Land use is known to exert a dominant impact on a range of essential soil functions like water
retention, carbon sequestration, organic 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 the differences in soil structure are the actual cause of the differences in soil functions
or if they only co-occur.
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 (upper 10 cm, n D 75) were sampled
from all land use types at the early growing season. Soil structure and microbial activity were measured
using X-ray-computed tomography and respirometry, respectively.
Differences in microstructural properties between land uses were small in comparison to the variation within
land uses. The most striking difference between land uses was larger macropore diameters in grassland soils due
to the presence of large biopores that are periodically destroyed in croplands. Grasslands had larger amounts
of particulate organic matter (POM), including root biomass, and also greater microbial activity than croplands,
both in terms of basal respiration and rate of carbon mineralization during growth. Basal respiration among
soil cores varied by more than 1 order of magnitude (0.08–1.42 μgCO2-C h����1 g����1 soil) and was best explained
by POM mass (R2 D 0:53, p<0:001). Predictive power was only slightly improved by considering all bulk,
microstructure and microbial properties jointly. The predictive power of image-derived microstructural properties
was low, because aeration did not limit carbon mineralization and was sustained by pores smaller than the image
resolution limit (<30 μm). The frequently postulated dependency of basal respiration on soil moisture was not
evident even though some cores were apparently water limited, as it was likely disguised by the co-limitation
of POM mass. This finding was interpreted in regards to the microbial hotspots which form on decomposing
plant residues and which are decoupled from water limitation in bulk soil. The rate of glucose mineralization
during growth was explained well by substrate-induced respiration (R2 D 0:84) prior to growth, which in turn
correlated with total microbial biomass, basal respiration and POM mass, and was not affected by pore metrics.
These findings stress that soil structure had little relevance in predicting carbon mineralization in well-aerated
soil, as mineralization appeared to by predominantly driven by the decomposition of plant residues in intact soil.
Land use therefore affects carbon mineralization in well-aerated soil mainly in the amount and quality of labile
|Schlüter, S., Roussety, T., Rohe, L., Guliyev, V., Blagodatskaya, E., Reitz, T. (2022):
Land use impact on carbon mineralization in well aerated soils is mainly explained by variations of particulate organic matter rather than of soil structure
Soil 8 (1), 253 - 267