Drivers of phosphorus cycling in temperate and boreal forest soils

• Main Author: Fetzer, Jasmin
• Other Authors: Frossard, Emmanuel, Hagedorn, Frank, Kaiser, Klaus, Doetterl, Sebastian
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ETH Zurich 2021
• Subjects: info:eu-repo/classification/ddc/500; Natural sciences; Tundra
• Online Access: https://hdl.handle.net/20.500.11850/542115; https://doi.org/10.3929/ethz-b-000542115

Understanding the main underlying drivers of soil nutrient cycles is essential for predicting the effects of global change on them. The overall aim of this thesis was to gain insights into the mechanisms of phosphorus (P) cycling in unmanaged forest ecosystems and to study how these mechanisms are linked to soil formation and global environmental changes. The soil P cycle was studied by quantifying P pools and fluxes. The influence of several factors of soil formation on P cycling was assessed at different experimental scales, ranging from a laboratory incubation, via semi-controlled field experiments, to studies at the ecosystem scale. First, litter decomposition rates were studied to assess the magnitude and controlling factors on nutrient release and microbial functioning. Litter of differing carbon:nitrogen:phosphorus (C:N:P) ratios was used and incubated in a laboratory study at 5°C and 15°C. Litter samples were taken along a natural gradient of plant growth forms in two forest-tundra ecotones in northern Russia. This study revealed that microorganisms, major mediators of litter decomposition, were able to adapt to a wide range of nutrient conditions by adjusting the C:N:P ratios of their biomass. The carbon use efficiency (CUE) of microorganisms decreased with increasing litter C:N:P ratios from forest to tundra, indicating the occurrence of “overflow respiration” where microorganisms respire C to acquire nutrients. Net N and P release was negatively correlated with litter C:N:P ratios, with almost no release of N and P from tundra litter. Experimental warming by 10°C had little influence on the nutrient release, indicating that litter quality is more important for nutrient release than temperature. The observed increase in nutrient release from tundra to forest strongly suggests that nutrient release contributes to the stability of the present vegetation types. The lower nutrient release in the tundra than in the forest potentially reduces plant growth and thereby decreases the forests’ ability to expand ...