Partitioning evapotranspiration fluxes from a Colorado grassland using stable isotopes: Seasonal variations and ecosystem implications of elevated atmospheric CO2

The stable isotopic composition of soil water is controlled by precipitation inputs, antecedent conditions, and evaporative losses. Because transpiration does not fractionate soil water isotopes, the relative proportions of evaporation and transpiration can be estimated using a simple isotopic mass balance approach. At our site in the shortgrass steppe in semi-arid northeastern Colorado, ¹⁸O values of soil water were almost always more enriched than those of precipitation inputs, owing to evaporative losses. The proportion of water lost by evaporation (E/ET) during the growing season ranged from nil to about 40% (to >90% in the dormant season), and was related to the timing of precipitation inputs. The sum of transpiration plus evaporation losses estimated by isotopic mass balance were similar to actual evapotranspiration measured from a nearby Bowen ratio system. We also investigated the evapotranspiration response of this mixed C₃/C₄ grassland to doubled atmospheric [CO₂] using Open-Top Chambers (OTC). Elevated atmospheric [CO₂] led to increased soil-water conservation via reduced stomatal conductance, despite greater biomass growth. We used a non-invasive method to measure the ¹⁸O of soil CO₂ as a proxy for soil water, after establishing a strong relationship between ¹⁸O of soil CO₂ from non-chambered control (NC) plots and ¹⁸O of soil–water from an adjacent area of native grassland. Soil–CO₂ ¹⁸O values showed significant treatment effects, particularly during a dry summer: values in ambient chambers (AC) were more enriched than in NC and elevated chamber (EC) plots. During the dry growing season of 2000, transpiration from the EC treatment was higher than from AC and lower than from NC treatments, but during 2001, transpiration was similar on all three treatments. Slightly higher evaporation rates from AC than either EC or NC treatments in 2000 may have resulted from increased convection across the soil surface from the OTC blowers, combined with lower biomass and litter cover on the AC treatment. Transpiration-use efficiency, or the amount of above-ground biomass produced per mm water transpired, was always greatest on EC and lowest on NC treatments.     

Organic matter transformations and soil fertility in a treed pasture in semiarid NE Brazil

Planted silvo-pastoral systems are formed by sparing selected native trees when land is cleared for pasture establishment, or by planting selected species – often known agroforestry species – into the establishing pasture. Isolated trees within pastures and savannas are often associated with `resource islands', characterized by higher fertility and organic matter levels under the tree canopies. We here examine the processes underlying the differences in fertility and organic matter in a buffel grass (Cenchrus ciliaris L.) pasture that contained two tree species (Ziziphus joazeiro Mart., Spondias tuberosa Arruda Cam.) preserved from the native thorn forest and a planted agroforestry species (Prospois juliflora Swartz D.C). The objective is to distinguish effects of soil variability from those induced by the presence of trees or the planting of pasture. The ¹³C signatures of the original (largely C3) vegetation, the preserved and planted trees, and the planted C4 grass were used to distinguish the provenance of organic matter in the top soil (0–15 cm). This allowed the conclusion that all trees maintained C3 derived C at the original thorn forest level, while lower levels under pasture were due to mineralisation of organic matter. The net rates of forest-derived C loss under pasture varied with soil type amounting to between 25 and 50% in 13 years after pasture establishment. Only on Alfisol, C inputs from the pasture compensated for the C3-C losses. Analysis of organic and inorganic P fractions indicated Z. joazeiro and P. juliflora enriched the soil under their canopy with P, whereas S. tuberosa had no positive effect on fertility. A combination of ANOVA and spatial analysis and mapping was used to show vegetation effects.     

Effects of mercury on microbial biomass and enzyme activities in soil

Mercury (Hg) is a persistent soil pollutant that affects soil microbial activity. We monitored the changes in soil microbial biomass and activity of enzymes, including alkaline phosphatase, arylsulfatase, fluorescein diacetate (FDA) hydrolytic activity, and o-diphenol oxidase (o-DPO) in three soils contaminated with different concentrations of Hg. Increasing levels of Hg, from 0.5 to 10 μmol/g of dried soil, generally depressed microbial activity; however, the effects of Hg on soil microbial activity depended on soil type and composition, particularly organic matter content. o-DPO was less affected by Hg than the other three enzymes tested. Our results indicate that the analysis of microbial biomass content and soil-enzyme activities may be used to predict the soil quality contaminated with Hg.     

Identification and analysis of expressed resistance gene sequences in wheat

Forty-eight resistance (R) genes conferring resistance to various types of pests have been cloned from 12 plant species. Irrespective of the host or the pest type, most R genes share a strong protein sequence similarity especially for domains and motifs. The objective of this study was to identify expressed R genes of wheat, the fraction of which is expected to be very low in the genome. Using modified RNA fingerprinting and data mining approaches we identified 220 expressed R-gene candidates. Of these, 125 sequences structurally resembled known R genes. In addition to 25-87% protein sequence similarity with the known R genes, the sequence, order, and distribution of the domains and motifs were also the same. Among the remaining 95, 17 were probable R-related, 21 were a new class of nucleotide-binding kinases, 21 were probable kinases, and 36 were p-loop-containing unknown sequences. About 76% were rare including 73 novel sequences. Three new R-gene specific motifs were also identified. Physical mapping of the 164 best R-gene candidates on 339 deletion lines localized 121 mappable R-gene candidates to 26 small chromosomal regions encompassing about 16% of the genome. About 90 of the 110 phenotypically characterized wheat R genes corresponding to 18 different pests also mapped in these regions.     

Changes in lymphokine receptor expression and fatty acid composition of phospholipids and triacylglycerols in rat adipocytes associated with lymph nodes following a transient immune challenge

Single-photon counting fluorimetry was used to record the time course of the expression of interleukin-10 receptors labelled with fluorescent antibodies on the surface of adipocytes over 24h, following an immune challenge to the rat popliteal lymph node. Homologous perinodal and remote-from-node samples from the stimulated and unstimulated popliteal depots were compared in rats fed on plain chow and chow supplemented with 10% w/w suet, fish or vegetable oils. Receptor expression was maximal 6 h after stimulation, and returned to baseline after 24 h, and was similar in the stimulated and unstimulated depots. Fewer receptors were elicited in tissues from rats fed lipid-supplemented diets compared with the control diet, with fewest of all following the fish oil diet. These data suggest that interleukin-10 is involved in local interactions between perinodal adipocytes and lymph node lymphoid cells. Both triacylglycerols and phospholipids contained more polyunsaturates and fewer saturates in perinodal adipose tissue than in samples from sites not associated with lymphoid tissue. These data are consistent with paracrine interactions between perinodal adipocytes and activated lymphoid cells.     

Effects of daily activities on ambulatory blood pressure during menstrual cycle in normotensive women

The purpose of this study was to determine whether (1) there is a menstrual phase effect on blood pressure (BP) and heart rate (HR), and (2) the effects of physical effort, posture, or moods on BP and HR is mediated by the menstrual phase. Twelve normotensive women, aged between 28 and 50, with normal menstrual cycles were studied. BP was measured at 30- to 60-min intervals during a 24-hr period using an ambulatory BP monitor on Days 1, 8, 15, and 22 of the menstrual cycle. Participants were asked to report their posture, physical effort, and mood (annoyed, tense, and happy) on 5-point Likert-type scales each time the ambulatory BP monitor took measurements. Systolic BP (SBP) was lower on Day 8 of the cycle. Diastolic BP (DBP) and HR were lower on Days 1 and 8. Daytime SBP was affected by the time of the day and posture, but not by moods, whereas daytime DBP was affected by posture and levels of tenseness. The level of physical effort only affected HR, not BP. The average daytime physical and emotional variables had little influence over the average daytime BP. In 1 normotensive women with a normal menstrual cycle, SBP was lower during the follicular phase and DBP and HR were lower during the follicular phase and menstruation even after controlling the effects of other factors. Physical activity or moods had only momentary effects on BP or HR. A cross-validation statistical method used is suggested to study how individuals are affected by various factors. With the use of this method, the inclusion of menstrual phase in the model improved the prediction of SBP for 5 out of the 12 women studied.     

Selenium and sulfur accumulation and soil selenium dissipation in planting of four herbaceous plant species in soil contaminated with drainage sediment rich in both selenium and sulfur

Four selenium (Se) nonaccumulator plant species, including a forage grass species, Tall Fescue (Festuca arundinacea Schreb.), a forage legume species, Alfalfa (Medicago sativa L.), a wetland species, Rush (Juncus tenuis Wild.), and a dry-land alkaline soil species, Saltgrass (Distichlis spicata L.), were grown in soil contaminated by agricultural drainage sediment having elevated levels of Se and sulfur (S). The above-ground plant tissues were consecutively harvested five times and examined for Se and S accumulation. Plant tissue Se concentrations ranged from 23.0 mg kg-1 to 8.3 mg kg-1. Tissue S concentrations ranged from 3239 mg kg-1 to 7034 mg kg-1. Both tissue Se and S concentrations were significantly different between harvests, species, and species/harvest interactions. Total Se accumulation by the plant biomass harvested ranged from 0.3 to 1.3 mg per soil column and total S accumulations ranged from 87.5 to 321.1 mg per soil column. The reduction in the percentage of total soil Se after 24 weeks growth of the plant species ranged from 12.0% in the Tall Fescue planting to 17.3% in the Rush planting. Over 90% of the soil Se losses were unidentified losses and leaching of Se was prevented. The accumulations of Se and S in the plant biomass were very small compared with the total soil Se and S losses, but substantial amounts of total soil Se (12.0 to 15.0%) and S (28.0 to 50.9%) inventories were dissipated by the growing and harvesting of the plants. The soil S concentration was several hundred times higher than the soil Se concentration, but Se accumulation by the plants and Se dissipation from the soil were not impaired by the high level of soil sulfur. For natural grassland habitat restoration, such as at the Kesterson Wildlife Refuge in the Central Valley of California, or for restoration of large-scale Se contaminated agricultural lands, Se nonaccumulator plant species are favorable candidates, because the possibility of introducing Se toxicity into the food chain can be minimized.     

Effect of 50 Hz, 0.2 mT magnetic fields on RBC properties and heart functions of albino rats

In this work the effect of sinusoidal 50 Hz, 0.2 mT magnetic fields on the red blood cells (RBCs) and heart functions of Albino rats were investigated. Twenty-four male Albino rats were equally divided into four groups, A, B, C, and D. Animals from groups B were continuously exposed to the magnetic field for 15 days; and groups C and D, for 30 days. Group A was used as control. Animals from group D were kept after exposure to the magnetic field for a period of 45 days for delayed effect studies. The osmotic fragility and shape of RBCs' membrane and hemoglobin (Hb) structure tests were carried out for all groups. The dielectric relaxation of Hb molecules was measured in the frequency range of 0.1-10 MHz and the dielectric increment (Deltaepsilon), relaxation time (tau), molecular radius (r), and Cole-Cole parameter (alpha) were calculated for all groups. The ECG was measured for all animals before and after exposure to the magnetic field. The results indicated that exposure of the animals to 50 Hz, 0.2 mT magnetic fields resulted in the decrease of RBCs membrane elasticity and permeability and changes in the molecular structure of Hb. The ECG of the exposed animals was considerably altered. The data also indicated that there was no sign of repair in the newly generated RBCs structure and the ECG after removing the animals from the magnetic field, which indicates that the blood generating system was severely injured. The injuries in the heart of the animals were attributed to the loss of some physiological functions of the RBCs as a result of exposures of the rats to the magnetic field.     

Mycelial colonization by bradyrhizobia and azorhizobia

This study examines mycelial colonization of common soil fungi by bradyrhizobia and an azorhizobial strain, resulting in the forming of biofilms. The effects of the fungal exudates on a bradyrhizobial strain have also been investigated. Bradyrhizobia gradually colonized the mycelia for about 18 days, after which the biofilm structures collapsed with the release of the rhizobial cell clusters to the culture medium. The azorhizobial strain showed differential colonization of the mycelia. In general, there were no considerable mycotoxin effects of the fungal exudates on the bradyrhizobial strain used, instead the rhizobial strain utilized the exudates as a source of nutrition. This study indicates that the present microbial association with biofilm formation has important implications in the survival of rhizobia under adverse soil conditions devoid of vegetation. Further, it could have developed an as yet unidentified nitrogen fixing system that could have contributed to the nitrogen economy of soils.     

Physical properties of an extracellular polysaccharide produced by Bacillus sp. CP912

AIMS: In this study, some physical properties of Bacillus sp. exo-polysaccharide were investigated. METHODS AND RESULTS: An extracellular polysaccharide was purified by sequential precipitations after homogenization of the diluted culture supernatant of Bacillus sp. CP912. Its physical properties were examined such as lipid emulsifying effect on several vegetable oils and flocculating activity against the activated carbon suspension. The melting point and endothermic calories of the polysaccharide were 128.7 degrees C and 50.864 kCal mol-1, respectively. Its pyrolysis temperature was 284.58 degrees C. The polysaccharide showed high lipid emulsifying activity on oil-water emulsion, against olive, peanut, sunflower and corn oils. It exhibited high flocculating activity as well against activated carbon. CONCLUSIONS: The present findings suggest that the extracellular polysaccharide produced by Bacillus sp. CP912 has a great industrial potential because of its high lipid emulsifying and flocculating activity. SIGNIFICANCE AND IMPACT OF THE STUDY: These data represent a novel Bacillus sp. extracellular polysaccharide possessing high emulsifying and flocculating effects.