Diverse Communities of hgcAB+ Microorganisms Methylate Mercury in Freshwater Sediments Subjected to Experimental Sulfate Loading.

Methylmercury (MeHg) is a bioaccumulative neurotoxin produced by certain sulfate-reducing bacteria and other anaerobic microorganisms. Because microorganisms differ in their capacity to methylate mercury, the abundance and distribution of methylating populations may determine MeHg production in the environment. We compared rates of MeHg production and the distribution of hgcAB genes in epilimnetic sediments from a freshwater lake that were experimentally amended with sulfate levels from 7 to 300 mg L-1. The most abundant hgcAB sequences were associated with clades of Methanomicrobia, sulfate-reducing Deltaproteobacteria, Spirochaetes, and unknown environmental sequences. The hgcAB+ communities from higher sulfate amendments were less diverse and had relatively more Deltaproteobacteria, whereas the communities from lower amendments were more diverse with a larger proportion of hgcAB sequences affiliated with other clades. Potential methylation rate constants varied 52-fold across the experiment. Both potential methylation rate constants and % MeHg were the highest in sediments from the lowest sulfate amendments, which had the most diverse hgcAB+ communities and relatively fewer hgcAB genes from clades associated with sulfate reduction. Although pore water sulfide concentration covaried with hgcAB diversity across our experimental sulfate gradient, major changes in the community of hgcAB+ organisms occurred prior to a significant buildup of sulfide in pore waters. Our results indicate that methylating communities dominated by diverse anaerobic microorganisms that do not reduce sulfate can produce MeHg as effectively as communities dominated by sulfate-reducing populations.

Transformation of Hospital Pharmacist Opioid Stewardship.

Purpose: The heightened involvement of government organizations to improve pain management and mitigate opioid adverse events brings to light the need for an opioid stewardship model. Summary: The US opioid epidemic has resulted in new hospital requirements for pain management by regulatory agencies. Opioid stewardship is a concept in the early development stage of pharmacy practice. There exists a need for a cohesive vision of opioid stewardship and the role of the pharmacist. Over the course of 17 years, the tracks for opioid stewardship in Fairview Health Services were laid through numerous initiatives to mitigate adverse events and improve the quality of pain management. This article will describe a transformation process for establishing the framework for opioid stewardship within Fairview Health Services and role of the pharmacist. Conclusions: The vision for opioid stewardship will ultimately be defined through the actions taken to improve quality care and patient safety. Opioid safety should be expanded to include stewardship of approaches that reduce the risk of diversion, overdose, and medication abuse. Pharmacists currently have a major role monitoring opioid medication in hospitals and this component will increase with new regulatory requirements.

Effects of sulfate and sulfide on the life cycle of Zizania palustris in hydroponic and mesocosm experiments.

Under oxygenated conditions, sulfate is relatively non-toxic to aquatic plants. However, in water-saturated soils, which are usually anoxic, sulfate can be reduced to toxic sulfide. Although the direct effects of sulfate and sulfide on the physiology of a few plant species have been studied in some detail, their cumulative effects on a plant's life cycle through inhibition of seed germination, seedling survival, growth, and seed production have been less well studied. We investigated the effect of sulfate and sulfide on the life cycle of wild rice (Zizania palustris L.) in hydroponic solutions and in outdoor mesocosms with sediment from a wild rice lake. In hydroponic solutions, sulfate had no effect on seed germination or juvenile seedling growth and development, but sulfide greatly reduced juvenile seedling growth and development at concentrations greater than 320 µg/L. In outdoor mesocosms, sulfate additions to overlying water increased sulfide production in sediments. Wild rice seedling emergence, seedling survival, biomass growth, viable seed production, and seed mass all declined with sulfate additions and hence sulfide concentrations in sediment. These declines grew steeper during the course of the 5 yr of the mesocosm experiment and wild rice populations became extinct in most tanks with concentrations of 250 mg SO4 /L or greater in the overlying water. Iron sulfide precipitated on the roots of wild rice plants, especially at high sulfate application rates. These precipitates, or the encroachment of reducing conditions that they indicate, may impede nutrient uptake and be partly responsible for the reduced seed production and viability.

Randomly organized lipids and marginally stable proteins: a coupling of weak interactions to optimize membrane signaling.

Eukaryotic lipids in a bilayer are dominated by weak cooperative interactions. These interactions impart highly dynamic and pliable properties to the membrane. C2 domain-containing proteins in the membrane also interact weakly and cooperatively giving rise to a high degree of conformational plasticity. We propose that this feature of weak energetics and plasticity shared by lipids and C2 domain-containing proteins enhance a cell's ability to transduce information across the membrane. We explored this hypothesis using information theory to assess the information storage capacity of model and mast cell membranes, as well as differential scanning calorimetry, carboxyfluorescein release assays, and tryptophan fluorescence to assess protein and membrane stability. The distribution of lipids in mast cell membranes encoded 5.6-5.8bits of information. More information resided in the acyl chains than the head groups and in the inner leaflet of the plasma membrane than the outer leaflet. When the lipid composition and information content of model membranes were varied, the associated C2 domains underwent large changes in stability and denaturation profile. The C2 domain-containing proteins are therefore acutely sensitive to the composition and information content of their associated lipids. Together, these findings suggest that the maximum flow of signaling information through the membrane and into the cell is optimized by the cooperation of near-random distributions of membrane lipids and proteins. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Enrichment in a general class of stoichiometric producer-consumer population growth models.

This paper presents the derivation and partial analysis of a general producer-consumer model. The model is stoichiometric in that it includes the growth constraints imposed by species-specific biomass carbon to nutrient ratios. The model unifies the approaches of other studies in recent years, and is calibrated from an extensive review of the algae-Daphnia literature. Numerical simulations and bifurcation analysis are used to examine the impact of energy enrichment under nutrient and stoichiometric constraints. Our results suggest that the variety of system responses previously cited for related models can be attributed to the size of the total system nutrient pool, which is here assumed fixed. New, more complicated bifurcation sequences, such as multiple homoclinic bifurcations, are demonstrated as well. The mechanistic basis of the model permits us to show the robustness of the system's dynamics subject to alternate approaches to modeling producer and consumer biomass production.

Nitrogen, phosphorus and light effects on growth and allocation of biomass and nutrients in wild rice.

Separating plastic from ontogenetic and growth-limiting responses of plants to changes in resource availability can be challenging because there are a total of eight combinations of these three types of responses. These can, however, be uniquely distinguished on plots of root:shoot ratios against total biomass through time. We used this approach to separate ontogenetic, plastic, and growth-limiting responses of wild rice (Zizania palustris L.) to changes in nitrogen, phosphorus, and light availabilities. Relative growth rate was limited primarily by nitrogen but responded to increased light and phosphorus after nitrogen limitations were alleviated. Nitrogen addition increased relative growth rate because it simultaneously increased unit leaf rate, specific leaf area, and leaf weight ratio. Increased light did not change relative growth rate because decreased specific leaf area and leaf weight ratio compensated the increased unit leaf rate. Phosphorus did not change either relative growth rate or its underlying components. Plants responded ontogenetically to increased nitrogen and light availabilities by accelerating their developmental rate, and plastically by decreasing or increasing their root:shoot ratios, respectively. Plants did not respond either ontogenetically or plastically to increased phosphorus availability. Ontogenetic changes in growth can be separated from plastic and growth-limiting responses by plotting root:shoot ratio against total biomass in the context of the eight possible responses identified above, and also by examining how the underlying components of relative growth rate respond.

Stable limit cycles and the paradox of enrichment in a model of chronic wasting disease.

Prions, which cause chronic wasting disease and other transmissible spongiform encephalopathies in ungulates, can remain active in soils for years. The reproductive age of ungulate populations is well within the residence time of prions in the soil. Reproduction and mortality in disease-free wildlife populations is regulated by density-dependent mechanisms, which also underlie the concept of carrying capacity. Here, we present a model of a susceptible deer population with density-dependent population regulation, an infected population, and an environmental pool of prions that infect the susceptible animals. When carrying capacity is low, the disease does not persist. As carrying capacity increases beyond a critical level, chronic wasting disease then invades a susceptible population and persists. Further increases in carrying capacity beyond a second, higher critical level produce stable limit cycles and recurrent epidemics between the animal population and the disease. This model therefore extends Rosenzweig's paradox of enrichment for predator-prey models to models of diseases in populations. The critical carrying capacities are reached sooner as the residence time of the prion in the soil increases. Wildlife management programs which increase carrying capacity may cause chronic wasting disease to persist and even destabilize animal populations, especially where prions persist for many years.

Landscape nutrition: seeing the forest instead of the trees.

Recent theories suggest that herbivores forage across many scales and that foraging decisions are driven by the distribution of nitrogen. However, experimental tests of these predictions across large landscapes are rare and difficult. Pretorius et al. (2011) present an elegant experimental design to test how patch size, local nutrient density and total nutrient load are detected by foraging African elephants (Loxodonta africana) in the Colophospermum mopane shrub veld in South Africa. This experiment should serve as a model for investigations of how herbivores detect and respond to high nutrient patches of different size; it also raises questions for further research, such as the fate of high nutrient patches as elephants disperse nutrients from them in urine, faecal material and carcasses deposited elsewhere in the landscape.

Mathematical Analysis of Melanocyte Patterns on Danio rerio.

The study of zebrafish skin pattern development could lead to a better understanding of how these patterns are generated and how they evolved. To compare and contrast wild-type (WT) striped and leopardt1 mutant spotted patterns, photographs were taken of the developing fish. Initial observations led to the hypothesis that the black melanocyte spots in leopardt1 mutants were not randomly distributed, but rather were located in "dashed" stripes. To test this, melanocyte-spot-sized transparent grids were overlaid onto photographs and the location of melanocyte clusters was recorded. The grid maps were used to identify whether a black, melanocyte positive, grid area was present adjacent to each melanocyte cluster in each cardinal and intercardinal direction. In addition, Python-based computer programs were used to analyze the photographs at the pixel level. When analyzed using analysis of variance and logistic regression models, the striped and spotted patterns expressed more similarities than expected. In the leopardt1 zebrafish, the spots were organized into dashed stripes that had similar locations to the WT stripes. This research suggests that spotted and striped patterns are related. Further, the leopardt1 spots were farther apart along the dorsal-ventral axis than in the anterior-posterior direction, suggesting that different mechanisms control spacing along these two axes.

Depression of belowground respiration rates at simulated high moose population densities in boreal forests.

Large herbivores can affect the carbon cycle in boreal forests by changing productivity and plant species composition, which in turn could ultimately alter litter production, nutrient cycling, and the partitioning between aboveground and belowground allocation of carbon. Here we experimentally tested how moose (Alces alces) at different simulated population densities affected belowground respiration rates (estimated as CO2 flux) in young boreal forest stands situated along a site productivity gradient. At high simulated population density, moose browsing considerably depressed belowground respiration rates (24-56% below that of no-moose controls) except during June, where the difference only was 10%. Moose browsing depressed belowground respiration the most on low-productivity sites. Soil moisture and temperature did not affect respiration rates. Impact of moose on belowground respiration was closely linked to litter production and followed Michaelis-Menten dynamics. The main mechanism by which moose decrease belowground respiration rates is likely their effect on photosynthetic biomass (especially decreased productivity of deciduous trees) and total litter production. An increased productivity of deciduous trees along the site productivity gradient causes an unequal effect of moose along the same gradient. The rapid growth of deciduous trees may offer higher resilience against negative effects of moose browsing on litter production and photosynthate allocation to roots.

Cumulative Sulfate Loads Shift Porewater to Sulfidic Conditions in Freshwater Wetland Sediment.

It is well established that sulfide can be toxic to rooted aquatic plants. However, a detailed description of the effects of cumulative sulfate loads on sulfide and iron (Fe) porewater geochemistry, plant exposure, and ecological response is lacking. Over 4 yr, we experimentally manipulated sulfate loads to self-perpetuating wild rice (Zizania palustris) populations and monitored increases in the ratio of sulfur (S) to Fe in sediment across a range of sulfide loading rates driven by overlying water sulfate. Because natural settings are complicated by ongoing Fe and S loads from surface and groundwater, this experimental setting provides a tractable system to describe the impacts of increased S loading on Fe-S porewater geochemistry. In the experimental mesocosms, the rate of sulfide accumulation in bulk sediment increased linearly with overlying water sulfate concentration up to 300 µg-SO4 cm-3 . Seedling survival at the beginning of the annual life cycle and seed mass and maturation at the end of the annual life cycle all decreased at porewater sulfide concentrations between 0.4 and 0.7 µg cm-3 . Changes to porewater sulfide, plant emergence, and plant nutrient uptake during seed production were closely related to the ratio of S to Fe in sediment. A mass balance analysis showed that porewater sulfide remained a small and relatively transient phase compared to sulfate in the overlying water and Fe in the sediment solid phase. The results illuminate the evolution of the geochemical setting and timescales over which 4 yr of cumulative sulfate loading resulted in a wholesale shift from Fe-dominated to sulfide-dominated porewater chemistry. This shift was accompanied by detrimental effects to, and eventual extirpation of, self-perpetuating wild rice populations. Environ Toxicol Chem 2019;38:1231-1244. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Temperature responses to infrared-loading and water table manipulations in peatland mesocosms.

We initiated a multi-factor global change experiment to explore the effects of infrared heat loading (HT) and water table level (WL) treatment on soil temperature (T) in bog and fen peatland mesocosms. We found that the temperature varied highly by year, month, peatland type, soil depth, HT and WL manipulations. The highest effect of HT on the temperature at 25 cm depth was found in June for the bog mesocosms (3.34-4.27 degrees C) but in May for the fen mesocosms (2.32-4.33 degrees C) over the 2-year study period. The effects of WL in the bog mesocosms were only found between August and January, with the wet mesocosms warmer than the dry mesocosms by 0.48-2.03 degrees C over the 2-year study period. In contrast, wetter fen mesocosms were generally cooler by 0.16-3.87 degrees C. Seasonal changes of temperatures elevated by the HT also varied by depth and ecosystem type, with temperature differences at 5 cm and 10 cm depth showing smaller seasonal fluctuations than those at 25 cm and 40 cm in the bog mesocosms. However, increased HT did not always lead to warmer soil, especially in the fen mesocosms. Both HT and WL manipulations have also changed the length of the non-frozen season.

Plant community dynamics, nutrient cycling, and alternative stable equilibria in peatlands.

Although observational data and experiments suggest that carbon flux and storage in peatlands are controlled by hydrology and/or nutrient availability, we lack a rigorous theory to account for the roles that different plant species or life-forms, particularly mosses, play in carbon and nutrient flux and storage and how they interact with different hydrologic sources of nutrients. We construct and analyze a model of peatlands that sheds some light on this problem. The model is a set of six coupled differential equations that define the flow of nutrients from moss and vascular plants to their litters, then to peat, and finally to an inorganic nutrient resource pool. We first analyze a simple version of this model (model 1) in which all nutrient input is from precipitation and enters the moss compartment directly, mimicking the dynamics of ombrotrophic bogs. There is a transcritical bifurcation that results in a switch of stability between two equilibrium bog communities: a moss monoculture and a community where mosses and vascular plants coexist. The bifurcation depends on the magnitudes of the input/output budget of the peatland and the life-history traits of the plants. We generalize model 1 to model 2 by dividing nutrient inputs between precipitation and groundwater, thus also allowing the development of minerotrophic fens that receive nutrient subsidies from both groundwater and precipitation and adding intraspecific competition (self-limitation) terms for both moss and vascular plants. Partitioning precipitation inputs between moss and the nutrient pool resulted in the greatest changes in model behavior, including the appearance of a lake and a vascular plant monoculture as well as the moss monoculture and coexistence equilibrium. As with model 1, these solutions are separated by transcritical bifurcations depending on critical combinations of parameters determining the input-output budget of the peatland as well as the life-history characteristics of the plant species. Model 2 also allowed for an early transient spike in vascular plant dominance followed by approach to near moss monoculture and then eventual approach to coexistence equilibrium. This generalized model mimics the broad features of successional development of peatlands from fens to bogs often found in the paleorecords of peat cores.

Comparing Spatial Pattern in Unaltered Old-Growth and Disturbed Forest Landscapes.

We used geographic information systems (GIS) to analyze the structure of a second-growth forest landscape (9600 ha) that contains scattered old-growth patches. We compared this landscape to a nearby, unaltered old-growth landscape on comparable landforms and soils to assess the effects of human activity on forest spatial pattern. Our objective is to determine if characteristic landscape structural patterns distinguish the primary old-growth forest landscape from the disturbed landscape. Characteristic patterns of old-growth landscape structure would be useful in enhancing and restoring old-growth ecosystem functioning in managed landscapes. Our natural old-growth landscape is still dominated by the original forest cover of eastern hemlock (Tsuga canadensis), sugar maple (Acer saccharum), and yellow birch (Betula allegheniensis). The disturbed landscape has only scattered, remnant patches of old-growth ecosystems among a greater number of early successional hardwood and conifer forest types. Human disturbances can either increase or decrease landscape heterogeneity depending on the parameter and spatial scale examined. In this study, we found that a number of important structural features of the intact old-growth landscape do not occur in the disturbed landscape. The disturbed landscape has significantly more small forest patches and fewer large, matrix patches than the intact landscape. Forest patches in the fragmented landscape are significantly simpler in shape (lower fractal dimension, D) than in the intact old-growth landscape. Change in fractal dimension with patch size, a relationship that may be characteristic of differing processes of patch formation at different scales, is present within the intact landscape but has been obscured by human activity in the disturbed landscape. Important ecosystem juxtapositions of the old-growth landscape, such as hemlock with lowland conifers, have been lost in the disturbed landscape. In addition, significant landscape heterogeneity in this glaciated region is produced by landforms alone, without natural or human disturbances. The features that distinguish disturbed and old-growth forest landscape structure that we have described need to be examined elsewhere to determine if such features are characteristic of other landscapes and regions. Such forest landscape structural differences that exist more broadly could form the basis of landscape principles to be applied both to the restoration of old-growth forest landscapes and the modification of general forest management for enhancing biodiversity. These principles may be particularly useful for constructing integrated landscapes managed for both commodity production and biodiversity protection.

State-of-the-Art of Models of Production-Decomposition Linkages in Conifer and Grassland Ecosystems.

We review the state-of-the-art of models of forests and grasslands that could be used to predict the impact of a future climate change arising from increased atmospheric carbon dioxide concentration. Four levels of resolution are recognized: physiologically based models, population models, ecosystem models, and regional or global models. At the physiological level a number of important processes can be described in great detail, but these models often treat inadequately interactions with nutrient cycles, which operate on longer time scales. Population and ecosystem models can, on the other hand, encapsulate relationships between the plants and the soil system, but at the expense of requiring more ad ho formulations of processes. At the regional and global scale we have so far only steady-state models, which cannot be used to predict transients caused by climate change. However, our conclusion is that, in spite of the gaps in knowledge, there are several models based on dominant processes that are well enough understood for the predictions of those models to be taken seriously.

Factors Controlling Nitrogen Cycling and Nitrogen Saturation in Northern Temperate Forest Ecosystems.

An analysis of the factors controlling rates of nitrogen cycling in northern temperate forest ecosystems is presented based on a quantitative analysis of an extensive data set for forests in Wisconsin and Massachusetts as those data are synthesized in a computer model (VEGIE) of organic matter and nutrient dynamics. The model is of the "lumped-parameter," nutrient-flux-density type, dealing with major components of forest ecosystems rather than stems or species. It deals explicitly with the interactions among light, water, and nutrient availability in determining transient and equilibrium rates of primary production and nutrient cycling. Data are presented for parameterizing the plant component of the system at either the species or community level. A major conclusion is that the ultimate control on equilibrium nitrogen-cycling rates resides not within the nitrogen cycle itself (for example in litter quality or net primary production [NPP] allocation patterns) but rather in ratios of resource-use efficiency by vegetation as compared with the ratios of resource availability. Litter quality and allocation patterns, along with rates of N deposition, do affect the rate at which a system approaches the equilibrium cycling rate. The model is used to explain observed variation in nitrogen-cycling rates among forest types, and to predict the timing and occurrence of "nitrogen saturation" (N availability in excess of biotic demand) as a function of nitrogen deposition rates and harvesting.

Nitrogen mineralization dynamics in grass monocultures.

Although Wedin and Tilman (1990) observed large differences in in situ N mineralization among monocultures of five grass species, the mechanisms responsible were unclear. In this study, we found that the species did not change total soil C or N, and soil C: N ratio (range 12.9-14.1) was only slightly, but significantly, changed after four years. Nor did the species significantly affect the total amount of N mineralized (per g soil N) in year-long aerobic laboratory incubations. However, short-term N mineralization rates in the incubations (day 1-day 17) differed significantly among species and were significantly correlated with annual in situ mineralization. When pool sizes and turnover rates of potentially mineralizable N (No) were estimated, the best model treated No as two pools: a labile pool, which differed among species in size (Nl, range 2-3% of total N) and rate constant (h, range 0.04-0.26 wk-1), and a larger recalcitrant pool with a constant mineralization rate across species. The rate constant of the labile pool (h) was highly correlated with annual in situ N mineralization (+0.96). Therefore, plant species need only change the dynamics of a small fraction of soil organic matter, in this case estimated to be less than 3%, to have large effects on overall system N dynamics.

Production and microtopography of bog bryophytes: response to warming and water-table manipulations.

Boreal peatlands, which contain a large fraction of the world's soil organic carbon pool, may be significantly affected by changes in climate and land use, with attendant feedback to climate through changes in albedo, fluxes of energy or trace gases, and soil carbon storage. The response of peatlands to changing environmental conditions will probably be dictated in part by scale-dependent topographic heterogeneity, which is known to interact with hydrology, vegetation, nutrients, and emissions of trace gases. Because the bryophyte community can contribute the majority of aboveground production in bogs, we investigated how microscale topography affects the response of bryophyte species production and cover to warming (using overhead infrared lamps) and manipulations of water-table height within experimental mesocosms. We removed 27 intact peat monoliths (2.1-m2 surface area, 0.5-0.7 m depth) from a bog in northern Minnesota, USA, and subjected them to three warming and three water-table treatments in a fully crossed factorial design. Between 1994 and 1998, we determined annual production of the four dominant bryophyte taxa within three microtopographic zones (low, medium, and high relative to the water table). We also estimated species cover and calculated changes in topography and roughness of the bryophyte surface through time. Total production of all bryophytes, and production of the individual taxa Polytrichum strictum, Sphagnum magellanicum, and Sphagnum Section Acutifolia, were about 100% greater in low microtopographic zones than in high zones, and about 50% greater in low than in medium zones. Production of bryophytes increased along the gradient of increasing water-table heights, but in most years, total production of bryophytes was negatively correlated with height above the set water table only for the wettest water-table treatment. Although bryophyte production was unaffected by the warming treatments, the bryophyte surface flattened in proportion to the degree of warming. These results indicate that production of bryophytes is driven most strongly by the absolute and relative height of the bryophyte surface above the water table. Predicted changes in water-table height commensurate with changes in surface temperature may thus affect both production and superficial topography of bryophyte communities.