( B ( -RRB- ( ( ( ( Energy ( is ( cycled ( through ecosystems ) ) ) ) ; ) ( matter ( is not ) ) ) . ) ) )
(ROOT (S (LST (JJ B)) (-RRB- -RRB-) (S (NP (NP (NNP Energy)) (SBAR (S (VP (VBZ is) (VP (VBN cycled) (PP (IN through) (NP (NNS ecosystems))))))))) (: ;) (S (NP (NN matter)) (VP (VBZ is) (RB not))) (. .)))
B) Energy is cycled through ecosystems; matter is not.
(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.