Carbon input and turnover in subsoil biopores
Plant Cultivation, Plant Nutrition, Agricultural Technology
Plant Breeding and Plant Pathology
Final Report Abstract
The legacy of the root biomass was apparent even two years after root death: C stocks were >2.5 times higher in root biopores than in bulk soil and consequently also microbial biomass and enzyme activities involved in more complex OM decomposition. The contributions of most plant biomarkers to SOC were not different from bulk soil, suggesting that the root pores were in a late decomposition stage. The increased biomarker stocks stem from the large single root biomass input, but its unique initial biomarker signature was lost within two years of biopore development. C turnover proxies like the lignin side-chain oxidation confirmed this. The microbial community reflected the ‘old’ root OM: more Gram-positive bacteria and actinobacteria were found than in the earthworm biopores. The entire community fingerprint in root pores was different from the earthworm-influenced pores, but not different from bulk soil. Given the elevated enzyme activities and the large initial C input, the hot moment of nutrient mobilization may hold up for up to two more years. Combining two C sources, i.e. incubating earthworms into root pores, made the largest impact on C stocks and on the microenvironment. After six months of earthworm activity, the former root pores’ biochemistry was overprinted. Earthworms as ecosystem engineers imported large amounts of non-degraded OM into the subsoil and increased C stocks by 200% and MBC (~ 30 times) relative to bulk soil (Table 1). Among the biopores, this induced the strongest increase in enzyme activities. All biomarker stocks were increased relative to bulk soil, but only this large input genuinely modified the biopore SOC composition. Mainly more easily available OM was respired as the turnover ratios reflecting turnover of polymeric, likely more stable C were mostly unchanged, e.g. lignin underwent less turnover than hemicelluloses. The microbial community reflected the higher C availability and the gut effects of Lumbricus terrestris: more fast-growing decomposers of easily available C (Gram-negative bacteria) were found than in bulk soil. The microbial community in these former root pores was not distinguishable from the native earthworm pores after six months. The main property of the native earthworm pores was the repeated input of fresh OM for up to five years. This long-term activity of earthworms increased C stocks by 200 % relative to bulk soil, i.e. slightly less than the combination of root detritus and earthworms. Like in the incubated earthworm pores, this boosted microbial biomass and increased enzyme activities at least 2 times. Resulting from the missing root detritus, the OM in native earthworm pores appeared to have undergone the least microbial turnover – despite high microbial biomass and activity. This suggests regular C inputs and a microbial community adapted to frequently supplied, easily available OM. It was hypothesized that the biopores‘ biochemical conditions would be different to the bulk soil’s. The microbial community in bulk soil was in fact not different to the biopores, likely because its broad SOM composition was not definitively different from the biopores. This may have not been enough to induce decisively different microbial communities, but only strongly boosted microbial activity.
Publications
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Earthworm borrows: Kinetics and spatial distribution of enzymes of C-, N- and P- cycles. Soil Biology and Biochemistry, Vol. 99. 2016, pp. 94-103.
Hoang, T.T.D, Razavi, B.S., Blagodatskaya, E., Kuzyakov, Y.
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Hotspots of microbial activity induced by earthworm burrows, old root channels, and their combination in subsoil. Biology and Fertility of Soils, Vol. 52. 2016, Issue 8, pp 1105–1119.
Hoang, D.T.T., Pausch, J., Razavi, B.S., Kuzyakova, I., Banfield, C.C., Kuzyakov, Y.
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Biopore history determines the microbial community composition in subsoil hotspots. Biology and Fertility of Soils, Vol. 53. 2017, Issue 5, pp 573–588.
Banfield, C.C., Dippold, M.A., Pausch, J., Hoang, D.T.T., Kuzyakov Y.
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Labelling plants in the Chernobyl way. A new 137Cs and 14C foliar application approach to investigate rhizodeposition and biopore reuse. Plant and Soil, Vol. 417. 2017, Issue 1–2, pp 301–315.
Banfield, C.C., Zarebanadkouki, M., Kopka, B., Kuzyakov, Y.
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Rolling in the deep: Priming effects in earthworm biopores in topsoil and subsoil. Soil Biology and Biochemistry, Vol. 114. 2017, pp. 59-71.
Hoang, T.T.D., Bauke, S.L., Kuzyakov, Y., Pausch, J.
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Six months of L. terrestris L. activity in root-formed biopores increases nutrient availability, microbial biomass and enzyme activity. Applied Soil Ecology, Vol. 120. 2017, pp. 135-142.
Athmann, M., Kautz, T., Banfield, C., Bauke, S., Hoang, D.T.T., Lüsebrink, M., Pausch, J., Amelung, W., Kuzyakov, Y., Köpke, U.
