Microbiological parameters as indicators of soil quality under various soil management and crop rotation systems in southern Brazil

The objective of this work was to identify soil parameters potentially useful to monitor soil quality under different soil management and crop rotation systems. Microbiological and chemical parameters were evaluated in a field experiment in the State of Paraná, southern Brazil, in response to soil management [no-tillage (NT) and conventional tillage (CT)] and crop rotation [including grain (soybean, S; maize, M; wheat, W) and legume (lupin, L.) and non-legume (oat, O) covers] systems. Three crop rotation systems were evaluated: (1) (O/M/O/S/W/S/L/M/O/S), (2) (O/S/L/M/O/S/W/S/L/M), and (3) (O/S/W/S/L/M/O/M/W/M), and soil parameters were monitored after the fifth year. Before ploughing, CO₂-emission rates were similar in NT and CT soils, but plough increased it by an average of 57%. Carbon dioxide emission was 13% higher with lupin residues than with wheat straw; decomposition rates were rapid with both soil management systems. Amounts of microbial biomass carbon and nitrogen (MB-C and MB-N, respectively) were 80 and 104% higher in NT than in CT, respectively; however, in general these parameters were not affected by crop rotation. Efficiency of the microbial community was significantly higher in NT: metabolic quotient (qCO₂) was 55% lower than in CT. Soluble C and N levels were 37 and 24% greater in NT than in CT, respectively, with no effects of crop rotation. Furthermore, ratios of soluble C and N contents to MB-C and MB-N were consistently lower in NT, indicating higher immobilization of C and N per unit of MB. The decrease in qCO₂ and the increase in MB-C under NT allowed enhancements in soil C stocks, such that in the 0–40 cm profile, a gain of 2500 kg of C ha⁻¹ was observed in relation to CT. Carbon stocks also varied with crop rotation, with net changes at 0–40 cm of 726, 1167 and −394 kg C ha⁻¹ year, in rotations 1, 2 and 3, respectively. Similar results were obtained for the N stocks, with 410 kg N ha⁻¹ gained in NT, while crop rotations 1, 2 and 3 accumulated 71, 137 and 37 kg of N ha⁻¹ year⁻¹, respectively. On average, microbial biomass corresponded to 2.4 and 1.7% of the total soil C, and 5.2 and 3.2% of the N in NT and CT systems, respectively. Soil management was the main factor affecting soil C and N levels, but enhancement also resulted from the ratios of legumes and non-legumes in the rotations. The results emphasize the importance of microorganisms as reservoirs of C and N in tropical soils. Furthermore, the parameters associated with microbiological activity were more responsive to soil management and crop rotation effects than were total stocks of C and N, demonstrating their usefulness as indicators of soil quality in the tropics.     

Benefits of inoculation of the common bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis>) crop with efficient and competitive<Emphasis Type="Italic"> Rhizobium tropici</Emphasis> strains

Cropping in low fertility soils, especially those poor in N, contributes greatly to the low common bean (Phaseolus vulgaris L.) yield, and therefore the benefits of biological nitrogen fixation must be intensively explored to increase yields at a low cost. Six field experiments were performed in oxisols of Paraná State, southern Brazil, with a high population of indigenous common bean rhizobia, estimated at a minimum of 10³ cells g^–1 soil. Despite the high population, inoculation allowed an increase in rhizobial population and in nodule occupancy, and further increases were obtained with reinoculation in the following seasons. Thus, considering the treatments inoculated with the most effective strains (H 12, H 20, PRF 81 and CIAT 899), nodule occupancy increased from an average of 28% in the first experiment to 56% after four inoculation procedures. The establishment of the selected strains increased nodulation, N₂ fixation rates (evaluated by total N and N-ureide) and on average for the six experiments the strains H 12 and H 20 showed increases of 437 and 465 kg ha^–1, respectively,in relation to the indigenous rhizobial population. A synergistic effect between low levels of N fertilizer and inoculation with superior strains was also observed, resulting in yield increases in two other experiments. The soil rhizobial population decreased 1 year after the last cropping, but remained high in the plots that had been inoculated. DGGE analysis of soil extracts showed that the massive inoculation apparently did not affect the composition of the bacterial community.     

Transgenic plants expressing immunosuppressive dsRNA improve entomopathogen efficacy against Spodoptera littoralis larvae

Journal of Pest Science - Transgenic plants that express double-stranded RNA (dsRNA) targeting vital insect genes have recently emerged as a valuable new tool for pest control. In this study,...     

Effects of population density on seabass (Dicentrarchus labrax, L.) gene expression

The issue of animal welfare in aquaculture is growing of interest and there is an increasing consumer demand for documentation of safe and ethically defendable food production. In this context, we have looked for molecular markers among those genes whose expression results modified by the different farming conditions. We have compared gene expression of seabass farmed at different population densities by differential display. We have obtained six bands differentially expressed whose sequences we have deposited in the public databases; two of them resulted suppressed by high population density, while four were induced by the treatment. Population density has, therefore, an effect at gene level by repressing or enhancing the expression of different genes. These genes can be used as biomarkers to rapidly detect, by polymerase chain reaction (PCR), the occurred exposure of the fish to the stressor.

We are certain that the new molecular techniques will find their place in the everyday management of fish farming; on the other hand, we are also aware that the scarcity of the genomic resources for some fish species, in spite of their economical interest, will retard the beneficial effects that modern biotechnology could bring to aquaculture industry. Therefore, an effort should be made to reduce, as far as it concerns genomics resources, the gap that separates farming species from “model organisms”.     

Evaluation of canine antimicrobial peptides in infected and noninfected chronic atopic skin

Background – Antimicrobial peptides (AMPs) are small immunomodulatory peptides produced by epithelial and immune cells. β‐Defensins (BDs) and cathelicidins (Caths) are the most studied AMPs. Recently, increased cutaneous expression of AMPs was reported in atopic humans and in beagles with experimentally induced atopy. Hypothesis/Objectives – Our goal was to analyse mRNA expression and protein levels of canine (c)BD1‐like, cBD2‐like/122, cBD3‐like, cBD103 and cCath in healthy and naturally affected atopic dogs, with and without active skin infection, along with their distribution in the epidermis using indirect immunofluorescence. Animals – Skin biopsies were taken from 14 healthy and 11 atopic privately owned dogs. Methods – The mRNA levels of cBD1‐like, cBD2‐like/122, cBD3‐like, cBD103 and cCath were quantified using quantitative real‐time PCR. The protein levels of cBD3‐like and cCath were analysed by relative competitive inhibition enzyme‐linked immunosorbent assay, while the distributions of cBD2‐like/122, cBD3‐like and cCath were detected by indirect immunofluorescence. Results – Dogs with atopic dermatitis had significantly greater mRNA expression of cBD103 (P = 0.04) than control dogs. Furthermore, atopic skin with active infection had a higher cBD103 mRNA expression (P = 0.01) and a lower cBD1‐like mRNA expression (P = 0.04) than atopic skin without infection. No significant differences in protein levels (cBD3‐like and cCath) or epidermal distribution of AMPs (cBD2‐like/122, cBD3‐like and cCath) were seen between healthy and atopic dogs. Conclusions and clinical importance – Expression of cBD103 mRNA was greater, while expression of cBD1‐like mRNA was lower in dogs with atopic dermatitis that had active infections. Work is needed to clarify the biological mechanisms and possible therapeutic options to maintain a healthy canine skin.     

Microbial biomass under various soil- and crop-management systems in short- and long-term experiments in Brazil

Management and cropping systems varying in soil mobilization rates and plant-residue inputs may have profound effects on the biological properties of soil. Therefore, the objective of this study was to quantify soil microbial biomass carbon and nitrogen (MB-C and MB-N)—by means of the fumigation-extraction method—under varied soil-management and crop-rotation/succession systems in southern Brazil, correlating the results with yields of soybean and maize crops. The microbial biomass and grain yields were examined at the 0–10 cm layer in four short- to long-term field experiments. Experiment 1 was a 26-year trial consisting of four soil-management systems: (1) no-tillage (NT), (2) conventional tillage [(CT) with disc plough], (3) field cultivator (FC) or (4) heavy-disc harrow (DH), each with a crop succession (CS) of soybean (summer) and wheat (winter). Experiment 2 was a 21-year trial consisting of one CS, soybean/wheat every year) and seven crop rotations (CRs) comprising soybean, maize, wheat and green manures (lupine, radish and black oat), under the NT system. Experiment 3 comprised a 14-year CT trial, and 4-year and 14-year NT trials, with both one CS and two CRs. Experiment 4, a 10-year trial consisted of CT and NT and three CRs. Analyses were performed during the summer and winter croppings. Differences in microbial parameters, as a function of crop succession and rotation, were not easily detected as they varied as a function of a complex combination of plant species and time of implementation of the experiment. In contrast, MB-C and MB-N values were consistently higher—up to more than 100%—under NT in comparison to CT and were associated with higher grain yields. Our results—from this wide range of experiments—suggest that MB-C and, particularly, MB-N are sensitive indicators of the effects of soil- and crop-management regimens.     

Apple juice clarification by immobilized pectolytic enzymes in packed or fluidized bed reactors

The catalytic behavior of a mixture of pectic enzymes, covalently immobilized on different supports (glass microspheres, nylon 6/6 pellets, and PAN beads), was analyzed with a pectin aqueous solution that simulates apple juice. The following parameters were investigated: the rate constant at which pectin hydrolysis is conducted, the time (tau(50)) in which the reduction of 50% of the initial viscosity is reached, and the time (tau(comp,dep)) required to obtain complete depectinization. The best catalytic system was proven to be PAN beads, and their pH and temperature behavior were determined. The yields of two bed reactors, packed or fluidized, using the catalytic PAN beads, were compared to the circulation flow rate of real apple juice. The experimental conditions were as follows: pH 4.0, T = 50 degrees C, and beads volume = 20 cm(3). The initial pectin concentration was the one that was present in our apple juice sample. No differences were observed at low circulation rates, while at higher recirculation rates, the time required to obtain complete pectin hydrolysis into the fluidized reactor was found to be 0.25 times smaller than in the packed bed reactor: 131 min for the packed reactors and 41 min for the fluidized reactors.     

Establishment of <Emphasis Type="Italic">Bradyrhizobium japonicum</Emphasis> and <Emphasis Type="Italic">B. elkanii</Emphasis> strains in a Brazilian Cerrado oxisol

The competition with established soil populations of Bradyrhizobium able to nodulate soybean has been one of the major constraints to the introduction of more efficient strains in Cerrados soils. The effects of nodulation establishment and persistence of four serologically distinct strains of Bradyrhizobium japonicum (CPAC 15 and CPAC 7, belonging to serogroups USDA 123 and CB 1,809) and B. elkanii (29 W and SEMIA 587, belonging to serogroups 29 W and 587) were examined. These strains were introduced in a dark-red oxisol, without indigenous populations of soybean bradyrhizobia, and were evaluated for 6 years. The experimental design was a completely randomized block with four replicates. In the first year, besides the inoculation treatments, there was also an uninoculated control. In the second year, the main plots were split into three sub-plots and treatments consisted of an uninoculated control, CPAC 7 and CPAC 15. In the third year, the entire area was inoculated with CPAC 7. In the fourth and sixth years, the plots were planted with soybean without inoculation, and in the fifth year the plots were left fallow. The strains introduced in the first year influenced nodule occupancy by strain CPAC 7 until the third successive growing season. By the fourth and sixth years, as a consequence of the dispersal of strains serologically related to serocluster 123 in the entire experimental area, this serogroup dominated the nodulation, occurring, on average, in more than 50% of the nodules of the treatments where it had never been inoculated.