Karlowsky Stefan, Buchen-Tschiskale Caroline, Odasso Luca, Schwarz Dietmar, Well Reinhard
Leibniz Institute of Vegetable and Ornamental Crops (IGZ) e.V., Großbeeren, Germany.
Thünen Institute of Climate-Smart Agriculture, Federal Research Institute for Rural Areas, Forestry and Fisheries, Braunschweig, Germany.
Front Microbiol. 2023 Jan 4;13:1080847. doi: 10.3389/fmicb.2022.1080847. eCollection 2022.
Hydroponic vegetable cultivation is characterized by high intensity and frequent nitrogen fertilizer application, which is related to greenhouse gas emissions, especially in the form of nitrous oxide (NO). So far, there is little knowledge about the sources of NO emissions from hydroponic systems, with the few studies indicating that denitrification could play a major role.
Here, we use evidence from an experiment with tomato plants () grown in a hydroponic greenhouse setup to further shed light into the process of NO production based on the NO isotopocule method and the N tracing approach. Gas samples from the headspace of rock wool substrate were collected prior to and after N labeling at two occasions using the closed chamber method and analyzed by gas chromatography and stable isotope ratio mass spectrometry.
The isotopocule analyses revealed that either heterotrophic bacterial denitrification (bD) or nitrifier denitrification (nD) was the major source of NO emissions, when a typical nutrient solution with a low ammonium concentration (1-6 mg L) was applied. Furthermore, the isotopic shift in N site preference and in δO values indicated that approximately 80-90% of the NO produced were already reduced to N by denitrifiers inside the rock wool substrate. Despite higher concentrations of ammonium present during the N labeling (30-60 mg L), results from the N tracing approach showed that NO mainly originated from bD. Both, N label supplied in the form of ammonium and N label supplied in the form of nitrate, increased the N enrichment of NO. This pointed to the contribution of other processes than bD. Nitrification activity was indicated by the conversion of small amounts of N-labeled ammonium into nitrate.
DISCUSSION/CONCLUSION: Comparing the results from NO isotopocule analyses and the N tracing approach, likely a combination of bD, nD, and coupled nitrification and denitrification (cND) was responsible for the vast part of NO emissions observed in this study. Overall, our findings help to better understand the processes underlying NO and N emissions from hydroponic tomato cultivation, and thereby facilitate the development of targeted NO mitigation measures.
水培蔬菜种植的特点是强度高且频繁施用氮肥，这与温室气体排放有关，尤其是一氧化二氮（N₂O）形式的排放。到目前为止，关于水培系统中N₂O排放源的了解甚少，少数研究表明反硝化作用可能起主要作用。
在此，我们利用在水培温室设置中种植番茄植株（）的实验证据，基于N₂O同位素方法和氮追踪方法，进一步阐明N₂O产生的过程。使用密闭箱法在两次氮标记前后收集岩棉基质顶空的气体样品，并通过气相色谱和稳定同位素比率质谱法进行分析。
同位素分析表明，当施用低铵浓度（1 - 6 mg·L）的典型营养液时，异养细菌反硝化作用（bD）或硝化细菌反硝化作用（nD）是N₂O排放的主要来源。此外，氮位点偏好和δO值的同位素变化表明，产生的N₂O中约80 - 90%已被岩棉基质内的反硝化细菌还原为氮气。尽管在氮标记期间铵浓度较高（30 - 60 mg·L），氮追踪方法的结果表明N₂O主要源自bD。以铵形式提供的氮标记和以硝酸盐形式提供的氮标记均增加了N₂O的氮富集。这表明除bD之外其他过程的贡献。少量氮标记铵转化为硝酸盐表明存在硝化活性。
讨论/结论：比较N₂O同位素分析和氮追踪方法的结果，很可能是bD、nD以及耦合硝化和反硝化作用（cND）的组合导致了本研究中观察到的大部分N₂O排放。总体而言，我们的研究结果有助于更好地理解水培番茄种植中N₂O和氮排放的潜在过程，从而促进针对性N₂O减排措施的制定。
