The decomposition of plant residues contributes a large amount of carbon dioxide to the atmosphere. An academic study in the Depressed Pampa found that applying herbicides to promote winter foraging increased this process.
Grasslands cover 25% of the planet and store a third of terrestrial carbon. Therefore, understanding how they work is key to troubleshooting problems that affect them. In Argentina’s depressed pampas, cattle producers use the herbicide glyphosate to boost production of much-needed winter forage. Although this agrochemical acts directly on some plants, little is known about its adverse effects. A study by the UBA Faculty of Agronomy (FAUBA) in that area found that applying glyphosate increased brush decomposition by 140%, the main route of CO2 loss to the atmosphere. They debate the vulnerability of these grasslands.
One fourth of the earth’s surface is covered by grasslands. These systems store vast amounts of carbon (C) and provide many benefits to humanity. In this sense, Lucía Vivanco, professor of ecology at FAUBA, pointed out that it is important to better understand the C cycle and, in particular, the decomposition of dead plant material – or brush-, among the most important ways CO2 is lost towards There is one. Climate.
In the natural pastures of our repressed pampa, ranchers seeking to increase beef and calf production use glyphosate to improve the quantity and quality of winter forage. “They use this herbicide in late summer to reduce competition from summer plant species and encourage winter production; In particular, it aims to promote Lolium multiflorum, a forage plant known as annual ryegrass”, explained Magdalena Druille, Professor of Forage Farming at our Faculty.
“For one thing, we wondered what effect glyphosate has on brush decomposition. And on the other hand, it inspired us to generate theoretical knowledge that served as a framework for understanding how, in general, how herbicides can affect this ecosystem process. In other words, we do not study the effects of an agrochemical simply on generating more brush or killing certain plants or soil organisms, nor do we The only time it has survived the effects of a single application is when it has been used regularly over the years in different agroecosystems.”, said Marina Omasini, a teacher in the same department as Lucia.
Vivanco said glyphosate is applied in liquid form to pasture. The problem is that the herbicide not only reaches the ‘target’ plants, but also other components of the ecosystem, such as brush or soil, where it can affect rotting microorganisms.
“We were also interested to learn how other grazing processes are affected when the application is repeated year after year. For example, what will happen to soil respiration closely linked to CO2 loss? Or, the boost per ryegrass What are the consequences of giving, given that it lives in symbiosis with an endophytic fungus within its tissues?” thought Lucia.
decomposition, a sensitive process
The researchers found that glyphosate can act in opposite ways when broken down based on the different pathways they studied. Regarding direct effects, “Applying it to live plants produces brush that naturally decomposes 140% faster than dead brush. In contrast, doing it on a dying brush naturally reduced its decomposition by 20%”, assures Vivanco.
“In addition, we observed that repeated herbicide applications decreased soil breathability by 57% over time. We also discovered that leaf brush decomposition increased by 53% and root decomposition by 18%”, Lucia explained.
Regarding the effect on decomposition of ryegrass with the endophyte, Omasini commented that “when the plant dies, the endophyte also dies, but it leaves a ‘legacy’ through the chemical composition of the brush. Our experiment shows that It was found that the decomposition of dead leaves of this grass was reduced by 22% by cohabitation with the fungus.
Lucía, Marina and Magdalena are also CONICET researchers at the IFEVA Institute (UBA-CONICET), and together with LiCiA graduate María Victoria Sánchez, they published these results in the journal Functional Ecology.
Based on his results, Vivanco concluded that glyphosate use favors CO2 loss from grassland. “This highly controversial herbicide has consequences on processes at the ecosystem level, as we observed with the decomposition of plant residues, which integrate multiple components. loss of carbon from them, further weakening their important role as a carbon store.”
In this sense, Druille pointed out that the promotion of ryegrass with herbicide has already degraded pastures, and now is the time to restore them. “In previous work by our group in 2015 and 2016, we observed that this practice, for example, reduced the density and functionality of arabscular mycorrhizal fungi in soil, which can hinder vegetation recovery, as these fungi are necessary so that replanted feed plants are set up”.
The researcher said one option would be to stop using glyphosate and incorporate the seeds into the soil to allow the plant community to recover. However – and what was said above – it is also necessary to inoculate the soil with mycorrhizal fungi to ‘prop up’ the recovery of the forage mats. Producing inoculum of these fungi is difficult to implement on a large scale and more studies are needed to evaluate its success in the field.
“In any case,” said Omasini, “this is not a call to vaccinate. Instead, we want to highlight the value of taking care of the ecosystem’s invisibles from the outset so that it is not degraded. Restoration is costly.” And that’s why we’re showing how important it is to be aware and take prevention.”
In closing, Vivanco went beyond grasslands and extended his questions to the potential consequences of glyphosate use in other systems. He stressed that this applies even in agricultural fields after harvest. “Certainly, the consequences on ecosystems in general, and carbon loss in particular, will vary according to the type and amount of cover, and the different pathways we have identified in our theoretical models. In this line, The present work provides a framework for initiating the investigation”.
By: Pablo Roset (SLT-FAUBA)