What happens when very many environmental factors act on soil at the same time?
The number and the dissimilarity of such factor matters
When people in papers write ‘multiple’ factors in their title, they typically actually mean: two. But in reality, there are going to be way more than two factors acting on a soil, for example factors of global environmental change. So we really need to study what really happens when a lot of factors jointly affect a soil or ecosystem; and this is in fact a focus of our lab and has been for a few years.
In the latest step forward, a lab study just recently published in Nature Communications and led by 4 PhD students, showed that the number of factors can explain outcomes. This we already knew. What Mohan, Huiying, Peter and Yanjie (along with co-author Masahiro Ryo) could show now is that the dissimilarity of factors also matters. That is, how different the factors in a set are from each other in terms of their effects on soil.
This was a rather massive experiment, hence the cooperation among the 4 doctoral candidates in the lab. They worked with 12 factors of global change, a really large number. And they assembled them into groups of 2, 5, and 8 factors, in addition to finding out what every one of the 12 factors does on its own. For each of the factor-number levels they made 50 (!) combinations, drawn at random from the pool of the 12. This was essential to obtain a range of dissimilarities, which Mohan/ Huiying & Co. then used to calculate dissimilarity.
Would it be worse if more dissimilar factors occur, or if the factors were rather more similar in their effect on soils? The answer was clear: the more dissimilar the worse the effects. This was because there was an increased incidence of synergistic factor interactions, i.e. cases where the factors made the effects of each other worse. In addition to the monster of an experiment, this also required a few thousand lines of code to figure out.
This brings us one step closer to understanding what is going on when very many factor together affect a soil. And it might be a clue how we could restore systems: maybe we should worry about the most dissimilar factors, and rather be concerned about the set of all factors rather than about factors one-by-one.
Very proud of the group of four doctoral students who joined forces to make this ambitious project a reality! Read their paper here, it is open access.