Does Faeces Excreted by Moxidectin-Treated Sheep Impact Coprophagous Insects and the Activity of Soil Microbiota in Subtropical Pastures?

Moxidectin (MOX) is used to control helminth parasites in ruminant livestock. It is released through feces and remains in the environment for a long period. This study aimed to evaluate the impact of faeces excreted by moxidectin-treated sheep on soil biodiversity (coprophagous insects, soil microbial biomass, and activity) to establish environment-related guidelines regarding the use of MOX in sheep livestock. The study consisted of two experiments. In the first one, faeces from MOX-treated (subcutaneous dose of 0.2 mg·kg-1 body weight) and nontreated rams were placed on an animal-free pasture field, protected or not against rain, for 88 days. Then, coprophagous insects were captured, identified, and counted, and faeces degradation was evaluated by measuring dry weight and carbon (C) and nitrogen (N) contents over time. Diptera, Hymenoptera, Isoptera, and Coleoptera were equally encountered in faeces from MOX-treated and nontreated animals. Faecal boluses of MOX-treated animals (with higher N content) not protected against rain degraded faster than faecal boluses of nontreated animals (with lower N content). In the second experiment, faeces from nontreated animals were amended with increasing amounts of MOX (75 to 3,000 ng·kg-1 faeces), mixed with soil samples from animal-free pasture (1.9 to 75 ng·kg-1 soil), and incubated in a greenhouse for 28 days. Increasing concentrations of MOX did not prevent the growth of cultivable bacteria, actinobacteria, or fungi in culture media. However, even the lower MOX concentration (1.9 ng·kg-1 soil) abruptly decreased soil microbial biomass, basal respiration, and N mineralization. Thus, the results indicate that faeces excreted from sheep treated with MOX under the experimental conditions of this study are not harmful to the coprophagous insects. However, adding MOX to faeces from drug-free sheep had a negative impact on soil microbial activity and biomass.

Coinoculation impact on plant growth promotion: a review and meta-analysis on coinoculation of rhizobia and plant growth-promoting bacilli in grain legumes.

Coinoculation of symbiotic N2-fixing rhizobia and plant growth-promoting Bacillus on legume seeds can increase crop productivity. We collected highly resolved data on coinoculation of rhizobia and bacilli on 11 grain legume crops: chickpea, common bean, cowpea, faba bean, groundnut, lentil, mung bean, pea, pigeon pea, soybean, and urad bean to verify the magnitude of additive effects of coinoculation in relation to single inoculation of rhizobia on plant growth and yield of grain legumes. Coinoculation of rhizobia and bacilli on legume seeds and/or soil during sowing significantly increased nodulation, nitrogenase activity, plant N and P contents, and shoot and root biomass, as well as the grain yield of most grain legumes studied. There were however a few instances where coinoculation decreased plant growth parameters. Therefore, coinoculation of rhizobia and Bacillus has the potential to increase the growth and productivity of grain legumes, and can be recommended as an environmental-friendly agricultural practice for increased crop yields.

Crop rotation reduces the frequency of anaerobic soil bacteria in Red Latosol of Brazil.

Crop diversity affects the processes of soil physical structuring and most likely provokes changes in the frequencies of soil microbial communities. The study was conducted for soil prokaryotic diversity sequencing 16S rDNA genes from a 25-year no-tillage experiment comprised of two crop systems: crop succession (Triticum aestivum-Glycine max) and rotation (Vicia sativa-Zea mays-Avena sativa-Glycine max-Triticum aestivum-Glycine max). The hypothesis was that a crop system with higher crop diversification (rotation) would affect the frequencies of prokaryotic taxa against a less diverse crop system (succession) altering the major soil functions guided by bacterial diversity. Soils in both crop systems were dominated by Proteobacteria (31%), Acidobacteria (23%), Actinobacteria (10%), and Gemmatimonadetes (7.2%), among other common copiotrophic soil bacteria. Crop systems did not affect the richness and diversity indexes of soil bacteria and soil archaea. However, the crop rotation system reduced only the frequencies of anaerobic metabolism bacteria Chloroacidobacteria, Holophagae, Spirochaetes, Euryarchaeota, and Crenarchaeota. It can be concluded that crop succession, a system that is poorer in root diversity over time, may have conditioned the soil to lower oxygen diffusion and built up ecological niches that suitable for anaerobic bacteria tolerating lower levels of oxygen. On the other hand, it appeared that crop rotation has restructured the soil over the years while enabling copiotrophic aerobic bacteria to dominate the soil ecosystem. The changes prompted by crop succession have implications for efficient soil organic matter decomposition, reduced greenhouse gas emissions, higher root activity, and overall soil productivity, which compromise to agriculture sustainability.

Rhizobial inoculation in black wattle plantation (Acacia mearnsii De Wild.) in production systems of southern Brazil.

Black wattle (Acacia mearnsii De Wild.) is a tree legume native to southeast Australia, but present in all continents. Today it covers about 142,400 ha in Brazil, with plantations concentrated in the southern region of the country. Black wattle may form nodules and establish rhizobial symbiosis capable of fixing N2, but rhizobial inoculation is not done in commercial plantations. About 40 kg ha-1 of urea is applied during seedling transplantation. In this review, evidences by which rhizobial inoculation affects monoculture, mixed cultivation, and agroforestry black wattle production systems were searched in literature. Previous measurements in cultivated forests have indicated that biological nitrogen fixation in black wattle may provide up to 200 kg of N ha-1 year-1 to the soil. Therefore, rhizobia inoculation may bring several opportunities to improve black wattle production systems. Black wattle is not a very selective partner in the rhizobial symbiosis, but the genus Bradyrhizobium dominates the rhizobial diversity of black wattle nodules. Investigation on rhizobial diversity in soils where the crop is cultivated may represent an opportunity to find more effective rhizobia strains for inoculants. The successful history of biological nitrogen fixation in grain legumes must inspire the history of tree legumes. Microbiology applied to forestry must overcome challenges on the lack of trained professionals and the development of new application technologies.

Soil fungal and bacterial biomass determined by epifluorescence microscopy and mycorrhizal spore density in different sugarcane managements / Biomassa fúngica e bacteriana do solo determinada por microscopia de epifluorescência e densidade de esporos micorrízicos em diferentes manejos de cana de açúcar

Crop productivity and sustainability have often been related to soil organic matter and soil microbial biomass, especially because of their role in soil nutrient cycling. This study aimed at measuring fungal and bacterial biomass by epifluorescence microscopy and arbuscular mycorrhizal fungal (AMF) spore density in sugarcane (Saccharum officinarum L.) fields under different managements. We collected soil samples of sugarcane fields managed with or without burning, with or without mechanized harvest, with or without application of vinasse and from nearby riparian native forest. The soil samples were collected at 10cm depth and storage at 4°C until analysis. Fungal biomass varied from 25 to 37µg C g-1 dry soil and bacterial from 178 to 263µg C g-1 dry soil. The average fungal/bacterial ratio of fields was 0.14. The AMF spore density varied from 9 to 13 spores g-1 dry soil. The different sugarcane managements did not affect AMF spore density. In general, there were no significant changes of microbial biomass with crop management and riparian forest. However, the sum of fungal and bacterial biomass measured by epifluorescence microscopy (i.e. 208-301µg C g-1 dry soil) was very close to values of total soil microbial biomass observed in other studies with traditional techniques (e.g. fumigation-extraction). Therefore, determination of fungal/bacterial ratios by epifluorescence microscopy, associated with other parameters, appears to be a promising methodology to understand microbial functionality and nutrient cycling under different soil and crop managements.

A produtividade e sustentabilidade das culturas têm sido frequentemente relacionadas com a matéria orgânica e a biomassa microbiana do solo, especialmente devido ao seu papel na ciclagem de nutrientes do solo. Este trabalho teve como objetivo avaliar a biomassa de fungos e bactérias do solo por microscopia de epifluorescência e a densidade de esporos de fungos micorrízicos arbusculares (FMAs) em lavouras de cana de açúcar (Saccharum officinarum L.) sob diferentes manejos. Foram coletadas amostras de solo de lavouras manejadas com ou sem queima, com ou sem colheita mecanizada, com ou sem aplicação de vinhaça e de matas ciliares adjacentes. As amostras de solo foram coletadas a 10 cm de profundidade e mantidas a 4°C até o momento das análises. A biomassa fúngica variou de 25 a 37µg C g-1 de solo seco e a bacteriana, de 178 to 263µg C g-1 de solo seco. A razão média entre a biomassa fúngica e bacteriana do solo nos diferentes manejos de canaviais foi de 0,14. A densidade de esporos de FMAs variou de 9 a 13 esporos g-1 de solo seco. Os diferentes manejos da cana de açúcar não afetaram significativamente a densidade de esporos de FMAs. Em geral, não foram encontradas mudanças significativas na biomassa microbiana nos diferentes manejos de solo com cana de açúcar em comparação com a mata ciliar. Todavia, a soma das biomassas fúngicas e bacterianas (208 a 301µg C g-1 de solo seco) determinadas por microscopia de epifluorescência foram similares a resultados da biomassa total do solo encontrados em outros estudos com métodos tradicionais (e.g. fumigação-extração). Os resultados evidenciam que a determinação da razão fungo/bactéria por microscopia de epifluorescência, associada a outros parâmetros, é uma metodologia promissora para compreender a funcionalidade microbiana e ciclagem de nutrientes sob diferentes manejos do solo.

Genetic variability in Bradyrhizobium japonicum strains nodulating soybean [Glycine max (L.) Merrill].

Brazil has succeeded in sustaining production of soybean [Glycine max (L.) Merrill] by relying mainly on symbiotic N(2) fixation, thanks to the selection and use in inoculants of very effective strains of Bradyrhizobium japonicum and Bradyrhizobium elkanii. It is desirable that rhizobial strains used in inoculants have stable genetic and physiological traits, but experience confirms that rhizobial strains nodulating soybean often lose competitiveness in the field. In this study, soybean cultivar BR 16 was single-inoculated with four B. japonicum strains (CIAT 88, CIAT 89, CIAT 104 and CIAT 105) under aseptic conditions. Forty colonies were isolated from nodules produced by each strain. The progenitor strains, the isolates and four other commercially recommended strains were applied separately to the same cultivar under controlled greenhouse conditions. We observed significant variability in nodulation, shoot dry weight, shoot total N, nodule efficiency (total N mass over nodule mass) and BOX-PCR fingerprinting profiles between variant and progenitor strains. Some variant strains resulted in significantly larger responses in terms of shoot total N, dry weight and nodule efficiency, when compared to their progenitor strain. These results highlight the need for intermittent evaluation of stock bacterial cultures to guarantee effective symbiosis after inoculation. Most importantly, it indicates that it is possible to improve symbiotic effectiveness by screening rhizobial strains for higher N(2) fixation capacity within the natural variability that can be found within each progenitor strain.