22 Jul 2021

22 Jul 2021

Review status: a revised version of this preprint is currently under review for the journal SOIL.

Land use impact on carbon mineralization is mainly caused by variation of particulate organic matter content rather than of soil structure

Steffen Schlüter1, Tim Roussety1, Lena Rohe1, Vusal Guliyev2, Evgenia Blagodatskaya2, and Thomas Reitz1,2 Steffen Schlüter et al.
  • 1Department Soil System Sciences, Helmholtz-Centre for Environmental Research – UFZ, Theodor-Lieser-Str. 4, 06120 Halle (Saale), Germany
  • 2Department Soil Ecology, Helmholtz-Centre for Environmental Research – UFZ, Theodor-Lieser-Str. 4, 06120 Halle (Saale), Germany

Abstract. Land use is known to exert a dominant impact on a range of essential soil functions like water retention, carbon sequestration, matter cycling and plant growth. At the same time, land use management is known to have a strong influence on soil structure, e.g. through bioturbation, tillage and compaction. However, it is often unclear whether differences in soil structure are the actual cause for differences in soil functions or just co-occurring.

This impact of land use (conventional and organic farming, intensive and extensive meadow, extensive pasture) on the relationship between soil structure and short-term carbon mineralization was investigated at the Global Change Exploratory Facility, in Bad Lauchstädt, Germany. Intact topsoil cores (n = 75) were sampled from each land use type at the early growing season. Soil structure and microbial activity were measured using X-ray computed tomography and respirometry, respectively.

Grasslands had a greater microbial activity than croplands, both in terms of basal respiration and rate of carbon mineralization during growth. This was caused by a larger amount of particulate organic matter (POM) in the topsoil of grasslands. The frequently postulated dependency of basal respiration on soil moisture was absent even though some cores were apparently water limited. This finding was related to microenvironments shaping microbial hotspots where the decomposition of plant residues was obviously decoupled from water limitation in bulk soil. Differences in microstructural properties between land uses were surprisingly small, mainly due huge variability induced by patterns of compacted clods and loose areas caused by tillage in cropland soils. The most striking difference was larger macropore diameters in grasslands soil due to the presence of large biopores that are periodically destroyed in croplands.

Variability of basal respiration among all soil cores amounted to more than one order of magnitude (0.08–1.42 µg CO2-C h−1 g−1 soil) and was best described by POM mass (R2 = 0.53, p < 0.001). Predictive power was hardly improved by considering all bulk, microstructure and microbial properties jointly. The predictive power of image-derived microstructural properties was low, because aeration was not limiting carbon mineralization and was sustained by pores smaller than the image resolution limit (< 30 µm). The rate of glucose mineralization during growth was explained well by substrate-induced respiration (R2 = 0.84) prior to growth, which was in turn correlated with total microbial biomass, basal respiration and POM mass and again not affected by pore metrics.

These findings stress that soil structure had little relevance in predicting carbon mineralization in well-aerated soil, as this predominantly took place in microbial hotspots around degrading POM that was detached from the pore structure and moisture of the bulk soil. Land use therefore affects carbon mineralization in well-aerated soil mainly by the amount and quality of labile carbon.

Steffen Schlüter et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on soil-2021-56', Anonymous Referee #1, 26 Aug 2021
    • AC1: 'Reply on RC1', Steffen Schlüter, 09 Sep 2021
      • RC2: 'Reply on AC1', Anonymous Referee #1, 13 Sep 2021
        • AC3: 'Reply on RC2', Steffen Schlüter, 21 Oct 2021
  • RC3: 'Comment on soil-2021-56', Anonymous Referee #2, 21 Sep 2021
    • AC2: 'Reply on RC3', Steffen Schlüter, 15 Oct 2021

Steffen Schlüter et al.

Steffen Schlüter et al.


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Short summary
We combined microstructure analysis via X-ray CT with carbon mineralization analysis via respirometry of intact soil cores from different land uses. We found that the amount of particulate organic matter (POM) exerted a dominant control on carbon mineralization in well-aerated topsoils, whereas soil moisture and macroporosity did not play role. This is because carbon mineralization mainly occurs in microbial hotspots around degrading POM, where it is decoupled from conditions of the bulk soil.