Tylosin (Tyl) is a veterinary antibiotic commonly used in swine and poultry production. Due to metabolic inefficiencies, it enters the environment through manure applications. Ion exchange is an ...important retention mechanism for Tyl, particularly for smectite clay. The objectives of this study are to characterize the exchange interactions of Tyl with common soil cations in subsoil horizons that contain smectite and to investigate the interactions using in situ Fourier transform infrared (FTIR) spectroscopy. Adsorbed Tyl in pH neutral, smectitic subsoil horizons is divided into exchangeable and nonexchangeable forms. The percentage of adsorbed Tyl that is exchangeable varies from 36% to 43% when Na+ is the competing cation, and from 57% to 66% when Ca2+ competes. In NaX-TylX binary exchange systems, neither Na+ nor Tyl+ is preferred by the clay exchange phase, and the Vanselow selectivity coefficients (KV) for the NaX→TylX exchange reaction range between 0.79 and 1.41. In the CaX2-TylX systems, Tyl+ is preferred by the clay exchange phase when the equivalent fraction of TylX (ETylX) is less than 0.4. The KV values for the CaX2→TylX exchange reaction are at a maximum at the lowest ETylX values, with 17.6 <KV < 58.1, then decrease with increasing ETylX to 1.34 <KV < 6.28. Adsorbed Tyl masks the CEC of the soil clays; the effect is greatest in systems that are initially Tyl-saturated, and is attributed to the steric effects of the large Tyl molecule. In situ FTIR indicates that Tyl interacts with soil iron oxides through the dimethylamine moiety.
•Tylosin is adsorbed by soil in exchangeable and nonexchangeable forms.•Tylosin is preferred relative the Ca by the soil clay minerals in Ca-tylosin exchange.•No ion preference is observed in Na-tylosin exchange.•Tylosin masks the cation exchange capacity of soil clay minerals.•Tylosin adsorption through the dimethylamine functional group is an important soil retention mechanism.
Ecosystems containing multiple nonnative plant species are common, but mechanisms promoting their co-occurrence are understudied. Plant-soil interactions contribute to the dominance of singleton ...species in nonnative ranges because many nonnatives experience stronger positive feedbacks relative to co-occurring natives. Plant-soil interactions could impede other nonnatives if an individual nonnative benefits from its soil community to a greater extent than its neighboring nonnatives, as is seen with natives. However, plant-soil interactions could promote nonnative co-occurrence if a nonnative accumulates beneficial soil mutualists that also assist other nonnatives. Here, we use greenhouse and field experiments to ask whether plant-soil interactions (1) promote the codominance of two common nonnative shrubs (
Ligustrum sinense
and
Lonicera maackii
) and (2) facilitate the invasion of a less-common nonnative shrub (
Rhamnus davurica
) in deciduous forests of the southeastern United States. In the greenhouse, we found that two of the nonnatives,
L. maackii
and
R. davurica
, performed better in soils conditioned by nonnative shrubs compared to uninvaded forest soils, which suggests that positive feedbacks among co-occurring nonnative shrubs can promote continued invasion of a site. In both greenhouse and field experiments, we found consistent signals that the codominance of the nonnatives
L. sinense
and
L. maackii
may be at least partially explained by the increased growth of
L. sinense
in
L. maackii
soils. Overall, significant effects of plant-soil interactions on shrub performance indicate that plant-soil interactions can potentially structure the co-occurrence patterns of these nonnatives.
Ecosystems containing multiple nonnative plant species are common, but mechanisms promoting their co-occurrence are understudied. Plant-soil interactions contribute to the dominance of singleton ...species in nonnative ranges because many nonnatives experience stronger positive feedbacks relative to co-occurring natives. Plant-soil interactions could impede other nonnatives if an individual nonnative benefits from its soil community to a greater extent than its neighboring nonnatives, as is seen with natives. However, plant-soil interactions could promote nonnative co-occurrence if a nonnative accumulates beneficial soil mutualists that also assist other nonnatives. Here, we use greenhouse and field experiments to ask whether plant-soil interactions (1) promote the codominance of two common nonnative shrubs (Ligustrum sinense and Lonicera maackii) and (2) facilitate the invasion of a less-common nonnative shrub (Rhamnus davurica) in deciduous forests of the southeastern United States. In the greenhouse, we found that two of the nonnatives, L. maackii and R. davurica, performed better in soils conditioned by nonnative shrubs compared to uninvaded forest soils, which suggests that positive feedbacks among co-occurring nonnative shrubs can promote continued invasion of a site. In both greenhouse and field experiments, we found consistent signals that the codominance of the nonnatives L. sinense and L. maackii may be at least partially explained by the increased growth of L. sinense in L. maackii soils. Overall, significant effects of plant-soil interactions on shrub performance indicate that plant-soil interactions can potentially structure the co-occurrence patterns of these nonnatives.
To assess the prevalence of Listeria monocytogenes in vacuum-sealed packages of frankfurters, about 33,000 packages (1 lb each) were obtained by a third-party contractor from 12 volunteer commercial ...manufacturers over a 2-year period. The 12 producers, each of which contributed about 2,700 packages of frankfurters from one production run, comprised 9 large and 3 small plants located in eight U.S. Department of Agriculture/Food Safety and Inspection Service (USDA/FSIS) districts in 10 states. Five days after manufacture, 500 packages were sampled at the USDA/Agricultural Research Service (ARS) Eastern Regional Research Center (ERRC) in Wyndmoor, Pa., by the USDA/ARS package rinse method. At regular intervals during subsequent storage at 4 and 10 degrees C, an additional 200 packages were tested for the pathogen at each sampling point. From a statistical perspective, L. monocytogenes was not recovered from any of the products of nine of the producers, whereas the pathogen was recovered at rates of 1.5% (plant 367), 2.2% (plant 439), and 16% (plant 133) from the products of the remaining three plants. In total, 532 of 32,800 (1.6%) packages of frankfurters tested positive for the pathogen. The recovery rates did not change appreciably over time, there was no appreciable difference in L. monocytogenes recovery rates with respect to frankfurter storage temperature (4 or 10 degrees C), and the seasonality of manufacture had no influence on recovery rate. Molecular subtyping of multiple L. monocytogenes-positive isolates from each plant revealed that profile A (serotype 1/2a) was displayed by about 90% of the 1,105 isolates tested. However, in some cases it was also possible to recover more than one profile from a given plant. This study provides estimates of the prevalence, types, and viability of L. monocytogenes associated with commercially prepared frankfurters during extended refrigerated storage.
