( ( ( Oxygen ( Plus ( Plant Food ) ) ) ( -LRB- ( OPTIONAL -RRB- ) ) ) ( 1 teaspoon ) )
(ROOT (NP (NP (NNP Oxygen) (NNP Plus) (NNP Plant) (NNP Food)) (PRN (-LRB- -LRB-) (NP (NNP OPTIONAL)) (-RRB- -RRB-)) (NP (CD 1) (NN teaspoon))))
Oxygen Plus Plant Food (OPTIONAL)   1   teaspoon
(ROOT (S (NP (NNS Plants)) (VP (CONJP (RB not) (JJ only)) (VP (VBP contribute) (NP (NN food))) (CC but) (VP (VBD oxygen) (PP (IN for) (NP (NNS organisms))))) (. .)))