Climate and geology overwrite land use effects on soil organic nitrogen cycling on a continental scale
- 1Division of Terrestrial Ecosystem Research, Department of Microbiology and Ecosystem Science, Center of Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria
- 2German Environment Agency, Dessau-Rosslau, Germany
- 3Lawrence Berkeley National Laboratory, Berkeley, USA
- 4International Institute for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg, Austria
- 1Division of Terrestrial Ecosystem Research, Department of Microbiology and Ecosystem Science, Center of Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria
- 2German Environment Agency, Dessau-Rosslau, Germany
- 3Lawrence Berkeley National Laboratory, Berkeley, USA
- 4International Institute for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg, Austria
Abstract. Soil fertility and plant productivity are globally constrained by N availability. Proteins are the largest N reservoir in soils and the cleavage of proteins into small peptides and amino acids has been shown to be the rate limiting step in the terrestrial N cycle. However, we are still lacking a profound understanding of the environmental controls of this process. Here we show that integrated effects of climate and soil geochemistry drive protein cleavage across large scales. We measured gross protein depolymerization rates in mineral and organic soils sampled across a 4000-km-long European transect covering a wide range of climates, geologies and land uses. Based on structural equation models we identified that soil organic N cycling was strongly controlled by substrate availability e.g. by soil protein content. Soil geochemistry was a secondary predictor by controlling protein stabilization mechanisms and protein availability. Precipitation was identified as the main climatic control on protein depolymerization by affecting soil weathering and soil organic matter accumulation. In contrast, land use was a poor predictor of protein depolymerization. Our results highlight the need to consider geology and precipitation effects on soil geochemistry when estimating and predicting soil N cycling at large scales.
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Lisa Noll et al.
Status: open (extended)
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RC1: 'Comment on bg-2022-41', Anonymous Referee #1, 10 Mar 2022
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This study studied the factors of land use and bedrock on protein depolymerization across a 4000-km transect in Europe, and highlighted the important role of climate and soil properties on N cycling at large scales. The sampling scheme is attractive, and many interesting biochemical indicators are measured. This study stated N cycling was controlled by substrate availability. This conclusion is not novel, actually which has been widely acknowledged for a long time. Generally, I think this paper fits the scope of this Journal, however, more should be added to highlight the novelty of this study. Some conclusions are confusing, the author had clarified the importance of substrate availability, which was related with OM input or vegetation, however, it also declared that the land use effect was insignificant. Those ideas are not consistent. It’s better to clarify them.  Besides, the writing should be improved. For instance, some paragraphs lack the key points, and some sentences are confusing or too long to understand. See the details as follows.
Line40: The key point of this paragraph is not clear, clarify it. And since land use is your main sampling scheme, you can introduce more about it.
Line 50. This reference was in contrast with your contents, discuss it later.
Line 64, add reference.
Line96, what’s the depth of the ‘organic layers’?
Line 180: This sentence is confusing, please rephrase it.
Line 340: Simplify the sentences
Lin 320-335: It’s confusing in 4.1.‘land use had no effect on the response of depolymerization rates’, however, above discussion was talking about the differences in different land use, and even attributed the difference to soil pH.
Line 343: pH was the main predictor in results, but the contribution of texture, mineral assemblage, how are they related to N cycling?
Line 360: I don’t think this indicate that ‘stabilized compounds are available for microbial utilization’
Line 365: Add reference
Line 376-378: this sentence is confusing, please simplify it
Line390: add support for this opinion
Line405-420: Do you mean that the climate factors influence soil pH and then regulate the depolymerization rates? However, your data doesn’t seem to support this, please explain it.
Line 450: can you compared the contributions in the combined model including land use, soil properties, climate together?
Line 462: It’s confusing, ‘peptidase activity is a proxy of microbial N or N limitation’?
Fig 5: ‘black arrows’ are missing in the figure. And how to identify the direct and indirect effects?
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Lisa Noll et al.
Lisa Noll et al.
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