Ocean acidification and coral skeletal density
Porites corals are dominant reef builders on most Indo-Pacific Reefs.
Coral reefs are among the most diverse ecosystems on Earth, and ocean acidification is considered a major threat to their future survival. However, field and laboratory studies examining the effect of acidification on corals have produced inconsistent results. Nathaniel Mollica et al. (pp. 1754–1759) developed a skeletal growth model for Porites, a dominant reef-building coral. The authors used the model to study the effect of acidification on coral skeletal density and extension—the processes of coral skeletal growth—and found that acidification influences skeletal density, but not extension. The model incorporates various factors that influence skeletal growth, including seawater conditions and polyp geometry, and reproduced skeletal densities of reef Porites reported in previous studies. The authors then used the model to evaluate the response of Porites to acidification under a business-as-usual emission scenario. The simulation predicted an average decline of around 12.4% in Porites skeletal density across global reef sites by the end of the 21st century. However, the level of decline varied among reefs, with the largest decreases in skeletal density observed in the Coral Triangle region. According to the authors, declines in coral skeletal density might increase the susceptibility of reef ecosystems to bioerosion and storm damage. — C.S.
Diamond anvil cell behavior near 400 GPa
X-ray imaging reveals diamond anvils cupping under extreme pressures.
Researchers have long simulated extreme pressure environments with the diamond anvil cell (DAC), a device that squeezes prepared samples between two opposing diamonds. Although numerous studies have demonstrated techniques to generate the 400-GPa maximum pressure of a conventional DAC, few have examined how the DAC behaves near this generally accepted upper limit. Bing Li et al. (pp. 1713–1717) present in situ high-pressure synchrotron X-ray diffraction and absorption experiments that provide a detailed picture of pressure loading and distribution, gasket thickness variation, and diamond anvil deformation in the region near 400 GPa. Using a submicrometer X-ray beam, the authors demonstrate that an s-shape loading behavior and cupping in both beveled and flat anvils are universal and unavoidable in conventional DAC experiments. Furthermore, the experiments offer an experimental example of double cupping in beveled diamond anvils, a phenomenon in which the diamonds deform elastically under immense pressure. Describing how the device’s core components interact with each other near 400 GPa could help extend the conventional DAC theoretical limit and improve future DAC designs, according to the authors. — T.J.
Risk factors for Alzheimer’s disease in the Chinese population
Most genome-wide association studies that have identified risk factors for Alzheimer’s disease (AD) were conducted in Caucasian populations. Xiaopu Zhou et al. (pp. 1697–1706) conducted a whole-genome sequencing study of AD in a cohort of Han Chinese ancestry. The authors identified variants in or near the APOE locus, a well-explored genetic marker of late-onset AD, as well as two other common variants, GCH1 and KCNJ15, associated with AD. The risk association of GCH1 and KCNJ15 with AD was also observed in non-Asian cohorts. The authors found that the rs928771 variant of KCNJ15 could affect the age of onset of AD, and that KCNJ15 transcript levels were significantly higher in the blood of people with AD, compared to controls. The authors also identified changes in the tissue transcriptome and plasma biomarker levels associated with the GCH1 and KCNJ15 risk variants. Network analysis of hippocampus and blood transcriptome datasets revealed that the APOE, GCH1, and KCNJ15 risk variants may exert their effects on AD by regulating immunity. According to the authors, GCH1 and KCNJ15 variants contribute to AD risk in the Chinese population. — S.R.