Abstract
The biological pattern of plants’ nitrous oxide (N2O) generation is not well understood because plant cells cannot form N2O from nitric oxide (NO) reduction. Hypothetically, we consider that plant-endophytic co-denitrification is potentially capable of making up for the functional loss of NO reduction in the plant cell and is thus the source of plant-derived N2O. In order to test the above hypothesis, field-cultured soybean seedlings and aseptic-cultured seedlings were used to establish plant holobionts with differentially established endophytes. The N2O fluxes, copies of the bacterial NO reductase encoding gene, and a diversity of endophytic denitrifying bacteria of these holobionts were observed by gas chromatography, real-time PCR, and 16s rDNA sequencing. The flux of N2O by the field seedlings was significantly higher than the fluxes of the aseptic seedlings and bulk soil. The N2O flux of the soybean seedlings was significantly correlated to the abundance of the bacterial NO reductase encoding gene. Eleven genera of denitrifying bacteria were observed in the soybean seedlings, and among them, two genera of aerobic denitrifying bacteria were specifically associated with colonizing plant samples. In this work we have also showed that plant N2O emission is affected by the abundance of total endophytic denitrifying bacteria. We conclude that plant sourced N2O is cooperatively generated by the plant-endophyte symbiotic system in which endophytic denitrifying bacteria help plants to emit N2O by taking over the NO–N2O reduction process.
Highlights
Nitrous oxide (N2 O), the third most important greenhouse gas, is an important indicator of biological nitrogen transformations [1]
ColleaguesInterestingly, previously showed that to thethe highest seedlings, the aseptic seedlings were significantly enriched with two genera of aerobic denitrifying value for N2O emission was obtained with aseptic Hibiscus cannabinus seedlings (0.45 ± 0.20 ng N2O/g bacteria: Eubacterium and Propionibacterium (40 Operational Taxonomic Units (OTUs) and 61 OTUs, respectively) (p = 0.50 and p = 0.47, respectively) (Table S2, Supporting information)
Results from a Q-polymerase chain reaction (PCR) assay firmly proved that the bacteria-derived norB exists in the plant holobiont
Summary
Nitrous oxide (N2 O), the third most important greenhouse gas, is an important indicator of biological nitrogen transformations [1]. Because of the uncertainty regarding the sources of N2 O, an imbalance has long existed between estimates of N2 O sources and sinks in the Global Greenhouse. Gas Inventory [2,3]. Soils are the main source of N2 O, which originates from microbial nitrification and denitrification, and are regarded as the main N2 O source in inventory calculations of global N2 O emissions. Plants and mammals are considered uncertain sources of N2 O. Li and Chen first provided an evidence that soybean plants could generate a considerable amount of N2 O during growth [4,5]. The N2 O fluxes from 17 species of plants were investigated by Hakata and colleagues, with 16 species of tested plants showing a tiny amount of N2 O emission [6]
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