Efeito da salinidade, temperatura e competição interespecífica sobre a distribuição de três espécies de macrófitas aquáticas tropicais
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Data
2022-08-19
Autores
Paulino, Rachel Santini
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Universidade Estadual Paulista (Unesp)
Resumo
Crinum americanum e Spartina alterniflora são as espécies nativas mais frequentes presentes no gradiente de salinidade presente em um estuário do sudeste do Brasil, enquanto que Urochloa arrecta é a espécie exótica invasora mais abundante na região de água doce neste estuário, mas também de outros ecossistemas aquáticos. Avaliamos os efeitos da salinidade no crescimento (ganho de biomassa), teor de nitrogênio total (NT) na biomassa do vegetal e no estresse oxidativo (peróxido de hidrogênio e malondialdeído) das três espécies distribuídas no estuário, além de estimar as implicações do aumento da temperatura (mudanças climáticas) na adequabilidade climática de U. arrecta em uma escala global. Para isso, nós dividimos a tese em três capítulos. No capítulo I nós desenvolvemos um experimento com dois fatores que foram constituídos por 3 culturas (monocultura de S. alterniflora, monocultura de C. americanum e cultura mista com às duas espécies), 3 salinidades (0, 20 e 30 ppt) e 5 réplicas, totalizando 45 unidades experimentas. O teor de NT foi semelhante em todas as unidades experimentais. Nós encontramos que a salinidade não afetou o crescimento das culturas de S. alterniflora, porém a monocultura em salinidade de 0 ppt foi mais estressante para a espécie em relação a cultura mista (na mesma salinidade). Na monocultura de S. alterniflora (0 ppt), o teor de nitrogênio total (fração emergente) foi menor e o estresse oxidativo (fração subterrânea) maior. Em C. americanum, no geral, a competição reduziu o teor de nitrogênio total (fração emergente) nas salinidades e promoveu maior estresse oxidativo (fração subterrânea) em 20 e 30 ppt. No entanto, o crescimento (ganho de biomassa emergente) foi reduzido apenas em 30 ppt. Nós concluímos que o tratamento na ausência de salinidade foi mais estressante para a monocultura de S. alterniflora. Porém, como o crescimento da espécie não foi reduzido, indicado que o estresse foi leve é possível que ausência da espécie em alto estuário esteja relacionada com as características do sedimento natural. O maior estresse de C. americanum em maior salinidade provavelmente se deve a menor habilidade competitiva da espécie nesta salinidade, reduzindo sua aptidão em combater os efeitos do estresse oxidativo neste tratamento. Isto explicaria a ausência de C. americanum na região do baixo estuário. No capítulo II nós desenvolvemos um experimento de um fator que foi constituído por 1 cultura (monocultura de U. arrecta), 3 salinidades (0, 20 e 30 ppt) e 5 réplicas, totalizando 15 unidades experimentais. O teor NT foi semelhante em todas as unidades experimentais. Nós encontramos que o crescimento da parte emergente de U. arrecta foi reduzido com o aumento da salinidade, mas o estresse oxidativo só foi maior em 30 ppt. Nós concluímos que a espécie provavelmente 10 apresenta ajustes fisiológicos que permitem sua sobrevivência em salinidade intermediária no estuário. No capítulo III nós utilizamos dados de distribuição global de U. arrecta e de variáveis bioclimáticas na projeção histórica e futura (2080) e aplicamos em um modelo de distribuição de espécies. Nós encontramos que as variáveis climáticas de temperatura foram as variáveis mais importantes para estimar a adequabilidade climática da espécie nas projeções estudadas. Nós concluímos que as áreas úmidas de clima quente (clima tropical) estão mais susceptíveis a invasão da espécie no contexto do aumento da temperatura devido as mudanças climáticas.
Crinum americanum and Spartina alterniflora are the most frequent native species present in the salinity gradient present in an estuary in southeastern Brazil, while Urochloa arrecta is the most abundant invasive species in the freshwater region of this estuary, but also in other aquatic ecosystems. We evaluated the effects of salinity on growth (biomass gain), total nitrogen content in plant biomass and oxidative stress (hydrogen peroxide and malondialdehyde) of the three species distributed in the estuary, in addition to estimating the implications of the increase in temperature (climate change) on the climate suitability of U. arrecta on a global scale. For this, we divided the thesis into three chapters. In the chapter I we developed an experiment with two factors that consisted of 3 cultures (monoculture of S. alterniflora, monoculture of C. americanum and mixed culture with both species), 3 salinities (0, 20 and 30 ppt) and 5 replicates , totaling 45 experimental units. Nutrient concentrations were similar in all experimental units. We found that salinity and cultures did not affect the growth of S. alterniflora, but monoculture at 0 ppt salinity was more stressful for the species than mixed culture (at the same salinity). In the monoculture of S. alterniflora (0 ppt), the total nitrogen content (emergent fraction) was lower and the oxidative stress (underground fraction) was higher. In C. americanum, in general, competition reduced the total nitrogen content (emergent fraction) in salinities and promoted higher oxidative stress (underground fraction) at 20 and 30 ppt. However, growth (emerging biomass gain) was reduced by only 30 ppt. We concluded that treatment in the absence of salt was more stressful for the monoculture of S. alterniflora. However, as the growth of the species was not reduced, indicating that the stress was light, it is possible that the 11 absence of the species in the high estuary is related to the characteristics of the natural sediment. The greater stress of C. americanum in high salinity is probably due to the lower competitive capacity of the species in high salinity, reducing its ability to combat the effects of oxidative stress in this treatment. This would explain the absence of C. americanm in the lower estuary region. In the chapter II we developed a one-factor experiment that consisted of 1 culture (monoculture of U. arrecta), 3 salinities (0, 20 and 30 ppt) and 5 replicates, totaling 15 experimental units. Nutrient concentrations were similar in all experimental units. We found that emergent growth of U. arrecta was reduced with increasing salinity, but oxidative stress was only greater at 30 ppt. We conclude that the species probably presents physiological adjustments that allow its survival in intermediate salinity in the estuary. In the chapter III we used data from the global distribution of U. arrecta and from bioclimatic variables in the historical and future projection (2080) and applied it to a species distribution model. We found that the climatic variables of temperature were the most important variables to estimate the environmental suitability of the species in the projections studied. We conclude that humid areas with a warm climate (tropical climate) are more susceptible to invasion by the species in a context of global warming. Keywords: Crinum americanum, Spartina alterniflora, Urochloa arrecta, saline stress, climate change.
Crinum americanum and Spartina alterniflora are the most frequent native species present in the salinity gradient present in an estuary in southeastern Brazil, while Urochloa arrecta is the most abundant invasive species in the freshwater region of this estuary, but also in other aquatic ecosystems. We evaluated the effects of salinity on growth (biomass gain), total nitrogen content in plant biomass and oxidative stress (hydrogen peroxide and malondialdehyde) of the three species distributed in the estuary, in addition to estimating the implications of the increase in temperature (climate change) on the climate suitability of U. arrecta on a global scale. For this, we divided the thesis into three chapters. In the chapter I we developed an experiment with two factors that consisted of 3 cultures (monoculture of S. alterniflora, monoculture of C. americanum and mixed culture with both species), 3 salinities (0, 20 and 30 ppt) and 5 replicates , totaling 45 experimental units. Nutrient concentrations were similar in all experimental units. We found that salinity and cultures did not affect the growth of S. alterniflora, but monoculture at 0 ppt salinity was more stressful for the species than mixed culture (at the same salinity). In the monoculture of S. alterniflora (0 ppt), the total nitrogen content (emergent fraction) was lower and the oxidative stress (underground fraction) was higher. In C. americanum, in general, competition reduced the total nitrogen content (emergent fraction) in salinities and promoted higher oxidative stress (underground fraction) at 20 and 30 ppt. However, growth (emerging biomass gain) was reduced by only 30 ppt. We concluded that treatment in the absence of salt was more stressful for the monoculture of S. alterniflora. However, as the growth of the species was not reduced, indicating that the stress was light, it is possible that the 11 absence of the species in the high estuary is related to the characteristics of the natural sediment. The greater stress of C. americanum in high salinity is probably due to the lower competitive capacity of the species in high salinity, reducing its ability to combat the effects of oxidative stress in this treatment. This would explain the absence of C. americanm in the lower estuary region. In the chapter II we developed a one-factor experiment that consisted of 1 culture (monoculture of U. arrecta), 3 salinities (0, 20 and 30 ppt) and 5 replicates, totaling 15 experimental units. Nutrient concentrations were similar in all experimental units. We found that emergent growth of U. arrecta was reduced with increasing salinity, but oxidative stress was only greater at 30 ppt. We conclude that the species probably presents physiological adjustments that allow its survival in intermediate salinity in the estuary. In the chapter III we used data from the global distribution of U. arrecta and from bioclimatic variables in the historical and future projection (2080) and applied it to a species distribution model. We found that the climatic variables of temperature were the most important variables to estimate the environmental suitability of the species in the projections studied. We conclude that humid areas with a warm climate (tropical climate) are more susceptible to invasion by the species in a context of global warming. Keywords: Crinum americanum, Spartina alterniflora, Urochloa arrecta, saline stress, climate change.
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Palavras-chave
Estresse abiótico, Competição (Biologia), Plantas Efeito do sal, Estuários, Ecossistemas costeiros, Mudanças climáticas