Mary C. Savin

Links between Phytoplankton and Bacterial Community Dynamics in a Coastal Marine Environment

Bacteria and phytoplankton dynamics are thought to be closely linked in coastal marine environments, with correlations frequently observed between bacterial and phytoplankton biomass. In contrast, little is known about how these communities interact with each other at the species composition level. The purpose of the current study was to analyze bacterial community dynamics in a productive, coastal ecosystem and to determine whether they were related to phytoplankton community dynamics. Near-surface seawater samples were collected in February, May, July, and September 2000 from several stations in the Bay of Fundy. Savin et al. (M.C. Savin et al., Microb Ecol 48: 51-65) analyzed the phytoplankton community in simultaneously collected samples. The attached and free-living bacterial communities were collected by successive filtration onto 5 μm and 0.22 μm pore-size filters, respectively. DNA was extracted from filters and bacterial 16S rRNA gene fragments were amplified and analyzed by denaturing gradient gel electrophoresis (DGGE). DGGE revealed that diversity and temporal variability were lower in the free-living than the attached bacterial community. Both attached and free-living communities were dominated by members of the Roseobacter and Cytophaga groups. Correspondence analysis (CA) ordination diagrams showed similar patterns for the phytoplankton and attached bacterial communities, indicating that shifts in the species composition of these communities were linked. Similarly, canonical CA revealed that the diversity, abundance, and percentage of diatoms in the phytoplankton community accounted for a significant amount of the variability in the attached bacterial community composition. In contrast, ordination analyses did not reveal an association between free-living bacteria and phytoplankton. These results suggest that there are specific interactions between phytoplankton and the bacteria attached to them, and that these interactions influence the composition of both communities.

Populations of antibiotic-resistant coliform bacteria change rapidly in a wastewater effluent dominated stream

Incomplete elimination of bacteria and pharmaceutical drugs during wastewater treatment results in the entry of antibiotics and antibiotic-resistant bacteria into receiving streams with effluent inputs. In Mud Creek in Fayetteville, AR, ofloxacin, trimethoprim, and sulfamethoxazole have been detected in water and sediment, and tetracycline has been detected in sediment downstream of treated effluent input. These antibiotics have been measured repeatedly, but at low concentrations (<1μg/L) in the stream. To determine if effluent input results in detectable and stable changes in antibiotic resistances downstream of effluent input, antibiotic resistance in Escherichia coli and total coliform bacteria in Mud Creek stream water and sediment were determined using a culture-based method. Isolated E. coli colonies were characterized for multiple antibiotic resistance (MAR) patterns on solid media and to evaluate E. coli isolate richness by amplification of a partial uidA gene followed by denaturant gradient gel electrophoresis (DGGE). Despite temporal variability, proportions of antibiotic-resistant E. coli were generally high in effluent and 640m downstream. The MAR pattern ampicillin-trimethoprim-sulfamethoxazole was associated with a DGGE profile that was detected in effluent and downstream E. coli isolates, but not upstream. Percent resistance among coliform bacteria to trimethoprim and sulfamethoxazole was higher 640m downstream compared to upstream sediment and water (with one exception). Resistance to ofloxacin was too low to analyze statistically and tetracycline resistance was fairly constant across sites. Resistances changed from 640m to 2000m downstream, although dissolved nutrient concentrations within that stream stretch resembled effluent. Antibiotic resistant bacteria are entering the stream, but resistances change within a short distance of effluent inputs, more quickly than indicated based on chemical water properties. Results illustrate the difficulty in tracking the input and fate of antibiotic resistance and in relating the presence of low antibiotic concentrations to selection or persistence of antibiotic resistances.

DYNAMICS OF CARBON AND NITROGEN MINERALIZATION, MICROBIAL BIOMASS, AND NEMATODE ABUNDANCE WITHIN AND OUTSIDE THE BURROW WALLS OF ANECIC EARTHWORMS (LUMBRICUS TERRESTRIS)

We conducted a laboratory study using soil cores to determine whether anecic earthworm (Lumbricus terrestris) burrow linings (the drilosphere) are sites for enhanced carbon and nitrogen mineralization and increased microbial biomass and nematode abundance. We compared microbial biomass C, C mineralization rates, metabolic quotient, levels of inorganic N (NO − [over] 3 and NH + [over] 4), and nematode abundance over the course of 11 weeks in soil from earthworm burrows, bulk soil away from burrows, and a control soil in cores to which no earthworms were added. Significant differences were observed in microbial biomass carbon, which was 38 to 84% lower, and carbon mineralization and metabolic quotient, which were 2.3 to 7.5 and 5.6 to 17.4 times, respectively, higher in burrow than in control soil. No significant differences were observed in these variables between bulk and control soil. In addition, nematodes were 3.7 to 6.5 times more abundant, and inorganic N levels 21 to 78% higher in burrow than in control soil, with no significant differences observed between bulk and control soil. Dynamics of microbial biomass carbon and inorganic N followed the same general pattern in burrow, bulk, and control soil. By contrast, dynamics of nematode abundance, carbon mineralization, and metabolic quotient differed between burrow and both bulk and control soil, with peak values observed at 5, 7, and 11 weeks for nematode abundance, C mineralization, and metabolic quotient, respectively. Our results suggest that earthworms may have an indirect effect on soil C and N dynamics by stimulating the activities of nematodes and their interaction with microbial biomass in the drilosphere to a greater degree than is observed in soil that has not come in direct contact with earthworms.

Biogeophysical factors influencing soil respiration and mineral nitrogen content in an old field soil

Microbivorous grazers are thought to enhance nutrient mineralization. The predicted effect of microbivory on nutrient cycling depends on the pore habitat model used. We evaluated CO2 evolution and mineral N content of an old field soil to test two alternative habitat hypotheses. The exclusion hypothesis predicts that nematodes are separated from their microbial food resources in water-filled pores when soils dry, resulting in slower rates of biogeochemical transformations. The enclosure hypothesis predicts that nematode densities increase relative to their forage in smaller, isolated water volumes when soils dry, accelerating rates of biogeochemical transformations. We investigated the effect of soil moisture on the relationship between microbial biomass, microbivorous and predaceous nematodes, soil respiration and mineral N concentrations in an old field five times during the course of a year. We could evaluate the validity of the two habitat hypotheses for the entire field only in August 1997 because that was the only sampling date when maximum water-filled pore diameters were smaller than microbivorous nematode body diameters in all sampled field locations. The mean microbivorous and predaceous nematode abundances for the field in August were greater than 6300 kg 21 and 80,000 kg 21 , respectively. Accordingly, the exclusion hypothesis was rejected. Predaceous nematode abundance was markedly higher in August than at any other sampling date. The high abundance of predators present suggests that detrital resources were not limiting productivity and that predators and microbivores were in enclosures, allowing predators to efficiently access their prey. Spatial maps, in agreement with linear correlation analyses, suggest that under our driest sampling conditions, soil respiration and mineral N content were controlled by microbivory and predation. q 2001 Elsevier Science Ltd. All rights reserved.

Fine-scale spatial variability of physical and biological soil properties in Kingston, Rhode Island

Abstract We evaluated the fine-scale (cm) variability of bulk density (ρB), organic matter content (%OM), volumetric water content (θV), and carbon mineralization rate (Cmin) at specific values of water potential in an old field soil. We measured these variables in soil samples obtained using paired abutting, 5-cm diameter, 10-cm deep cores. To compare abutting core properties, abutting cores were randomly assigned to one of two groups, A or B, using permutation procedures in order to account for the possibility of chance effects. Comparisons were made using either 10 (θV and Cmin) or 40 (% OM and ρB) pairs of samples in May, August, and November of 1997 and March of 1998. No differences were observed in the distribution of values among groups of cores for all the variables measured. Furthermore, there were no seasonal differences in coefficient of variation for any of the variables. Values of coefficient of variation followed the order: Cmin>θV>% OM>ρB. The difference between paired cores relative to population means (RD) was highest for Cmin (29.7%), followed by %OM (12.3%), θV (9.1%) and ρB (5.9%). Our results indicate that variability in soil properties (RD) at the centimeter scale is lowest for physical properties (θV and ρB) and highest for biological properties (%OM and Cmin). The assumption of identity among adjacent cores does not appear to be justified for the soil properties evaluated in our study.

Grazing in a porous environment. 2. Nematode community structure

The influence of soil matric potential on nematode community composition and grazing associations were examined. Undisturbed cores (5 cm diameter, 10 cm depth) were collected in an old field dominated by perennial grasses on a Hinckley sandy loam at Peckham Farm near Kingston, Rhode Island. Ten pairs of cores were incubated at −3, −10, −20 and −50 kPa matric potential after saturation for 21–28 or 42–58 days. Nematodes were extracted using Cobbs decanting and sieving method followed by sucrose centrifugal-flotation and identified to family or genus. Collembola and enchytraeids present were also enumerated because they are grazers that reside in air-filled spaces. Direct counts of bacteria and fungi were made to estimate biovolume using fluorescein isothiocyanate and fluorescein diacetate stains, respectively. Trophic diversity and maturity indices were calculated for nematode communities. Three patterns of matric potential effect were observed for nematode taxa. One, there was a consistent effect of matric potential for all seasons for Alaimus, Monhysteridae, Prismatolaimus, Paraxonchium and Dorylaimoides. Two, some effects of matric potential were consistent among seasons and other effects were inconsistent for Aphelenchoides, Aphelenchus, Cephalobidae, Coomansus, Eudorylaimus, Huntaphelenchoides, Panagrolaimidae, Paraphelenchus, Sectonema, and Tripyla. Third, effects of matric potential were always inconsistent among seasons for Aphanolaimus, Aporcelaimellus, Bunonema, Rhabditidae, and Tylencholaimus. As predicted, fungal and bacterial biomass responded oppositely to matric potential. Total bacterial biomass was greater at −3 kPa than −10, −20 and −50 kPa (P=0.0095). Total fungal biomass was greater at −50, −20 and −10 kPa than −3 kPa (P=0.0095). Neither bacterial-feeding, fungal-feeding nor predacious nematodes correlated significantly with bacterial or fungal biomass. Omnivorous and predacious nematodes correlated positively with number of bacterial-feeding nematodes; predacious nematodes also correlated positively with fungal-feeding nematodes. Numbers of Collembola and enchytraeids were more often correlated positively with microbial-grazing nematode numbers in drier than moist soils. From this study, we propose two mechanisms that may explain nematode community structure changes with matric potential: differential anhydrobiosis and/or enclosure hypotheses. The later suggests that drying of soil generates pockets of moisture in aggregates that become isolated from one another enclosing nematodes and their food in relatively high concentrations creating patches of activity separated by larger areas of inactivity.

Performance by spring and fall-calving cows grazing with full, limited, or no access to toxic Neotyphodium coenophialum-infected tall fescue1

Replacing toxic, wild-type Neotyphodium coenophialum-infected tall fescue (E+) with nontoxic, N. coenophialum-infected tall fescue (NE+) has improved cow performance, but producer acceptance of NE+ has been slow. The objective was to compare performance by spring- and fall-calving cows grazing either E+ or NE+ at different percentages of the total pasture area. Gelbvieh×Angus crossbred cows (n=178) were stratified by BW and age within calving season and allocated randomly to 1 of 14 groups representing 5 treatments for a 3-yr study: i) Fall-calving on 100% E+ (F100); ii) Spring-calving on 100% E+ (S100); iii) Fall-calving on 75% E+ and 25% NE+ (F75); iv) Spring-calving on 75% E+ and 25% NE+ (S75); and v) Spring-calving on 100% NE+ (SNE100). Groups allocated to F75 and S75 grazed E+ until approximately 28 d before breeding and weaning, then were then moved to their respective NE+ pasture area for 4 to 6 wk; those allocated to F100, S100, and SNE100 grazed their pastures throughout the entire year. Samples of tall fescue were gathered from specific cells within each pasture at the time cows were moved into that particular cell (∼1 sample/mo). Blood samples were collected from the cows at the start and end of the breeding season. Stocking rate for each treatment was 1 cow/ha. Forage IVDMD, CP, and total ergot alkaloid concentrations were affected (P<0.05) by the treatment×sampling date interaction. Hay offered, cow BW, and BCS at breeding, end of breeding, and at weaning were greater (P<0.05) from fall-calving vs. spring-calving. Cow BW at weaning was greater (P<0.05) from F75 and S75 vs. F100 and S100. The calving season×NE+ % interaction affected (P<0.05) calving rates. Preweaning calf BW gain, actual and adjusted weaning BW, ADG, sale price, and calf value at weaning were greater (P<0.05) from fall-calving vs. spring-calving and from SNE100 vs. S75 except for sale price which was greater (P<0.05) from S75 vs. SNE100. Cow concentrations of serum prolactin at breeding and serum NEFA at the end of breeding were affected (P<0.05) by the calving season×NE+ % interaction. Serum Zn and Cu concentrations from cows were affected (P<0.05) by calving season. A fall-calving season may be more desirable for cows grazing E+, resulting in greater calving rates, cow performance, and calf BW at weaning, whereas limited access to NE+ may increase calving rates, serum prolactin, and NEFA concentrations during certain times in the production cycle, particularly in spring-calving cows.

Short-term Effects of Poultry Litter Form and Rate on Soil Bulk Density and Water Content

Abstract Poultry litter is an organic amendment that has been used successfully as an alternative nutrient source to inorganic, commercial fertilizers. Poultry litter also has the potential to improve other aspects of soil quality. However, few field studies have been conducted to ascertain the effects of poultry litter on soil physical properties. The objectives of this study were to evaluate the short-term effects of poultry litter form (i.e., fresh vs. pelletized) and rate on soil bulk density and water content and early-season stand development in three fine-textured soils of the Mississippi River Delta region of eastern Arkansas that are commonly cropped to rice (Oryza sativa L.). Six litter rates were used representing a range of total nitrogen (N) rates. Soil samples were collected from the 0- to 10-cm depth between four and six weeks after litter application and incorporation for bulk density and volumetric water content determination. Leaf area index was measured as an indicator of early-season stand development. Litter form did not affect soil bulk density, water content, or leaf area index in two silt loams, and a silty-clay soil. In contrast, soil bulk density decreased significantly (p < 0.01) as litter rate increased and leaf area index decreased as bulk density increased in one silt-loam soil, but was unaffected by litter rate in the other silt-loam and silty-clay soil. Litter rate generally did not affect soil volumetric water content, but results indicate that the effects of litter rate may be manifested more at relatively low soil water contents. The results of this study demonstrate that poultry litter has positive short-term effects on physical properties of fine-textured soils. These results are agronomically significant for many crops in terms of the potential for creating a less compacted seedbed for seedling emergence, improved stand development, and ultimately increased crop yields.

Reducing Phosphorus Runoff and Leaching from Poultry Litter with Alum: Twenty-Year Small Plot and Paired-Watershed Studies.

Treating poultry litter with alum has been shown to lower ammonia (NH) emissions and phosphorus (P) runoff losses. Two long-term studies were conducted to assess the effects of alum-treated poultry litter on P availability, leaching, and runoff under pasture conditions. From 1995 to 2015, litter was applied annually in a paired watershed study comparing alum-treated and untreated litter and in a small plot study comparing 13 treatments (an unfertilized control, four rates of alum-treated litter, four rates of untreated litter, and four rates of NHNO). In the paired watershed study, total P loads in runoff were 231% higher from pasture receiving untreated litter (1.96 kg P ha) than from that receiving alum-treated litter (0.85 kg P ha). In both studies, alum-treated litter resulted in significantly higher Mehlich III P (M3-P) and lower water-extractable P at the soil surface, reflecting greater retention of applied P and lesser availability of that P to runoff or leaching. In soils fertilized with alum-treated litter, M3-P was much higher when analyzed by inductively coupled argon plasma emission spectrometry than by colorimetry, possibly due to the formation of aluminum phytate. Indeed, alum-treated poultry litter leached less P over the 20-yr study: M3-P at 10 to 50 cm was 266% greater in plots fertilized with untreated litter (331 kg M3-P ha) than with alum-treated litter (124 kg M3-P ha). This research provides compelling evidence that treating poultry litter with alum provides short-term and long-term benefits to P conservation and water quality.

Tall Fescue Toxicosis Mitigation Strategies: Comparisons of Cow-Calf Returns in Spring- and Fall-Calving Herds

Tall fescue toxicosis adversely affects calving rate and weight gains reducing returns to cow-calf producers in the south–central United States. This grazing study estimated animal and economic performance implications of endophyte-infected fescue and calving season. Establishing novel endophyte-infected tall fescue on 25% of pasture acres resulted in improved calving rates (87% vs. 70%), weaning weights (532 lbs vs. 513 lbs), and partial returns per acre (