Some temperate tree species mitigate the negative impacts of frost-induced xylem cavitation by restoring impaired hydraulic function via positive pressures, and may therefore be more resistant to frost fatigue (the phenomenon that post-freezing xylem becomes more susceptible to hydraulic dysfunction) than nonpressure-generating species. We test this hypothesis and investigate underlying anatomical/physiological mechanisms. Using a common garden experiment, we studied key hydraulic traits and detailed xylem anatomical characteristics of 18 sympatric tree species. These species belong to three functional groups, that is, one generating both root and stem pressures (RSP), one generating only root pressure (RP), and one unable to generate such pressures (NP). The three functional groups diverged substantially in hydraulic efficiency, resistance to drought-induced cavitation, and frost fatigue resistance. Most notably, RSP and RP were more resistant to frost fatigue than NP, but this was at the cost of reduced hydraulic conductivity for RSP and reduced resistance to drought-induced cavitation for RP. Our results show that, in environments with strong frost stress: these groups diverge in hydraulic functioning following multiple trade-offs between hydraulic efficiency, resistance to drought and resistance to frost fatigue; and how differences in anatomical characteristics drive such divergence across species.
Background In China, less than one third of infants under 6 months of age are being exclusively breastfed. Maternal rural-to-urban migration contributes to these low rates of breastfeeding practices. Therefore, the aim of this study was to assess the prevalence of breastfeeding practices and associated factors among rural-to-urban migrant children and local children with infants aged 0–12 months in China, 2018. Methods Data were collected from a population-based cross-sectional survey in 2018 that included 6995 infants from eight urban areas (four metropolis and four medium sized/small cities) in China. The prevalence of breastfeeding practices was calculated using a 24-h recall questionnaire for all infants aged under 12 months. Logistic regression was conducted to examine the association between the prevalence of breastfeeding practices and maternal migrant status, after adjusting for sociodemographic characteristics, mother-infant health information and supportive information. For exclusive breastfeeding, we further analyzed its association with maternal rural-to-urban migration, stratified by maternal education level, maternal resident place and maternal ethnicity, respectively. Results The overall prevalence of ever breastfeeding, exclusive breastfeeding, predominant breastfeeding and age-appropriate breastfeeding (exclusive breastfeeding of infants under 6 months of age and complementary feeding from six to 12 months of age) was 97.51, 29.84, 59.89 and 45.07%, respectively. Rural-to-urban migrant children were less likely to be exclusively breastfed compared to local children (AOR 0.81, 95% CI 0.68, 0.95). Stratified by different sociodemographic variables, a negative association between exclusive breastfeeding and rural-to-urban migration was only found in the group with high education level, in the group living in metropolis and in the group of minorities, respectively. Conclusions The overall prevalence of breastfeeding practices was low in both rural-to-urban migrant children and local children. Besides common strategies, special approaches should be provided for urban highly educated migrants.
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