In the present study, we assessed the seed germination responses of Cereus jamacaru DC. ssp. jamacaru (Cactaceae) to environmental factors. The seeds were collected from an area within Caatinga, a semiarid vegetation area located in north-eastern Brazil. We determined the optimal temperature for germination of C. jamacaru seeds and evaluated the effect of temperature, light intensity, light quality, water and saline stress on seed germination. Cereus jamacaru was classified as a positive photoblastic species. Maximum germination (95.8 Ϯ 2.6%) was found under white light, and seed germination was not observed in darkness in any of the temperature, water or saline stress treatments. The optimum temperature for seed germination was 30°C because this temperature favored most of the parameters evaluated. Seed germinability responded positively to a wide range of temperatures, but was affected neither by light intensity nor by light quality. A reduction in water availability and an increase in saline concentration affected germinability and promoted slower, unsynchronized germination. The positive response of C. jamacaru seed germination to the environmental factors investigated may account for the abundant occurrence and wide distribution of the species in the Caatinga area.

The aim of the present study was to evaluate how dung beetle communities respond to both environment and rainfall in the Caatinga, a semi-arid ecosystem in northeastern Brazil. The communities were sampled monthly from May 2006 to April 2007 using pitfall traps baited with human feces in two environments denominated “land use area” and “undisturbed area.” Abundance and species richness were compared between the two environments and two seasons (dry and wet season) using a generalized linear model with a Poisson error distribution. Diversity was compared between the two environments (land use area and undisturbed area) and seasons (dry and wet) using the Two-Way ANOVA test. Non-metric multidimensional scaling was performed on the resemblance matrix of Bray-Curtis distances (with 1000 random restarts) to determine whether disturbance affected the abundance and species composition of the dung beetle communities. Spearman's correlation coefficient was used to determine whether rainfall was correlated with abundance and species richness. A total of 1097 specimens belonging to 13 species were collected. The most abundant and frequent species was Dichotomius geminatus Arrow (Coleoptera: Scarabaeidae). The environment exerted an influence over abundance. Abundance and diversity were affected by season, with an increase in abundance at the beginning of the wet season. The correlation coefficient values were high and significant for abundance and species richness, which were both correlated to rainfall. In conclusion, the restriction of species to some environments demonstrates the need to preserve these areas in order to avoid possible local extinction. Therefore, in extremely seasonable environments, such as the Caatinga, seasonal variation strongly affects dung beetle communities.

Environmental factors are used by plants as spatio-temporal indicators of favorable conditions for seed germination. Thus, the objective of this study was to determine the effect of light and temperature on seed germination of 30 taxa of Cactaceae occurring in northeastern Brazil and to evaluate whether fluctuations in temperature are capable of altering light sensitivity. The seeds were tested for germination under two light conditions (12 h photoperiod and continuous darkness) and 10 temperature treatments: eight constant temperatures (10, 15, 20, 25, 30, 35, 40 and 45°C) and two alternating temperatures (30/ 20°C and 35/25°C). The species studied showed two photoblastic responses. All cacti from the Cactoideae subfamily (22 taxa) were classified as positive photoblastic (i.e., no germination in darkness), regardless of the temperature treatment used. Likewise, temperature fluctuation did not alter the seed sensitivity to light. On the other hand, the species of the Opuntioideae (five taxa) and Pereskioideae (three taxa) subfamilies are indifferent to light (i.e., germinated both in the presence and absence of light). The cacti from the areas of Caatinga and Cerrado showed an optimal germination temperature of 30°C, while the species from Atlantic Forest and Restinga areas showed an optimal germination temperature of 25°C.

The water uptake by the seed in arid and semi-arid ecosystems may not be continuous, but may occur in hydration and dehydration cycles (HD). In order to investigate the benefits of discontinuous hydration on seed germination of Pilosocereus catingicola subsp. salvadorensis subjected to environmental stresses, an imbibition curve was determined and times X, Y and Z selected, corresponding to 25, 50 and 75% of the first phase of imbibition, respectively. Seeds of two populations (Caatinga and Restinga) were subjected to 0, 1, 2 and 3 HD cycles, with 48 h of dehydration. Water and saline stress responses were tested at five osmotic potentials (0.0, –0.1, –0.3, –0.6 and –0.9 MPa). Discontinuous hydration provided greater tolerance to water and saline stress in the seeds from the Caatinga region. When the seeds were subjected to water stress, the reduction of the mean germination time (MGT) provided by HD cycles decreased with increasing concentration of the solution. In saline stress, the reduction of MGT was greater in the solutions with the highest concentrations. We conclude that the seeds of the same species collected from populations located in different ecosystems have different germination responses after passage through discontinuous hydration and HD cycles. This provides greater tolerance to environmental stresses but with different responses among populations.

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Leguminous species, Piptadenia moniliformes (Benth.) and Trischidium molle (Benth.) H. E. Ireland, both prevalent in the Caatinga vegetation, were submitted to varying watering regimes under greenhouse conditions. In experiment I, 60-day-old P. moniliformes plants were maintained under suspended irrigation for 12 days. Assessment on day 12 of drought revealed that leaf relative water content decreased to 40% and stomatal conductance and transpiration were also strongly diminished. Apparent electron transport rate (ETR) and photochemical quenching (qP) values were reduced by water deficit treatment compared to controls, while non-photochemical quenching (NPQ) increased; however, the basal values were recovered in moisturized plants when analyzed after 48 h of rewatering. In experiment II, T. molle plants were watered once (1 9), 3 (3 9) or 5 times (5 9) per week, up to day 65 after emergence. Chlorophyll a, chlorophyll b and carotenoid contents were reduced in the 3 9 and 5 9 watering treatments. Photosystem II maximum efficiency (F v 0 /F m 0 ), ETR and qP values strongly decreased when drainage frequency and NPQ values were increased. Observation verified that chlorophyll fluorescence is a suitable tool for evaluating the developmental characteristics of the arboreal leguminous species studied. Analysis of the data obtained suggest that plant tolerance to the dry climate conditions of the Caatinga ecosystem is directly associated with fast physiological adaptation to water deficit, by accumulating biomass in the root system in detriment to the shoots. The data presented contribute to further understanding the developmental and physiological mechanisms that enable plant adaptation to dry climates and, particularly, to the unique dry environmental conditions of the Caatinga region.

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