Effects of nutrient addition and soil drainage on germination of N-fixing and non-N-fixing tropical dry forest tree species

To develop generalised predictions regarding the effects of atmospheric nitrogen (N) and phosphorus (P) deposition on vegetation communities, it is necessary to account for the impacts of increased nutrient availability on the early life history stages of plants. Additionally, it is important to determine if these responses (a) differ between plant functional groups and (b) are modulated by soil drainage, which may affect the persistence of added nutrients. We experimentally assessed seed germination responses (germination proportion and germination energy, i.e. time to germination) of commonly occurring N-fixing and non-N-fixing tropical dry forest tree species found in India to simulated N and P deposition in well-drained soils, as well as soils with impeded drainage. When soils were not allowed to drain, germination proportion declined with nutrient addition, while germination energy remained unchanged. Stronger declines in germination proportion were observed for N-fixing species. In free-draining soils, nutrient addition did not affect germination proportion in either functional group. However, we detected a trend of delayed germination with nutrient addition, especially in N-fixers. Our results suggest that nutrient deposition can lead to potential shifts in functional dominance and tree community composition of tropical dry forests in the long term through its effects on early life stages of trees, although the mechanisms underlying the observed germination responses remain unclear. Further, such effects are likely to be spatially variable across the geographic range in which tropical dry forests occur depending on soil drainage properties

A dominant dwarf shrub increases diversity of herbaceous plant communities in a Trans-Himalayan rangeland

Plant communities are structured by both competition and facilitation. The interplay between the two interactions can vary depending on environmental factors, nature of stress, and plant traits. But, whether positive or negative interactions dominate in regions of high biotic and abiotic stress remains unclear.We studied herbaceous plant communities associated with a dwarf shrub Caragana versicolor in semi-arid, high altitude Trans Himalayan rangelands of Spiti, India. We surveyed 120 pairs of plots (within and outside shrub canopies) across four watersheds differing in altitude, aspect and dominant herbivores. Herbaceous communities within shrub canopies had 25% higher species richness, but similar abundance when compared to communities outside the canopy, with the shrub edge having higher diversity than the center of the canopy. Grasses and erect forbs showed positive associations with the shrub, while prostrate plants occurred at much lower abundance within the canopy. Rare species showed stronger positive associations with Caragana than abundant species. Experimental removal of herbaceous vegetation from within shrub canopies led to 42% increase in flowering in Caragana, indicating a cost to the host shrubs. Our study indicates a robust pattern of a dwarf shrub facilitating local community diversity across this alpine landscape, increasing diversity at the plot level, facilitating rare species, and yet incurring a cost to hosts from the presence of herbaceous plants. Given these large influences of this shrub on vegetation of these high altitude rangelands, we suggest that the shrub microhabitat be explicitly considered in any analyses of ecosystem health in such rangelands

Sensitivity of grasslands to rainfall variation: the role of resource colimitation

University of Minnesota Ph.D. dissertation. August 2020. Major: Ecology, Evolution and Behavior. Advisors: Elizabeth Borer, Eric Seabloom. 1 computer file (PDF); ix, 94 pages.Identifying the factors shaping ecosystem sensitivity to global change is an important unresolved question in ecology. Grasslands and savannas account for one-third of Earth's terrestrial primary production, and variation in that production is strongly driven by rainfall. The sensitivity of ecosystems to rainfall should depend on the availability of other co-limiting resources, such as nutrients. However, it is unclear how the strength of that co-limitation varies among sites - across gradients of aridity, soil fertility and community composition. I leverage long term experiments within the Nutrient Network research cooperative to analyse how fertilization affects the sensitivity of grassland plant communities to rainfall. I expected that sensitivity to rainfall would decline from arid to mesic ecosystems, while the effects of fertilization on sensitivity would increase along that same gradient. I found the sensitivity of grasslands to extreme drought in 13 sites did not change with aridity, but it was increased by fertilization. For 37 grassland sites around the world, fertilization generally increased the sensitivity of biomass to rainfall variation irrespective of aridity. This showed that grasslands are co-limited by nutrients and water all across the aridity gradient present among our sites. Finally, I found that community shifts due to chronic nutrient addition at more than half the sites studied will still retain species that perform well in both high and low rainfall years. Thus composition change is unlikely to amplify the effects of nutrient addition on biomass sensitivity to precipitation

Baseline differences in characteristics and risk behaviors among people who inject drugs by syringe exchange program modality: an analysis of the Miami IDEA syringe exchange

Abstract Background In March of 2016, Florida passed the Infection Disease Elimination Act (IDEA), legalizing the formation of the first syringe exchange program in Florida, which opened in December of 2016 at a fixed site in Overtown, Miami. Since that time, the exchange expanded in April of 2017 to include a mobile van unit that provides the same services at different locations throughout Miami-Dade County. Methods Trained interviewers conducted face-to-face interviews from all first-time participants at the IDEA Exchange, both at the fixed site and the mobile van unit. Results Among 718 first-time enrollees, 74.8% were male, 52.1% were non-Hispanic White, 85.9% completed high school, 59.8% were unemployed, 42.1% were homeless, 54.2% reported an annual income of less than $15,000, and the mean age was 38 years. Participants at the fixed site and mobile van unit reported differences in socioeconomic status, injection drug-related behaviors, and pre-existing hepatitis C virus (HCV) infection status. Conclusions Taken together, these results suggest that the mobile unit is capturing a subset of PWID in Miami that the fixed site is not, and vice-versa. As the opioid crisis extends into all demographics, such multimodal efforts to target various populations of PWID should be kept in mind, especially when unveiling future syringe exchanges in Florida and other late-adopting states

Discomfort discussing HIV/AIDS and lack of awareness are barriers to partner-to-partner pre-exposure prophylaxis education

We suggest that people living with HIV (PLWH) may serve as pre-exposure prophylaxis (PrEP) educators for partners when informed about PrEP. Participants in this study were a convenience sample of PLWH at a public hospital in Miami. A cross-sectional survey assessed the frequency of serostatus disclosure, PrEP awareness, and willingness to recommend PrEP to intimate partners. To evaluate stigma surrounding human immunodeficiency virus (HIV), comfort discussing HIV with family, friends and intimate partners was interrogated. Surveys were completed by 137 participants; 39.5% had potentially sero-discordant sexual partners. Among respondents, 29.2% reported that they ‘occasionally’ or ‘never’ disclose HIV status to sexual partners. In all, 66.4% of patients reported that they had never heard of PrEP. After being educated about PrEP, 86.0% of respondents reported that they would encourage partners to use it. Participants were asked how often the subject of HIV comes up in conversations. Most indicated that ‘rarely’ or ‘never’ does it come up with friends and family; 46.1% indicated that ‘never’ or ‘rarely’ does it come up with partners. In bivariate analyses, participants with prior awareness of PrEP were more likely to indicate higher frequency of conversations regarding HIV with intimate partners. It is concluded that interventions which utilize partner education to increase PrEP uptake should address stigma and knowledge among other barriers