MV Treatments Research Articles

Suitability of Athena Monolithic Active Pixel Sensor for upstream monitoring of 6 MV, 6 FFF and 10 MV treatments

We are developing a thin, real-time radiotherapy verification sensor based on the Athena, a large-scale MAPS. The goal in radiotherapy verification is to measure the multileaf collimator positions and beam intensity to ensure the accuracy and safety of treatment delivery. Previously, results on this have been published. In this paper, we present results that clearly demonstrate that the Athena does not saturate, even at the highest beam intensities in a 6 FFF 10 × 10 cm2 field and thus is suitable for clinical deployment.

Methodology of a Large Multicenter Observational Study of Patients with COVID-19 in Spanish Intensive Care Units

IntroductionThe COVID-19 pandemic created tremendous challenges for health-care systems. Intensive care units (ICU) were hit with a large volume of patients requiring ICU admission, mechanical ventilation, and other organ support with very high mortality. The Centro de Investigación Biomédica en Red-Enfermedades Respiratorias (CIBERES), a network of Spanish researchers to investigate in respiratory disease, commissioned the current proposal in response to the Instituto de Salud Carlos III (ISCIII) call. MethodsCIBERESUCICOVID is a multicenter, observational, prospective/retrospective cohort study of patients with COVID-19 admitted to Spanish ICUs. Several work packages were created, including study population and ICU data collection, follow-up, biomarkers and miRNAs, data management and quality. ResultsThis study included 6102 consecutive patients admitted to 55 ICUs homogeneously distributed throughout Spain and the collection of blood samples from more than 1000 patients. We enrolled a large population of COVID-19 ICU-admitted patients including baseline characteristics, ICU and MV data, treatments complications, and outcomes. The in-hospital mortality was 31%, and 76% of patients required invasive mechanical ventilation. A 3-6 month and 1 year follow-up was performed. Few deaths after 1 year discharge were registered. Low anti-SARS-CoV-2 S antibody levels predict mortality in critical COVID-19. These antibodies contribute to prevent systemic dissemination of SARS-CoV-2. The severity of COVID-19 impacts the circulating miRNA profile. Plasma miRNA profiling emerges as a useful tool for risk-based patient stratification in critically ill COVID-19 patients. ConclusionsWe present the methodology used in a large multicenter study sponsored by ISCIII to determine the short- and long-term outcomes in patients with COVID-19 admitted to more than 50 Spanish ICUs.

NMR-based metabolomic investigation of antimicrobial mechanism of electrolysed water combined with moderate heat treatment against Listeria monocytogenes on salmon

Heat and acidic electrolysed water (AEW) are considered effective for inactivation of microorganisms. While a previous study elucidated their bactericidal mechanism on Listeria innocua through metabolomics in vitro, the fundamental mechanism for inaction of L. monocytogenes using this method in food system is poorly understood. This work determined the survival population and injury of three L. monocytogenes strains (SSA81, LM44, and LM3) inoculated on salmon under heat (60 °C) and AEW (100 mg/L available free chlorine, pH 2.42, oxidation reduction potential 1182 mV) treatments, when applied alone or in combination. The bactericidal mechanism was explored by utilising nuclear magnetic resonance (NMR) and multivariate data analysis. Our results indicated that the individual heat and AEW treatment led to 0.4 and 1.2 log CFU/g reductions of L. monocytogenes, respectively. The combined treatment of heat and AEW resulted in notable reductions which were 2.1–2.2 log CFU/g for L. monocytogenes. More than 25%, 35%, and 55% injury of L. monocytogenes were observed under heat, AEW, and the combined treatment, respectively. Overall, 43 metabolites were characterised in three strains. Short time heat might activate protective system of the cells by accumulating amino acids and organic acids. AEW resulted in the reductions of metabolites due to oxidative and acid stress. In the combined treatment, AEW played the main role and its bactericidal ability was strengthened by heat. Significant decreases of Val, Leu, Tyr, and Trp were detected in all strains under the synergic stress of heat and AEW (P < 0.05). There were 15, 7, and 6 pathways, mainly included amino acid, energy, and carbohydrate metabolisms, changed significantly under the combined treatment for SSA81, LM44, and LM3, respectively. The strain LM3 presented the strongest resistance to oxidative stress by the enhancement of Glu decarboxylase system, whereas this compensatory pathway was diminished in SSA81 and LM44. These findings suggest that the bactericidal mechanism can be well explained by disturbed pathways.

Grid therapy vs. conventional radiotherapy – 18 MV treatments: Photoneutron contamination along the maze of a linac bunker

The present Monte Carlo study was devoted to the comparison of photoneutron contamination (per 1 Gy photon dose), along the maze of a radiotherapy bunker, between two 18-MV modalities: grid therapy (with grids made of brass, cerrobend, and lead) and conventional radiotherapy. It was turned out that both in grid therapy and in conventional radiotherapy, with increasing distance from the entrance of treatment hall (toward the maze entrance), fluence and ambient dose equivalent of neutrons decrease. Evidence also shows that in grid therapy, independent of materials used in the grid construction, photoneutron contamination along the maze is 45±6 % larger than conventional radiotherapy.

Overexpression of native Musa-miR397 enhances plant biomass without compromising abiotic stress tolerance in banana

Plant micro RNAs (miRNAs) control growth, development and stress tolerance but are comparatively unexplored in banana, whose cultivation is threatened by abiotic stress and nutrient deficiencies. In this study, a native Musa-miR397 precursor harboring 11 copper-responsive GTAC motifs in its promoter element was identified from banana genome. Musa-miR397 was significantly upregulated (8–10) fold in banana roots and leaves under copper deficiency, correlating with expression of root copper deficiency marker genes such as Musa-COPT and Musa-FRO2. Correspondingly, target laccases were significantly downregulated (>−2 fold), indicating miRNA-mediated silencing for Cu salvaging. No significant expression changes in the miR397-laccase module were observed under iron stress. Musa-miR397 was also significantly upregulated (>2 fold) under ABA, MV and heat treatments but downregulated under NaCl stress, indicating universal stress-responsiveness. Further, Musa-miR397 overexpression in banana significantly increased plant growth by 2–3 fold compared with wild-type but did not compromise tolerance towards Cu deficiency and NaCl stress. RNA-seq of transgenic and wild type plants revealed modulation in expression of 71 genes related to diverse aspects of growth and development, collectively promoting enhanced biomass. Summing up, our results not only portray Musa-miR397 as a candidate for enhancing plant biomass but also highlight it at the crossroads of growth-defense trade-offs.

Whole-body dose equivalent including neutrons is similar for 6 MV and 15 MV IMRT, VMAT, and 3D conformal radiotherapy.

PurposeThis study investigates the difference in whole‐body dose equivalent between 6 and 15 MV image‐guided radiotherapy (IGRT) for the treatment of a rhabdomyosarcoma in the prostate.MethodsA previously developed model for stray radiation of the primary beam was improved and used to calculate the photon dose and photon energy in the out‐of‐field region for a radiotherapy patient. The dose calculated by the treatment planning system was fused with the model‐calculated out‐of‐field dose, resulting in a whole‐body photon dose distribution. The peripheral neutron dose equivalent was calculated using an analytical model from the literature. A daily cone beam CT dose was added to the neutron and photon dose equivalents. The calculated 3D dose distributions were compared to independent measurements conducted with thermoluminescence dosimeters and an anthropomorphic phantom. The dose contributions from the IGRT treatments of three different techniques applied with two nominal X‐ray energies were compared using dose equivalent volume histograms (DEVHs).ResultsThe calculated and measured out‐of‐field whole‐body dose equivalents for the IGRT treatments agreed within (9 ± 10) % (mean and type A SD). The neutron dose equivalent was a minor contribution to the total out‐of‐field dose up to 50 cm from the isocenter. Further from the isocenter, head leakage was dominating inside the patient body, whereas the neutron dose equivalent contribution was important close to the surface. There were small differences between the whole‐body DEVHs of the 6 and 15 MV treatments applied with the same technique, although the single scatter contributions showed large differences. Independent of the beam energy, the out‐of‐field dose of the volumetric‐modulated arc therapy (VMAT) treatment was significantly lower than the dynamic intensity‐modulated radiation therapy (IMRT) treatment.ConclusionThe calculated whole‐body dose helped to understand the importance of the dose contributions in different areas of the patient. Regarding radiation protection of the patient for IGRT treatments, the choice of beam energy is not important, whereas the treatment technique has a large influence on the out‐of‐field dose. If the patient is treated with intensity‐modulated beams, VMAT should be used instead of dynamic IMRT in terms of radiation protection of the patient. In general, the developed models for photon and neutron dose equivalent calculation can be used for any patient geometry, tumor location, and linear accelerator.

Effect of pre-treatment processes on physicochemical aspects of vacuum-fried banana chips

The objective of this study was to investigate the influence of various pre-treatments on the physicochemical and sensory characteristics of vacuum-fried (VF) banana chips (120°C, 41.3 kPa) and consequently compare them to atmospheric-fried (AF) banana chips (170°C). Pre-treatments comprised of osmotic dehydration with sucrose solution (ODSu), osmotic dehydration with salt solution (ODSa), microwave heating (MV), and hot air-drying (HD). The moisture content, oil content, L*, b*, and index of firmness of all pre-treated banana chips were significantly decreased, whereas values for a*, volume shrinkage, and hardness were increased when compared to those without pre-treatment. The ODSu sample provided the lowest oil content. The highest volume shrinkage was obtained from HD and MV treatments. Sensory evaluation revealed that VF chips exhibited the highest scores in color, crispiness, and oiliness when compared to AF chips. ODSu and ODSa samples positively affected the color, crispiness, and taste properties. Practical applications Although there have been several techniques aimed at reducing the oil content of chips, the particular method investigated in the current work, pre-treatment before VF, has not so far been investigated. The application of pre-treatment processes prior vacuum or atmospheric frying in this study could reduce oil absorption and increase the score in sensory properties of fried banana chips. This process could be applied in other fried products in commercial scale.

Effects of Exogenous Melatonin on Methyl Viologen-Mediated Oxidative Stress in Apple Leaf.

Oxidative stress is a major source of damage of plants exposed to adverse environments. We examined the effect of exogenous melatonin (MT) in limiting of oxidative stress caused by methyl viologen (MV; paraquatin) in apple leaves (Malus domestica Borkh.). When detached leaves were pre-treated with melatonin, their level of stress tolerance increased. Under MV treatment, melatonin effectively alleviated the decrease in chlorophyll concentrations and maximum potential Photosystem II efficiency while also mitigating membrane damage and lipid peroxidation when compared with control leaves that were sprayed only with water prior to the stress experiment. The melatonin-treated leaves also showed higher activities and transcripts of antioxidant enzymes superoxide dismutase, peroxidase, and catalase. In addition, the expression of genes for those enzymes was upregulated. Melatonin-synthesis genes MdTDC1, MdT5H4, MdAANAT2, and MdASMT1 were also upregulated under oxidative stress in leaves but that expression was suppressed in response to 1 mM melatonin pretreatment during the MV treatments. Therefore, we conclude that exogenous melatonin mitigates the detrimental effects of oxidative stress, perhaps by slowing the decline in chlorophyll concentrations, moderating membrane damage and lipid peroxidation, increasing the activities of antioxidant enzymes, and changing the expression of genes for melatonin synthesis.

Effects of different winter cover crops on soil organic carbon in a double cropping rice paddy field.

In a double cropping rice field experiment, effects of five winter cover crops on the total organic carbon (TOC), active organic carbon (AOC), carbon pool management index (CPMI) and organic carbon storage were studied in three soil layers (0-5, 5-10 and 10-20 cm).Winter cover crops of ryegrass (Ry), Chinese milk vetch (Mv), potato (Po), and rape (Ra) between two rice crops were compared with fallow as control (CK). The results showed that the TOC and AOC contents under Ry, Mv, Po and Ra treatments were higher than those of CK in all three la-yers. Meanwhile, the TOC and AOC contents in Po treatment were higher than those of other treatments. Compared with CK, the AOC, activity index (AI), carbon pool index (CPI) and CPMI in the soil were improved through the recycling of winter cover crops straw. The AOC, AI, CPI and CPMI in the studied layers increased in order of Po>Mv>Ry>Ra>CK. The results indicated that the recycling of winter cover crops straw promoted the storage of SOC in the 0-20 cm soil profile as compared with CK. The strongest effect of the winter cover crops on the SOC storage occurred in Mv treatment, followed by Mv and Po treatments, and the SOC storage increased with the increasing soil depth.

FEM design and simulation of a short, 10 MV, S-band Linac with Monte Carlo dose simulations.

Current commercial 10 MV Linac waveguides are 1.5 m. The authors' current 6 MV linear accelerator-magnetic resonance imager (Linac-MR) system fits in typical radiotherapy vaults. To allow 10 MV treatments with the Linac-MR and still fit within typical vaults, the authors design a 10 MV Linac with an accelerator waveguide of the same length (27.5 cm) as current 6 MV Linacs. The first design stage is to design a cavity such that a specific experimental measurement for breakdown is applicable to the cavity. This is accomplished through the use of finite element method (FEM) simulations to match published shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength from an electric breakdown study. A full waveguide is then designed and tuned in FEM simulations based on this cavity design. Electron trajectories are computed through the resulting radio frequency fields, and the waveguide geometry is modified by shifting the first coupling cavity in order to optimize the electron beam properties until the energy spread and mean energy closely match values published for an emulated 10 MV Linac. Finally, Monte Carlo dose simulations are used to compare the resulting photon beam depth dose profile and penumbra with that produced by the emulated 10 MV Linac. The shunt impedance, Q factor, and ratio of peak to mean-axial electric field strength are all matched to within 0.1%. A first coupling cavity shift of 1.45 mm produces an energy spectrum width of 0.347 MeV, very close to the published value for the emulated 10 MV of 0.315 MeV, and a mean energy of 10.53 MeV, nearly identical to the published 10.5 MeV for the emulated 10 MV Linac. The depth dose profile produced by their new Linac is within 1% of that produced by the emulated 10 MV spectrum for all depths greater than 1.5 cm. The penumbra produced is 11% narrower, as measured from 80% to 20% of the central axis dose. The authors have successfully designed and simulated an S-band waveguide of length of 27.5 cm capable of producing a 10 MV photon beam. This waveguide operates well within the breakdown threshold determined for the cavity geometry used. The designed Linac produces depth dose profiles similar to those of the emulated 10 MV Linac (waveguide-length of 1.5 m) but yields a narrower penumbra.

The soybean GmDi19-5 interacts with GmLEA3.1 and increases sensitivity of transgenic plants to abiotic stresses.

Drought-induced (Di19) proteins played important roles in plant growth, development, and abiotic stress responses. In the present study, a total of seven Di19 genes were identified in soybean. Each soybean Di19 gene showed specific responses to salt, drought, oxidative, and ABA stresses based on expression profiles. With a relatively higher transcript level among Di19 members under four stress treatments, GmDi19-5 was selected for detailed analysis. Inhibitor assays revealed that ABA inhibitor (Fluridone) or H2O2 inhibitor (DMTU) was involved in the drought- or salt-induced transcription of GmDi19-5. The GUS activity driven by the GmDi19-5 promoter was induced by salt, PEG, ABA, and MV treatments and tended to be accumulated in the vascular bundles and young leaves. A subcellular localization assay showed that GmDi19-5 protein localized in the nucleus. Further investigation showed that GmDi19-5 protein was involved in the interaction with GmLEA3.1. Overexpression of GmDi19-5 increased sensitivity of transgenic Arabidopsis plants to salt, drought, oxidative, and ABA stresses and regulated expression of several ABA/stress-associated genes. This present investigation showed that GmDi19-5 functioned as a negative factor under abiotic stresses and was involved in ABA and SOS signaling pathway by altering transcription of stress-associated genes.

Hydrogen peroxide and nitric oxide promote reproductive growth in Litchi chinensis

Vegetative growth and reproductive growth strongly competes with each other during panicle development in litchi (Litchi chinensis Sonn.). We herein investigated the roles of hydrogen peroxide and nitric oxide in the competition between growth of rudimentary leaves and panicle development. The results show that the chilling-induced flowering increased H2O2 and NO contents in the mixed buds. Treatments with sodium nitroprusside (SNP), the NO donor, and methyl viologen dichloride hydrate (MV), the superoxide generator, increased NO and H2O2 contents in the mixed buds. MV and SNP treatments promoted abscission of rudimentary leaves and encouraged panicle development before or at the stage of panicle emergence. The nitric oxide synthase inhibitor N &omega; -nitro-L-arginine methyl ester (L-NAME) and the H2O2 trapper dimethylthiourea (DMTU) inhibited a chilling-induced flowering. SNP promoted the expression of litchi LEAFY homolog (LcLFY). These promotive effects were suppressed by the NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl3-oxide (PTIO) and the H2O2 trapper, DMTU. The results suggest that H2O2 and NO promote reproductive growth by inhibiting the growth of rudimentary leaves as well as by promoting the expression of the flower related gene, LcLFY.

Hydrogen peroxide and nitric oxide promote reproductive growth in Litchi chinensis

Vegetative growth and reproductive growth strongly competes with each other during panicle development in litchi (Litchi chinensis Sonn.). We herein investigated the roles of hydrogen peroxide and nitric oxide in the competition between growth of rudimentary leaves and panicle development. The results show that the chilling-induced flowering increased H2O2 and NO contents in the mixed buds. Treatments with sodium nitroprusside (SNP), the NO donor, and methyl viologen dichloride hydrate (MV), the superoxide generator, increased NO and H2O2 contents in the mixed buds. MV and SNP treatments promoted abscission of rudimentary leaves and encouraged panicle development before or at the stage of panicle emergence. The nitric oxide synthase inhibitor N &omega; -nitro-L-arginine methyl ester (L-NAME) and the H2O2 trapper dimethylthiourea (DMTU) inhibited a chilling-induced flowering. SNP promoted the expression of litchi LEAFY homolog (LcLFY). These promotive effects were suppressed by the NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl3-oxide (PTIO) and the H2O2 trapper, DMTU. The results suggest that H2O2 and NO promote reproductive growth by inhibiting the growth of rudimentary leaves as well as by promoting the expression of the flower related gene, LcLFY.

AtERF71/HRE2 transcription factor mediates osmotic stress response as well as hypoxia response in Arabidopsis

Various transcription factors are involved in the response to environmental stresses in plants. In this study, we characterized AtERF71/HRE2, a member of the Arabidopsis AP2/ERF family, as an important regulator of the osmotic and hypoxic stress responses in plants. Transcript level of AtERF71/HRE2 was highly increased by anoxia, NaCl, mannitol, ABA, and MV treatments. aterf71/hre2 loss-of-function mutants displayed higher sensitivity to osmotic stress such as high salt and mannitol, accumulating higher levels of ROS under high salt treatment. In contrast, AtERF71/HRE2-overexpressing transgenic plants showed tolerance to salt and mannitol as well as flooding and MV stresses, exhibiting lower levels of ROS under high salt treatment. AtERF71/HRE2 protein was localized in the nucleus, and the C-terminal region of AtERF71/HRE2 was required for transcription activation activity. Taken together, our results suggest that AtERF71/HRE2 might function as a transcription factor involved in the response to osmotic stress as well as hypoxia.

Calculated organ doses from selected prostate treatment plans using Monte Carlo simulations and an anatomically realistic computational phantom

There is growing concern about radiation-induced second cancers associated with radiation treatments. Particular attention has been focused on the risk to patients treated with intensity-modulated radiation therapy (IMRT) due primarily to increased monitor units. To address this concern we have combined a detailed medical linear accelerator model of the Varian Clinac 2100 C with anatomically realistic computational phantoms to calculate organ doses from selected treatment plans. This paper describes the application to calculate organ-averaged equivalent doses using a computational phantom for three different treatments of prostate cancer: a 4-field box treatment, the same box treatment plus a 6-field 3D-CRT boost treatment and a 7-field IMRT treatment. The equivalent doses per MU to those organs that have shown a predilection for second cancers were compared between the different treatment techniques. In addition, the dependence of photon and neutron equivalent doses on gantry angle and energy was investigated. The results indicate that the box treatment plus 6-field boost delivered the highest intermediate- and low-level photon doses per treatment MU to the patient primarily due to the elevated patient scatter contribution as a result of an increase in integral dose delivered by this treatment. In most organs the contribution of neutron dose to the total equivalent dose for the 3D-CRT treatments was less than the contribution of photon dose, except for the lung, esophagus, thyroid and brain. The total equivalent dose per MU to each organ was calculated by summing the photon and neutron dose contributions. For all organs non-adjacent to the primary beam, the equivalent doses per MU from the IMRT treatment were less than the doses from the 3D-CRT treatments. This is due to the increase in the integral dose and the added neutron dose to these organs from the 18 MV treatments. However, depending on the application technique and optimization used, the required MU values for IMRT treatments can be two to three times greater than 3D CRT. Therefore, the total equivalent dose in most organs would be higher from the IMRT treatment compared to the box treatment and comparable to the organ doses from the box treatment plus the 6-field boost. This is the first time when organ dose data for an adult male patient of the ICRP reference anatomy have been calculated and documented. The tools presented in this paper can be used to estimate the second cancer risk to patients undergoing radiation treatment.

Comments on shielding for dual energy accelerators

Determination of shielding requirements for medical linear accelerators has been greatly facilitated by the publication of the National Council on Radiation Protection and Measurements (NCRP) latest guidelines on this subject in NCRP Report No. 151. In the present report the authors review their own recent experience with patient treatments on conventional dual energy linear accelerators to examine the various input parameters needed to follow the NCRP guidelines. Some discussion is included of workloads, occupancy, use factors, and field size, with the effects of intensity modulated radiotherapy (IMRT) treatments included. Studies of collimator settings showed average values of 13.1 x 16.2 cm2 for 6 MV and 14.1 x 16.8 cm2 for 18 MV conventional ports, and corresponding average unblocked areas of 228 and 254 cm2, respectively. With an average of 77% of the field area unblocked, this gives a mean irradiated area of 196 cm2 for the 18 MV beam, which dominates shielding considerations for most dual energy machines. Assuming conservatively small room dimensions, a gantry bin angle of 18 degrees was found to represent a reasonable unit for tabulation of use factors. For conventional 18 MV treatments it was found that the usual treatment angles of 0, 90, 180, and 270 degrees were still favored, and use factors of 0.25 represent reasonable estimates for these beams. As expected, the IMRT fields (all at 6 MV) showed a high degree of gantry angle randomization, with no bin having a use factor in excess of 0.10. It is concluded that unless a significant number of patients are treated with high energy IMRT, the traditional use factors of 0.25 are appropriate for the dominant high energy beam.

Does 4 MV perform better compared to 6 MV in the presence of air cavities in the head and neck region?

Background and purpose The underdose near air cavities in the head and neck region at photon energies of 4 MV and 6 MV was studied in search for clinical advantages of the 4 MV over 6 MV treatments. Materials and methods The on-axis and off-axis dose distributions were measured with a parallel-plate ionization chamber and films in polystyrene phantoms containing an air cavity of appropriate size based on the results of computed tomography scans. Results Although most results are similar for both energies, the 4 MV photon beams give a somewhat smaller underdose effect and a faster re-build up than the 6 MV. For both energies a significant underdose effect was observed at the edge of the field in the larynx phantom. This proved to be true for small and large fields, for smaller and larger cavities, for one-beam as well as parallel-opposed beams. Conclusion For most clinically relevant situations there is no remarkable benefit in the use of either of the two energies.

Airspace Effects on the Yield and Quality of Ewe Milk

Three groups of 12 midlactating Comisana ewes were housed in separate rooms of the same building and assigned to treatments of low (LV, 4.1m3), medium (MV, 5.6m3), or high (HV, 7.3m3) airspace/animal. The concentrations of airborne microorganisms in the experimental rooms were measured twice weekly at 0930 and 1630. Ewe milk yield was recorded daily. Individual milk samples were analyzed weekly for milk composition, coagulating properties, somatic cell concentration (SCC), and polymorphonuclear neutrophil leukocyte count (PMNLC), and fortnightly for bacteriological characteristics; samples with more than 106 somatic cells/ml were cultured for mastitis-related pathogens. The LV and MV treatments resulted in higher relative humidity and air concentrations of staphylococci than the HV treatment. Greater amounts of air mesophilic bacteria were also found in the LV than in the HV room. Ewes in the HV group gave greater yields of milk than those in the LV and MV groups. LV milk also had a lower casein content than HV milk. Significant interactions of treatment x time were found for milk protein and fat content as well as for clotting time and clot firmness, with LV milk having the poorest composition and deteriorated renneting ability during the last 3 wk of the trial. The HV ewes had lower SCC and PMNLC and psychrotroph counts in their milk than LV and MV ewes and smaller amounts of mesophilic bacteria and fecal coliforms than LV animals. Subclinical mastitis occurred in two ewes of the LV and one of the MV groups, while no cases were recorded in the HV group. Results suggest that airspace is a critical factor in dairy sheep housing and indicate that a volume allocation of less than 7m3/animal may adversely affect the performance and health of the lactating ewe.

Influence of soil redox potential on nitrogen uptake and growth of wetland Oak seedlings

A study was conducted to determine ammonium nitrogen uptake by cherrybark oak and overcup oak as affected by soil redox conditions. Seedlings of the two species were grown in laboratory microcosms for 60 days in soil suspensions incubated at three separate Eh levels (+560, +340, and + 175 mV). In both species, uptake of added 15N labeled nitrogen (N) (NH4Cl) and photosynthesis activity decreased with decreasing soil redox potentials. Net photosynthesis in cherrybark oak decreased by 72.9 and 100% in response to the +340 and + 175 mV treatments as compared to control plants, respectively. Similarly, net photosynthetic rates were reduced by 53.7 and 65.8% in overcup oak under + 340 and + 175 mV treatments, respectively. A significant correlation between net photosynthesis and leaf 15N content was found in cherrybark oak (r=0.866, P=0.01) but not in overcup oak (r=0.648, p>0.05). However, in overcup oak, the correlation between net photosynthesis and total leaf N content was significant (r=0.911, P=0.01). Maximum 15N uptake was measured at the highest soil redox level (+560 mV). Uptake of 15N in cherrybark oak decreased from a maximum of 1.83 mg under aerated (+560 mV) treatment to 0.11 mg under reduced conditions (+175 mV). Similarly, 15N uptake in overcup oak decreased from 2.37 mg under the + 560 mV treatment to 0.28 mg under + 175 mV treatment. Greater uptake of soil and fertilizer nitrogen was measured under the soil redox conditions in which adequate plant growth was recorded. Moderately reducing soil redox conditions (+340 and + 175 mV) adversely affected both plant nitrogen uptake and net photosynthetic activities of the two species.

Carbon assimilation and biomass partitioning in Avicennia germinans and Rhizophora mangle seedlings in response to soil redox conditions

Under controlled environmental conditions, seedlings of black mangrove ( Avicennia germinans (L.) Stearn) and red mangrove ( Rhizophora mangle L.) obtained from the Florida coastal zone were subjected to a range of soil redox conditions (Eh) plus 20 p.p.t. salinity to assess the effects of reducing soil Eh condition on selected plant functions. The hypotheses tested were: (1) the two species differ in their tolerance of reduced soil Eh conditions and (2) such differences are reflected in gas exchange and carbon allocation patterns. Plant gas exchange, growth and biomass partitioning were studied under +400, +210, 0 and −180 mV Eh treatments. Net photosynthesis ( P n) was reduced significantly in the lowest Eh treatment (−180 mV) in both species averaging 31.1 and 39.7% as compared to control (+400 mV) treatment in A. germinans and R. mangle, respectively. In addition, P n was significantly ( P < 0.05) greater in R. mangle than A. germinans under most treatments, averaging 36.2% greater in R. mangle than A. germinans across treatments. Total dry weights (shoot and root) in A. germinans were reduced significantly to 61.6, 37, and 48.3% of control in +210, 0 and −180 mV treatments, respectively. In contrast, total dry weight in R. mangle was not reduced significantly (except in the +210 mV treatment) averaging 76.2, 102, and 83.5% of the control in +210, 0 and −180 mV treatments, respectively. Overall, seedlings of A. germinans showed a greater sensitivity to low Eh conditions than R. mangle seedlings and the level of sensitivity was closely related to the intensity of soil reduction. The present study demonstrated that seedlings of the two species differ in their responses to low soil Eh conditions and such differences may be partially explained by the differences in net photosynthetic rates and by the patterns of biomass partitioning, i.e. under low soil Eh conditions, there is a greater photosynthetic rate and a shift in biomass allocation to the roots in R. mangle compared to A. germinans.