bivalve Perna perna é o Mytilidae de maior tamanho e o mais abundante na costa brasileira. Apresenta uma grande importância sócio-econômica devido ao seu uso na mitilicultura, disponibilizando para o consumo humano uma fonte protéica barata proporcionado pelos sistemas de cultivos costeiros. Entretanto, existe uma carência de estudos fisiológicos da espécie, que poderiam ser úteis na avaliação de novas áreas de cultivo, assim como no monitoramento de ambientes contaminados. Neste trabalho foram realizadas testes fisiológicos para determinar as taxas de respiração, clareamento, excreção e eficiência de absorção em laboratório, sob condições crônicas e agudas, em diferentes temperaturas e salinidades. Desta forma, foi possível determinar as oscilações e a capacidade de aclimatação da espécie que servem como base para o entendimento do organismo no ambiente natural, além de gerar conhecimento básico para estimativas do seu potencial de crescimento. Todos os experimentos foram realizados em condições estáticas com dez réplicas e com um mexilhão por frasco teste. A taxa de respiração foi estimada pela diminuição do oxigênio dissolvido na água de incubação, a taxa de clareamento pela diminuição da concentração do fitoplâncton oferecido como alimento, a taxa de excreção pelo aumento da concentração do N-NH4+ e a eficiência de absorção pela diferença entre os conteúdos de matéria orgânica do alimento e das fezes produzidas. Perna perna apresentou capacidade de aclimatação total para as taxas de clareamento e para a eficiência de absorção (15 a 30 °C) e parcial para as taxas de respiração e excreção sob condições crônicas de temperatura. Em condições de choque térmico, as taxas de clareamento e respiração dobraram em magnitude como resposta ao metabolismo de atividade. Para a salinidade, P. perna apresentou uma maior capacidade de aclimatação (20 a 40 ‰). Para o crescimento líquido, P. perna apresentou uma diminuição de sua eficiência...

Crescimento e desenvolvimento de plantas de alface provenientes de mudas com diferentes idades fisiológicas

The aim of the work was to determine the effect of the physiological age of lettuce transplants on further growth and development of plants in the field. Transplants were sown in polystyrene trays using a commercial substrate mixture, without any additional supply of nutrients. Water was delivered periodically to compensate evapotranspiration losses, as done in the commercial practice of growing lettuce seedlings. Sowing was done in four dates: 5, 11, 19 and 26 July, named T1, T2, T3 and T4 treatments, respectively. Planting in the field was done at 3 September, at 60, 54, 46 and 39 days after sowing, respectively. At this date, average number of leaves was 6.0, 6.0, 4.8 and 4.0 and dry mass was 0.7, 0.5, 0.5 and 0.3g/transplant, respectively. Number of leaves, dry mass and specific leaf area (SLA) in a per plant basis were determined at 25, 30, 35, 42, 46 and 51 days after planting (DAP). Average number of leaves at ending date was similar in T1, T2 and T3 plants: 21.2, 21.2 and 20.6 leaves/plant, respectively. In T4 plants, the number of leaves/plant was 15.4. At the same period, growth was also similar in T1, T2 and T3 plants: 12.4, 12.2 and 11.2 g/plant, respectively. In T4 plants, this variable reached only 6.0g/plant. For SLA, values increased during growth of plants and were higher at 46 DAP, decreasing thereafter, and did not differed among T1, T2 and T3. In T4, values decreased during the experimental period and differed significantly at last harvest. It was concluded that planting can be done at 5.0 leaves/transplant and 0.5g/transplant and that in winter and spring grown periods it may be delayed until 6.0 leaves/transplant and 0.7g/transplant.

O trabalho teve como objetivo determinar o efeito da idade fisiológica das mudas de alface no momento do transplante sobre o crescimento e desenvolvimento das plantas na lavoura. As mudas foram produzidas em bandejas de poliestireno, empregando substrato comercial, sem aplicação de nutrientes. A água foi fornecida por irrigação, feita periodicamente para compensar as perdas por evapotranspiração, da mesma forma como praticado na produção comercial de mudas. Os tratamentos consistiram de quatro datas de semeadura: 5, 11, 19 e 26 de julho, respectivamente T1, T2, T3 e T4. O transplante para os canteiros de produção foi feito em 3 de setembro, aos 60; 54; 46 e 39 dias após a semeadura, respectivamente. Nessa data, o número médio de folhas por muda foi de 6,0; 6,0; 4,8 e 4,0 e a massa seca de 0,7; 0,5; 0,5 e 0,3g/muda, respectivamente. Foi determinado o número de folhas, a massa seca e a superfície foliar específica (SLA) das folhas das plantas de cada tratamento aos 25, 30, 35, 42, 46 e 51 dias após o transplante (DAT). Ao final do experimento, o número médio de folhas foi similar em T1, T2 e T3, totalizando 21,2; 21,2 e 20,6 folhas/planta, respectivamente, enquanto em T4 foi inferior com 15,4 folhas/planta. O crescimento foi similar em T1, T2 e T3, totalizando ao final do experimento 12,4; 12,2 e 11,2g/planta, respectivamente, sem diferenças significativas, enquanto T4 diferiu com 6,0g/planta. Quanto ao SLA, os valores de T1, T2 e T3 foram crescentes até os 46 DAT, decrescendo apenas na última coleta, sem diferenças significativas. Em T4, esses valores decresceram durante todo o período, diferindo dos demais no final do experimento. Concluiu-se que o transplante pode ser efetuado com 5,0 folhas/muda e 0,5g/muda, podendo ser retardado no período de inverno e primavera até as mudas atingirem 6,0 folhas/muda e 0,7g/muda.

Crescimento e desenvolvimento de plantas de alface provenientes de mudas com diferentes idades fisiológicas

The aim of the work was to determine the effect of the physiological age of lettuce transplants on further growth and development of plants in the field. Transplants were sown in polystyrene trays using a commercial substrate mixture, without any additional supply of nutrients. Water was delivered periodically to compensate evapotranspiration losses, as done in the commercial practice of growing lettuce seedlings. Sowing was done in four dates: 5, 11, 19 and 26 July, named T1, T2, T3 and T4 treatments, respectively. Planting in the field was done at 3 September, at 60, 54, 46 and 39 days after sowing, respectively. At this date, average number of leaves was 6.0, 6.0, 4.8 and 4.0 and dry mass was 0.7, 0.5, 0.5 and 0.3g/transplant, respectively. Number of leaves, dry mass and specific leaf area (SLA) in a per plant basis were determined at 25, 30, 35, 42, 46 and 51 days after planting (DAP). Average number of leaves at ending date was similar in T1, T2 and T3 plants: 21.2, 21.2 and 20.6 leaves/plant, respectively. In T4 plants, the number of leaves/plant was 15.4. At the same period, growth was also similar in T1, T2 and T3 plants: 12.4, 12.2 and 11.2 g/plant, respectively. In T4 plants, this variable reached only 6.0g/plant. For SLA, values increased during growth of plants and were higher at 46 DAP, decreasing thereafter, and did not differed among T1, T2 and T3. In T4, values decreased during the experimental period and differed significantly at last harvest. It was concluded that planting can be done at 5.0 leaves/transplant and 0.5g/transplant and that in winter and spring grown periods it may be delayed until 6.0 leaves/transplant and 0.7g/transplant.

O trabalho teve como objetivo determinar o efeito da idade fisiológica das mudas de alface no momento do transplante sobre o crescimento e desenvolvimento das plantas na lavoura. As mudas foram produzidas em bandejas de poliestireno, empregando substrato comercial, sem aplicação de nutrientes. A água foi fornecida por irrigação, feita periodicamente para compensar as perdas por evapotranspiração, da mesma forma como praticado na produção comercial de mudas. Os tratamentos consistiram de quatro datas de semeadura: 5, 11, 19 e 26 de julho, respectivamente T1, T2, T3 e T4. O transplante para os canteiros de produção foi feito em 3 de setembro, aos 60; 54; 46 e 39 dias após a semeadura, respectivamente. Nessa data, o número médio de folhas por muda foi de 6,0; 6,0; 4,8 e 4,0 e a massa seca de 0,7; 0,5; 0,5 e 0,3g/muda, respectivamente. Foi determinado o número de folhas, a massa seca e a superfície foliar específica (SLA) das folhas das plantas de cada tratamento aos 25, 30, 35, 42, 46 e 51 dias após o transplante (DAT). Ao final do experimento, o número médio de folhas foi similar em T1, T2 e T3, totalizando 21,2; 21,2 e 20,6 folhas/planta, respectivamente, enquanto em T4 foi inferior com 15,4 folhas/planta. O crescimento foi similar em T1, T2 e T3, totalizando ao final do experimento 12,4; 12,2 e 11,2g/planta, respectivamente, sem diferenças significativas, enquanto T4 diferiu com 6,0g/planta. Quanto ao SLA, os valores de T1, T2 e T3 foram crescentes até os 46 DAT, decrescendo apenas na última coleta, sem diferenças significativas. Em T4, esses valores decresceram durante todo o período, diferindo dos demais no final do experimento. Concluiu-se que o transplante pode ser efetuado com 5,0 folhas/muda e 0,5g/muda, podendo ser retardado no período de inverno e primavera até as mudas atingirem 6,0 folhas/muda e 0,7g/muda.

PRODUÇÃO E DISTRIBUIÇÃO DA MATÉRIA SECA DO PEPINO PARA CONSERVA EM DIFERENTES POPULAÇÕES DE PLANTAS

The aim of this work was to determine the effect of plant density on dry matter accumulation and distribution to fruits of pickling cucumber plants. Experiments were carried out inside a polyethylene greenhouse, where plants were grown in densities of 2.00, 2.50, 3.33 and 5.00 plants m-2 in spring 1999, and of 4.00, 5.00, 6.66 and 10.00 plants m-2 in summer-autumn 2000, in order to determine the effect of plant density on dry matter accumulation and partitioning between vegetative parts and fruits. Plants grew in rows and were trained according to the high-wire system. Dry matter accumulation of stem, leaves and fruits was measured weekly. Fruits were harvested daily, the dry matter measured and values were summed together to determine the cumulative week weight. In the first experiment, a positive effect of the higher plant density was observed on dry matter accumulation of shoot and fruits, with a mean fraction of 49.5% allocated to fruits. In the second experiment, this effect was recorded only on the stem and the fraction of dry matter allocated to fruits decreased when plant density changed from four to 10 plants.m-2. Cumulative fruit yield in the first experiment showed a linear response to plant density while in the second experiment no effect of this variable was observed on fruit yield. It was concluded that it is not possible to use a pre-fixed plant density all over the year for the commercial production of pickling cucumber crops.

O trabalho teve como objetivo determinar o efeito da população de plantas na acumulação e distribuição da matéria seca entre as partes vegetativas e os frutos de plantas de pepino tipo conserva. Os experimentos foram realizados em uma estufa de polietileno, em populações de plantio de 2,00; 2,50; 3,33 e 5,00 plantas m-2 na primavera de 1999 e de 4,00; 5,00; 6,66 e 10,00 plantas m-2 no verão-outono de 2000. As plantas foram dispostas em fileiras distanciadas de um metro e tutoradas com fitas plásticas verticais. Determinou-se a evolução semanal da acumulação de matéria seca do caule, folhas e frutos. Os frutos foram colhidos diariamente e a matéria seca diária foi somada para obter o valor semanal acumulado. No primeiro experimento, houve resposta positiva da maior população tanto sobre a produção de matéria seca vegetativa como de frutos. A fração média da matéria seca total alocada para os frutos foi de 49,5%, independente da população de plantas. No segundo experimento, houve efeito significativo da maior população apenas sobre a acumulação de matéria seca do caule e a fração alocada para os frutos decresceu com o aumento da população. No primeiro experimento, o rendimento acumulado de frutos respondeu linearmente ao aumento da população de plantas. No segundo experimento, essa resposta não foi observada. Concluiu-se que não é possível recomendar uma única população de plantas a ser empregada ao longo do ano para o cultivo do pepino para conserva.

Produção e distribuição da matéria seca do pepino para conserva em diferentes populações de plantas

The aim of this work was to determine the effect of plant density on dry matter accumulation and distribution to fruits of pickling cucumber plants. Experiments were carried out inside a polyethylene greenhouse, where plants were grown in densities of 2.00, 2.50, 3.33 and 5.00 plants m-2 in spring 1999, and of 4.00, 5.00, 6.66 and 10.00 plants m-2 in summer-autumn 2000, in order to determine the effect of plant density on dry matter accumulation and partitioning between vegetative parts and fruits. Plants grew in rows and were trained according to the high-wire system. Dry matter accumulation of stem, leaves and fruits was measured weekly. Fruits were harvested daily, the dry matter measured and values were summed together to determine the cumulative week weight. In the first experiment, a positive effect of the higher plant density was observed on dry matter accumulation of shoot and fruits, with a mean fraction of 49.5% allocated to fruits. In the second experiment, this effect was recorded only on the stem and the fraction of dry matter allocated to fruits decreased when plant density changed from four to 10 plants.m-2. Cumulative fruit yield in the first experiment showed a linear response to plant density while in the second experiment no effect of this variable was observed on fruit yield. It was concluded that it is not possible to use a pre-fixed plant density all over the year for the commercial production of pickling cucumber crops.

O trabalho teve como objetivo determinar o efeito da população de plantas na acumulação e distribuição da matéria seca entre as partes vegetativas e os frutos de plantas de pepino tipo conserva. Os experimentos foram realizados em uma estufa de polietileno, em populações de plantio de 2,00; 2,50; 3,33 e 5,00 plantas m-2 na primavera de 1999 e de 4,00; 5,00; 6,66 e 10,00 plantas m-2 no verão-outono de 2000. As plantas foram dispostas em fileiras distanciadas de um metro e tutoradas com fitas plásticas verticais. Determinou-se a evolução semanal da acumulação de matéria seca do caule, folhas e frutos. Os frutos foram colhidos diariamente e a matéria seca diária foi somada para obter o valor semanal acumulado. No primeiro experimento, houve resposta positiva da maior população tanto sobre a produção de matéria seca vegetativa como de frutos. A fração média da matéria seca total alocada para os frutos foi de 49,5%, independente da população de plantas. No segundo experimento, houve efeito significativo da maior população apenas sobre a acumulação de matéria seca do caule e a fração alocada para os frutos decresceu com o aumento da população. No primeiro experimento, o rendimento acumulado de frutos respondeu linearmente ao aumento da população de plantas. No segundo experimento, essa resposta não foi observada. Concluiu-se que não é possível recomendar uma única população de plantas a ser empregada ao longo do ano para o cultivo do pepino para conserva.