DeepEarthshape - Biogeochemistry: Microbial element cycling as a driver of soil formation

• Applicant: Professorin Dr. Eva Lehndorff, since 6/2020
• Subject Area: Physical Geography
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 280395121

Phosphorus (P) solubilization in soils is a crucial process for ecosystem nutrition and ecosystem development. Previous research on biogenic P solubilization focused on single microbial strains, but little is known about P solubilization as a process of soil formation and ecosystem development. The general objective of the project is to gain understanding on how microbial and plant mediated P solubilization and silicate weathering influence the formation of soil and its P forms. For this purpose, we will quantify the rates of P solubilization and of silicate weathering in a sequence of soils on granites of different stages of development in the coastal range of Chile. We aim at determining mechanisms of microbial P solubilization such as the release of protons and organic acid anions, the factors controlling P solubilization, and the abundance of P-solubilizing bacteria at different stages of soil development. The rates of P solubilization and silicate weathering will be related to soil P fractions (Hedley fractions) that have formed during pedogenesis. We will test the hypothesis that mechanisms, rates, controlling factors and abundances of P-solubilizing bacteria strongly change during soil development. The main value of the project will be that it relates microbial P solubilization taking place at a time scale of several weeks to the development of soils and P fractions taking place over hundreds of years.So far, it is not known how microbial activity in soil affects soil formation in different soil depths and under different climatic conditions. The overarching aim of the project proposed here is therefore to study how microbial cycling of C, N, P and Si affects soil formation. For this purpose, we will, first, study microbial biomass, microbial respiration, and the age of total organic C and respired C in soil and saprolite along a climate gradient in the Costal Cordillera of Chile. Second, we aim at quantifying non-symbiotic N2 fixation along the climate gradient, and at understanding the factors that limit N2 fixation, microbial respiration and silicate weathering. We will test the hypotheses (i) that microbial respiration in the saprolite that advances weathering is fueled by young organic matter, (ii) that CO2 concentrations in saprolite are positively correlated with the net primary production, and that (iii) N2 fixation is strongly limited by water availability along the climate gradient in the Costal Cordillera of Chile. In order to test these hypotheses, we will quantify microbial biomass in 10 m deep saprolite cores taken from four study sites along the climate gradient, and we will quantify the age of total organic C and respired C based on radiocarbon dating. Furthermore, we will quantify N2 fixation in incubations with 15N-N2. Finally, we will synthesize and model the results on biogenic weathering and microbial C, N, P, and Si cycling along the climate gradient in the Costal Cordillera that have been collected during the first and second phase of the priority program. The main value of the project will be that it relates microbial cycling of C, N, P and Si to the formation of soils.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1803: EarthShape: Earth Surface Shaping by Biota
• Cooperation Partner: Dr. Carlos A. Sierra
• Ehemalige Antragstellerin: Professorin Dr. Marie Anneke Spohn, until 6/2020