Deforestation fills the soil with fungi that cause diseases in plants – 03/16/2024 – Reinaldo José Lopes

The effects of deforestation on macroscopic biodiversity (that which we are all capable of seeing with the naked eye) existing above ground are not difficult to imagine. In tropical forest environments like those that predominate in Brazil, ipês, embaúbas, monkeys and curassows disappear, exchanged for grass, sugarcane or soybeans. But the repercussions of deforestation are literally deeper than what I just described, and a new study shows in detail what happens to the communities of microorganisms that populate the soil on which a forest once grew. “Spoiler”: it’s not the most inspiring scenario.

The results of this analysis have just been published in the specialized journal PNAS, in an article written by Xinjing Qu, from the University of Forest Studies in Nanjing, China, and Manuel Delgado-Baquerizo, from the Institute of Natural Resources and Agrobiology in Seville (Spain), among other experts.

The work of the team coordinated by the two compared the before and after deforestation in a very wide range of environments, ranging from temperate forests in China, the USA and Canada to the equatorial jungles of Africa and Brazil, passing through subtropical forests of Australia. In total, there were almost 700 pairs of forest versus area with agricultural use (this last category was divided into commercial tree plantations, pasture and crops).

The focus of Delgado-Baquerizo, Qu and company is the microbial diversity of forest and post-forest soil – and, more importantly, its ability to offer environmental services.

If you think that sewage collection and public transport are “essential services” (and they are), imagine what would happen if systems of this type were turned off or affected at an ecosystem level. Because it is the biological equivalent of these things – services such as decomposition of organic matter, recycling of nutrients, incorporation of chemical elements, etc. – that soil microorganisms do for free, all the time, around the world.

There is some variation in the comparative results, depending on the type of economic use given to the deforested area. It appears that commercial tree plantations and pastures have less radical effects on soil biota (set of microbes) than crops. But all, to some extent, promote an aggressive reorganization of microbial communities.

The most important of these is to exchange symbiotic fungi – which, in a natural environment, are companions of plants and help them absorb nutrients – for parasitic fungi. This happens because the concentration of the same species of plants of commercial interest creates a feast for these microorganisms, as if they were the measles virus entering, all splendid, into a classroom full of unvaccinated children.

Secondly, the diversity of bacteria even increases, but they are species with very fast metabolism and reproduction (with a speed even faster than the already dizzying average of bacteria) that are there to quickly devour the artificial fertilizers used commercially. In this sense, soil dynamics begin to become “abiotic,” the researchers write — it’s almost as if the earth is no longer alive.

All of this causes post-deforestation soil to lose up to 48% of its organic carbon and 23% of its nitrogen when it no longer contains forest. Over the decades, these indicators even slowly improve – but not when the soil continues to be constantly used for planting commercial crops. In these cases, it is as if he continues to “breathe on life support” only thanks to the use of artificial fertilizers.

Nobody here is advocating that we put an end to commercial agriculture, without which, in fact, we would have serious difficulties feeding the population. But data like this study shows how the soil’s most precious resources depend on biodiversity in the long term. You need to know how to preserve them, even if it’s for the sake of your wallet and a long-term vision.

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