Como o fogo e a invasão biológica afetam a dinâmica de carbono em ecossistemas campestres e savânicos do Cerrado?
Data
2022-10-11
Autores
Teixeira, Juliana Macedo Gitahy
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Promover o estoque de carbono torna-se uma ferramenta importante para a mitigação de mudanças climáticas. Os ecossistemas neotropicais campestres e savânicos são ambientes inflamáveis, com alta diversidade de espécies e alto potencial para a provisão de serviços ecossistêmicos, como o estoque de carbono. Porém, a provisão deste serviço ecossistêmico pode ser modificada por mudanças no regime de fogo e pela invasão biológica, que são grandes ameaças a estes ecossistemas. O papel da mudança de regime de fogo (i.e., diferentes frequências) e da invasão biológica na dinâmica de carbono dos ecossistemas campestres e savânicos precisam ser analisados. O objetivo principal desta tese foi entender como o fogo e a invasão biológica afetam a dinâmica de carbono em ecossistemas campestres e savânicos do Cerrado. Para isso, avaliamos: (i) como o fogo afeta os fluxos de entrada e de saída de carbono (C) analisando os processos e os caminhos de mudanças destes fluxos (i.e., biomassa, diversidade); (ii) como o fogo afeta a biomassa subterrânea e a composição dos órgãos subterrâneos; e (iii) como diferentes frequências de fogo e gramíneas africanas invasoras afetam os fluxos de entrada e saída do C. Para responder essas perguntas, utilizamos: áreas de campo sujo nas quais o fogo foi manipulado com diferentes frequências de fogo (pergunta i ,ii e iii), em um experimento na região central do Brasil (Reserva Natural Serra do Tombador, RNST); quatro outras áreas que compreendem ecossistemas campestres e savânicos ocorrendo do limite norte até a região sudeste do Cerrado (pergunta ii) ; e áreas invadidas por Urochloa brizantha e não invadidas (pergunta iii), localizadas também na região central do Cerrado (RNST). Foram mensurados a troca líquida de dióxido de carbono do ecossistema (NEE), a eficiência do uso de água no ecossistema (eWUE), e o carbono orgânico do solo (SOC), representando o fluxo de entrada de C no sistema. Medimos também a evapotranspiração do ecossistema (ET) e a respiração do solo, representando a saída de carbono do ecossistema. Coletamos atributos funcionais aéreos (área foliar específica, forma de crescimento, altura) e subterrâneos (área específica de raiz, matéria seca de raiz, densidade do tecido de raiz) relacionados com a dinâmica do C nas comunidades de campo sujo, além da biomassa aérea e subterrânea, incluindo raízes e órgãos. Os órgãos subterrâneos foram classificados de acordo com as suas funções relacionadas ao banco de gemas. No capítulo 1, demonstramos que o fogo aumenta o SOC, a diversidade funcional, e o investimento em biomassa de raízes. Porém, a relação entre o fogo e as modificações dos processos ligados ao fluxo de entrada de carbono (SOC e NEE) e a diversidade funcional não foi evidenciada em nosso estudo. No capítulo 2, evidenciamos que o fogo aumentou a biomassa total de raízes e a proporção de xilopódios. Também demonstramos que sem o fogo a biomassa de órgãos subterrâneos se manteve mesmo após 12 anos de exclusão, porém, houve variação na composição dos órgãos subterrâneos. No capítulo 3, demonstramos que áreas submetidas a alta frequência de fogo recuperam rapidamente as taxas de entrada de carbono (NEE), e que a presença de espécies invasoras leva a ausência de variação sazonal no fluxo de C como foi observado em áreas não invadidas. Os resultados desta tese ajudam a entender melhor como a dinâmica do C acontece no Cerrado, ajudando a criação de modelos e ações que contemplem o potencial serviço de estoque de C destes ecossistemas.
Increasing carbon stocks become an important tool for mitigating climate change. Neotropical grassland and savanna ecosystems are fire-prone ecosystems, with high species diversity and a high potential for the provision of ecosystem services, such as carbon stock. However, the provision of this ecosystem service can be strongly modified by changes in the fire regime and by biological invasion, which are two of the major threats to these ecosystems. The role of fire (in the context of changes in fire regime, i.e., different frequencies) and biological invasion on carbon dynamics of grassland and savanna ecosystems needs to be analyzed. The main goal of this work was to understand how fire and biological invasion can affect carbon dynamics in Cerrado grassland and savanna ecosystems. We assessed: (i) how fire affects carbon (C) fluxes (outputs and inputs) by analyzing the pathways between fire and C fluxes (i.e., biomass, diversity); (ii) how fire affects belowground biomass and belowground organ composition; and (iii) how different fire frequencies and biological invasion by African grass affect C fluxes. To answer these questions, we used: areas of campo sujo where fire was manipulated according to different fire frequencies (question i, ii and iii), in an experiment in central Brazil (Reserva Natural Serra do Tombador, RNST); four other areas comprising grassland and savanna ecosystems occurring from the northern limit to the southeastern region of the Cerrado (question ii); and areas invaded by Urochloa brizantha and uninvaded areas (question iii), also located in the central region of the Cerrado (RNST). Net ecosystem exchange carbon dioxide (NEE), ecosystem water use efficiency (eWUE), and soil organic carbon (SOC) were measured, representing ecosystem C input. We also measured ecosystem evapotranspiration (ET) and soil respiration, representing ecosystem C output. We collected aerial (i.e. specific leaf area, growth form, height) and belowground (i.e. specific root area, root dry matter content, root tissue density) functional traits related to the dynamics of C in the campo sujo communities, as well as the aerial and belowground biomass (including roots and organs). The belowground organs were classified according to their bud-bearing functions. In Chapter 1, we demonstrated that fire increased SOC, functional diversity, and root biomass investment. However, the pathways between C input (SOC and NEE) and the functional diversity were not evidenced in our study. In chapter 2, we showed that fire increased the total root biomass and the proportion of xylopodia. We also demonstrated that 12 years of fire exclusion were not enough to change total belowground organs biomass. However, fire exclusion led to variation in the composition of belowground organs. In Chapter 3, we demonstrated that areas subjected to high fire frequencies quickly recovered C input rates (NEE). The presence of invasive species led to the absence of seasonal variation in C flux as observed in non-invaded areas. The results of this thesis help to better understand how C dynamics can be modified in the Cerrado, thus assisting the creation of models and actions implementation that addresses the potential C stock service of the Cerrado grassland and savanna ecosystem.
Increasing carbon stocks become an important tool for mitigating climate change. Neotropical grassland and savanna ecosystems are fire-prone ecosystems, with high species diversity and a high potential for the provision of ecosystem services, such as carbon stock. However, the provision of this ecosystem service can be strongly modified by changes in the fire regime and by biological invasion, which are two of the major threats to these ecosystems. The role of fire (in the context of changes in fire regime, i.e., different frequencies) and biological invasion on carbon dynamics of grassland and savanna ecosystems needs to be analyzed. The main goal of this work was to understand how fire and biological invasion can affect carbon dynamics in Cerrado grassland and savanna ecosystems. We assessed: (i) how fire affects carbon (C) fluxes (outputs and inputs) by analyzing the pathways between fire and C fluxes (i.e., biomass, diversity); (ii) how fire affects belowground biomass and belowground organ composition; and (iii) how different fire frequencies and biological invasion by African grass affect C fluxes. To answer these questions, we used: areas of campo sujo where fire was manipulated according to different fire frequencies (question i, ii and iii), in an experiment in central Brazil (Reserva Natural Serra do Tombador, RNST); four other areas comprising grassland and savanna ecosystems occurring from the northern limit to the southeastern region of the Cerrado (question ii); and areas invaded by Urochloa brizantha and uninvaded areas (question iii), also located in the central region of the Cerrado (RNST). Net ecosystem exchange carbon dioxide (NEE), ecosystem water use efficiency (eWUE), and soil organic carbon (SOC) were measured, representing ecosystem C input. We also measured ecosystem evapotranspiration (ET) and soil respiration, representing ecosystem C output. We collected aerial (i.e. specific leaf area, growth form, height) and belowground (i.e. specific root area, root dry matter content, root tissue density) functional traits related to the dynamics of C in the campo sujo communities, as well as the aerial and belowground biomass (including roots and organs). The belowground organs were classified according to their bud-bearing functions. In Chapter 1, we demonstrated that fire increased SOC, functional diversity, and root biomass investment. However, the pathways between C input (SOC and NEE) and the functional diversity were not evidenced in our study. In chapter 2, we showed that fire increased the total root biomass and the proportion of xylopodia. We also demonstrated that 12 years of fire exclusion were not enough to change total belowground organs biomass. However, fire exclusion led to variation in the composition of belowground organs. In Chapter 3, we demonstrated that areas subjected to high fire frequencies quickly recovered C input rates (NEE). The presence of invasive species led to the absence of seasonal variation in C flux as observed in non-invaded areas. The results of this thesis help to better understand how C dynamics can be modified in the Cerrado, thus assisting the creation of models and actions implementation that addresses the potential C stock service of the Cerrado grassland and savanna ecosystem.
Descrição
Palavras-chave
Dinâmica do carbono, Regime de fogo, Invasões biológicas, Diversidade funcional, Alocação de biomassa, Cerrado, Carbon dynamics, Fire regime, Biological invasion, Functional diversity, Biomass allocation