PhD project: Assessing belowground biochemical traits of different tree species and their effects on soil nutrient cycling
International Max Planck Research School for Global Biogeochemical Cycles
In cooperation with the Friedrich Schiller University Jena, the Max Planck Institute for Biogeochemistry houses a unique and flexible research program that grants German and foreign students a broad selection of learning opportunities while still maintaining a research focus.
The IMPRS-gBGC offers a PhD program specializing in global biogeochemistry and related Earth System sciences.
Geosciences Instrumentation and Data Systems (GI)
Soil System Sciences (SSS)
by Beate Michalzik , Susan Trumbore
In terrestrial ecosystems, nutrient cycling is primarily driven by the interaction between plants, decomposer organisms, and soil quality. Plant community composition and vertical allocation of plant biomass defines the distribution as well as the amount and quality of organic matter (OM) inputs to soils, which in turn determine energy resource and nutrient availability (i.e., fluxes, chemical complexity, and stoichiometric nutrient ratios such as C:N and C:P) to microbes (Tischer et al. 2014, 2015). Furthermore, turnover of soil carbon, as the dominant part of OM in soils, and soil respiration differ among tree species (Vesterdal et al. 2012). Lastly, OM inputs and turnover rates are also influenced by soil quality (Leppällammi-Kujansuu et al. 2014).
Regarding the role of belowground OM input, the rhizosphere is shown to form “hot spots” (McClain et al., 2003; Kuzyakov and Blagodatskaya 2015) of amplified microbial and enzyme activity fueled by root exudation/deposition (Razavi et al. 2016). The interactions within the rhizosphere appear quantitatively crucial for soil nutrient cycling and availability (Finzi et al. 2015). We hypothesize that the growth and root development of trees during natural forest regeneration creates species- and developmental stage-specific conditions and interactions within the rhizospheres (Zwetsloot et al., 2018).
This projects aims at testing how root development and morphology as well as its biochemical functionality differ among tree species and soil quality (i.e., soil texture, pH, C:N, C:P). The focus of this project is therefore on plant root traits (e.g., root chemistry, root morphology, root to shoot ratio) of tree species representative for central Europe (e.g., beech, spruce) and their functional significance in shaping microbial-driven turnover processes within the respective rhizospheres. This will be assessed by 1) description of root traits and 2) the determination of kinetics of exo-enzymes involved in C, N and P cycling in radial distance around the roots using greenhouse experiments. We hypothesize that species differ in the exudation of phenolic compounds and that soil microbial respiration will be lowest beneath species with roots and root exudates rich in phenolics (see Zwetsloot et al., 2018).
For tracing root turnover and soil respiration rates with and without root exudation, radiocarbon measurements will be performed. Investigations will be conducted from the micro-, meso- to the macro-scale encompassing bioassays, incubation experiments in -cosms under controlled climatic conditions and field observations. The project is strongly connected to the DFG-Collaborative Research Center (CRC 1076) “AquaDiva”, which deals with the coupling of surface biota, microbial processes, and ecological functions in the soil and the deeper subsurface. Fieldwork will be conducted at the Hainich Critical Zone Exploratory (for more information see Küsel et al. 2016).
Finzi, A.C., Abramoff, R.Z., Spiller, K.S., Brzostek, E.R., Darby, B.A., Kramer, M.A., Phillips, R.P., 2015. Rhizosphere processes are quantitatively important components of terrestrial carbon and nutrient cycles. Glob Change Biol 21, 2082–2094.
Kuzyakov, Y., Blagodatskaya, E., 2015. Microbial hotspots and hot moments in soil. Concept & review. Soil Biology and Biochemistry 83, 184–199.
Küsel, K., Totsche, K. U., Trumbore, S. E., Lehmann, R., Steinhäuser, C., Herrmann, M. 2016. How deep can surface signals be traced in the Critical Zone? Merging biodiversity with biogeochemistry research in a central German Muschelkalk landscape. Front. Earth Sci. 4: 32.
Leppällammi-Kujansuu, J., Aro, L., Salemaa, M., Hansson, K., Berggren Kleja, D., Helmisaari, H.- S. 2014. Fine root longevity and carbon input into soil from below- and aboveground litter in climatically contrasting forests. Forest Ecology and Management 326, 79-90.
McClain, M. E., et al. 2003. Biogeochemical Hot Spots and Hot Moments at the Interface of Terrestrial and Aquatic Ecosystems. Ecosystems (2003) 6: 301–312.
Razavi, B.S., Zarebanadkouki, M., Blagodatskaya, E., Kuzyakov, Y. 2016. Rhizosphere shape of lentil and maize. Spatial distribution of enzyme activities. Soil Biology and Biochemistry 96, 229–237.
Tischer, A., Potthast, K., Hamer, U. 2014. Land-use and soil depth affect resource and microbial stoi-chiometry in a tropical mountain rainforest region of southern Ecuador. Oecologia 175, 375-393.
Tischer, A., Werisch, M., Döbbelin, F., Camenzind, T., Rillig, M. C, Potthast, K., Hamer, U. 2015. Above- and belowground linkages of a nitrogen and phosphorus co-limited tropical mountain pasture system – responses to nutrient enrichment. Plant and Soil, 1-20.
Vesterdal, L., Elberling, B., Christiansen, J.R., Callesen, I., Kappel Schmidt, I. 2012. Soil respiration and rates of soil carbon turnover differ among six common European tree species. Forest Ecology and Management 264, 185-196.
Zwetsloot, M.J., Kessler, A., Bauerle, T.L. 2018. Phenolic Root Exudate and Tissue Compounds Vary Widely Among Temperate Forest Tree Species and Have Contrasting Effects on Soil Microbial Respiration. New Phytol 218 (2), 530-541.
Applications to the IMPRS-gBGC are open to well-motivated and highly-qualified students from all countries. Prerequisites for this PhD project are
- a Master’s degree in soil science, biogeochemistry,(landscape-) ecology, geography, forestry or geoecology
- experience in ecosystem research and its relevant methodology (e.g. assessment of element flux rates and cycling)
- excellent oral and written communication skills in English
- for conducting the field campaigns a car driver´s licence is mandatory
The Max Planck Society seeks to increase the number of women in those areas where they are underrepresented and therefore explicitly encourages women to apply. The Max Planck Society is committed to increasing the number of individuals with disabilities in its workforce and therefore encourages applications from such qualified individuals.