Recent research topics
Microbial biomass stoichiometry as a driver of element cycling in soils
- Do stoichiometric relationships explain element cycling in soil?
The soil microbial biomass has a constrained stoichiometry, while the stoichiometry of the pool of bioavailable elements in soil can vary strongly. With my group, I have explored to which extent the relationship between the microbial biomass stoichiometry and the soil stoichiometry determines the rates of processes in soils.
- Schleuss, P. M., Widdig, M., Heintz-Buschart, A., Guhr, A., Martin, S., Kirkman, K., & Spohn, M. (2019). Stoichiometric controls of soil carbon and nitrogen cycling after long-term nitrogen and phosphorus addition in a mesic grassland in South Africa. Soil Biology and Biochemistry, 135, 294-303.
- Spohn, M. (2016). Element cycling as driven by stoichiometric homeostasis of soil microorganisms. Basic and applied ecology, 17(6), 471-478.
- Spohn, M. (2015). Microbial respiration per unit microbial biomass depends on litter layer carbon-to-nitrogen ratio. Biogeosciences, 12(3).
- Spohn, M., & Chodak, M. (2015). Microbial respiration per unit biomass increases with carbon-to-nutrient ratios in forest soils. Soil Biology and Biochemistry, 81, 128-133.
- Heuck, C., Weig, A., & Spohn, M. (2015). Soil microbial biomass C: N: P stoichiometry and microbial use of organic phosphorus. Soil Biology and Biochemistry, 85, 119-129.
- Spohn, M., & Kuzyakov, Y. (2013). Phosphorus mineralization can be driven by microbial need for carbon. Soil Biology and Biochemistry, 61, 69-75.
Microbial carbon use efficiency and microbial biomass turnover
- Does the availability of carbon and nutrients affect soil microbial carbon use efficiency and how can we measure this?
Microbial carbon use efficiency quantifies how microbes partition carbon between respiration and growth. In order to analyze soil microbial carbon use efficiency and microbial growth, we developed a new technique, which allows us to determine soil microbial growth and carbon use efficiency in a substrate independent way, based on the incorporation of 18O from water into the microbial DNA. The results show that microbial carbon use efficiency varies less strongly than expected and that soil C storage is more affect by the turnover of the microbial biomass than by microbial carbon use efficiency
- Widdig, M., Schleuss, P. M., Biederman, L. A., Borer, E. T., Crawley, M. J., Kirkman, K. P., ... & Spohn, M. (2020). Microbial carbon use efficiency in grassland soils subjected to nitrogen and phosphorus additions. Soil Biology and Biochemistry, 107815.
- Spohn, M., Pötsch, E. M., Eichorst, S. A., Woebken, D., Wanek, W., & Richter, A. (2016). Soil microbial carbon use efficiency and biomass turnover in a long-term fertilization experiment in a temperate grassland. Soil Biology and Biochemistry, 97, 168-175.
- Spohn, M., Klaus, K., Wanek, W., & Richter, A. (2016). Microbial carbon use efficiency and biomass turnover times depending on soil depth – Implications for carbon cycling. Soil Biology and Biochemistry, 96, 74-81.
- Do root exudates affect mineralization of organic phosphorus?
I have studied the effects of root exudates on mineralization of organic phosphorus and phosphatase activity using isotopes and soil chemical analyses. In addition, I developed soil zymography, an imaging technique which can be used to visualize and analyze the activities of enzymes involved in element cycling. Together the results show that plant root exudates can strongly contribute to mobilization of phosphorus from different pools in the rhizosphere directly and also indirectly by stimulating microbial activity.
- Holz, M., Zarebanadkouki, M., Carminati, A., Hovind, J., Kaestner, A., & Spohn, M. (2019). Increased water retention in the rhizosphere allows for high phosphatase activity in drying soil. Plant and Soil, 443(1-2), 259-271.
- Hofmann, K., Heuck, C., & Spohn, M. (2016). Phosphorus resorption by young beech trees and soil phosphatase activity as dependent on phosphorus availability. Oecologia, 181(2), 369-379.
- Spohn, M., & Kuzyakov, Y. (2013). Distribution of microbial- and root-derived phosphatase activities in the rhizosphere depending on P availability and C allocation – Coupling soil zymography with 14C imaging. Soil Biology and Biochemistry, 67, 106-113.
- Spohn, M., Ermak, A., & Kuzyakov, Y. (2013). Microbial gross organic phosphorus mineralization can be stimulated by root exudates–a 33P isotopic dilution study. Soil Biology and Biochemistry, 65, 254-263.
Microbial mobilization of inorganic phosphorus pools
- What controls mobilization of inorganic phosphorus in soils?
Little is known so far about the mobilization of bound inorganic P in soils by microorganisms and plants. Therefore, we conducted experiments which allowed us to gain insights into microbial mobilization of P bound in minerals and sorbed to the solid soil phase.
- Brucker, E., Kernchen, S., & Spohn, M. (2020). Release of phosphorus and silicon from minerals by soil microorganisms depends on the availability of organic carbon. Soil Biology and Biochemistry, 143, 107737.
- Pastore, G., Kaiser, K., Kernchen, S., & Spohn, M. (2020). Microbial release of apatite-and goethite-bound phosphate in acidic forest soils. Geoderma, 370, 114360.
- Spohn, M., Zeißig, I., Brucker, E., Widdig, M., Lacher, U., & Aburto, F. (2020). Phosphorus solubilization in the rhizosphere in two saprolites with contrasting phosphorus fractions. Geoderma, 366, 114245.
- Widdig, M., Schleuss, P. M., Weig, A. R., Guhr, A., Biederman, L. A., Borer, E. T., ... & Spohn, M. (2019). Nitrogen and phosphorus additions alter the abundance of phosphorus-solubilizing bacteria and phosphatase activity in grassland soils. Frontiers in Environmental Science, 7, 185.
The carbon-to-phosphorus ratio of soil organic matter
- What affects the carbon-to-phosphorus ratio of soil organic matter?
The stoichiometry of soil organic matter is affected by organic matter inputs, microbial decomposition and sorption of organic compounds. Soil organic matter is very rich in phosphorus compared for instance to dead wood or other plant residues. Thus, an increase in the soil organic carbon stock in mineral soils goes along with the sequestration large amounts of phosphorus.
- Spohn, M. (2020). Phosphorus and carbon in soil particle size fractions: A synthesis. Biogeochemistry, 147(3), 225-242.
- Spohn, M. (2020). Increasing the organic carbon stocks in mineral soils sequesters large amounts of phosphorus. Global Change Biology.