A paradigm shift towards low-nitrifying production systems: the role of biological nitrification inhibition (BNI).

BACKGROUND: Agriculture is the single largest geo-engineering initiative that humans have initiated on planet Earth, largely through the introduction of unprecedented amounts of reactive nitrogen (N) into ecosystems. A major portion of this reactive N applied as fertilizer leaks into the environment in massive amounts, with cascading negative effects on ecosystem health and function. Natural ecosystems utilize many of the multiple pathways in the N cycle to regulate N flow. In contrast, the massive amounts of N currently applied to agricultural systems cycle primarily through the nitrification pathway, a single inefficient route that channels much of this reactive N into the environment. This is largely due to the rapid nitrifying soil environment of present-day agricultural systems. SCOPE: In this Viewpoint paper, the importance of regulating nitrification as a strategy to minimize N leakage and to improve N-use efficiency (NUE) in agricultural systems is highlighted. The ability to suppress soil nitrification by the release of nitrification inhibitors from plant roots is termed 'biological nitrification inhibition' (BNI), an active plant-mediated natural function that can limit the amount of N cycling via the nitrification pathway. The development of a bioassay using luminescent Nitrosomonas to quantify nitrification inhibitory activity from roots has facilitated the characterization of BNI function. Release of BNIs from roots is a tightly regulated physiological process, with extensive genetic variability found in selected crops and pasture grasses. Here, the current status of understanding of the BNI function is reviewed using Brachiaria forage grasses, wheat and sorghum to illustrate how BNI function can be utilized for achieving low-nitrifying agricultural systems. A fundamental shift towards ammonium (NH4(+))-dominated agricultural systems could be achieved by using crops and pastures with high BNI capacities. When viewed from an agricultural and environmental perspective, the BNI function in plants could potentially have a large influence on biogeochemical cycling and closure of the N loop in crop-livestock systems.

Evidence for biological nitrification inhibition in Brachiaria pastures.

Nitrification, a key process in the global nitrogen cycle that generates nitrate through microbial activity, may enhance losses of fertilizer nitrogen by leaching and denitrification. Certain plants can suppress soil-nitrification by releasing inhibitors from roots, a phenomenon termed biological nitrification inhibition (BNI). Here, we report the discovery of an effective nitrification inhibitor in the root-exudates of the tropical forage grass Brachiaria humidicola (Rendle) Schweick. Named "brachialactone," this inhibitor is a recently discovered cyclic diterpene with a unique 5-8-5-membered ring system and a gamma-lactone ring. It contributed 60-90% of the inhibitory activity released from the roots of this tropical grass. Unlike nitrapyrin (a synthetic nitrification inhibitor), which affects only the ammonia monooxygenase (AMO) pathway, brachialactone appears to block both AMO and hydroxylamine oxidoreductase enzymatic pathways in Nitrosomonas. Release of this inhibitor is a regulated plant function, triggered and sustained by the availability of ammonium (NH(4)(+)) in the root environment. Brachialactone release is restricted to those roots that are directly exposed to NH(4)(+). Within 3 years of establishment, Brachiaria pastures have suppressed soil nitrifier populations (determined as amoA genes; ammonia-oxidizing bacteria and ammonia-oxidizing archaea), along with nitrification and nitrous oxide emissions. These findings provide direct evidence for the existence and active regulation of a nitrification inhibitor (or inhibitors) release from tropical pasture root systems. Exploiting the BNI function could become a powerful strategy toward the development of low-nitrifying agronomic systems, benefiting both agriculture and the environment.

Extradural spinal synovial cysts in nine dogs.

Nine dogs presenting for investigation of cervical or thoracolumbar myelopathies were diagnosed with extradural spinal synovial cysts. Degenerative disease affecting the articular facets or intervertebral discs was present on plain spinal radiographs in all cases. Myelography was consistent with dorsolateral, extradural spinal cord compression. Two groups of dogs were identified: (1) young, giant breed dogs with multiple cysts involving one or more levels of the cervical spinal cord; and (2) older, large breed dogs with solitary cysts involving the thoracolumbar spinal cord. The synovial cysts constituted the major compressive lesions in four of the dogs. Analysis of lumbar cerebrospinal fluid demonstrated albuminocytological dissociation, consistent with chronic compressive myelopathy, in six dogs. All dogs underwent decompressive surgery and the diagnosis of synovial cysts was confirmed histologically. The mean follow-up period was 17 months (range four to 36 months). At the time of follow-up, all dogs were fully ambulatory with improved neurological function compared with that at initial presentation.

Magnetic resonance imaging features of multilobular osteochondrosarcoma in 3 dogs.

Three dogs with multilobular osteochondrosarcoma of the skull were evaluated using magnetic resonance (MR) imaging. Spin echo T1, T2, proton weighted and post contrast T1W images were obtained with a 1.5 Tesla magnet. The MR imaging findings were similar in all three dogs with mixed signal intensities in the T1W, T2W and proton weighted images and fairly large areas of contrast enhancement in the post contrast T1W images. The extent of brain and soft tissue involvement were well delineated and provided useful information concerning surgical planning. MR imaging provided a useful method of evaluating dogs with skull tumors.

Magnetic resonance imaging features of cervical stenotic myelopathy in 21 dogs.

The cervical spine of 21 dogs with clinical signs of cervical stenotic myelopathy was evaluated using magnetic resonance (MR) imaging. Spin echo T1, T2 and gradient echo T2 weighted images were obtained with a 1.5 Tesla magnet in 12 dogs and a 1.0 Tesla magnet in 9 dogs. Sagittal or parasagittal T1W and T2W images were helpful in determining the presence of spinal cord compression or degenerative disease of the articular processes. Transverse T1W and T2W images were the most useful for the identification of dorsolateral spinal cord compression secondary to soft tissue and ligament hypertrophy, as well as synovial cysts, associated with the articular processes. The MR imaging findings were consistent with the surgical findings in all 14 dogs that underwent surgery. Magnetic resonance imaging provided a safe, non-invasive method of evaluating the cervical spine in dogs suspected of having cervical stenotic myelopathy. Veterinary

Spirocerca lupi esophageal granulomas in 7 dogs: resolution after treatment with doramectin.

Seven dogs with Spirocerca lupi esophageal granulomas were identified based on the site of involvement (ie, distal esophagus) and characteristic endoscopic appearance. Six dogs presented with signs of esophageal disease and 1 dog was asymptomatic. Ova were only identified in the feces of 2 dogs. On thoracic radiographs, 4 dogs had evidence of a caudodorsal mediastinal mass, and 2 of these dogs had spondylitis of midthoracic vertebrae. On endoscopy, single esophageal nodules were observed in 5 dogs, 1 dog had 3 nodules, and 1 dog had 6 nodules. All 7 dogs were treated with doramectin at a dosage of 200 microg/kg SC at 14-day intervals for 3 treatments. Dogs had physical and endoscopic examinations at 2, 4, and 6 weeks after treatment. By 6 weeks, clinical signs had resolved in 6 dogs (1 dog was asymptomatic), and the esophageal nodules had completely resolved in 4 dogs, and incompletely resolved in 3 dogs. Two dogs with incomplete resolution were treated again with doramectin at 500 microg/kg PO daily for an additional 6 weeks. Complete resolution of the esophageal nodules was confirmed by endoscopy in all dogs. Nodules had resolved in 4 dogs by 6 weeks, in 2 dogs by 12 weeks (after 6 weeks additional daily oral therapy), and in 1 dog 22 months after the initial 200 microg/kg treatment regimen. No dog experienced adverse effects to the drug, and all symptomatic dogs have been free of disease for periods ranging from 3 to 4 years.

Caudal cervical disc protrusion in a Bengal tiger (Panthera tigris tigris).

A young adult male white Bengal tiger (Panthera tigris tigris) presented with hindlimb ataxia. Cervical and lumbar myelography revealed a compressive lesion of the cord at C(6-7). Corticosteroid therapy and confinement failed to provide lasting remission of signs. A modified, inverted cone ventral slot decompression was used to remove the fibrous material causing cord compression at C(6-7). Temporary Horner's syndrome and laryngeal paresis developed postsurgically because of excessive tissue retraction. The animal recovered normal ambulatory function 6 wk after surgery.

Salivary gland necrosis in dogs: a retrospective study of 19 cases.

Salivary gland necrosis has been described in dogs and is characterised by enlarged, hard, painful salivary glands, retching and vomiting or regurgitation. The cause has yet to be determined. A retrospective study of 19 dogs with the same clinical signs was undertaken for breed, age, gender, history and presenting signs, diagnostic evaluations and findings, treatment and outcome. An underlying association was identified in 16 of the 19 dogs. This included Spirocerca lupi infestation (seven dogs), megaoesophagus (three dogs) and oesophagitis, oesophageal diverticulum, giardiasis and suspected autoimmune sialadenitis. Almost all associated lesions involved the oesophagus. Where the associated disease was successfully treated, the salivary glands returned to normal and all clinical signs resolved. It is hypothesised that an afferent vagal reflex may be involved, and that the mechanism of disease is similar to the neural pathogenesis suggested for hypertrophic osteopathy; in this instance, the efferent targets are the salivary glands rather than the limbs.

Effect of elevated carbon dioxide on nutritional quality of tomato.

Tomato (Lycopersicon esculentum Mill.) cvs. Red Robin (RR) and Reimann Philipp (RP) were grown hydroponically for 105 d with a 12 h photoperiod, 26 degrees C/22 degrees C thermoperiod, and 500 micromol m-2 s-1 PPF at either 400, 1200, 5000, or 10,000 micromol mol-1 (0.04, 0.12, 0.50, 1.00 kPa) CO2. Harvested fruits were analyzed for proximate composition, total dietary fiber, nitrate, and elemental composition. No trends were apparent with regard to CO2 effects on proximate composition, with fruit from all treatments and both cultivars averaging 18.9% protein, 3.6% fat, 10.2% ash, and 67.2% carbohydrate. In comparison, average values for field-grown fruit are 16.6% protein, 3.8% fat, 8.1% ash, and 71.5% carbohydrate (Duke and Atchely, 1986). Total dietary fiber was highest at 10,000 micromol mol-1 (28.4% and 22.6% for RR and RP) and lowest at 1000 micromol mol-1 (18.2% and 15.9% for RR and RP), but showed no overall trend in response to CO2. Nitrate values ranged from 0.19% to 0.35% and showed no trend with regard to CO2. K, Mg, and P concentrations showed no trend in response to CO2, but Ca levels increased from 198 and 956 ppm in RR and RP at 400 micromol mol-1, to 2537 and 2825 ppm at 10,000 micromol mol-1. This increase in Ca caused an increase in fruit Ca/P ratios from 0.07 and 0.37 for RR and RP at 400 micromol mol-1 to 0.99 and 1.23 for RR and RP at 10,000 micromol mol-1, suggesting that more dietary Ca should be available from high CO2-grown fruit.

Pulmonary cryptococcoma and cryptococcal meningoencephalomyelitis in a king cheetah (Acinonyx jubatus).

A captive king cheetah (Acinonyx jubatus) was evaluated for a subacute onset of ataxia in all four limbs. The ataxia appeared to be spinal in origin, evidenced by apparent conscious proprioceptive deficits in all limbs, and there was no evidence of cerebellar involvement. Anesthesia was performed and survey spinal radiographs were normal. Cerebrospinal fluid analysis revealed an apparently sterile meningitis of unknown etiology. Although transient improvement was noted with glucocorticoid and antimicrobial therapy, the condition deteriorated subsequently and the animal became quadriparetic and paraplegic. Follow-up cerebrospinal fluid analysis and culture revealed the presence of Cryptococcus neoformans. Myelography demonstrated obstruction of the subarachnoid space at the level of the seventh cervical vertebra. Pathological examination following euthanasia revealed a solitary pulmonary cryptococcoma and confirmed cryptococcal meningoencephalomyelitis.

Suspected poisoning of puppies by the mushroom Amanita pantherina.

Amanita pantherina poisoning is suspected as the cause of a severe, transient neurological disorder in three 5-week-old German shepherd puppies. There was very strong circumstantial evidence that this mushroom had been eaten, and the signs encountered were similar to those described in confirmed field cases of intoxication in dogs. It was also in many respects consistent with the syndrome seen in humans. A veterinary perspective on the hallucinogenic Amanita spp. is given and the veterinary literature on mushroom intoxication is briefly reviewed as, in contrast to humans, it is not often reported in animals. This is the 1st report of suspected mushroom intoxication of animals in South Africa.

Multifocal Aspergillus terreus discospondylitis in two German shepherd dogs.

Multifocal fungal (Aspergillus terreus) discospondylitis was diagnosed in 2 German shepherd dogs. In one dog, the aetiology was established by means of fluoroscopic-guided disc aspiration, cytology and culture of disc material and urine. Disseminated aspergillosis was confirmed at necropsy and A. terreus cultured from numerous organs in this dog. The aetiology in the other dog was not established until therapeutic failure forced surgical curettage of disc material from which the fungus was cultured. Ketoconazole therapy failed to effect an improvement, and at necropsy, disease was localised to the spinal column, with A. terreus cultured from the affected discs and associated vertebrae. Immunodeficiency was suspected in both cases. In the case of disseminated disease a reduced lymphocyte blastogenic response was demonstrated. Reduced IgA was shown in both cases. The German shepherd breed seems to be predisposed to Aspergillus infections and IgA deficiency.

Lymphangiomatosis of the pelvic limb in a Maltese dog.

A case of lymphangiomatosis is described affecting the right pelvic limb of an 18-month-old, female Maltese dog. A progressive swelling around the stifle had developed subsequent to a routine tibial crest transposition. The swollen area eventually progressed to involve the entire limb circumferentially, to end abruptly in the mid-metatarsal region. The skin of the affected area was deep red in colour, devoid of hair, and had numerous large, thin-walled vesicles that were easily ruptured and from which a serosanguineous fluid exuded. The swelling pitted on digital pressure and showed fluctuant mobility. The microscopic appearance of biopsied and post mortem material mimicked that of lymphangioma. However, the signalment, clinical presentation and histological features are consistent with a diagnosis of the recently reported variant of human lymphangiomatosis, lymphangiomatosis of the limb.

Changes in haematocrit after treatment of uncomplicated canine babesiosis: a comparison between diminazene and trypan blue, and an evaluation of the influence of parasitaemia.

It has been suggested that the antibabesial drug diminazene causes a rapid decline in haematocrit after treatment of dogs with high Babesia canis parasitaemias, compared with trypan blue. To test this, 19 dogs with clinically mild to moderate, uncomplicated babesiosis were placed in low, moderate or high parasitaemia groups, based on venous parasitaemias, and were allotted randomly to diminazene or trypan blue treatment groups. Haematocrit and parasitaemia were determined before treatment, and at 2, 6, 12, 18 and 24 hours. The drugs were compared for effects on haematocrit and parasite clearance. Changes in haematocrit after treatment were analysed. There were no significant differences between diminazene and trypan blue for haematocrit or parasite clearance. There was no correlation between initial parasitaemia and initial or post-treatment haematocrit. In all dogs, haematocrit fell following treatment. The maximum mean reduction from the baseline (0 h) was 0.046 l/l (range 0.02-0.07 l/l); this most often occurred at 6 or 12 h. The 24 h haematocrit ranged from 70.5-113.6% of baseline (mean absolute haematocrit 0.019 l/l below baseline). All dogs improved clinically during the study period. It was concluded that either diminazene or trypan blue can be safely used to treat dogs with clinically mild or moderate, uncomplicated babesiosis. Parasitaemia need not be taken into account when deciding which antibabesial drug to administer and does not appear to be related to the degree of anaemia.

Evaluation of the effect of whole-blood transfusion on the oxygen status and acid-base balance of Babesia canis infected dogs using the oxygen status algorithm.

The usefulness of whole-blood transfusion in normalising the blood-gas, acid-base, and arterial oxygen status in severe babesiosis was demonstrated in 6 severely affected Babesia canis infected dogs. These dogs all demonstrated a metabolic acidosis at admission and yet were not acidaemic. It is possible that this may reflect a mixed acid-base disorder (metabolic acidosis with respiratory alkalosis). They all showed severe hypoxaemia at admission. A number of derived blood-gas and acid-base parameters as determined by the Oxygen Status Algorithm (OSA) were shown to be a superior way of assessing and monitoring the temporal response of severe babesiosis cases to blood transfusion. It was shown that fresh whole-blood transfusion is a safe and physiological way of reversing acid-base and blood-gas derangements associated with severe babesiosis in dogs. Intravenous alkalinisation with sodium bicarbonate for the treatment of the metabolic acidosis of babesiosis is questioned.

Proximate composition of CELSS crops grown in NASA's Biomass Production Chamber.

Edible biomass from four crops of wheat (Triticum aestivum L.), four crops of lettuce (Lactuca sativa L.), four crops of potato (Solanum tuberosum L.), and three crops of soybean (Glycine max (L.) Merr.) grown in NASA's CELSS Biomass Production Chamber were analyzed for proximate composition. All plants were grown using recirculating nutrient (hydroponic) film culture with pH and electrical conductivity automatically controlled. Temperature and humidity were controlled to near optimal levels for each species and atmospheric carbon dioxide partial pressures were maintained near 100 Pa during the light cycles. Soybean seed contained the highest percentage of protein and fat, potato tubers and wheat seed contained the highest levels of carbohydrate, and lettuce leaves contained the highest level of ash. Analyses showed values close to data published for field-grown plants with several exceptions: In comparison with field-grown plants, wheat seed had higher protein levels; soybean seed had higher ash and crude fiber levels; and potato tubers and lettuce leaves had higher protein and ash levels. The higher ash and protein levels may have been a result of the continuous supply of nutrients (e.g., potassium and nitrogen) to the plants by the recirculating hydroponic culture.

Charge balance--a theoretical basis for modulating pH fluctuations in plant nutrient delivery systems.

Existing control systems for pH and nutrient supply in hydroponic space plant growth units and bioregenerative life support (BLS) systems require acid and base additions to correct plant-induced charge imbalances in the nutrient solution. Plant growth is dependent on nutrient availability, and the active uptake of ions by roots changes the pH of the nutrient solution. This change in pH is an integrated response to nutrient and organic ion influx/efflux by the plant. Plant nutrient requirements, as a function of crop development and driven by specific environmental conditions, influence the magnitude of the charge balance requirement. Nitrogen is the dominant nutrient taken up by plant species. If the daily crop nutrient (N) requirement at each developmental stage is known, and the daily addition of nutrients (relative addition rate = RAR) to the plant growth system is calculated, controlling the daily addition of ammonium (NH4+) and nitrate (NO3-) offers a mechanism whereby pH fluctuations in the nutrient solution could be largely minimized and controlled, reducing acid or base additions to the system.

Proximate nutritional composition of CELSS crops grown at different CO2 partial pressures.

Two CELSS candidate crops, soybean (Glycine max) and potato (Solanum tuberosum), were grown hydroponically in controlled environments maintained at carbon dioxide (CO2) partial pressures ranging from 0.05 to 1.00 kPa (500 to 10,000 ppm at 101 kPa atmospheric pressure). Plants were harvested at maturity (90 days for soybean and 105 days for potato) and all tissues analyzed for proximate nutritional composition (i.e. protein, fat, carbohydrate, crude fiber, and ash content). Soybean seed ash and crude fiber were higher and carbohydrate was lower than values reported for field-grown seed. Potato tubers showed little difference from field-grown tubers. With the exception of increased crude fiber of soybean seed with increased CO2, no trends were apparent with regard to CO2 effects on proximate composition of soybean seed and potato tubers. Crude fiber of soybean stems and leaves increased with increased CO2, as did soybean leaf protein (total nitrogen). Potato leaf and stem (combined) protein levels also increased with increased CO2, while leaf and stem carbohydrates decreased. Values for leaf and stem protein and ash were higher than values generally reported for field-grown plants for both species. Results suggest that CO2 partial pressure should have little influence on proximate composition of potato tubers or soybean seed, but that high ash and protein levels might be expected from leaves and stems of crops grown in controlled environments of a CELSS.

Growth and gas exchange by lettuce stands in a closed, controlled environment.

Two studies were conducted in which 'Waldmann's Green' lettuce (Lactuca sativa L.) was grown hydroponically from seed to harvest in a large (20-m2), atmospherically closed growth chamber for the National Aeronautics and Space Administration's controlled ecological life support system (CELSS) program. The first study used metal-halide (MH) lamps [280 micromoles m-2 s-1 photosynthetic photon flux (PPF)], whereas the second used high-pressure sodium (HPS) lamps (293 micromoles m-2 s-1). Both studies used a 16-hour photoperiod, a constant air temperature (22 to 23C), and 1000 micromoles mol-1 CO2 during the light period. In each study, canopy photosynthesis and evapotranspiration (ET) rates were highly correlated to canopy cover, with absolute rates peaking at harvest (28 days after planting ) at 17 micromoles CO2/m2 per sec and 4 liters m-2 day-1, respectively. When normalized for actual canopy cover, photosynthesis and ET rates per unit canopy area decreased with age (between 15 and 28 days after planting). Canopy cover increased earlier during the study with HPS lamps, and final shoot yields averaged 183 g fresh mass (FM)/plant 8.8 g dry mass (DM)/plant. Shoot yields in the first study with MH lamps averaged 129 g FM/plant and 6.8 g DM/plant. Analysis of leaf tissue showed that ash levels from both studies averaged 22% and K levels ranged from 15% to 17% of tissue DM. Results suggest that lettuce should be easily adaptable to a CELSS with moderate lighting and that plant spacing or transplant schemes are needed to maximize canopy light interception and sustained efficient CO2 removal and water production.