Soil penetration by maize roots is negatively related to ethylene-induced thickening

Radial expansion is a classic response of roots to a mechanical impedance that has generally been assumed to aid penetration. We analysed the response of maize nodal roots to impedance to test the hypothesis that radial expansion is not related to the ability of roots to cross a compacted soil layer. Genotypes varied in their ability to cross the compacted layer, and those with a steeper approach to the compacted layer or less radial expansion in the compacted layer were more likely to cross the layer and achieve greater depth. Root radial expansion was due to cortical cell size expansion, while cortical cell file number remained constant. Genotypes and nodal root classes that exhibited radial expansion in the compacted soil layer generally also thickened in response to exogenous ethylene in hydroponic culture, that is, radial expansion in response to ethylene was correlated with the thickening response to impedance in soil. We propose that ethylene insensitive roots, that is, those that do not thicken and can overcome impedance, have a competitive advantage under mechanically impeded conditions as they can maintain their elongation rates. We suggest that prolonged exposure to ethylene could function as a stop signal for axial root growth

Modelling biome-scale root reinforcement and slope stability

Rapid changes in the composition of hillslope vegetation due to a combination of changing climate and land use make estimating slope stability a significant challenge. The dynamics of root growth on any individual hillslope result in a wide range of root distributions and strengths that are reflected as up to an order of magnitude variability in root cohesion. Hence the challenge of predicting the magnitude of root reinforcement for hillslopes requires both an understanding of the magnitude and variability of root distributions and material properties (e.g. tensile strength, elasticity). Here I develop a model for estimating the reinforcement provided by plant roots based on the distribution of biomass measured at the biome level and a compilation of root tensile strength measurements measured across a range of vegetation types. The model modifies the Wu/Waldron method of calculating root cohesion to calculate the average lateral root cohesion and its variability with depth using the Monte Carlo method. The model was validated in two ways, the first against the predicted depth‐reinforcement characteristics of Appalachian soils and the second using a global dataset of landslides. Model results suggest that the order of magnitude difference in root cohesions measured on individual hillslopes can be captured by the Monte Carlo approach and provide a simple tool to estimate of root reinforcement for data‐poor areas. The model also suggests that future hotspots of slope instability will occur in areas where land use and climate convert forest to grassland, rather than changes between different forest structures or forest and shrubland

Mental well-being and physical activity of young people experiencing homelessness before and during COVID-19 lockdown: A longitudinal study

Background While lockdown restrictions in response to COVID-19 indisputably mitigated virus transmission, the aim of this longitudinal study was to establish indirect effects on vulnerable young people's mental well-being and physical activity (PA) levels. Methods Surveys conducted at time 1 (February 2020), and time 2 (April 2020) comprised of the short Warwick Edinburgh Mental Well-Being Scale, the Rosenberg Self-Esteem Scale, and self-reported moderate and vigorous PA levels. Repeated measures analyses established changes pre-post lockdown restrictions, and differences between sub-groups. Associations between changes in well-being, self-esteem and PA over time were explored through further regression analyses. Results 65 respondents completed the survey at time 1, and 50 respondent at time 2. Wellbeing increased significantly over time, yet remained significantly lower than the population average. Self-esteem increased significantly post-lockdown, however remained significantly lower for females, compared with males. Overall, PA levels increased-whereby ‘inactive’ participants at time 1 reported significant increases in moderate and total activity levels at time 2. Increased PA levels significantly predicted increased well-being: F(1, 48) = 4.15, p < .05; while participants who had become less active accounted for 69.2% with low self-esteem at time 2. Conclusions Findings indicate that increased PA accounted for improved mental well-being, while decreased PA was associated with reduced levels of self-esteem. PA may represent a modifiable means of mitigating risk, and promoting resilience for vulnerable young people experiencing adverse condition

Dispositional mindfulness and its relationship with distress and functioning in adolescents with chronic pain and low-level pain

© The Author(s) 2018. Published by Oxford University Press on behalf of the Society of Pediatric Psychology. Objective Dispositional mindfulness is the general tendency to pay attention to present-moment awareness without judgment. The main aim of this cross-sectional study was to determine (a) whether dispositional mindfulness is associated with psychological distress in adolescents with chronic pain and low-level pain, and (b) whether it accounts for unique variance in distress after controlling for key variables from the pain literature. A secondary aim was to explore the relationship between dispositional mindfulness and functioning. Method 54 adolescents seeking help for chronic pain and 94 “healthy” adolescents with recent low-level pain from the general population completed the same battery of measures, including the Child and Adolescent Mindfulness Measure of dispositional mindfulness. Results As predicted, dispositional mindfulness was associated with mood and anxiety in both groups and also accounted for unique variance in mood and anxiety in standard regression models after controlling for group, age, pain-intensity, pain-catastrophizing, and pain-acceptance. Dispositional mindfulness did not differ significantly across the two groups and did not predict physical functioning. However, it did account for unique variance in social functioning. Conclusions Dispositional mindfulness may be an important construct to consider in the context of adolescents experiencing mood and anxiety problems in both low-level and chronic pain samples. Further research should aim to replicate these findings in larger clinical samples and explore the predictive power of dispositional mindfulness using longitudinal designs

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