Álvaro García
In agricultural greenhouse gas (GHG) research, attention has centered on reducing emissions from livestock, especially ruminants like cattle, which produce methane (CH₄) through enteric fermentation. This focus arises from the substantial impact of livestock on global GHG emissions, particularly methane, which has a significantly higher global warming potential than carbon dioxide (CO₂). There is extensive study of animal emissions at the present time, with less attention to emissions from fermented feeds, such as silage, which also contribute to the GHG footprint of livestock production. As a primary feed source for ruminants in livestock production systems all over the world, silage undergoes microbial fermentation that generates gases—including CO₂, CH₄, and nitrous oxide (N₂O)—that add to the overall emissions profile of livestock systems.
Despite the increasing reliance on silage as a stable, weather-independent feed source, research on its GHG emissions remains limited. The fermentation process within silage involves a complex interaction of microbial communities that not only determines the nutritional quality of the feed but also affects the types and amounts of gases emitted. As silage production grows globally to support ruminant agriculture, understanding these emissions and microbial involvement becomes essential for both climate change mitigation and agricultural sustainability.
One silage inoculant that makes a difference
A recent study by Hu et al. (2024) addresses this knowledge gap by analyzing the greenhouse gas emissions associated with silage and exploring how microbial activities during fermentation contribute to these emissions. This research sheds light on the specific gases produced during silage fermentation and investigates the role of microbial communities, with a focus on the impact of Lactiplantibacillus (formerly Lactobacillus) bacteria in regulating these emissions. By examining how fermentation conditions and microbial interactions influence GHG production, this study provides potential pathways for reducing emissions from silage, supporting broader sustainability efforts in the agricultural sector.
Lactiplantibacillus plays a vital role in the silage fermentation process, significantly influencing greenhouse gas emissions and overall silage quality. By rapidly lowering the pH of the silage environment, this bacteria creates acidic conditions that inhibit the activity of gas-producing bacteria and restrict plant cell respiration. This quick acidification, especially in the preliminary stages of ensiling, reduces carbon dioxide (CO₂) production and limits total gas output, which aligns with the broader goal of minimizing greenhouse gas emissions in agricultural processes.
Enhanced fermentation efficiency
The introduction of L. plantarum accelerates lactic acid production, significantly improving fermentation efficiency. By quickly lowering the pH, it prevents the growth of spoilage bacteria and yeasts that could degrade the nutritional quality of the silage. Faster acidification also helps reduce the loss of valuable sugars and nutrients, ensuring that more energy and protein remain available for livestock. The graph below shows the study by Vamanu et al. (2005) depicting the growth and lactic acid production of L. plantarum in ensiled forage.
Optical Density (O.D.), is a measure of the light absorbed by a sample at a specific wavelength. In the context of microbial growth or fermentation, O.D. measures the concentration of cells or particles in a solution. At 570 nm (the wavelength shown in the graph), O.D. measurements used to track the growth of bacteria or other cells over time. Higher O.D. values indicate more cells, suggesting increased growth or biomass.
The presence of Lactiplantibacillus has a direct negative correlation with CO₂ production; higher populations of the bacterium are associated with lower overall CO₂ levels during fermentation. This is because Lactiplantibacillus effectively outcompetes other microorganisms that would otherwise contribute to gas production. Although the bacteria’s influence on methane (CH₄) and nitrous oxide (N₂O) emissions is less direct, the acidic environment they foster can suppress other microbial groups that might generate these potent greenhouse gases. Consequently, Lactiplantibacillus indirectly aids in controlling CH₄ and N₂O emissions due to its role in acidifying the silage and stabilizing the microbial ecosystem.
Temperature also impacts the efficacy of Lactiplantibacillus in silage fermentation. Ideal fermentation occurs between 20°C and 30°C, where Lactobacillus thrives and supports optimal fermentation conditions. In cooler conditions, such as 5°C to 10°C, Lactiplantibacillus activity decreases, leading to lower production of lactic and acetic acids, which can result in increased sugar content and potentially alter gas emissions. On the other hand, at higher temperatures (around 40°C), Lactobacillus populations decline, giving way to other bacterial species, which can affect silage quality and alter greenhouse gas composition.
The y-axis on this graph at A600, refers to the absorbance at six hundred nanometers (nm). In microbiology, this measure monitors the growth of bacterial cultures, as it indicates the optical density (O.D.) of the sample, which correlates with the concentration of bacteria in the medium. A higher A600 value reflects a greater bacterial population in the culture over time.
In summary, Lactiplantibacillus is essential for reducing greenhouse gas emissions during silage fermentation through its rapid pH-lowering effect, suppression of competing bacteria, and stabilization of the silage environment. The impact of Lactobacillus is also temperature-dependent, highlighting the need for optimal storage conditions to maximize its emission-reducing benefits. Further research could focus on enhancing specific Lactobacillus strains and refining ensiling conditions to improve both fermentation quality and environmental sustainability in agricultural practices.
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