Ecologia e funções adaptativas da dormência em sementes de gramíneas campestres brasileiras

Tese (doutorado)—Universidade de Brasília, Instituto de Ciências Biológicas, Departamento de Botânica, Programa de Pós-Graduação em Botânica, 2015.O Cerrado, a savana brasileira, caracteriza-se por um clima com precipitação sazonal e com recorrente passagem de fogo. Em teoria, o número de espécies com sementes dormentes tende a ser maior em ambientes com sazonalidade hídrica do que em ambientes não-sazonais, porque a estação seca constitui um forte limitante ao recrutamento de plântulas. No entanto, apesar da reprodução das gramíneas nativas no Cerrado ser limitada pela sazonalidade, existe ampla variação entre espécies na presença e duração da dormência. As causas desta variação, bem como suas consequências ecológicas, permanecem desconhecidas. Assim, o objetivo deste estudo foi determinar os padrões de longevidade, germinação e dormência (i.e. estratégia de germinação) de sementes de 29 espécies de gramíneas nativas do Cerrado, investigando possíveis causas evolutivas e consequências ecológicas dessas estratégias, além da potencial aplicabilidade das sementes dessas espécies em restauração ecológica. No capítulo 1, investiguei duas hipóteses para a evolução de dormência: (1) restrição hídrica e (2) competição intraespecífica durante o recrutamento de plântulas. Assumindo que a dispersão limitada resulta em adensamento de sementes e, consequentemente, maior competição durante o desenvolvimento das plântulas, comparei as estratégias de germinação de espécies de habitats que diferem em umidade do solo (campo sujo vs. campo úmido) e épocas de dispersão contrastantes em termos de sazonalidade hídrica (início ou fim da estação chuvosa e estação seca), e diferentes síndromes de dispersão (anemocórica vs. barocórica). Sementes de campos úmidos perderam a dormência mais rapidamente e permaneceram vivas por mais tempo do que sementes de campos sujos. Sementes dispersas na seca e no início da estação chuvosa tiveram maior germinação do que sementes dispersas no final da estação chuvosa. Sementes com dispersão barocórica foram mais dormentes do que sementes com dispersão anemocórica. No capítulo 2, verifiquei se a a probabilidade de uma semente passar por um evento de queima e se as diferenças de temperaturas que ocorrem durante a passagem do fogo nos habitats das espécies de gramíneas determinam a tolerância das sementes a altas temperaturas. Assumindo que sementes dormentes passam mais tempo no solo do que sementes não dormentes e, portanto, estão mais susceptíveis a passar por um evento de queima, comparamos a tolerância a choques-térmicos (80 °C e 110 °C) em sementes dormentes e não dormentes. Também testamos a tolerância a choques-térmicos em sementes de espécies coletadas em habitats com menores temperaturas do fogo (campo úmido) e maiores temperaturas do fogo durante a queima (campo sujo). Sementes de ambos os habitats foram negativamente afetadas por altas temperaturas. Entretanto, sementes dormentes foram mais tolerantes a altas temperaturas do que sementes não dormentes. Por fim, no capítulo 3, verificamos as variações temporais nos padrões de longevidade e germinação de 29 espécies de gramíneas, e identificamos 20 espécies com potencial para utilização na recuperação de áreas degradadas. Em conclusão, nossos resultados sugerem que (1) a dormência em sementes de gramíneas do Cerrado evoluiu em resposta à restrição hídrica e à competição intraespecífica; (2) e a tolerância ao fogo é possivelmente uma consequência ecológica da dormência.Cerrado, the Brazilian savanna, is characterized by a climate with seasonal precipitation and frequent fire events. In theory, the number of species with seed dormancy is higher in seasonal environments compared to species in non-seasonal environments, due to the fact that dry seasons may strongly limit seedling recruitment. However, although reproduction of grass species in the Cerrado is limited by seasonality, there is a high variation in the presence of seed dormancy and its duration among these species. The origin and the ecological consequences of this variation remain unknown. Therefore, the aim of this study was to determine the longevity, germination, and dormancy patterns (i.e. germination strategies) of seeds from 29 native grass species from the Cerrado. This study also aimed to investigate the possible evolutionary causes and ecological consequences of these strategies, as well as the potential applicability of these species in restoration ecology. In chapter 1, we investigated two hypotheses for seed evolution: (1) water restriction and (2) intraspecific competition during seedling recruitment. We assumed that limited dispersion results in seed crowding and, consequently, higher competition during seedling growth. Thus, comparisons were conducted regarding the germination strategies of species from contrasting habitats (open savanna vs. wet grassland), seed dispersal season in terms of water availability, and different dispersal syndromes (anemochoric vs. barochoric). Seeds from wet grassland species lost dormancy faster and were viable for longer periods than seeds from open savanna species. Seeds dispersed during the dry season or early in the rainy season germinated more than those dispersed late in the rainy season. Species with barochoric seeds had more seed dormancy than species with anemochoric seeds. In chapter 2, the aim was to verify if the likelihood of a seed to burn and the differences in temperature that occur during fires in species’ habitats may determine seed tolerance to heat. Assuming that dormant seeds might remain in the soil longer than non-dormant seeds, increasing their likelihood to burn, the heat tolerance (80 and 110 °C) of species with dormant and non-dormant seeds was compared. In addition, the heat tolerance of seeds from species from habitats with lower (wet grasslands) and higher (open savannas) fire temperatures was also tested. Seeds from both habitats were negatively affected by high temperatures, but dormant seeds had a higher tolerance than non-dormant seeds. Finally, in chapter 3, the variation in temporal patterns of seed longevity and germination in 29 grass species were verified, and 20 species with ecological restoration potential were identified. In conclusion, the results suggest that (1) seed dormancy in grass seeds from the Cerrado evolved in response to water restriction and intraspecific competition; (2) and seed tolerance to fire is probably an ecological consequence of seed dormancy

Environmental drivers of water use for Caatinga woody plant species: combining remote sensing phenology and sap flow measurements

Abstract: We investigated the water use of Caatinga vegetation, the largest seasonally dry forest in South America. We identified and analysed the environmental drivers of phenology in woody species and their relationship with transpiration. To monitor the phenological evolution we used remote sensing indices at different spatial and temporal scales: normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), and green chromatic coordinate (GCC). To represent the phenology we used the GCC extracted from in-situ automated digital camera images; indices calculated based on sensors included NDVI, SAVI and GCC from Sentinel-2A and B satellites images, and NDVI products MYD13Q1 and MOD13Q1 from moderate-resolution imaging spectroradiometer (MODIS). Environmental drivers included continuously monitored rainfall, air temperature, soil moisture, net radiation, and vapour pressure deficit. To monitor soil water status and vegetation water use we installed soil moisture sensors along three soil profiles and sap flow sensors for five plant species. Our study demonstrated that the near-surface GCC data played an important role in allowing individual monitoring of species whereas the species’ sap flow data correlated better with NDVI, SAVI and GCC than with species’ near-surface GCC. The wood density appeared to affect the transpiration cessation times in the dry season given species with the lowest wood density reach negligible values of transpiration earlier in the season than those with high woody density. Our results show that soil water availability is the main limiting factor for transpiration during more than 80 % of the year, and that both the phenological response and water use are directly related to water availability when relative saturation of the soil profile falls below 0.25

Expanding tropical forest monitoring into Dry Forests: The DRYFLOR protocol for permanent plots

This is the final version. Available on open access from Wiley via the DOI in this recordSocietal Impact Statement Understanding of tropical forests has been revolutionized by monitoring in permanent plots. Data from global plot networks have transformed our knowledge of forests’ diversity, function, contribution to global biogeochemical cycles, and sensitivity to climate change. Monitoring has thus far been concentrated in rain forests. Despite increasing appreciation of their threatened status, biodiversity, and importance to the global carbon cycle, monitoring in tropical dry forests is still in its infancy. We provide a protocol for permanent monitoring plots in tropical dry forests. Expanding monitoring into dry biomes is critical for overcoming the linked challenges of climate change, land use change, and the biodiversity crisis.Newton FundNatural Environment Research Council (NERC)Fundação de Amparo à Pesquisa do Estado de São PauloCYTE

Cross-sectional analysis of students and school workers reveals a high number of asymptomatic SARS-CoV-2 infections during school reopening in Brazilian cities

Brazil experienced one of the most prolonged periods of school closures, and reopening could have exposed students to high rates of SARS-CoV-2 infection. However, the infection status of students and school workers at the time of the reopening of schools located in Brazilian cities is unknown. Here we evaluated viral carriage by RT-PCR and seroprevalence of anti-SARS-CoV-2 antibodies (IgM and IgG) by immunochromatography in 2259 individuals (1139 students and 1120 school workers) from 28 schools in 28 Brazilian cities. We collected the samples within 30 days after public schools reopened and before the start of vaccination campaigns. Most students (n = 421) and school workers (n = 446) had active (qRT-PCR + IgM− IgG− or qRT-PCR + IgM + IgG−/+) SARS-CoV-2 infection. Regression analysis indicated a strong association between the infection status of students and school workers. Furthermore, while 45% (n = 515) of the students and 37% (n = 415) of the school workers were neither antigen nor antibody positive in laboratory tests, 16% of the participants (169 students and 193 school workers) were oligosymptomatic, including those reinfected. These individuals presented mild symptoms such as headache, sore throat, and cough. Notably, most of the individuals were asymptomatic (83.9%). These results indicate that many SARS-CoV-2 infections in Brazilian cities during school reopening were asymptomatic. Thus, our study highlights the need to promote a coordinated public health effort to guarantee a safe educational environment while avoiding exacerbating pre-existent social inequalities in Brazil, reducing social, mental, and economic losses for students, school workers, and their families

Phenology behavior of grasses in a grassland of Cerrado : from induction of flowering until seedling emergence

Dissertação (mestrado)—Universidade de Brasília, Departamento de Botânica, 2011.A fenologia é o estudo de manifestações rítmicas, ou eventos naturais recorrentes,apresentadas por animais e plantas em resposta a estímulos endógenos ou ambientais. Afenologia da reprodução em plantas se inicia com a floração, seguida de frutificação,dispersão e finaliza-se com a germinação e estabelecimento da nova plântula. Osprincipais objetivos deste trabalho foram: (1) descrever a fenologia circanualreprodutiva de dez espécies de gramíneas em um campo sujo de Cerrado, (2) testarquais os fatores ambientais utilizados como sinais por essas gramíneas para escolha deperíodo de floração e (3) testar se a dormência em cariopses de gramíneas é umaestratégia para o estabelecimento de plântulas em épocas de precipitação favoráveis(hipótese da sazonalidade hídrica). Para a fenologia amostramos dez indivíduos de dezespécies, quinzenalmente, durante um ano (2009 a 2010). As estratégias fenológicasforam descritas por estatística circular. Para testar quais sinais induzem a floração,foram feitas correlações e regressões entre a duração da floração e fatores ambientaisclimáticos (precipitação, temperatura) e celestiais (fotoperíodo, radiação, nascer e pordo sol). Aferimos a ocorrência de dormência nas sementes a partir de testes degerminação com oito destas espécies de gramíneas sob diferentes períodos dearmazenamento. Por fim, coletadas plântulas em 40 parcelas (20x20 cm) para identificara fenologia da emergência destas plântulas. O período reprodutivo da comunidade degramíneas foi sazonal, com concentração na estação chuvosa. Porém, as fenofases defrutificação e dispersão, em algumas espécies, também ocorreram no período seco. Combase no início, duração e sincronia da reprodução, foi possível distinguir grupos deespécies com estratégias fenológicas distintas. Corroboramos a hipótese de fotoperíodocomo principal sinal indutor de floração nessas gramíneas. A hipótese de temperaturafoi rejeitada. Da mesma forma, não foi registrada relação entre a precipitação e afloração das espécies, sugerimos que precipitação e umidade atuam mais como fatoreslimitantes do que sinalizadores à floração nessas gramíneas. Os diásporos de Paslpalumgardnerianum e Echinolaena inflexa possuem dormência, sendo que esta é superadacomo o período de armazenamento. A espécie Andropogon selloanus não apresentoudormência. A emergência de plântulas se concentrou no início da estação chuvosa.Corroboramos a hipótese de sazonalidade hídrica para explicar a dormência em E.inflexa e P. gardnerianum. _______________________________________________________________________________ ABSTRACTPhenology is the study of rhythmic events, or recurring natural events, presented by animals and plants in response to endogenous or environmental stimuli. The phenology of reproduction in plants begins with flowering, then fruiting, dispersal and ends with the germination and establishment of new seedlings. The main objectives were: (1) describe the circannual reproductive phenology of ten species of grass in a grassland of Savannah, (2) test which environmental factors are used as signs for these grasses to choose the flowering period (3) test whether dormancy in caryopses of grasses is a strategy for the establishment of seedlings in times of favorable precipitation (hypothesis of water seasonal stress). For the phenology, were sampled ten individuals of ten species, fortnightly, for one year (2009-2010). Phenological strategies were described by circular statistics. To test which signals induce flowering, correlations and regressions were done among the time of flowering and environmental factors climatic (precipitation, temperature) and celestial (photoperiod, radiation, sunrise and sunset). We found the incidence of seed dormancy from germination tests with eight species of these grasses under different storage periods. Finally, we collected seedlings in 40 plots (20x20 cm) to identify the phenology of the emergence of these seedlings. The reproductive period of the community of grasses was seasonal, with an increase in the rainy season. However, both phenophases of fruiting and dispersal, in some species, also occurred in the dry season. Based on the onset, duration and synchrony of reproduction, it was possible to distinguish groups of species with different phenological strategies. We corroborate the hypothesis of photoperiod as the primary signal inducing flowering in these grasses. The temperature hypothesis was rejected. Likewise, no relationship was recorded between precipitation and flowering species, we suggest that rainfall and moisture act as limiting factors more than these inducers to flowering grasses. The diaspore of Paslpalum gardnerianum and Echinolaena inflexa has dormancy, and this is overcome as the storage period. The species Andropogon selloanus showed no dormancy. The seedling emergence was concentrated at the beginning of the rainy season. Corroborate the hypothesis of water seasonal stress for explaining dormancy in E. inflexa and P. gardnerianum