Does simultaneous phosphorus fertilization negate the suppressive effect of nitrogen fertilization on polyphenol oxidase activity?

• Published in: Geoderma Vol. 430; p. 116287
• Main Authors: Mori, Taiki, Imai, Nobuo, Kitayama, Kanehiro
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2023
• Subjects: Decomposition; Nitrogen; Phosphorus; Polyphenol oxidase; Tropical forest; Phosphorus; Decomposition; Tropical forest; Nitrogen; Polyphenol oxidase
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2022.116287

•We tested if P fertilization mitigate N fertilization-induced suppression of PPO.•N fertilization did not suppress PPO due to relatively small sample size.•P fertilization did not necessarily mitigate N fertilization-induced suppression of PPO. Hindered decomposition of recalcitrant organic matter after nitrogen (N) fertilization is widely reported, but the underlying mechanisms remain unclear. The “P-depletion hypothesis” suggests that suppression of decomposition by N fertilization occurs as follows: N fertilization stimulates microbial competition for phosphorus (P) acquisition, leading to P deficiency in lignin decomposers and simultaneous suppression of polyphenol oxidase (PPO) activity. This hypothesis can be tested through simultaneous N and P fertilization and examination of whether the suppression of PPO activity with N fertilization is negated by additional P fertilization. Here, we tested this hypothesis through meta-analysis of literature studies. To obtain additional data for this analysis, a field fertilization experiment with simultaneous N and P fertilization was conducted in two lowland dipterocarp rain forests in Borneo. Based on the P-depletion hypothesis, we hypothesized that N fertilization would suppress PPO activity, but the negative impact would disappear with simultaneous P treatment. However, the meta-analysis did not support the P-depletion hypothesis. Out of 11 studies, 6 (including our field experiment) did not demonstrate suppressive effects of N fertilization on PPO activity, so the hypothesis could not be tested. Only five studies reported suppressive effects of N fertilization on PPO activity, three of which did not support the P-depletion hypothesis because P fertilization did not negate the suppression of PPO activity caused by N fertilization. Overall, our analysis indicates that the P-depletion hypothesis cannot comprehensively explain the mechanism underlying the negative impact of N fertilization on PPO activity.