Immediate and adaptational temperature effects on nitric oxide production and nitrous oxide release from nitrification and denitrification in two soils

 Nitrification and denitrification are, like all biological processes, influenced by temperature. We investigated temperature effects on N trace gas turnover by nitrification and denitrification in two soils under two experimental conditions. In the first approach ("temperature shift experiment") soil samples were preincubated at 25  °C and then exposed to gradually increasing temperatures (starting at 4  °C and finishing at 40–45  °C). Under these conditions the immediate effect of temperature change was assessed. In the second approach ("discrete temperature experiment") the soil samples were preincubated at different temperatures (4–35  °C) for 5 days and then tested at the same temperatures. The different experimental conditions affected the results of the study. In the temperature shift experiment the NO release increased steadily with increasing temperature in both soils. In the discrete temperature experiment, however, the production rates of NO and N₂O showed a minimum at intermediate temperatures (13–25  °C). In one of the soils (soil B9), the percent contribution of nitrification to NO production in the discrete temperature experiment reached a maximum (>95% contribution) at 25  °C. In the temperature shift experiment nitrification was always the dominant process for NO release and showed no systematic temperature dependency. In the second soil (soil B14), the percent contribution of nitrification to NO release decreased from 50 to 10% as the temperature was increased from 4  °C to 45  °C, but no differences were evident in the discrete temperature experiment. The N₂O production rates were measured in the discrete temperature experiment only. The contribution of nitrification to N₂O production in soil B9 was considerably higher at 25–35  °C (60–80% contribution) than at 4–13  °C (15–20% contribution). In soil B14 the contribution of nitrification to N₂O production was lowest at 4  °C. The effects of temperature on N trace gas turnover differed between the two soils and incubation conditions. The experimental set-up allowed us to distinguish between immediate effects of short-term changes in temperature on the process rates, and longer-term effects by which preincubation at a particular temperature presumably resulted in the adaptation of the soil microorganisms to this temperature. Both types of effects were important in regulating the release of NO and N₂O from soil. Received: 20 October 1998     

Screening of mango (Mangifera indica L.) cultivars for their contents of flavonol O- and xanthone C-glycosides, anthocyanins, and pectin

With respect to their browning potential and in consideration of a combined recovery of pectin and phenolic compounds, peels of 14 cultivars and the flesh of nine cultivars of mango (Mangifera indica L.) fruits were analyzed for their contents of flavonol O- and xanthone C-glycosides by high-performance liquid chromatography (HPLC)-diode array detection-electrospray ionization mass spectrometry (ESI-MS). While total amounts of up to 4860 mg/kg dry matter demonstrated the peels to be a rich source of phenolic compounds, only traces could be detected in the flesh. The profile of flavonol glycosides of the peels proved to be highly characteristic and may therefore serve as a tool for authenticity control of mango puree concentrate, which is often produced from unpeeled fruits and represents an important intermediate for the production of mango nectars. Two compounds were isolated by preparative HPLC, and their structures were elucidated on the basis of ESI-MS as well as NMR spectroscopy, establishing the two compounds as rhamnetin 3-O-beta-galactopyranoside and rhamnetin 3-O-beta-glucopyranoside, respectively. In the peels of red-colored cultivars, cyanidin 3-O-galactoside and an anthocyanidin hexoside so far not reported in mango could tentatively be identified. The contents and degrees of esterification of pectins extracted from the lyophilized peels ranged from 12.2 to 21.2% and from 56.3 to 65.6%, respectively, suggesting mango peels also as a promising source of high-quality pectin.     

Detection of phloridzin in strawberries (Fragaria x ananassa Duch.) by HPLC-PDA-MS/MS and NMR spectroscopy

The phenolic profile of strawberry fruits (Fragaria x ananassa Duch., Rosaceae) was investigated by high-performance liquid chromatography with photodiode array detection. A peak displaying retention time and UV spectral data identical to those of phloridzin (phloretin 2'-O-beta-d-glucoside), a dihydrochalcone glucoside so far considered characteristic of apples, was monitored. For further characterization, crude extracts of strawberries were purified on polyamide, and the target compound was isolated by preparative and analytical HPLC. Structure elucidation was performed on the basis of APCI- and ESI-MS in the negative ion mode as well as by 1D and 2D NMR spectroscopy using authentic phloridzin for comparison. The d-configuration of the sugar moiety was established by HPLC analysis of the corresponding acyclic 1-deoxy-1-(N-acetyl-alpha-methylbenzylamino)alditol acetate. Apart from its chemotaxonomic relevance, this first report on the occurrence of phloridzin in strawberries is of particular interest for the authenticity control of strawberry products such as juices, jams, and fruit preparations since phloridzin has so far been used for the detection of fraudulent admixtures.     

Neospora-like protozoan infection as a major cause of abortion in California dairy cattle

Ninety-five aborted bovine fetuses received from California dairies over a 4.5-year period had histologic lesions of focal encephalitis. Protozoa that reacted with Neospora caninum antiserum were detected in the brain of 88 of these fetuses and in the heart of 1 fetus. Sarcocystis spp schizonts were seen in the vascular endothelium of 1 fetus. It was concluded that a Neospora-like cyst-forming coccidian may be a major cause of abortion in California dairy cattle.     

The effect of a monensin ruminal delivery device on performance of cattle grazing pasture

A total of 28 trials utilizing 2,262 steers and heifers were conducted to evaluate a sustained monensin2 ruminal delivery device (RDD) on the daily gain of grazing cattle. Five series of trials, with four to eight trials per series within a grazing season, were conducted to evaluate the daily gain response under different environmental conditions and locations. Pastures grazed included both summer (cool- and warm-season grasses and native range) and winter (rye, ryegrass and wheat) growing pastures. The experimental design for all trials in each of five series was a randomized complete block with initial weight or breed as the blocking factor. The treatments compared in series I, III, IV and V (20 trials) were a control and a single RDD, whereas in series II (eight trials), a 2 x 2 factorial was utilized that compared RDD and estradiol 17-beta controlled release implants. In the five series of trials, the monensin RDD increased daily gain .04 (P = .002), .03 (P = .07), .09 (P = .01), .05 (P = .10) and .08 kg (P = .04) compared with the controls. Use of the RDD provided an effective method of achieving consistent monensin delivery and weight gain improvement without requiring the extra labor needed to administer monensin via hand-feeding or self-feeding supplements, blocks or loose mineral.     

Demonstration of two different H2-oxidizing activities in soil using an H2 consumption and a tritium exchange assay

H₂-oxidizing activities were assayed in slurries of four soils by measuring the consumption of H₂ and the exchange of ³H₂ with H₂O at increasing mixing ratios of H₂ or ³H₂. Both H₂ consumption and ³H₂ exchange were abolished by autoclaving or the addition of formaldehyde. The rates of H₂ consumption and ³H₂ exchange were proportional to the quantity of soil used. Both activities increased with increasing concentrations of H₂ or ³H₂ and displayed biphasic kinetics, demonstrating the existence of two different H₂-oxidizing activities, one with a relatively low K _m and V _max, and a second with a relatively high K _m und V _max. The first type of activity was characteristic of abiontic soil hydrogenases, and the second of aerobic H₂-oxidizing bacteria. In contrast to H₂ consumption, which required the presence of either O₂ or ferricyanide, ³H₂ exchange operated equally well without an external electron acceptor. The ³H₂ exchange assay may thus be particularly useful for enrichment of soil hydrogenases which have not yet been isolated and for which no natural electron acceptor is known.     

Effects of exogenous progesterone and/or prolactin on Haemonchus contortus infections in ovariectomized ewes

Reproduction can alter the course of ovine nematodiasis; fecal nematode egg concentrations often increase near lambing and throughout lactation, a phenomenon referred to as the periparturient rise. To identify the host mechanisms that might link these disparate events, i.e. lactation and the fecundity of gastrointestinal trichostrongyles, ovariectomized ewes were injected daily with progesterone and/or prolactin, or saline. Progesterone treatment commenced 20 days before inoculation with Haemonchus contortus and prolactin was administered throughout the 30-day infection period. Ovariectomized ewes receiving prolactin during the experimental infection maintained higher daily fecal egg concentrations than the progesterone, progesterone/prolactin, or the control treatment groups. However, ovariectomized ewes that received 20 days of pre-inoculation exposure to progesterone, as well as prolactin during the infection, had greater numbers of nematodes that were larger than the other treatment groups. Thus, the sequential delivery of these hormones that are associated with the reproductive cycle in ewes produced some of the same results that occur during periparturient rise.     

Etiology of ammoniated hay toxicosis

Some animals consuming hay treated with anhydrous ammonia have developed neurological signs including hyperexcitability, circling and convulsions. A series of experiments was conducted to identify tentatively the toxin and determine its mode of action. Three out of four sheep fed ammoniated orchardgrass hay (approximately 4% ammonia on a dry basis) developed convulsions. Two of the three sheep died within 18 h of the onset of signs. The concentrations of blood lactate and pyruvate were elevated in the symptomatic sheep (P less than .05). A proposed toxin, 4-methyl imidazole, did not induce the syndrome when 750 mg/d (approximately 10 times the dietary amount) were administered orally. Four out of five calves that received milk from cows fed ammoniated oat hay (approximately 5% ammonia on dry basis) displayed hyperexcitability and circling. Concentrations of blood lactate and pyruvate were also elevated in the calves. The crude alkaloid fraction of the toxic milk produced neurological signs similar to those of the calves when injected into mice. A fluorescent compound was found in the alkaloid fraction of toxic milk and ammoniated hay, but not in control milk or untreated hay. The fluorescent compound was quite labile; hence, characterization has been unsuccessful thus far.