Is the combination of the Task Force on Reactive Nitrogen and the Task Force on Techno-Economic Issues either (a) the task forces on reactive nitrogen and techno-economic issues, or (b) the Task Forces on Reactive Nitrogen and Techo-Economic Issues?
If you want to refer to them collectively then do not use their names (use (a)).
If you refer to the task forces by name then use the actual (individual) names, even if it sounds repetitive. They are proper names, just as different as X and Y, and there is (presumably) no proper name for the pair. That is, the proper name Task Forces on Reactive Nitrogen and Techo-Economic Issues does not exist.
I would use
the task forces on reactive nitrogen and on techno-economic issues.
Repeating the on makes it much clearer that these are two different task forces on two different subjects, rather than two task forces on a combined subject of Reactive Nitrogen and Techno-Economic Issues.
Apart from signifying proper nouns (names), capitalisation is also used to emphasize and highlight esp. in headings/titles. So if your sentence is a heading of an article then you can use (b), but if it is a sentence in a paragraph, then (a) is the way to go.
You should consider Peter Shor's version w.r.t the sentence structure though.