Its not clickbait, its just efficient language. We have a symbiotic relationship with bacteria in our gut but don't explicitly distinguish it every time we refer to human digestion.
Actually this article and study is not intending to reveal anything new about how trees and other plants fix nitrogen (using microbes). It is revealing that the symbiotic arrangements (far from entirely understood) also cause the breakdown and release of scarce nutrients from rocks, enabling increased growth and building soil fertility over time.
We wouldn't say that a people perform some very specific, detailed process that is attributed to gut bacteria. E.g. "humans break down oligosaccharides".
Digestion, as such, is a concept independent of gut bacteria.
I've given this a few minutes of thought. Basically, the situation is that some bacteria take nitrogen from the atmosphere and then spew out ammonia and related compounds, which are taken up by the roots of the symbiotic plants. I would call this "fertilization" (in the agricultural sense).
But then it becomes ambiguous whether you're talking about fertilising the tree, or the tree fertilising something else. Perhaps self fertilising? But that sounds like reproduction.
And that's assuming we're living in a world where you can petition the World English Language Governing Body to make the necessary changes to the language.
But for better or worse that body doesn't exist so we are stuck with what we've got, and at the moment people talk about nitrogen fixing plants, so if you want to communicate with people, you need to use those terms.
That isn't clickbait, that's just making sure a headline doesn't turn into an off topic essay.
"red alder ... through its symbiotic relationship with nitrogen-fixing bacteria"
That's more like it. No such thing as a nitrogen-fixing tree, as far as we know; only micro-organisms perform nitrogen fixation.