The effects of temperature on the physiological response to low oxygen in Atlantic sturgeon

Atlantic sturgeon (Acipenser oxyrhynchus), which are bottom dwelling and migratory fish, experience environmental hypoxia in their natural environment. Atlantic sturgeon, acclimated to either 5 or 15°C, were subjected to a 1 h severe (<10 mm Hg) hypoxia challenge in order to document their physiological responses. We measured hematological parameters, including O₂ transport (hemoglobin, hematocrit), ionic (chloride, osmolality), and metabolic (glucose, lactate) variables under normoxic conditions (~160 mm Hg), immediately following a 1 h exposure to hypoxic water, and following a further 2 h of recovery from this challenge in normoxic water. In a second experiment, we assessed the opercular beat frequency before, during, and after hypoxic exposure. Hemoglobin concentrations and hematocrit were significantly different between fish held at 5°C vs. 15°C and also significantly different between normoxia prior to hypoxia and following recovery. Plasma lactate concentrations increased following hypoxia at both temperatures, indicative of an increase in anaerobic metabolism. In contrast, a significant increase in plasma glucose concentrations in response to hypoxia only occurred at 5°C, suggesting different fuel demands under different temperatures. Changes in opercular beat frequency (OBF) were dependent on temperature. At 5°C, OBF increased upon exposure to hypoxia, but returned to pre-exposure levels within 35 min for the remainder of the experiment. During hypoxia at 15°C, OBF increased very briefly, but then rapidly (within 20 min) decreased to levels below control values. Following a return to normoxia, OBF quickly increased to control levels. Overall, these findings suggest that Atlantic sturgeons are relatively tolerant to short-term and severe hypoxic stress, and the strategies for hypoxia tolerance may be temperature dependent.     

<Emphasis Type="Italic">Oryza sativa</Emphasis> straw restricts <Emphasis Type="Italic">Phalaris minor</Emphasis> growth: allelochemicals or soil resource manipulation?

Unharvested stubbles or harvested straw of rice (Oryza sativa L.) gets incorporated into soil and interferes with the seedling growth of crop plants. In this paper, we investigated whether rice straw, either through releasing allelochemicals and/or through manipulating soil properties, influences seedling growth of Phalaris minor Retz., a non-native weed largely restricted to wheat (Triticum aestivum L.) fields. One hundred twenty grams of soil was amended with rice straw (0.5, 1, 2, 4, or 6 g/pot) and its effect on fresh shoot biomass of P. minor was examined. Any modification of rice straw phytotoxicity through the use of washed rice straw, activated charcoal, soil sterilization, or nitrogen fertilization was also studied. We carried out chemical and microbial analysis of soils to examine the role of soil properties in influencing P. minor growth. Incorporation of rice straw into soil suppressed the growth of P. minor through modifying soil properties. A dose-dependent increase in total phenolics was observed in soil amended with rice straw. Activated carbon or washing of rice straw, however, could not ameliorate the phytotoxic effects of rice straw. Our results provide initial evidence that rice straw restricts P. minor growth by manipulating soil chemical and microbiological properties. Authors contributions IJ conceived of and supervised the study, and wrote the paper; SK carried out the work.     

Genetic relationships among resynthesized,semi-resynthesized and natural <Emphasis Type="Italic">Brassica napus</Emphasis> L. genotypes

The allopolyploidization event that created cultivated oilseed rape Brassica napus L, followed by intense breeding, reduced its genetic diversity. Resynthesized (RS) B. napus L. obtained by interspecific hybridization between genotypes of B. rapa L. and B. oleracea L. can be a valuable source for broadening genetic diversity in cultivated oilseed rape. In this study, we determined the extent of DNA polymorphism among natural accessions of oilseed rape, resynthesized B. napus, their parental species and double-low quality semi-RS lines carrying the Rfo gene. Using 10 selected primer combinations, 522 polymorphic AFLP markers were scored in the complete set of 100 Brassica sp. To detect relationships between these genotypes, a cluster analysis was performed using the Jaccard’s distance. Resynthesized allopolyploids clustered directly between their diploid parents. Cultivated accessions of oilseed rape created a compact group away from resynthesized allopolyploids as well as semi-RS lines. The natural oilseed rape group, which consists of 49 cultivars and breeding lines of oilseed rape, is characterized by lower genetic diversity than the group of 33 accessions of resynthesized oilseed rape, and the analysis showed that the double-low quality semi-RS lines represent a specific genetic variation of B. napus. The de novo resynthesized B. napus lines and the semi-RS lines of double-low quality generated from them, provide a significant opportunity for enrichment the gene pool of oilseed rape.     

Responses of microbial biomass and respiration of soil to topography,burning, and nitrogen fertilization in a temperate steppe

Temporal dynamics of microbial biomass and respiration of soil and their responses to topography, burning, N fertilization, and their interactions were determined in a temperate steppe in northern China. Soil microbial indices showed strong temporal variability over the growing season. Soil microbial biomass C (MBC) and N (MBN) were 14.8 and 11.5% greater in the lower than upper slope, respectively. However, the percentage of organic C present as MBC and the percentage of total N present as MBN were 16.9 and 26.2% higher in the upper than lower slope, respectively. Neither microbial respiration (MR) nor metabolic quotient (qCO₂) was affected by topography. Both MBC and MBN were increased by burning, on average, by 29.8 and 14.2% over the growing season, and MR and qCO₂ tended to reduce depending on the sampling date, especially in August. Burning stimulated the percentage of organic C present as MBC and the percentage of total N present as MBN in the upper slope, but did not change these two parameters in the lower slope. No effects of N fertilization on soil microbial indices were observed in the first growing season after the treatment. Further research is needed to study the long-term relationships between changes in soil microbial diversity and activity and plant community in response to burning and N fertilization.     

Variation of soil enzyme activity and microbial biomass in poplar plantations of different genotypes and stem spacings

To improve the productivity of poplar plantations, a field experiment of split-plot design with four tree spacings and three poplar clones was established, and four soil enzyme activities and microbial biomass were monitored in the trial.Soil enzyme activities, in most cases,were significantly higher in topsoil(0–10 cm) than in lower horizons(10–20 cm).Soil cellulase, catalase and protease activities during the growing season were higher than during the non-growing season, while invertase activity followed the opposite trend.Soil invertase, cellulase and catalase activities varied by poplar clone but soil protease activity did not.Cellulase and protease activities in the plantation at 5×5 m spacing were significantly higher than in the other spacings.The highest catalase activity was recorded at 6×6 m spacing.At the same planting density, invertase activity was greater in square spacings than in rectangular spacings.Soil microbial biomass was also significantly affected by seedling spacing and poplar clone.The mean soil MBC was significantly lower in topsoil than in the lower horizon, while MBN showed the opposite pattern.Significantly positive correlations were observed among soil cellulase, protease and catalase activities(p0.01), whereas soil invertase activity was negatively and significantly correlated with cellulase, protease and catalase activities(p0.01).Soil microbial biomass and enzyme activities were not correlated except for a significantly negative correlation between soil MBC and catalase activities.Variations in soil enzyme activity and microbial biomass in different poplar plantations suggest that genotype and planting spacing should be considered when modeling soil nutrient dynamics and managing for long-term site productivity.     

Effects of forest harvesting on runoff and sediment characteristics in the Hyrcanian forests,northern Iran

Loss of canopy cover by forest harvesting generally increases the average surface runoff volume and sediment. Selective cutting (single and group selection method) is the most usual forest harvesting method in the Hyrcanian forests in the north of Iran. The purpose of this study is to find the effect of selective logging technique on the hydrological behavior of runoff and sediment in the Kheyrud forests located in northern Iran over 1 year. Four treatments were implemented: natural forest without harvesting (C), forest with selective harvesting (H) and area without canopy cover (WC) and skid trail (S). Three types of data were measured in each plot including soil chemical and physical properties, runoff and sediment load after each rainfall. The results indicate significant differences (P ≤ 0.05) in runoff generation and sediment production with respect to the treatments cover. The runoff in all treatments showed relatively similar response to rainfall, while the highest runoff and sediment were observed in skid trails, and the area without canopy cover (1.13 and 0.62 mm, and 1.2 and 0.51 g m^?2), averagely. In contrast, the natural forest without harvesting and the forest with selective harvesting treatments exhibited the lowest amounts of runoff (0.2 and 0.44 mm) and sediment (0.1 and 0.17 g m^?2), averagely. Implementation of low logging technique was useful to control the effects of logging on the runoff and sediment yield.     

First record of the entomopathogenic fungus <Emphasis Type="Italic">Entomophaga aulicae</Emphasis> on the Bihar hairy caterpillar <Emphasis Type="Italic">Spilarctia obliqua</Emphasis> in Manipur,India

Entomophaga aulicae (Hoffman in Bail) Batko (Zygomycotina: Entomophthorales) was found to cause epizootics in Spilarctia obliqua (Walker) (Arctiidae: Lepidoptera), a polyphagous pest in Manipur, India. Infected caterpillars climbed to elevated positions on plants where they hung upside down, attached by their abdominal prolegs. Infection levels reached up to 57%. The conidiophores are simple, conidia are ovoid to pyriform in shape, and the nuclei stained readily in aceto-orcein. Secondary, tertiary conidia and resting spores were also observed. No rhizoids and cystidia were found. This is the first report of E. aulicae infecting S. obliqua in Manipur.     

Spatial heterogeneity of soil organic carbon in tree-based intercropping systems in Quebec and Ontario,Canada

Land use affects the carbon sequestration potential of soils across landscapes. Tree-based intercropping (TBI) systems where annual crops are grown between established tree rows are expected to exhibit spatial heterogeneity in the soil organic carbon (SOC) content due to differences in carbon input and decomposition rates of litter from trees and herbaceous plants. This study aimed to quantify variability in the SOC of TBI systems, compare the SOC content of TBI and nearby conventional agroecosystems, and determine if SOC was related to soil fertility. The TBI research sites were established 4 years (St. Paulin and St. Edouard, Quebec, Canada), 8 years (St. Remi, Quebec, Canada) and 21 years (Guelph, Ontario, Canada) before soil samples were collected for this study. The SOC content was greater within 0.75 m of the tree row than in the intercropped space at the St. Edouard and St. Remi sites. At the Guelph site, the SOC was spatially heterogeneous in plots with Norway spruce (Picea abies L.) but not hybrid poplar (Populus deltoides × P. nigra clone DN-177), probably due to litterfall distribution. Formerly a tree plantation, the TBI system at St. Remi contained 77% more SOC than a nearby conventional agroecosystem, while there was 12% more SOC in the TBI system than the conventional agroecosystem at Guelph. There was no difference in the SOC content of 4-year old TBI sites and nearby conventional agroecosystems. However, an increase in SOC at all TBI sites was positively related to the plant-available N concentrations, indicating the benefit of temperate TBI systems for soil fertility.     

Influence of improved fallow systems and phosphorus application on arbuscular mycorrhizal fungi symbiosis in maize grown in western Kenya

A field study was carried out on a six-year-old on-farm field trial during long-rains season (April–August) 2003 to investigate the effect of improved fallow systems and phosphorus application on arbuscular mycorrhiza fungi (AMF) symbiosis in maize. The trial comprised of maize rotated with a fast growing leguminous Crotalaria grahamiana fallow and a non-leguminous Tithonia diversifolia fallow for 3 years followed by continuous maize. The experiment was randomized complete block design with three cropping (continuous maize, Crotalaria fallow and Tithonia fallow) systems and two phosphorus levels (0 and 50 kg P/ha). AMF colonization in maize roots, maize yield and macro-nutrients uptake were recorded. Phosphorus applications improved (P < 0.05) early (<8 weeks old maize) AMF colonization, nutrient uptake and maize yield in improved fallow systems. Greater differences due to phosphorus application were noted in maize in Tithonia fallow than in Crotalaria fallow. Following phosphorus application, a positive relationship existed between early AMF colonization and maize yield (r = 0.38), and phosphorus and nitrogen uptake (r = 0.40 and r = 0.43, respectively), demonstrating the importance of phosphorus fertilization in enhancing low-input technologies (improved fallows systems) in phosphorus deficient and acidic soils of western Kenya.     

Changes in aboveground and belowground properties during secondary natural succession of a cool-temperate forest in Japan

Forest development in temperate regions is considered to be a global carbon sink. Many studies have examined forest development after harvesting or fire from aboveground (e.g., biomass) or belowground (e.g., soil nutrient) perspectives. However, few studies have explored forest development from both perspectives simultaneously in cool-temperate forests in Japan. In this study, we examined changes over 105 years in both aboveground and belowground components during secondary natural succession. The aboveground biomass increased for 50 years and reached a plateau in a 105-year-old stand. The N mineralization rate increased during succession for 50 years, but showed a decline in the 105-year-old stand due to the decrease in the nitrification rate in late succession. The percent nitrification (i.e., relative contribution of nitrification to N mineralization) decreased significantly with increasing forest stand age. The N mineralization rates had significant relationships with N concentrations of the dominant tree foliage and litter fall and with the amount of litter fall N. Meanwhile, other belowground properties (i.e., soil pH, phenol concentration, soil microbial respiration, and litter mass loss) did not show any significant relationship with forest stand age. This may be because the soil at the study sites was heterogeneous and consisted of Cambisols and Andosols, the latter of which originally has high organic matter content, and thus may have buffered the effect of the aboveground development. These results indicate that belowground N dynamics are more closely associated with aboveground development than other belowground properties in these forests.