A large‐scale approach can help detect general processes driving the dynamics of brown trout populations in extensive areas

Abstract – Most studies on the population dynamics of stream‐living salmonids have been conducted at the scale of a reach, a stream or a river basin. This can lead to overestimating the importance of local factors acting on a reduced scale compared to the more general factors that drive the dynamics of several populations. Two models were built on the basis of a data set from 60 sampling stations representing separated populations inhabiting a large heterogeneous area encompassing 18 years of quantifications. Our analyses showed the following: (i) Population growth rate (pgr) of a set of independent brown trout populations can be described by means of a single model; (ii) the youngest and the oldest year classes of these populations seem to be limited by the same constraints; (iii) there is a climatic control of the recruitment because of spring weather conditions, but also the abundance of oldest age class may be controlled by the climate, (iv) there is a nonlinear positive effect of winter North Atlantic Oscillation on pgr; (v) there is a 3‐year lagged positive feedback tracing the upward trend of a stock‐recruitment curve, and 1‐year lagged negative feedback showing the downward trend of the curve; (vi) a strong cohort has a positive effect on the whole population that can be detected throughout the time. Our fitted models allowed to predict the mean population densities at a regional scale with <10% error and shed light onto the main factors and associated ecological processes that control these large‐scale dynamics.     

Use of electrical nerve stimulation to monitor lumbosacral epidural needle placement in cats

ObjectiveTo determine the minimal electrical threshold (MET) necessary to elicit muscle contraction of the pelvic limb or tail when an insulated needle is positioned outside (MET_out) and inside (MET_in) the lumbosacral epidural space in cats.Study designProspective, blinded study.AnimalsTwelve mixed-breed healthy adult cats, scheduled for a therapeutic procedure where lumbosacral epidural administration was indicated.MethodsUnder general anesthesia, an insulated needle was advanced through tissues of the lumbosacral interspace until its tip was thought to be just dorsal to the interarcuate ligament. An increasing electrical current (0.1 ms, 2 Hz) was applied through the stimulating needle in order to determine the MET necessary to obtain a muscle contraction of the pelvic limb or tail (MET_out), and then 0.05 mL kg^?1 of iohexol was injected. The needle was further advanced until its tip was thought to be in the epidural space. The MET was determined again (MET_in) and 0.2 mL kg^?1 of iohexol was injected. The cats were maintained in sternal position. Contrast medium spread was determined through lateral radiographic projections.ResultsThe radiographic study confirmed the correct needle placement dorsal to the interarcuate ligament in all cats. When the needle was placed ventrally to the interarcuate ligament, iohexol was injected epidurally in ten and intrathecally in two cats. The MET_out and MET_in was 1.76 ± 0.34 mA and 0.34 ± 0.07 mA, respectively (p < 0.0001).Conclusion and clinical relevanceNerve stimulation can be employed as a tool to determine penetration of the interarcuate ligament but not the piercing of the dura mater at the lumbosacral space in cats.     

Dry matter intake and milk production of grazing dairy cows supplemented with corn silage or a total mixed ration offered ad libitum in a subtropical area

This study aimed to evaluate the feeding choice, dry matter (DM) intake, and milk production of dairy cows that strip grazed on a mixed perennial species pasture receiving different supplementation strategies. The treatments were without supplementation (WS) or with supplementation of either corn silage (CS) or a total mixed ration (TMR) based on CS and concentrates, in a subtropical area. The supplements were provided ad libitum after the afternoon milking. Twelve Holstein × Jersey cows in mid-lactation (133 ± 43 days in milk) were divided into six groups (two cows/group) and distributed in accordance with a replicated 3 × 3 Latin square design, with three 21 day periods (15 adaptation days and 6 evaluation days). The total DM intake, milk production, milk fat, and milk protein production were greater in the TMR treatment than in the WS and CS treatments and were similar between the WS and CS treatments. The herbage DM intake and proportion of time spent grazing were greater in the CS treatment than in the TMR treatment. CS supplementation did not affect the total DM intake or milk production/cow, whereas TMR supplementation greatly improved the total DM intake and milk production of the dairy cows grazing on mixed perennial species.     

Effect of artificial chilling on the depth of endodormancy and vegetative and flower budbreak of peach and nectarine cultivars using excised shoots

Stem cuttings were obtained from 12 peach and nectarine cultivars during leaf fall, placed in plastic bags at 3.0 ± 0.1 °C to simulate 0–800 h of chilling and forced to budbreak at 20.0 ± 1.0 °C for a period of 6 weeks. Some cultivars showed high blooming and leafing without exposure to chilling; chilling enhances leafing and blooming but the percentage increment was higher in leaf buds. In general, maximum budbreak was reached with less chilling accumulation (<100–200 h) in flower buds compared with leaf buds; excessive chilling caused a reduction of the percentage budbreak in flower but not in leaf buds. Additionally, chilling modified the proportion of blooming that occurred before leafing. In non-chilled shoots, blooming occurred earlier than leafing, except in cv. ‘San Pedro 16–33’ but the proportion of blooming before leafing decreased significantly with chilling in most cases. By studying the mean time to budbreak, we conclude that the flower bud generally has a lower intensity of rest; the intensity of rest declines at a slower rate in flower than in leaf buds with chilling; flower buds had greater heat requirements than leaf buds when the chilling requirement had been covered, so that each peach cultivar had a point of critical chilling accumulation below which blooming tended to occur earlier, and above which leafing tends to occur first. Flower and leaf buds had different depths of endodormancy but similar chilling requirements in the majority of peach and nectarine cultivars studied. Finally, different varieties with similar chilling requirements showed different responses to chilling. Therefore, the cutting test measuring the response of vegetative and floral buds provides considerable information on the characterisation of the variety, compared with the sole and traditional data of chilling requirements.     

Impact of the suppression of lipoxygenase and hydroperoxide lyase on the quality of the green odor in green leaves

Most of the volatile compounds responsible for the "green" notes to the aroma of fruits and vegetables are produced by the degradation of polyunsaturated fatty acids through the lipoxygenase pathway. The most determinant steps of this pathway are the peroxidation of free linoleic or linolenic acid by the action of lipoxygenase and then the lysis of the resulting hydroperoxides through a reaction catalyzed by the hydroperoxide lyase. This work analyzes the impact of the depletion of these enzymes on the volatile composition of leaves from potato plants. A characterization of the volatile profiles of the different potato mutants, a study of the metabolism of radiolabeled linoleic acid, and a determination of lipoxygenase activity have been carried out. The depletion of hydroperoxide lyase induced an increase in the lipoxygenase activity and the content of C5 volatiles, whereas the lipoxygenase silencing caused a severe decrease in the amount of volatiles produced by the leaves and always in the intensity of their aroma. The changes in the sensory evaluation of leaf aroma, as correlated to depletion of the two enzymes, have been investigated. The perspectives of producing vegetable products with a modified aroma by genetic engineering are discussed in light of the statistical results.     

Azospirillum brasilense Az39 and Bradyrhizobium japonicum E109, inoculated singly or in combination,promote seed germination and early seedling growth in corn (Zea mays L.) and soybean (Glycine max L.)

Inoculants are biological formulations that combine a stable microorganism population and various types of compounds produced and released during fermentation, such as phytohormones and plant growth regulators. Azospirillum brasilense strain Az39 and Brayrhizobium japonicum strain E109 were previously shown to produce indole 3-acetic acid (IAA), gibberellic acid (GA₃) and zeatin (Z). We tested the hypothesis that such compounds are responsible for early growth promotion in inoculated corn (Zea mays L.) and soybean (Glycine max L.) seedlings. Seeds were inoculated with Az39, E109, or both, and kept in a chamber at 20–30 °C under a controlled photoperiod to evaluate seed germination. To evaluate root and shoot length and dry weight, and number of nodules and percentage of nodulated seedlings, in soybean, seedlings were kept in a growth chamber for 14 days under similar photoperiod and temperature conditions. Az39 and E109, singly or in combination, showed the capacity to promote seed germination, nodule formation, and early development of corn and soybean seedlings. Both strains were able to excrete IAA, GA₃ and Z into the culture medium, at a concentration sufficient to produce morphological and physiological changes in young seed tissues.     

Chromosome numbers and ploidy levels of<Emphasis Type="Italic"> Paspalum</Emphasis> species from subtropical South America (Poaceae)

Somatic chromosome numbers of 131 accessions belonging to 55 Paspalum species from subtropical South America have been determined. All species had x = 10 as a basic chromosome number, except P. almum which had x = 6. Six ploidy levels were found among species with tetraploidy as the most frequent condition. New diploid and octoploid counts were reported. For Paspalum lilloi and P. glabrinode (both 2n = 2x = 20), and for P. ellipticum, P. erianthoides, P. ovale and P. remotum (all 2n = 8x = 80) sporophytic chromosome numbers are presented for the first time. Records that differ from previously reported counts are given for the following species: P. paucifolium (2n = 2x = 20), P. ceresia (2n = 6x = 60), P. conjugatum (2n = 6x = 60), P. alcalinum (2n = 6x = 60) and P. aff. arundinellum (2n + 1 = 5x + 1 = 51). These chromosome data are discussed in light of ploidy-level variation and implications for breeding systems within and among species.     

Influence of tillage systems on biological properties of a Typic Argiudoll soil under continuous maize in central Argentina

Farmers are increasingly using zero tillage in Central Argentina to replace other tillage systems. Intensive tillage decreases soil organic matter content and causes physical degradation. The objective of this work was to evaluate changes in some soil biological properties induced by different tillage systems. A 6 year experiment in which continuous maize (Zea mays L.) was grown using three tillage systems (conventional tillage, reduced tillage and zero tillage) was carried out at Córdoba Province, Argentina, on a Typic Argiudoll. Variations in total organic C content, microbial biomass C, metabolic quotient (qCO₂) and the proportion of the organic C present in the microbial biomass were evaluated at two sampling depths (0–5 and 5–15 cm). Additional samples from a nearby site (undisturbed grassland) were also taken and considered as a control. Concentrations of soil organic C and microbial biomass C were higher under zero tillage as compared with conventional tillage, at the 0–5 cm soil depth. Differences were not evident among tillage systems at the 5–15 cm soil depth. An analysis of the microbial biomass C content, in relation to the organic C, revealed higher values at the 0–5 cm soil depth only for those systems which provoke less disturbance of the soil (i.e. reduced tillage and zero tillage). Significantly greater amounts of CO₂---C were released from zero tillage and reduced tillage soils than from conventionally tilled soils. This release was positively correlated with microbial biomass C. qCO₂ values were not significantly different between tillage systems. Zero tillage proved to be more efficient in the conservation of organic C and microbial biomass C. The tillage system's impact on respiration was due to its effect on the microbial biomass.     

AMMONIUM AND NITRATE IN SOIL AND RATOON SUGARCANE GROWN IN FUNCTION OF NITROGEN ON OXISOL

After harvest, sugarcane residues left on the soil surface can alter nitrogen (N) dynamics in the plant-soil system. In Oxisols, the nitrogen fertilizer applied had its effects on the levels of ammonium and nitrate in the soil, N concentration in the plant leaves, and on the growth and productivity of second ratoon plants. The N rates tested were of 0, 60, 120, 180, and 240 kg ha^?1. Each treatment was replicated four times. Four months after the experiment was started, ammonium and nitrate concentration in the soil, N levels in plant leaves, and plant growth were evaluated. Productivity was evaluated 11 months after the experiment was set. By increasing the content of mineral N in soil, plant growth variables reflected differences in the production of stems; however, it did not affect foliar N. The use of leaf analysis was not important to assess the nutritional status of nitrogen in the ratoon sugarcane. Nitrogen concentration in soil was affected by nitrogen fertilization, but not the N content in leaves. The rate of 138 kg N ha^?1enabled greater production of sugarcane stalks (140 t ha^?1).