( Thus ( , ( ( ( the ( energy source ) ) ( that ( sustains ( this ( deep-ocean ecosystem ) ) ) ) ) ( ( ( ( is not ) ( ( sunlight ( but rather ) ) ( the energy ) ) ) ( from ( ( chemical reaction ) ( -LRB- ( chemosynthesis -RRB- ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB Thus)) (, ,) (NP (NP (DT the) (NN energy) (NN source)) (SBAR (WHNP (WDT that)) (S (VP (VBZ sustains) (NP (DT this) (JJ deep-ocean) (NN ecosystem)))))) (VP (VBZ is) (RB not) (NP (NP (NN sunlight)) (CONJP (CC but) (RB rather)) (NP (DT the) (NN energy))) (PP (IN from) (NP (NP (NN chemical) (NN reaction)) (PRN (-LRB- -LRB-) (NP (NNS chemosynthesis)) (-RRB- -RRB-))))) (. .)))
Thus, the energy source that sustains this deep-ocean ecosystem is not sunlight but rather the energy from chemical reaction (chemosynthesis).
(ROOT (S (NP (NP (JJS Most)) (PP (IN of) (NP (NP (NN food) (POS 's)) (NN chemical) (NN energy)))) (ADVP (RB ultimately)) (VP (VBZ comes) (PP (IN from) (NP (NN sunlight)))) (. .)))