Autor:innen:
Fatemeh Dehghani Mohammad Abadi | Helmholtz Centre for Environmental Research - UFZ | Germany
Robin Wagner | Helmholtz Centre for Environmental Research - UFZ
Dr. Steffen Schlüter | Helmholtz Centre for Environmental Research - UFZ | Germany
Dr. Thomas Reitz | Helmholtz Centre for Environmental Research - UFZ | Germany
PD. Dr. Evgenia Blagodatskaya | Helmholtz Centre for Environmental Research - UFZ | Germany
Organic compounds are decomposed by soil microorganisms as a source of carbon (C), energy, and nutrients for microbial metabolic processes, resulting in either C storage or losses as CO2. The current challenge to increase C sequestration in soils entails the understanding of C turnover processes during the microbial decomposition of numerous organic compounds under environmental constraints such as nutrient and water availability.
We studied the effect of moisture and nutrient availability on the decomposition of cellulose, which is the most abundant polysaccharide in plant residues. We monitored the CO2 efflux from a fertilized and an unfertilized Haplic Cambisol at two water contents (pF 1.8 and 2.5). To account for substrate quality and quantity, we amended the soil with either regular or carboxymethyl cellulose (CMC) whereby the amount of added cellulose-C was related (10, 100, 400, 800, and 1600%) to the microbial biomass C (MBC) in the samples.
All implemented factors strongly affected the pattern of CO2 release. Microbial respiratory response in fertilized soil nonlinearly increased with substrate amount, showing a clear peak at the cellulose-C concentrations above 400% of MBC. At the peak point, CO2 efflux increased 1.8 and 2 times at 800 and 1600% of MBC, respectively, compared to 400% of MBC, therefore approaching saturation at concentrations above 800% of MBC. In the unfertilized soil amended with cellulose-C at the ratio of 10% and 100% of MBC, the respiration gradually increased by a factor of 1.3 and 2.9, respectively, compared to the non-amended soil. The effects of moisture increase from pF 2.5 to 1.8 and soil fertilization in the soil amended with 400% of MBC cellulose, were similar in terms of the pattern of CO2 emission curves, resulting in earlier, higher and narrower peak because of better nutrient access. However, fertilization affected cumulative CO2 release 1.5 times stronger than higher water availability during the intensive decomposition stage. In the long term, an increase in water content altered the dynamics of CO2 release, but it did not affect the cumulative CO2 amount. Finally, when amending the soil with CMC, the CO2 efflux was much weaker than that of the soil amended with regular cellulose at the same amount of 400% of MBC.
This study confirms the strong dependency of decomposition dynamics on substrate properties and soil conditions, which is based on complex regulatory mechanisms of energy and matter turnover in soil