Training in Adolescent Substance and Opioid Misuse in Pediatric Residency Programs

This study describes pediatric residency program training in adolescent substance use and opioid misuse, correlates training to local overdose rates, and identifies gaps in training.

HIV preexposure prophylaxis for adolescents and young adults

PURPOSE OF REVIEW

The review describes the evidence for HIV preexposure prophylaxis (PrEP) with daily combined tenofovir disoproxil fumarate and emtricitabine for adolescents and young adults. Current recommendations are described, as are the unique medical, socioeconomic, and legal considerations regarding the use of PrEP for youth.

RECENT FINDINGS

PrEP with daily oral tenofovir disoproxil fumarate-emtricitabine has been shown to help prevent new HIV infection among adults at substantial risk. Evidence suggests a protective benefit of PrEP for youth at risk for HIV, although low adherence is emerging as a barrier to effective use.

SUMMARY

Effective use of antiretrovirals for PrEP represents a seminal development in HIV prevention efforts. Improving access and adherence to PrEP for youth has the potential to substantially reduce the incidence of HIV in this population.

Nitrogen critical loads and management alternatives for N-impacted ecosystems in California

Empirical critical loads for N deposition effects and maps showing areas projected to be in exceedance of the critical load (CL) are given for seven major vegetation types in California. Thirty-five percent of the land area for these vegetation types (99,639 km(2)) is estimated to be in excess of the N CL. Low CL values (3-8 kg N ha(-1) yr(-1)) were determined for mixed conifer forests, chaparral and oak woodlands due to highly N-sensitive biota (lichens) and N-poor or low biomass vegetation in the case of coastal sage scrub (CSS), annual grassland, and desert scrub vegetation. At these N deposition critical loads the latter three ecosystem types are at risk of major vegetation type change because N enrichment favors invasion by exotic annual grasses. Fifty-four and forty-four percent of the area for CSS and grasslands are in exceedance of the CL for invasive grasses, while 53 and 41% of the chaparral and oak woodland areas are in exceedance of the CL for impacts on epiphytic lichen communities. Approximately 30% of the desert (based on invasive grasses and increased fire risk) and mixed conifer forest (based on lichen community changes) areas are in exceedance of the CL. These ecosystems are generally located further from emissions sources than many grasslands or CSS areas. By comparison, only 3-15% of the forested and chaparral land areas are estimated to be in exceedance of the NO(3)(-) leaching CL. The CL for incipient N saturation in mixed conifer forest catchments was 17 kg N ha(-1) yr(-1). In 10% of the CL exceedance areas for all seven vegetation types combined, the CL is exceeded by at least 10 kg N ha(-1) yr(-1), and in 27% of the exceedance areas the CL is exceeded by at least 5 kg N ha(-1) yr(-1). Management strategies for mitigating the effects of excess N are based on reducing N emissions and reducing site N capital through approaches such as biomass removal and prescribed fire or control of invasive grasses by mowing, selective herbicides, weeding or domestic animal grazing. Ultimately, decreases in N deposition are needed for long-term ecosystem protection and sustainability, and this is the only strategy that will protect epiphytic lichen communities.

Reconstruction of the historical changes in mycorrhizal fungal communities under anthropogenic nitrogen deposition

Archived soil samples (1937-1999) and historic air quality data from the Los Angeles Basin were used for reconstructing the record of change between atmospheric NO(x) loads, soil delta(15)N values and the diversity of arbuscular mycorrhizae (AM), which are ubiquitous plant-fungus mutualists that control plant community productivity. A tripling of atmospheric NO(x) loads between 1937 and the 1970s was paralleled by soil nitrogen enrichment (delta(15)N = 3.18). From 1975 onwards, atmospheric NO(x) declined, but soils became nitrogen saturated (delta(15) N = -4 and NO(3)-nitrogen = 171mgkg(-1)). The shifts in the AM community followed 28 years of atmospheric nitrogen enrichment and coincided with the onset of soil nitrogen saturation. Such changes were manifest in the loss of AM productivity, species richness (one species per year), three genera (Acaulospora, Scutellospora and Gigaspora) in the spore community and Gigaspora within the roots. Nitrogen enrichment also enhanced the proliferation of potentially less mutualistic species of Glomus. Autoregressive models implied that such patterns will persist and be driven by soil nitrogen cycling patterns. Chronic nitrogen enrichment from air pollution thus alters the diversity and mutualistic functioning of AM communities, which, in turn, may influence the plant community.

Response to ammonium and nitrate by a mycorrhizal annual invasive grass and native shrub in southern California

The goal of this study was to determine the interaction of mycorrhizae and two N sources, ammonium (NH(4)(+)) and nitrate (NO(3)(-)), on the growth of a coastal sage scrub (CSS) species, Artemisia californica, and an exotic annual grass, Bromus madritensis ssp. rubens. Anthropogenic nitrogen deposition may be influencing the decline of CSS and replacement by exotic grasses, but the extent to which mycorrhizae are involved in shrubland decline is unknown. NO(3)(-) is the dominant form of deposition in southern California, although the native, uneutrophied soils have a greater concentration of NH(4)(+). Seeds of each species were germinated in pots of sterile soil, inoculated with native soil containing mycorrhizal spores and infective root fragments, and fertilized with 50 μg/g of either NO(3)(-) or NH(4)(+). NH(4)(+) enhanced the growth of both mycorrhizal species, while NO(3)(-) did not. Control plants of B. madritensis under low N had a significant response to mycorrhizae, but A. californica did not. Nitrate increased the growth of nonmycorrhizal A. californica as much as the mycorrhizal NH(4)(+)-treated plants. There is no evidence in this study to suggest that the decline of A. californica or increase in B. madritensis is due to a mycorrhizal response to NO(3)(-). Other life history traits of the two species must be used to explain the invasive behavior of the annual grass. Mycorrhizae may be more important in controlling plant growth in native uneutrophied soils dominated by NH(4)(+) rather than NO(3)(-).

The Effects of Irrigation on Revegetation of Semi-Arid Coastal Sage Scrub in Southern California

/ To test the appropriateness and applicability of irrigation for restoration of coastal sage scrub, a semi-arid vegetation type native to southern California, a field study comparing four irrigation schedules-no irrigation, spring irrigation only, summer irrigation only, and irrigation year round as needed-was established. A seed mixture of six native shrub species was broadcast, and the effect of irrigation on emergence and establishment was evaluated. Restoration of arid and semi-arid vegetation is challenging because of the severe environmental conditions inherent to these ecosystems. In particular, the low and unpredictable nature of precipitation can limit the chances for successful establishment of perennial species. Under conditions where supplemental irrigation is available, irrigation may make the difference between successful or failed restoration. However, increasing the availability of water through irrigation may result in poor plant adaptation to surviving arid conditions or only temporary success followed by failure once supplemental water is withdrawn. In this study, irrigation stimulated germination in the irrigated plots about a month earlier than the plots dependent on natural rainfall, but this had little lasting effect. Spring and summer irrigation did not improve survival compared to the plots receiving no supplemental water. The largest effect of irrigation was a reduction in survival of several species grown under irrigated conditions as compared to nonirrigated conditions. In plots where water was applied all year long a single species, Artemisia californica, represented nearly 100% of the species present at the end of two growing seasons. Irrigation may speed revegetation under some conditions, but was not very effective in establishing natural vegetation structure.

The effects of oxalates produced by Salsola tragus on the phosphorus nutrition of Stipa pulchra

Oxalic acid is produced by some species of plants and mycorrhizal fungi and it may solubilize unavailable soil phosphorus (P) bound by cations (Ca⁺⁺, Al⁺⁺, Fe⁺⁺⁺). Field and greenhouse experiments were conducted to show whether oxalate produced by the annual Salsola tragus or added oxalic acid would solubilize P from the inorganic-bound soil P pool, making it available for uptake by Stipa pulchra. Oxalate could be leached in the laboratory from the senescent canopy of Salsola, and leaching by rainfall was hypothesized to be a source of potential increased soil P under the Salsola canopy. Both oxalate leached from the canopy of Salsola and added oxalic acid increased the availability of soil P in greenhouse experiments. The source of the increase in available soil P in the greenhouse experiment was shown to be the inorganic-bound P pool, as the total P concentration of the soil decreased with increasing oxalate. There were significant increases in Stipa shoot P in response to Salsola leachates and in response to added oxalate in the greenhouse studies. These results suggest an important role for oxalate in P cycling. On disturbed sites where Salsola invades it may act to facilitate the establishment of later seral species like Stipa by creating a nutrient island of available P.

Ab initio studies of the decomposition of nitrosourea in the presence of cations

Self-consistent (Hartree-Fock) calculations of the process of decomposition of protonated and lithiated syn-N-nitrosourea show that the presence of cations perturbs the electron distribution significantly. The decomposition of nitrosourea is facilitated when a proton or lithium ion is positioned at the oxygen of the nitroso group. These results may suggest clinical experimentation with nitrosoureas used in conjunction with lithium salts.

WATER RELATIONS OF XERIC GRASSES IN THE FIELD: INTERACTIONS OF MYCORRHIZAS AND COMPETITION

The effects of vesicular-arbuscular mycorrhizal inoculum and competition from non-mycorrhizal annual plants were tested on Agropyron smithii Rydb. and Agropyron dasystachyum (Hook.) Scribn. growing in an inoculum-poor soil. Mycorrhizal A. smithii decreased stomatal resistance (r_s ) and increased leaf water potential compared to the non-inoculated plants, but only during the driest portion of the growing season. The presence of annuals caused increased r_s of A. smithii, but only of non-inoculated plants. Mycorrhizal plants had the same r_s with or without annuals, indicating that mycorrhizas may alleviate the detrimental effects of competition on r_s of A. smithii. By contrast, neither inoculation nor annuals significantly affected water relations of A. dasystachyum. Mycorrhizas also did not increase N and P concentrations or percentage cover of either grass, but both had delayed phenology when mycorrhizal. This research was done during a wet year when the effects of mycorrhizas may be subtle. Long-term observations are necessary to determine the importance of mycorrhizas under field conditions.