Nitrogen fixation in six forage legumes in Mediterranean central Chile

Abstract

The contribution of biological nitrogen fixation (BNF) to the N nutrition of six annual forage legumes, subterranean clover (Trifolium subterraneum), burr medic (Medicago polymorpha), balansa clover (Trifolium michelianum), Persian clover (Trifolium resupinatum), yellow serradela (Ornithopus compressus), and pink serradela (Ornithopus sativus) was evaluated by the ¹⁵N natural abundance technique, using four grass species (Briza máxima, Bromus mollis, Hordeum berteroanum, Avena barbata) and two composite species (Leontodon leysseri and Hedipnois cretica) as reference plants. An additional objective was to determine whether alternative legume species to those in common use (T. subterraneum and M. polymorpha) in the area, could improve BNF. The field studies were conducted in two edaphic conditions, granitic (Entisol) and clay (Vertisol) soil, located in Cauquenes, VII Region, in the sub-humid Mediterranean zone of Chile. In the granitic soil the percentages of N derived from fixation were high in all species (74 to 94%); yellow serradela cv. Tauro presented the greatest N content in dry matter and N fixation, equivalent to 91 kg N ha^?1. In contrast, pink serradela cv. Cádiz and subterranean clover cv. Gosse presented the lowest N fixation. In the clay soil, under periodically waterlogged conditions, balansa clover cv. Paradana and persian clover cv. Prolific had high percentage values of BNF (>95%) and fixed more N (100.2 and 82.5 kg N ha^?1, respectively) than burr medic and subterranean clover cv. Gosse. The present study allowed the identification of new germplasm of high capacity of N fixation which is an additional criterion for selecting species for infertile and waterlogged soil conditions in the Mediterranean area of Chile.     

Influence of Rhizobium/Azotobacter and Rhizobium/Azospirillum combined inoculation on mineral composition of faba bean (Vicia faba L.)

 Mixed inoculation of Vicia faba L. with four different Rhizobium/Azospirillum and Rhizobium/Azotobacter combinations led to changes in total content, concentration and/or distribution of the mineral macro- and micronutrients, K, P, Ca, Mg, Fe, B, Mn, Zn and Cu, when compared with plants inoculated with Rhizobium only. The effects varied to a great extent among the Azotobacter and Azospirillum strains selected for combined inoculation. Received: 6 June 1998     

Daily rhythms of blood glucose differ in diurnal and nocturnal European sea bass (Dicentrarchus labrax L.) undergoing seasonal phase inversions

Sea bass change their feeding rhythms from diurnal to nocturnal in winter, returning to diurnal feeding in spring. Despite behavioral data, the physiological changes that take place during such changes remain unexplored. In this paper, blood glucose rhythms of European sea bass with diurnal/nocturnal self-feeding rhythms were investigated during phase inversions of their feeding behavior (in winter and spring) when both diurnal and nocturnal fish coexist. Blood glucose showed daily variations in both seasons (ANOVA, p < 0.03), fitting a cosine function (COSINOR, p < 0.05) in all cases, except in diurnal fish in spring. The average blood glucose levels of nocturnal fish in winter (2.67 ± 0.09 mmol/l, mean ± SEM) were significantly (t test, p < 0.01) higher than in spring (2.20 ± 0.08 mmol/l), while they were similar (~2.25 mmol/l) in diurnal fish in both seasons. These findings revealed for the first time insights into the seasonal physiological changes that accompany changes in behavioral rhythms in diurnal and nocturnal sea bass.     

Water temperature,time of exposure and population density are key parameters in Enteromyxum leei fish-to-fish experimental transmission

Enteromyxum leei is a myxozoan histozoic parasite that infects the intestine of several teleost fish species. In gilthead sea bream (Sparus aurata), it provokes a chronic disease, entailing anorexia, delayed growth, reduced marketability and mortality. Direct fish-to-fish transmission, relevant in aquaculture conditions, has been demonstrated for E. leei via effluent, cohabitation, and oral and anal routes. However, the minimum time of exposure for infection has not been established, nor the possible effect on the fish immune response. Two effluent trials were performed at different temperatures (high: average of 25.6°C; and low: constant at 18°C), different times of exposure to the effluent (1, 3, 5 and 7 weeks) and different population densities. The results showed that 1 week was enough to infect 100% of fish at high temperature and 58.3% at low temperature. High temperature not only increased the prevalence of infection in posterior intestine, but also induced a higher production of specific antibodies, limiting the progression of the infection along the intestine. Longer time of exposure to the parasite and higher fish densities facilitated E. leei infection. These results show that effective diagnosis, lowering animal density and removal of infected fish are key aspects to manage this disease in aquaculture facilities.     

Analytical study of trichlorfon residues in Kaki fruit and cauliflower samples by liquid chromatography-electrospray tandem mass spectrometry

A detailed analytical study on trichlorfon residues in selected vegetables samples has been carried out, focused on the reliable quantification and confirmation of this compound, and on stability of residues under storage. As a consequence, a rapid and sensitive LC-ESI-MS/MS method has been developed for the determination of residues of this insecticide in kaki fruit (flesh and peel) and cauliflower samples. Extraction was performed with acetonitrile using a high-speed blender. After 4-fold dilution of the extract with water, 20 microL was directly injected in the LC-ESI-MS/MS system (triple quadrupole), using matrix-matched standards calibration for quantification. Under optimized MS/MS conditions, limit of detections between 0.006 and 0.013 mg/kg were reached, and a limit of quantification of 0.05 mg/kg was established, with a runtime of only 15 min. Recoveries from spiked blank samples at 0.05 and 0.5 mg/kg were in the range 83-101% with relative standard deviations lower than 10%. The method was applied to treated and untreated samples collected from field residues trials, using quality control samples analysis for the evaluation of the method. Despite the acquisition of two MS/MS transitions in selected reaction monitoring mode, the analysis of treated samples revealed the presence of a chromatographic peak close to the analyte that corresponded to a trichlorfon isobaric compound that shared the same MS/MS transitions. This unusual situation in LC-MS/MS-based procedures required the application of an efficient chromatographic separation to avoid this interference. All experiments have been made in compliance with the principles of Good Laboratory Practices (GLP) and following the European SANCO guidelines for pesticides residue analysis (PRA).     

Management effectiveness in marine protected areas for conservation of Antillean manatees on the eastern coast of the Yucatan Peninsula,Mexico

1. This study evaluated management effectiveness in three marine protected areas (MPAs) for conservation of the Antillean manatee (Trichechus manatus manatus Linnaeus 1758), located on the eastern coast of the Yucatan Peninsula, Mexico. The MPAs evaluated were the Yum‐Balam Flora and Fauna Reserve, Sian Ka'an Biosphere Reserve, and Chetumal Bay Manatee Sanctuary. The extent of the traditional, popular, and scientific manatee knowledge and research were assessed, as well as the prescribed conservation management actions, relevant stakeholders, and the degree of inclusion of manatee species in the management schemes of these MPAs.
2. Four general criteria, 12 specific criteria, and 62 indicators were developed. In total, 199 interviews were completed in seven communities of the MPAs in order to determine the perception of the social, economic, and conservation impacts of the manatee and its management.
3. Although the evaluated MPAs were not wholly comparable among themselves due to their different management categories and schemes, administration, socio‐economic context, and the dynamics and conflicts encountered, a comparison was conducted using standardized criteria and a categorical scale in order to evaluate the level of effectiveness of each MPA.
4. The MPA with the highest management effectiveness in manatee conservation was found to be the Chetumal Bay, with an effectiveness classed as good (71%), followed by Sian Ka'an with intermediate effectiveness (53%) and Yum‐Balam, also with intermediate effectiveness (43%).
5. The relationships between the key stakeholders of the three MPAs and economic activities such as fishing and tourism are the factors that most influence the effectiveness of management for manatee conservation.

     

A study of gross,histological and blood biochemical changes in rainbow trout,Oncorhynchus mykiss (Walbaum), with rainbow trout gastroenteritis (RTGE)

The mechanisms behind the pathogenesis of rainbow trout gastroenteritis (RTGE) are still unknown. This study examined the macroscopic and microscopic changes in trout with RTGE (RTGE+), as well as the blood chemistry. A total of 464 rainbow trout were sampled from 11 sites in the UK, comprising 152 RTGE+ fish and 330 random, apparently healthy fish. A case definition for RTGE was assessed by the analysis of its agreement with three laboratory tests: histopathology, packed cell volume and kidney bacteriology. Cluster analysis indicated the presence of three distinct presentations within the population of RTGE+ fish. Cluster A included gross signs associated with moribund RTGE+ fish, and clusters B and C identified gross signs consistent with concurrent diseases, notably furunculosis, enteric redmouth and proliferative kidney disease. The information gained was used to select RTGE+ fish without concurrent disease for the analysis of RTGE pathogenesis with blood biochemistry. This analysis revealed a severe osmotic imbalance and a reduced albumin/globulin ratio as indicatives of selective loss of albumin. These findings are compatible with a protein losing enteropathy.