No abstract

The effects of osmolytes, osmotic potential (Ψs), temperature, and their interactions on the germinability, germination rate, and other germination parameters of the invasive shrub Prosopis juliflora, which grows in the semiarid environmental conditions of the Caatinga in northeast Brazil, were evaluated. To study the effects of polyethylene glycol (PEG) and NaCl stress and temperature on germination, two separate experiments were carried out at the Plant Ecophysiology Laboratory of the Federal University of Pernambuco in 2011. The overall germinability decreased significantly with increases in both PEG (one-way ANOVA, F4,75 = 111.21, P ≤ 0.001) and NaCl (one-way ANOVA, F4,75 = 12.82, P ≤ 0.001); however, the effects were more accentuated with PEG than NaCl. The PEGtreated seeds maintained their germinability, even when they were subjected to a Ψs = −1 MPa after being rinsed and allowed to germinate on deionized water. In contrast, NaCl-treated seeds usually lost their ability to germinate; this fact was possibly linked to the accumulation of Na + and Cl − in the cells, which may have contributed to a loss of membrane function that led to the death of the embryos. Although numerous studies describing seed germination in the presence of osmolytes have been conducted, studies that show the interactions between osmolytes, osmotic potentials, and temperature are scarce. The present study is the first to describe these interactions for P. juliflora seeds.

Invasive plant species are the second most important threat to global biodiversity loss after land-use change. Invasive species can modify native community composition, deplete species diversity and affect ecosystem processes. The Caatinga is one of the most human-affected Brazilian ecosystems owing to non-sustainable use of its natural resources. Prosopis juliflora is an important invasive plant species in the Caatinga ecosystem. Seed germination is a critical stage in plant life cycles and is a major factor in the establishment and success of invasive plant species. Among the factors that affect seed germination and dormancy, coat-imposed seems to be the most important for P. juliflora. In Prosopis species, the ingestion of fruits by wild and domestic animals may promote and accelerate germination, enhancing the dispersal of seeds and fruits of these species. We investigated the germination capacity of P. juliflora seeds after artificial mechanical and chemical scarification and analyzed the changes in seedling vigor caused by the scarification treatments. Germination rate, germination time (TMG) and germination synchrony (E) differed significantly with the length of the scarification treatments in H2SO4 for both seeds with endocarps and seeds without endocarps (non-endocarp seeds). Sulfuric acid affected plant survival more strongly than germination rate, particularly in non-endocarp seeds.

Reliable information on vegetation cover and its dynamics over time is essential for managing life, resources, and supporting policies. Although many related initiatives have been undertaken in Brazil since the 1980s, knowledge about its dry forests is still limited. In this study, we address the drivers of deforestation and their threat to the Brazilian dry forest called Caatinga. We evaluated the land cover dynamics and landscape metrics in the watershed of the Pontal River, as it has become one of the most socially and environmentally important areas in Brazil. The overall process consists of a systematic sampling grid of hydrological samples, where Landsat images (1975 to 2013) combined with the FRAGSTATS package were used to evaluate landscape metrics indices for the Caatinga. Data showed that the relative area (RA) decreased from 90.25% to 60.98% over the 38-year period, while fragmentation (PD) presented an increasing bias. In addition, the spatial distribution of both indices became more heterogeneous and clustered in the north. We suggest that appropriateness of land for farming was the leading cause of deforestation; rainfall is 112% more intense in the north of the watershed than in the south. Therefore, the northern fauna and flora have been significantly altered and reduced. The relationship between deforestation and time shows an increasing threat. Further studies evaluating these causes are needed to improve our understanding of the vegetation dynamics in this region.

Evapotranspiration (ET) is normally considered as the sum of all water that evaporates from the soil and transpires from plants. However, accurately estimating ET from complex landscapes can be difficult because of its high spatial heterogeneity and diversity of driver factors, which make extrapolation of data from a point to a larger area quite inaccurate. In this paper, we hypothesize that MODIS products can be of use to estimate ET in areas of Caatinga vegetation, the hydrology of which has not been adequately studied. The experiment was conducted in a preserved level area of Caatinga in which meteorological and water flux measures were taken throughout 2012 by eddy covariance. Evapotranspiration estimates from eddy covariance were compared with remotely sensed evapotranspiration estimates from MOD16A2 and SAFER products. Correlations were performed at monthly, 8-day, and daily scales; and producedr2values of monthly scale = 0.92, 8-day scale = 0.88, and daily scale = 0.85 for the SAFER algorithm. Monthly MOD16A2 data produced a value ofr2=0.82, and they may be useful because they are free, downloadable, and easy to use by researchers and governments.