Leaf gas exchange and growth of flood-tolerant and flood-sensitive tree species under low soil redox conditions

Seedlings of Taxodium distichum L., Quercus lyrata Walt. and Q. falcata var. pagodaefolia Ell. were grown for 22 days in a rhizotron system providing two soil redox potential regimes, +170 mV (low Eh) and +560 mV (high Eh). Leaf chlorophyll concentration and gas exchange, root alcohol dehydrogenase (ADH) activity, root and leaf ethylene production, and growth and biomass partitioning were measured. In response to the low Eh soil treatment, stomatal conductance was reduced in Q. falcata and Q. lyrata but not in T. distichum, whereas net photosynthesis was reduced significantly in all species; however, net photosynthesis in T. distichum began to recover within 2 weeks of treatment initiation. Within each treatment, mean stomatal conductance and net photosynthesis were significantly greater in T. distichum than in the oak species. Leaf chlorophyll concentration was not affected by the soil treatments. All species showed significant reductions in root and leaf dry weights in response to the low Eh soil condition. The low Eh soil treatment resulted in increased root ADH activity and ethylene production in T. distichum, but had no effect on root ADH activity and ethylene production in the oak species.     

Potential for Enhancement of Biodegradation of Crude Oil in Louisiana Salt Marshes using Nutrient Amendments

Salt marsh ecosystems in Louisiana are at high risk of an oil contamination event while remediation of these systems is mainly limited to intrinsic bioremediation due to the physical sensitivity of salt marshes. This study investigated both the intrinsic and nutrient enhanced rates of crude oil degradation both in microcosm and core studies. In addition, limiting elements, loading rates and optimum nitrogen forms (NH ₄ ⁺ or NO ₃ ^- ) were determined. Salt marshes have relatively low intrinsic degradation rates (0–3.9% day^-1) of the alkane component (C11-C44) but high rates (8–16% day^-1) of degradation of the polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, C1, and C2-Naphthalene and Phenanthrene, C1, and C2-Phenanthrene). Additions of nitrogen statistically enhanced degradation of many alkanes and total PAHs while naturally present phosphorous was found to be sufficient. Nitrogen was found to be most effective if applied as NH ₄ ⁺ in the range of 100-500-N mg kg^-1 of soil producing a pore water range of 100-670-N mg L^-1. Core studies indicate that similar trends are observed when applying fertilizers to intact portions of salt marsh.     

Chromosomal localization of mouse satellite DNA

Hybridization of radioactive nucleic acids with the DNA of cytological preparations shows that the sequences of mouse satellite DNA are located in the centromeric heterochromatin of the mouse chromosomes. Other types of heterochromatin in the cytological preparations do not contain satellite DNA.     

Effects of vitamin C supplementation on plasma ascorbic acid and oxalate concentrations and meat quality in swine

Two experiments were conducted to determine the effects of vitamin C supplementation 48 h before slaughter on plasma ascorbic acid and oxalate concentrations and its effect on pork quality. In Exp. 1, 16 pigs (87.8+/-2.13 kg BW) were blocked by sex and weight and assigned randomly within block to one of three vitamin C treatments: 1) control; 2) 1,000 mg/L; or 3) 2,000 mg/L supplemented in the drinking water for a 48-h period. This was then followed by an additional 48-h period without supplemental vitamin C. Vitamin C increased plasma ascorbic acid concentrations (11.6, 19.5, and 23.4 microg/mL for 0, 1,000, and 2,000 mg/L of vitamin C; P < 0.05) within 6 h of supplementation. Plasma ascorbic acid concentrations from treated pigs decreased and did not differ from those of control pigs (13.7, 18.2, and 18.6 microg/mL for 0, 1,000, and 2,000 mg/L of vitamin C; P = 0.30) within 2 h of ending supplementation. No differences in plasma ascorbic acid concentrations were found between the two levels of supplementation. Vitamin C did not affect plasma oxalate or cortisol; however, cortisol tended to increase quadratically (P = 0.077) with vitamin C after 96 h. In Exp. 2, 30 pigs (107.5+/-0.54 kg BW) were blocked by sex and weight and assigned randomly within block to one of three vitamin C treatments: 1) control; 2) 500 mg/L; or 3) 1,000 mg/L supplemented in the drinking water 48 h before slaughter. Pigs were slaughtered 4 to 5 h after vitamin C supplementation ended, and loin samples were collected for meat quality measurements. At the time of slaughter, no differences in plasma ascorbic acid or cortisol were observed, but oxalate tended (P = 0.074) to increase quadratically with increasing vitamin C. Muscle ascorbic acid at slaughter and lactic acid in muscle at 0 and 1.5 h after slaughter were not different; however, lactic acid increased (P = 0.048) quadratically at 24 h after slaughter. Vitamin C did not affect initial or ultimate pH. Initial fluid loss (P = 0.041), and fluid loss on d 4 (P = 0.014) and 8 (P = 0.076) of simulated retail display; L* on d 0 (P = 0.038), 4 (P = 0.010), and 8 (P = 0.051); a* on d 0 (P = 0.021); and b* on d 0 (P = 0.006), 4 (P = 0.035), and 8 (P = 0.017) were negatively affected in a quadratic manner when vitamin C was supplemented. Vitamin C tended (P = 0.086) to increase oxidation in chops on d 0, but not d 4 or 8. Results indicate that on-farm supplementation of vitamin C was generally not effective in improving pork quality, which may be related to timing relative to slaughter.     

Nutrient Enhanced Biodegradation of Crude Oil in Tropical Salt Marshes

Tropical salt marshes in Louisiana are at risks ofaccidental oil spills and remediation of these ecosystemsis mainly limited to natural biodegradation due tophysical sensitivity of the ecosystems. This studyinvestigated both intrinsic and nutrient enhanced ratesof crude oil degradation in core studies. In addition,loading rates of nitrogen and optimal porewater nitrogenconcentrations were determined. Nitrogen additionsincreased biodegradation rates of some alkanes andpolycyclic aromatic hydrocarbons (PAHs). Addition ofNH₄ ⁺-N increased zero-order mineralizationconstants of labeled hexadecane and phenanthrene up to15.4–19.2% (Fourchon marsh) and 56.2% (Ugly Shack Bayoumarsh) and rates of total carbon dioxide production up to14.0–33.1% (Fourchon marsh) and 3.0% (Ugly Shack Bayoumarsh), respectively. Efficient biodegradation of crudeoil was achieved when NH₄ ⁺ was applied at theloading rate of 28.3–56.6 g N m^-2 producing porewaterconcentration at the level of 80–450 mg NH₄ ⁺-N L^-1. No significant lag time was observed indicating thatnitrogen application directly stimulates biodegradationof crude oil in tropical salt marshes in Louisiana.     

Bioavailability of Reversibly Sorbed and Desorption-Resistant 1,3-Dichlorobenzene from a Louisiana Superfund Site Soil

Microcosm batch studies were conducted to study the biodegradation of 1,3-dichlorobenzene (1,3-DCB) from the aqueous (soil free) and soil phases. For soil phase experiments, a freshly contaminated soil and a soil containing only the desorption-resistant or irreversibly bound or non-labile fraction of the contaminant were used. These experiments were designed to simulate biodegradation at Superfund site assuming sorption/desorption equilibrium was reached. The presence of the soil reduced the rates of biodegradation significantly. Nearly 100% of the total 1,3-DCB in the aqueous phase was biodegraded by enriched bacterial cultures within 7 days compared to about 55% over a 6-week incubation period from the freshly contaminated soil. The biodegradation in the soils containing only the desorption-resistant fraction of the contaminant was considerably lower (about 30%). It is believed that for freshly contaminated soil, 1,3-DCB readily desorbed into the aqueous phase and was available for microbial consumption whereas for soils containing mostly the desorption-resistant fraction of 1,3-DCB, the contaminant availability was limited by the mass transfer into the aqueous phase. Our earlier studies concluded that about 20–30% of the sorbed contaminant is tightly bound (even larger for weathered or aged soils) and is not easily extractable. This fraction is typically present in micropores or chemically bound to soil humic matter and thus is not readily accessible for microbial utilization. The findings presented here for 1,3-DCB are in agreement with those reported for other chemicals in the literature and could have implications to the current remedy, the monitored natural attenuation at the Petro Processors Inc. Superfund site in Louisiana.     

Effect of sediment pH and oxidation-reduction potential on PCB mineralization

Microbial mineralization rates of a ¹⁴C-labelled PCB mixture were determined in PCB-contaminated Capitol Lake, LA, sediment under controlled pH and redox conditions. Mineralization rates were inferred from the activity of ¹⁴CO₂ evolved from the sediment suspensions. Sediment pH and redox potential significantly affected PCB mineralization. Mineralization rates were higher under moderately aerobic conditions (microaerophilic) ( + 250 mV) than under aerobic conditions ( + 500 mV) or anaerobic conditions (0 mV and ?200 mV). PCB mineralization rates in moderately aerobic sediment were 30 to 40 fold higher than those in anaerobic sediment. Sediment conditions in the oxidized surface layer would promote PCB mineralization. Sediment pH and redox potential were shown to be two sediment parameters which can be managed to enhance degradation of PCBs in contaminated sediment.     

Bioremediation of an Experimental Oil Spill in a Coastal Louisiana Salt Marsh

The massive oil release from the Deep Water Horizon disaster has reemphasized the need to remediate oil impacted marshes. Due to the physically fragile nature of salt water marshes, bioremediation is often proposed as an appropriate technology and nutrient amendment is often proposed as a means of accelerating biodegradation of crude oil. However, no information is currently available concerning the efficacy of in situ nutrient amendments in Gulf Coast salt marshes. An experimental crude oil spill (142 l over 100 m²) was conducted to evaluate the efficacy of nitrogen amendment to stimulate bioremediation in a Spartina alterniflora dominated Louisiana salt marsh. A randomized complete block design with replication (n = 10) was utilized to test the hypothesis that additions of fast-release ammonium nitrate (60 g N/m²) and slow-release urea (30 g N/m²) fertilizers could enhance biodegradation of selected crude oil components in the marsh. Crude oil degradation was monitored by analyzing sediment samples for branched and unbranched alkanes over the 180-day study period. The compound/hopane ratio was used to correct for nonbiological losses. No consistent statistically significant effect of fertilizer addition on degradation rates was observed, despite success in increasing the porewater ammonium and NaCl-extractable ammonium over the time frame of the trial. Intrinsic pseudo-first order degradation rates of alkanes in all plots were substantial (0.003–0.008 day⁻¹). Existing, background levels of N did not appear to limit biodegradation rates in Spartina-dominated salt marshes. These results suggest that nutrient amendments will not be successful in stimulation biodegradation of crude oil in these systems.