Severe effects of long-term drought on calcareous grassland seed banks

Climate change models project shifts in precipitation patterns at regional and global scales. Increases in dry areas and the occurrence of drought predicted in future scenarios are likely to threaten grassland ecosystems. Calcareous grassland seed banks have proven to be resistant to short-term drought, but their responses to long-term drought are unknown. Here we show that 14 years of summer drought changed calcareous grassland seed bank composition, reducing its size and richness, and that these responses do not simply reflect patterns in the above-ground vegetation. Moreover, the effect of drought was larger on seed banks than on vegetation, and above-ground responses mediated by soil depth were less evident in the seed bank than in the vegetation. These results demonstrate that the severity of drought effects on calcareous grasslands is larger than previously thought, and show that this ecosystem is highly vulnerable and has low resilience to predicted decreases in soil moisture

Germination in Aesculus hippocastanum seeds following cold-induced dormancy loss can be described in relation to temperature-dependent reduction in base temperature (Tb) and themal time

• The effect of moist stratification at cool temperatures on Aesculus hippocastanum (horse chestnut) seed dormancy release and subsequent thermal time requirement for germination has been investigated. • Germination performance following over 50 different treatments, each varying in time and temperature of stratification and germination to a total test time of over 3 yr, was used to develop a predictive model for dormancy release and germination. • Stratification at 2–16°C caused a reduction in base (minimum) temperature for germination (Tb), being fastest at the colder temperatures. Using the sigmoid relationship between rate of reduction in Tb and stratification temperature, seed germination can be predicted in relation to thermal time accumulation above a gradually reducing Tb. Newly shed unstratified seeds, seeds with reduced viability, and seeds on the brink of germination because of Tb being close to stratification temperature, did not conform to the model. • Tb is not constant during dormancy release in horse chestnut seeds. A reduction in Tb in response to cold stratification may be characteristic of summer annuals, suggesting future applications for this approach in seed ecology studies

The association between global self-esteem, physical self-concept and actual vs ideal body size rating in Chinese primary school children

OBJECTIVE: To investigate whether the discrepancy between actual and ideal body size rating is related to Chinese children's global self-esteem and global physical self-concept. DESIGN: A cross-sectional study of school children who completed questionnaires related to global self-esteem, global physical self-concept, and actual vs ideal body size. SUBJECTS: A total of 386 Chinese children (44% girls and 56% boys) aged 7-13 y from a primary school in Hong Kong, China. MEASUREMENTS: Global self-esteem and physical self-concept were measured using the physical self-descriptive questionnaire. Actual vs ideal body size discrepancy was established using the silhouette matching task. RESULTS: No significant relationship was found between global self-esteem and actual-ideal body size discrepancy of children. Global physical self-concept had a moderate negative correlation (r = -0.12) with the body size discrepancy score and the discrepancy score explained very limited variance (R2 = 0.015; F(1, 296) = 4.51; P < 0.05) in global physical self-concept. Three body size discrepancy groups (none, positive, and negative) were examined to see if there were any significant differences in global self-esteem, global physical self-concept, and specific dimensions of physical self-concept. A significant overall difference was found between groups for global physical self-concept (F = 3.73, P < 0.05) and the physical self-concept subscales of physical activity (F = 3.25, P < 0.05), body fat (F = 61.26, P < 0.001), and strength (F = 5.26, P < 0.01). Boys scored significantly higher than girls on global physical self-concept-especially in the sport competence, strength, and endurance subscales. CONCLUSION: This study revealed that the actual-ideal body size discrepancy rating of Chinese children was not predictive of global physical self-concept and global self-esteem. These findings are contrary to those reported in Western children, which may mean that culture plays a role in the formation of body attitude.link_to_subscribed_fulltex