( Sometimes ( ( producer organisms ) ( ( are ( called autotrophs ) ) . ) ) )
(ROOT (S (ADVP (RB Sometimes)) (NP (NN producer) (NNS organisms)) (VP (VBP are) (VP (VBN called) (NP (NNS autotrophs)))) (. .)))
Sometimes producer organisms                   are called autotrophs.
(ROOT (S (NP (NNS Autotrophs)) (VP (VBZ is) (NP (NP (DT another) (NN name)) (PP (IN for) (NP (NNS producers))))) (. .)))