The University of Sydney - Biogeochemistry Group

Dijkstra Laboratory 

Dijkstra Lab

Drought effects on soil carbon and nutrient cycling mediated by rhizosphere processes

Drought effects on carbon and nutrient dynamics are examined in a grassland at John Pye Farm, Bringelly, NSW. This project will improve understanding of drought impacts on processes that occur at the interface between plant roots and soil that are vital for soil carbon storage and climate feedbacks, and sustainability of grasslands.

CliFer experiment: effects of clipping and nutrients on grassland functioning and services

The interactive effects of grazing (clipping), nitrogen and phosphorus addition on carbon and nutrient dynamics are examined in a grassland near the Centre for Carbon, Water and Food in Camden, NSW. This project will fill important knowledge gaps in managing grasslands for sustainable production.

Carbon costs for plant uptake of nutrients and water

This project will investigate how much carbon plants need to invest belowground in return for water and nutrients. By using economic principles of supply and demand the project quantifies carbon expenditure for water and nutrients in grasslands and crops under different climate and land management scenarios. Novel triple and quadruple isotope labelling techniques are used to explore the dependency of carbon investment on plant-microbial interactions and availability of belowground resources.

Impacts of biochar on soil nitrogen and phosphorus dynamics

Effects of biochar on nutrient mineralisation, sorption/desorption are examined for biochars at different stages of oxidation. Biochar is a stable form of carbon, which could be used to enhance soil carbon. Biochar in soil is progressively more oxidised with time, and it is unclear how this aging process affects nutrient dynamics. In this project the effect of biochar aging on sorption and desorption of phosphorus are investigated, as well as nitrogen dynamics using 15N tracer techniques. The role of plants on nutrient dynamics is also investigated.

Effects of phosphorus availability on nitrogen mineralisation and loss

Effects of soil phosphorus availability on nitrogen dynamics are explored for a variety of soil types. Most nitrogen transformations in soil, including gross nitrogen mineralisation, nitrification, and denitrification are mediated by microbes. All of these microbes require phosphorus, but little is known how phosphorus availability affects these microbial processes. In this project the effect phosphorus availability on nitrogen transformations and loss (e.g., nitrous oxide emission) will be explored for soil types that differ in phosphorus and carbon content, pH and texture.