( ( 8.4 ( ( ( how ( ( ( ( water ( , ( carbon ( and ( nitrogen cycle ) ) ) ) ) ( between ( abiotic resources ) ) ) and ) ( ( organic matter ) ( in ( the ecosystem ) ) ) ) ) and ) ( how ( ( oxygen cycles ) ( via ( ( photosynthesis and ) respiration ) ) ) ) ) ) . )
(ROOT (S (VP (VB 8.4) (S (S (ADVP (WRB how)) (NP (NP (NP (NN water) (, ,) (NN carbon) (CC and) (NN nitrogen) (NN cycle)) (PP (IN between) (NP (JJ abiotic) (NNS resources)))) (CC and) (NP (NP (JJ organic) (NN matter)) (PP (IN in) (NP (DT the) (NN ecosystem)))))) (CC and) (S (ADVP (WRB how)) (NP (NP (NN oxygen) (NNS cycles)) (PP (IN via) (NP (NN photosynthesis) (CC and) (NN respiration))))))) (. .)))
8.4 how water, carbon and nitrogen cycle between abiotic resources and organic matter in the ecosystem and how oxygen cycles via photosynthesis and respiration.
(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.