Spatial patterns of organic matter formation in subsoil: Nutritional control of microbial hot spot formation and dynamics
Final Report Abstract
Preferential flow paths (FP) affect the spatial distribution of water, substrates, and nutrients, impacting microbial carbon turnover rates in soils. As nutrient-rich soil regions FP often host microbial hot spots with higher carbon turnover than surrounding soil. This is particularly important in subsoil, where fresh inputs are scarce and localized. Matric soil is more affected by nutrient limitations than flow paths, leading to more dormant microorganisms and lower C- turnover rates. To investigate C-turnover and nutrient limitations in FP and matric soils (MA), we conducted a field experiment by irrigating (20mm h-1 over 10 hours) three SUBSOM observatories in a sandy soil of a beech forest stand with a tracer to track water fluxes into the subsoil. Soil samples from FP and MA were taken at different depths and analysed for microbial and extracellular enzyme activities (EEA), substrate and nutrient limitations, and the spatial extent of flow path effects. Our results showed that microbial hot spots were fewer (38% less) and smaller (75% smaller) in the lower subsoil (15-27 cm) compared to deeper subsoil regions (80-92 cm), with less stimulation by substrate and nutrient additions compared to non-hot spot areas. Dormant microorganisms in non-hot spot soils were much more activated by C and nutrient addition than organisms in hot spots. Looking at the FP system it became evident that FP had higher water contents than MA samples at all depths (0-160 cm). Organic carbon contents were higher in FP soils, only below 80 cm depth. EEA increased in flow path soils at all depths except 50-80 cm compared to MA soil. Nutrient limitation analysis showed no significant difference between FP and MA soils, though P-limiting conditions were present throughout the profile, and C and N limitations increased in deeper soil regions. Substrate and nutrient addition led to positive priming in 0-30 cm depth in both FP and MA soils, with a stronger effect in MA soils. In 110-160 cm depth, negative priming was detected with nearly all substrate and nutrient additions, with a stronger effect in FP compared to MA soils indicating the presence of a microbial community more adapted to easily available substrates which was shown by a higher presence of Actinobacteria and Acidobacteria in MA soils in comparison to a stronger share of β-proteobacteria in FP soils. The differences in microbial C-turnover and nutrient acquisition were not strongly pronounced between FP and MA soil along the soil profiles. Increased water flow showed a negative correlation with C and nutrient contents potentially induced by leaching or dilution in deeper soil regions in FP systems. In conclusion, the studies showed that FP were not identified as exclusive nutrient and substrate hot spots favouring soil microbial habitat conditions and removing its limitations in subsoil regions in comparison to MA significantly. The strong interaction of water flow intensity and flow path surrounding soil potentially did not allow a pronounced C- and nutrient accumulation in that sandy soil.
Publications
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Response of soil microbial enzyme activity to substrate and nutrient additions on undisturbed forest top-and subsoil. Eurosoil 2021 (online)
Theresa Reinersmann (PhD), Bernd Marschner & Stefanie Heinze
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Follow the way – A tracer approach to elucidate microbial C-turnover in flow pathways in the subsoil. Deutsche Boden kundliche Gesell schaftstagung Trier (2022)
Stefanie Heinze (PI), Theresa Reinersmann & Bernd Marschner
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Going deep - Microbial C-turnover in flow path and matric subsoil (Oral presentation). 22nd World Con gress of Soil Sci ence (Glasgow, GB; 2022)
Stefanie Heinze (PI) & Bernd Marschner
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Hotspots of the underground – Spatial distribu tion of enzyme activities along preferential flow paths in a subsoil. (Poster). 22nd World Con gress of Soil Sci ence (Glasgow, GB; 2022)
Theresa Reinersmann (PhD), Bernd Marschner & Stefanie Heinze
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Impact of substrate and nutrient additions on soil microbial activity of undisturbed top- and subsoil samples (Oral presentation). Deutsche Boden kundliche Gesell schaftstagung Trier (2022)
Theresa Reinersmann (PhD), Bernd Marschner & Stefanie Heinze
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Different nutritional controls of microbial activity in flow paths and matrix soil (Oral presentation). Deutsche Boden kundliche Gesell schaftstagung Halle an der Saale (2023)
Theresa Reinersmann (PhD), Michael Herre, Bernd Marschner & Stefanie Heinze
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Limitation in the Underground – Einfluss von Nährstoff- und Substratzugaben auf den mikro biellen C-Umsatz im Unterboden (Poster). Deutsche Boden kundliche Gesell schaftstagung Halle an der Saale (2023)
Tom Escher (Student), Bernd Marschner, Michael Herre, Theresa Reinersmann & Stefanie Heinze
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Limitation in the Underground – Einfluss von Nährstoff- und Substratzugaben auf den mikrobiellen C-Umsatz im Unterboden (Poster)
Tom Escher, Bernd Marschner, Michael Herre, Theresa Reinersmann & Stefanie Heinze
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Soil Enzyme Activity Response to Substrate and Nutrient Additions on Undisturbed Forest Subsoil Samples. Soil Systems, 7(2), 57.
Reinersmann, Theresa; Herre, Michael; Marschner, Bernd & Heinze, Stefanie
