( ( ( ( role ( of microbes ) ) ( in ( carbon ( and ( nitrogen cycles ) ) ) ) ) ( in ( aquatic ecosystems ) ) ) ; )
(ROOT (NP (NP (NN role)) (PP (IN of) (NP (NNS microbes))) (PP (IN in) (NP (NN carbon) (CC and) (NN nitrogen) (NNS cycles))) (PP (IN in) (NP (JJ aquatic) (NNS ecosystems))) (: ;)))
role of microbes in carbon and nitrogen cycles in aquatic ecosystems;
(ROOT (S (NP (NP (DT A) (JJ primary) (NN role)) (PP (IN of) (NP (NP (NNS decomposers)) (PP (IN in) (NP (DT an) (NN ecosystem)))))) (VP (VBZ is) (SBAR (IN that) (S (NP (PRP they)) (VP (VBZ cycle) (NP (NN matter)) (PP (IN by) (S (VP (VBG returning) (NP (NN carbon) (CC and) (JJ other) (NN matter)) (PP (TO to) (NP (DT the) (NN ecosystem)))))))))) (. .)))
A primary role of decomposers in an ecosystem is that they cycle matter by returning carbon and other matter to the ecosystem.