Search

Drylands are predicted to become more arid and saline due to increasing global temperature and drought. Although species from the Caatinga, a Brazilian tropical dry forest, are tolerant to these conditions, the capacity for germination to withstand extreme soil temperature and water deficit associated with climate change remains to be quantified. We aimed to evaluate how germination will be affected under future climate change scenarios of limited water and increased temperature. Seeds of three species were germinated at different temperatures and osmotic potentials. Thermal time and hydrotime model parameters were established and thresholds for germination calculated. Germination performance in 2055 was predicted, by combining temperature and osmotic/salt stress thresholds, considering soil temperature and moisture following rainfall events. The most pessimistic climate scenario predicts an increase of 3.9 °C in soil temperature and 30% decrease in rainfall. Under this scenario, soil temperature is never lower than the minimum and seldomly higher than maximum temperature thresholds for germination. As long as the soil moisture (0.139 cm 3  cm 3 ) requirements are met, germination can be achieved in 1 day. According to the base water potential and soil characteristics, the minimum weekly rainfall for germination is estimated to be 17.5 mm. Currently, the required minimum rainfall occurs in 14 weeks of the year but will be reduced to 4 weeks by 2055. This may not be sufficient for seedling recruitment of some species in the natural environment. Thus, in future climate scenarios, rainfall rather than temperature will be extremely limiting for seed germination.

When bryophytes, lichens, eukaryotic algae, cyanobacteria, bacteria, and fungi live interacting intimately with the most superficial particles of the soil, they form a complex community of organisms called the biological soil crust (BSC or biocrust). These biocrusts occur predominantly in drylands, where they provide important ecological services such as soil aggregation, moisture retention, and nitrogen fixation. Unfortunately, many BSC communities remain poorly explored, especially in the tropics. This review summarizes studies about BSCs in Brazil, a tropical megadiverse country, and shows the importance of ecological, physiological, and taxonomic knowledge of biocrusts. We also compare Brazilian BSC communities with others around the world, describe why BSCs can be considered ecosystem engineers, and propose their use in the colonization of other worlds. [ABSTRACT FROM AUTHOR]

Functional traits related to regeneration responses to the environment are highly determinants of distribution patterns of plant communities. A large body of studies on seed traits suggests that regional climate may act as a strong filter of plant recruitment; however, few studies have evaluated the relative importance of seed traits and environmental filters for seed persistence at the population level. We tested the role of seed mass, water content and desiccation tolerance, as well as the germination time as proxies for seed tolerance to environmental filters (water deficit, heat shock and high temperatures) by comparing the response of tree species co-occurring in savannas located in different regions: Cerrado biome of Central Brazil and the Rio Branco savannas of northern Brazil. Seeds collected in savannas of Rio Branco showed a higher tolerance to environmental filters than those collected in savannas of the Cerrado. While the germination percentages largely varied in response to the treatments, the germination times were virtually unaffected by them, irrespective of seed origin, seed mass and water content. At the population level, the regional environment was a key determinant of seed tolerance to stress, irrespective of seed traits. Germination time was shown to represent a conservative seed trait and more linked to a species-specific germination strategy than to regional characteristics. Our results suggest that recruitment patterns of Cerrado savannas may be more impacted than Rio Branco savannas by the climate scenarios predicted for the future. [ABSTRACT FROM AUTHOR]

Seed germination is regulated by temperature and can thus be quantified by thermal models, which can predict germination occurrence in biomes and plant survival under possible climate change scenarios. The objective of this study was to quantify germination based on thermal time and survival risk of 14 species in the Brazilian Cerrado in scenarios of future climate change. Seeds were collected in the warmer regions of the Cerrado, central Brazil, placed in incubators to germinate at constant temperatures of 10–50°C and evaluated every hour or day. Germination rate (R50), time for germination of 50% of the seeds (T50) and dent-like function were used to determine cardinal temperatures. Thermal time parameters were estimated using the Weibull model. Seed germination forecasts were made based on the International Panel on Climatic Change (IPCC) scenarios of global temperature increase. Base temperatures (Tb) ranged from 3.5 to 16.5°C, maximum temperatures (Tmax) from 35 to 50°C and optimum temperatures (To) from 30 to 35°C. Estimated thermal time varied from 484°C h to 400°C d at sub-optimal temperatures and 108°C h at 126°C d at supra-optimal temperatures. Species more distributed showed a higher thermal range of germination and are less susceptible to extinction in temperature increase scenarios. The results of this study suggest that seeds that are non-dormant after dispersal may be the most vulnerable in the future. In this context, our predictions contribute to understand how the survival of trees and shrubs will be affected in the Cerrado in the future. [ABSTRACT FROM AUTHOR]

Temperature may regulate seed dormancy and germination and determine the geographical distribution of species. The present study investigated the thermal limits for seed germination of Polygonum ferrugineum (Polygonaceae), an aquatic emergent herb distributed throughout tropical and subtropical America. Seed germination responses to light and temperature were evaluated both before (control) and after stratification at 10, 15 and 20°C for 7, 14 and 28 d. Germination of control seeds was ~50% at 10 and 15°C, and they did not germinate from 20 to 30°C. The best stratification treatment was 7 d at 10°C, where seed germination was >76% in the dark for all temperatures, except at 30°C, and < 60% in light conditions. A thermal time approach was applied to the seed germination results. Base temperature (Tb) was 6.3°C for non-dormant seeds and optimal temperature (To) was 20.6°C, ceiling temperature (Tc (<50)) was 32.8°C, and thermal time requirement for 50% germination was 44.4°Cd. We concluded that a fraction of P. ferrugineum seeds is dormant, has a narrow thermal niche to germinate (10 and 15°C) and that cold stratification (10°C) alleviated dormancy and amplified the thermal range permissive for germination of the species. Consequently, P. ferrugineum is expected to occur in colder environments, for example, at high altitudes. Higher temperatures decrease the probabilities of alleviate dormancy and the ability of their seeds to germinate. [ABSTRACT FROM AUTHOR]

Brazil has committed to fulfilling international restoration goals and to enforcing environmental legislation that will require private landowners to undertake ecological restoration of 21 million hectares of degraded and deforested landscapes. To support a broad range of restoration practices, a well‐established supply chain capable of representing regional plant diversity is essential. This study investigated the restoration species pool in native plant nurseries in São Paulo state, located in southeastern Brazil, and evaluated their geographic distribution, similarity of their plant stocks, and the proportion of species represented from regional floras. Despite a lack of technical assistance and a significant presence of nonnative species (126 species, average 7.5 species/nursery), we found an impressive native species richness in plant nurseries (561 species, average 86.4 species/nursery) from both the Atlantic Forest and Cerrado domains, representing 38–44% of regional floras. There was a huge bias toward tree and shrub species (96.6%) and an absence or underrepresentation of other growth forms, as well as of savanna specialists, animal‐dispersed, and threatened species. The dissimilarity of species observed among the different nurseries surveyed highlights their role in representing regional diversity, which reflects their regional seed collection practices. Effective assistance and training are essential to address issues related to misidentification of species, underrepresentation of most functional plant groups, and the presence of nonnative species, as well as to support the supply chain, which is currently undergoing a market downturn. [ABSTRACT FROM AUTHOR]

For the effective use of native plants for mineland revegetation, an understanding of seed dormancy break and germination requirements, and seed storage tolerance is indispensable. In the present study, eight native species (Bauhinia pulchella, Bauhinia longipedicellata, Dioclea apurensis, Mimosa camporum, Mimosa acutistipula var. ferrea, Mimosa pudica, Parkia platycephala, and Stryphnodendron pulcherrimum) from the metalliferous savannas (cangas) and forests of Carajás Mineral Province, eastern Amazon-Brazil, were studied to determine seed size, seed quality (X-ray and tetrazolium tests), germination, and dormancy break requirements (boiling water, acid and mechanical scarification), and seed storage behavior. Our results showed considerable variation in seed size and percentage germination among the species. There was a strong relationship between seed size and germination, and the germination was greater for larger seeds from forests than smaller seeds from canga. All three scarification methods increased germination of M. camporum and M. acutistipula var. ferrea. Seeds of D. apurensis, M. acutistipula var. ferrea, M. pudica, and P. platycephala did not show a significant decline in germination after storage, indicating possible orthodox behavior. In contrast, B. pulchella, B. longipedicellata, M. camporum, and S. pulcherrimum showed behavior typical of recalcitrant or intermediate seeds since the germination of these species was reduced after storage. Further studies addressing seed dormancy break and seed storage in other native species are encouraged for a better use of native species in mineland revegetation. [ABSTRACT FROM AUTHOR]

Large‐scale ecological restoration programs across the world involve a voluminous demand for native seeds of diverse native plant species. In this article, we explore how institutional systems have operated and impacted native seed supply in Brazil. Native seed supply for restoration is essentially a community‐based activity which faces broad barriers to operating within regulations because of requirements for excessive and costly technical documentation, scarcity of seed laboratories, and lack of instructions for native seed quality testing. Although decentralized seed networks have stimulated arrangements for local organizations to promote seed supply, policies constrain the development of local capacities and the ongoing sustainability of these organizations. These conditions have resulted in a vast network of informal collectors and producers who are largely "invisible" and unknown to the regulatory authorities. Policies have decentralized responsibilities from the state without devolving decision‐making power to the multiple stakeholders engaged in policy elaboration. The policies maintain the centralized regulation of native seed supply. After examining Brazilian seed networks' experiences and conducting discussions with stakeholders and experts, we suggest adapting the current regulations to more local level contexts, encompassing the following strategies: (1) ensuring native seed origin and identity; (2) relaxation of the laboratory accreditation process for native seed quality assurance; (3) fostering seed markets for restoration; (4) research to provide technological innovation; (5) supporting local, diverse, and small seed‐based businesses. [ABSTRACT FROM AUTHOR]