An overlooked mechanism underlying the attenuated temperature response of soil heterotrophic respiration

Biogeochemical reactions occurring in soil pore space underpin gaseous emissions measured at macroscopic scales but are difficult to quantify due to their complexity and heterogeneity. We develop a volumetric-average method to calculate aerobic respiration rates analytically from soil with microscopic soil structure represented explicitly. Soil water content in the model is the result of the volumetric-average of the microscopic processes, and it is nonlinearly coupled with temperature and other factors. Since many biogeochemical reactions are driven by oxygen (O2) which must overcome various resistances before reaching reactive microsites from the atmosphere, the volumetric-average results in negative feedback between temperature and soil respiration, with the magnitude of the feedback increasing with soil water content and substrate quality. Comparisons with various experiments show the model reproduces the variation of carbon dioxide emission from soils under different water content and temperature gradients, indicating that it captures the key microscopic processes underpinning soil respiration. We show that alongside thermal microbial adaptation, substrate heterogeneity and microbial turnover and carbon use efficiency, O2 dissolution and diffusion in water associated with soil pore space is another key explanation for the attenuated temperature response of soil respiration and should be considered in developing soil organic carbon models

Violence against women in sex work and HIV risk implications differ qualitatively by perpetrator.

PMC3852292BACKGROUND: Physical and sexual violence heighten STI/HIV risk for women in sex work. Against this backdrop, we describe the nature of abuse against women in sex work, and its STI/HIV implications, across perpetrators. METHODS: Adult women involved in sex work (n = 35) in Baltimore, MD participated in an in-depth interview and brief survey. RESULTS: Physical and sexual violence were prevalent, with 43% reporting past-month abuse. Clients were the primary perpetrators; their violence was severe, compromised women's condom and sexual negotiation, and included forced and coerced anal intercourse. Sex work was a factor in intimate partner violence. Police abuse was largely an exploitation of power imbalances for coerced sex. CONCLUSIONS: Findings affirm the need to address physical and sexual violence, particularly that perpetrated by clients, as a social determinant of health for women in sex work, as well as a threat to safety and wellbeing, and a contextual barrier to HIV risk reduction.JH Libraries Open Access Fun

Relationship between soil carbon sequestration and the ability of soil aggregates to transport dissolved oxygen

A key finding in soil carbon studies over the past decade is that soil organic carbon (SOC) stabilization is not controlled by its molecular complexity and clay content but by its physicochemical protections including occlusion in aggregates and sorption/precipitation with organo-mineral associations. The organo-mineral complexes and the adsorbed SOC could be dissolved microbially under anoxic conditions, which is an important pathway in the carbon cycle but has been overlooked by most carbon models. As it is reported that organo-mineral associations are formed in aerobic conditions and could be lost under anaerobic conditions, there should be a positive correlation between SOC and ability of the aggregates to transport dissolved oxygen. We test this using two long-term experiments with a SOC gradient at Rothamsted Research in the UK: One experiment compares the effects of different fertilizations on yield of winter wheat and the other experiment aims to study the consequence of cropping system change for SOC dynamics. Aggregates in samples taken from plots under different treatments on the two experiments were scanned using X-ray computed tomography at 1.5 μm resolution; the ability of each aggregate to transport oxygen was calculated based on the pore-scale lattice Boltzmann simulation assuming that the aggregate is saturated as this is the most anaerobic scenario. We compared porosity and diffusion coefficient of all aggregates and link them to soil carbon measured from different treatments on the two experiments. The results showed that the agronomic practice changes occurring 67 and 172 years ago substantially reshaped the intra-aggregate structure, and that the accrual of SOC is positively correlated with diffusion coefficient of the aggregates to transport oxygen. However, the diffusion coefficient increases with SOC asymptotically, plateauing when SOC exceeds a threshold value. We also found that diffusion coefficient of the aggregates in cropped soils chemically fertilized trended with their porosity approximately in the same way, deviating from those for other non-cropped treatments or fertilized with farmyard manure