Soil microbiota and climate change

Climate change is putting a strain on our agricultural and cultural models. Even if there are those, including researchers, who are committed to denial or frame the meteorological anomalies that we have been witnessing, for a while now, as part of a cycle which the Earth’s climate has already experienced in its history, it is obvious that the conditions of our planet today are not those of 1,000 or 5,000 years ago. From an agricultural perspective, the state of “today” must be both understood as well as managed, to avoid the risk of insufficient food resources for the entire world population.

The link between soil microbiota and climate change is closer than most, non-professionals, can imagine. We are talking about a bidirectional link, because if it is true that the disturbances associated with climate change can significantly alter the soil microbial community and its related functional profiles, it is equally true that this leads to the alteration of the carbon and/or nitrogen cycles in the soil as a consequence. This in turn affects climate change, due to increase/decrease in the emission of greenhouse gases from the land, on the one hand, and the accumulation of carbon in soil biomass, on the other.

This link between microorganisms (not only of the soil) and climate change is of such high importance that it has led the international scientific community to repeatedly emphasize the urgency to deepen their knowledge, since the state of health of microbial communities (not only of the soil) depends to a large extent on the future sustainability of human activities, agriculture first of all.

One of the best-known effects of climate change is the progressive increase in temperatures, air and consequently in soils.

In the short term, the increase in average soil temperatures causes an acceleration in the decomposition rates of organic carbon and a global increase in microbial biomass. In the medium term, however (5-8 years), with high soil temperature conditions persisting both the composition of the microbiota and its functional profiles change, due to an adaptation to the scarcity of easy to claim and  labile Carbon and the need to eat, at the expense of stable forms of organic matter which are more difficult to claim. These changes are linked to a greater or lower emission of CO2 from the ground into the atmosphere above.

The loss of water from the soil through evaporation (resulting from the soil temperature) and its possible reintegration due to precipitation, has an important influence on this equilibrium. In the presence of high temperatures and adequate humidity, the degradation of labile carbon is further accelerated. The mineralization rate of stable organic matter, on the other hand, does not seem to be influenced by the soil’s water content.

This type of response to changes in temperature will be different at different depths, due to the different water content and the temperature gradient.

The temperature of the soil also affects the composition of the microbial groups involved in all phases of the Nitrogen cycle: from the fixation of atmospheric nitrogen, with its transformation into ammonia, to the oxidation of the latter with transformation into nitrates, from denitrification to the mineralization of the nitrogen contained in the organic substance. The temperature-function correlations are not always linear and in some cases have yet to be clarified.

Temperatures and rainfall are just two of the many climate-related variables that can influence the soil microbiota. Above all, their effects (as was partially evident in the previous paragraph) can never be considered separately, since they are interconnected with each other.

Taking charge of all the variables involved and the possible interactions, is the subject of study by the scientific community, which is developing forecast models capable of predicting with varying degrees of accuracy the repercussions of environmental disturbances on ecosystem services rendered by soil microorganisms. The application of these tools to the management of agricultural land, and in particular to fertilization, could give an important impetus to the rationalization of inputs and the reduction of waste.

Reducing the considerations made so far in the agricultural context, means understanding that the variations induced by climate change in the soil microbiota influence the physical, chemical and biological properties of cultivated land and consequently the nutrients availability for crops, whether they are already present in the soil or distributed through fertilization.

It also means understanding which useful microorganisms work best under certain environmental conditions, to determine in a targeted way how to formulate and use nutrition and biostimulation products containing microorganisms, often in consortium.

In this context, it is also important to remember that the microbial biomass of the soil is influenced, both in quantitative and qualitative terms, by the plants’ production of radical exudates, the type and quantity of which may vary substantially depending on the methods and rates of growth of these plants, which change as climatic conditions change.

But which taxonomic groups of the soil microbiota can be considered useful in agriculture? And what functions do they perform? We’ll talk about it in-depth in the next articles.