( ( Cloudy days ) ( ( ( slow down ) ( ( photosynthesis , ) ( ( in which ) ( ( aquatic plants ) ( ( ( ( are ( in ( ( the process ) of ) ) ) ( to ( make oxygen ) ) ) , ) ( making ( ( less oxygen ) available ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Cloudy) (NNS days)) (VP (VB slow) (PRT (RP down)) (NP (NP (NN photosynthesis)) (, ,) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (JJ aquatic) (NNS plants)) (VP (VBP are) (PP (IN in) (NP (NP (DT the) (NN process)) (PP (IN of)))) (S (VP (TO to) (VP (VB make) (NP (NN oxygen))))) (, ,) (S (VP (VBG making) (S (NP (JJR less) (NN oxygen)) (ADJP (JJ available)))))))))) (. .)))
Cloudy days slow down photosynthesis, in which aquatic plants are in the process of to make oxygen, making less oxygen available.
(ROOT (S (NP (NNP Oxygen)) (VP (VBZ is) (VP (VBN made) (PP (IN by) (NP (NP (NNS trees)) (CC and) (NP (JJ other) (NNS plants)))) (PP (IN during) (NP (NN photosynthesis))))) (. .)))