Soil carbon, nutrient, and microbial interactions in a phosphorus limited ecosystem exposed to elevated CO2

Abstract

Research presented in this thesis aims to advance research in the field of biogeochemistry and plant soil interaction under eCO2 using a stoichiometric framework to understand microbial processes of carbon (C) and N and their effects on soil nutrient availability in the rhizosphere using field-based and controlled environment experiments combined with stable isotope methods. I have contributed to understanding of how eCO2 influences belowground processes of C cycling and nitrogen (N) uptake as regulated by nutrient availability. This thesis evaluates stoichiometric impacts on microbial transformations of C, N and phosphorus (P) and their interactions for soil C in a future high CO2 world. In chapter 2 I show that soil depth is an important factor that cannot be ignored in terrestrial ecosystems where plants have deep reaching root systems and future work needs to explicitly consider depth and processes taking place below the top-soil level to detect impacts of eCO2. In chapter 3 I establish that the soil C pools of SOM and plant derived soil C are decoupled in P limited soil and are controlled by different mechanisms. However, if both N and P availability can be improved, the findings in this thesis show that a gain in new soil C could occur, by increased plant-derived C accumulating in the soil and decreasing SOM derived C loss. In chapter 4 I show that microbes are strong competitors for inorganic N uptake even in a P limited soil, but that plants can increase their take of available resources with improved nutrient availability. Improved availability of both N and P in P limited ecosystems may be needed to promote an increase in soil C in P limited soils exposed to eCO2 though future research will need to also incorporate CO2 interactions with water limitation and account for seasonal variability.

Date of Award	2022
Original language	English