( however ( , ( ( those ( responsible ( for ( most ( of ( the fixation ) ) ) ) ) ) ( ( are ( ( ( ( ( ( ( certain species ) ( of ( bluegreen algae ) ) ) , ) ( ( the ( soil bacterium ) ) Azotobacter ) ) , ) and ) ( ( the ( symbiotic association ) ) ( of ( plants ( of ( ( ( the ( legume variety ) ) and ) ( the ( bacterium Rhizobium ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB however)) (, ,) (NP (NP (DT those)) (ADJP (JJ responsible) (PP (IN for) (NP (NP (JJS most)) (PP (IN of) (NP (DT the) (NN fixation))))))) (VP (VBP are) (NP (NP (NP (JJ certain) (NNS species)) (PP (IN of) (NP (NN bluegreen) (NN algae)))) (, ,) (NP (NP (DT the) (NN soil) (NN bacterium)) (NP (NNP Azotobacter))) (, ,) (CC and) (NP (NP (DT the) (JJ symbiotic) (NN association)) (PP (IN of) (NP (NP (NNS plants)) (PP (IN of) (NP (NP (DT the) (NN legume) (NN variety)) (CC and) (NP (DT the) (NN bacterium) (NN Rhizobium))))))))) (. .)))
however, those responsible for most of the fixation are certain species of bluegreen algae, the soil bacterium Azotobacter , and the symbiotic association of plants of the legume variety and the bacterium Rhizobium .
(ROOT (S (NP (NNS Bacteria)) (VP (VBP are) (NP (NP (DT the) (RBS most) (JJ numerous) (NNS species)) (PP (IN on) (NP (DT the) (NN planet))))) (. .)))