Como o sombreamento influencia a secreção de néctar extrafloral em Chamaecrista nictitans (Fabaceae)?
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Data
2022-01-25
Autores
Bartsch, Lucas José Reis 
Orientadores
Leal, Laura Carolina
Tipo
Trabalho de conclusão de curso
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Resumo
Plantas produzem néctar extrafloral como uma defesa indireta contra herbívoros pela atração de formigas protetoras. No entanto, a produção de néctar impõe custos energéticos às plantas. O custo relativo desse néctar deve ser mais alto quanto menor o desempenho fotossintético da planta. Nesse estudo, avaliamos primeiramente como a variação no sombreamento afeta a produção de néctar extrafloral na leguminosa Chamaecrista nictitans. Para tanto, investigamos como a atividade dos nectários e o sombreamento interfere na performance das plantas. Desse modo, realizamos um experimento 2x3 fatorial no qual cultivamos um total de 60 plantas sob três níveis de sombreamento (0, 30 e 50%) e duas condições de atividade dos nectários extraflorais (nectários ativos e inativos). Ao longo de 45 dias, medimos a massa total de açúcar no néctar extrafloral nas 30 plantas com nectários ativos sob os diferentes níveis de sombreamento. Em seguida, comparamos o acúmulo de biomassa, a densidade da madeira e a área foliar específica nas 60 plantas, comparando plantas com nectários ativos e bloqueados sob os diferentes níveis de sombreamento. O sombreamento não influenciou a massa de açúcares do néctar secretado pelas plantas de C. nicititans, e todas as plantas aumentaram a produção de açúcares ao longo do tempo. Além disso, a atividade dos nectários não influenciou a alocação de biomassa da planta (aérea ou radicular), embora plantas mais sombreadas (>30%) tenham investido menos em biomassa radicular. Por outro lado, a atividade secretora dos nectários influenciou a área específica foliar, modificando o padrão de expansão foliar das plantas sob 50% de sombreamento. Nosso estudo mostra que, na presença de herbivoria, a qualidade do néctar extrafloral não se altera, independente do nível de sombreamento. Por outro lado, o custo energético relativo do néctar é maior em plantas sob níveis de sombreamento mais altos. Por fim, a atividade do nectário extrafloral influencia o tipo de resposta que as plantas apresentaram ante às condições de sombreamento.
Plants produce extrafloral nectar as an indirect defense against herbivores by attracting protective ants. However, nectar production imposes energy costs on plants. The relative cost of this nectar should be higher the lower the photosynthetic performance of the plant. In this study, we first evaluated how variation in shading affects extrafloral nectar production in the legume Chamaecrista nictitans. Therefore, we investigated how nectary activity and shading interfere with plant performance. Thus, we carried out a 2x3 factorial experiment in which we cultivated a total of 60 plants under three levels of shading (0, 30 and 50%) and two conditions of extrafloral nectary activity (active and inactive nectaries). Over 45 days, we measured the total sugar mass in the extrafloral nectar in the 30 plants with active nectaries under different shade levels. Then, we compared biomass accumulation, wood density and specific leaf area in the 60 plants, comparing plants with active and inactive nectaries under different shade levels. Shading did not influence the sugar mass of nectar secreted by C. nicititans, and all plants increased sugar production over time. Furthermore, nectary activity did not influence plant biomass allocation (shoot or root), although more shaded plants (>30%) invested less in root biomass. On the other hand, the secretory activity of the nectaries influenced the specific leaf area, modifying the pattern of leaf expansion in plants under 50% shading. Our study shows that, in the presence of herbivory, the quality of extrafloral nectar does not change, regardless of the shading level. On the other hand, the relative energy cost of nectar is higher in plants under higher shading levels. Finally, the activity of the extrafloral nectary influences the type of response that the plants presented to the shading conditions.
Plants produce extrafloral nectar as an indirect defense against herbivores by attracting protective ants. However, nectar production imposes energy costs on plants. The relative cost of this nectar should be higher the lower the photosynthetic performance of the plant. In this study, we first evaluated how variation in shading affects extrafloral nectar production in the legume Chamaecrista nictitans. Therefore, we investigated how nectary activity and shading interfere with plant performance. Thus, we carried out a 2x3 factorial experiment in which we cultivated a total of 60 plants under three levels of shading (0, 30 and 50%) and two conditions of extrafloral nectary activity (active and inactive nectaries). Over 45 days, we measured the total sugar mass in the extrafloral nectar in the 30 plants with active nectaries under different shade levels. Then, we compared biomass accumulation, wood density and specific leaf area in the 60 plants, comparing plants with active and inactive nectaries under different shade levels. Shading did not influence the sugar mass of nectar secreted by C. nicititans, and all plants increased sugar production over time. Furthermore, nectary activity did not influence plant biomass allocation (shoot or root), although more shaded plants (>30%) invested less in root biomass. On the other hand, the secretory activity of the nectaries influenced the specific leaf area, modifying the pattern of leaf expansion in plants under 50% shading. Our study shows that, in the presence of herbivory, the quality of extrafloral nectar does not change, regardless of the shading level. On the other hand, the relative energy cost of nectar is higher in plants under higher shading levels. Finally, the activity of the extrafloral nectary influences the type of response that the plants presented to the shading conditions.