No, in turn does not mean the opposite. Wiktionary shows four senses:
- One after the other; one at a time; in succession; successively
- In due order; in proper sequence; in a determined or measured sequence, as a waiting line or queue
- In response; in return [eg] The musical ambassadors finished their performance, and the local musicians in turn played for them a traditional ballad
- Having a relationship sequentially comparable to one just mentioned; accordingly or similarly, with respect to sequence, precedence, or hierarchy.
None of those senses really apply in the quoted passage. There is no sequence, no before and after, no in-response or in-return relationship between the stated sets of needs. (Which are, on the one hand, the poorer nations' needs for goods produced in developed nations, and on the other, the needs of developed countries to find new markets to revive faltering economies.) It is true that the two sets of needs complement each other, but it is not true that they are related “in turn”. In short, the phrase is inappropriate and has been misused.
Edit: Transitional phrases that could be used here (in place of “in turn”) include “for their part”, “on the other hand”, “by contrast”, etc.
A problem with the original text –
Even given the desire of the poorer nations for greater autonomy, many of their needs can only be satisfied via the productive capacity of the developed nations; the developed nations, in turn, will have to find new markets for their product if they are to revive their faltering economies.
– is that it confusingly conflates its notions. If poor nations need products from developed nations, then there is a market for those products. Treating of whether the market is new, whether the developed-nation economy is faltering, whether the poor nation seeks autonomy – all that would be better done in separate sentences.