Doctor Chioma Igwenagu


Graduated PhD 2023

Thesis Title

The effects of drought on soil and microbial nutrients and their relationship with plant growth in pasture systems

Research Project

The productivity of Australian grassland pastures play a crucial role in Australia’s economy and thus it is important that the productivity of the system be maintained. Escalating evidence suggests that current climate change such as drought and warming may negatively affect nitrogen (N), phosphorus (P), potassium (K) cycles and their availability in terrestrial ecosystem which supports grassland productivity. While attention has been given to drought and warming effects on soil nutrients availability, little effort has been invested in understanding climate effects on soil microbial processes responsible for nutrient cycling for plant use.

Furthermore, climate effect on soil nutrient availability and concentration in microbes and plants is driven by soil processes, plant nutrient demand and stoichiometric flexibility of plants and microbes. This implies that studies targeting climate effects on soil nutrient cycles in grassland ecosystem should be evaluated across species, growing seasons and soil types, but this is often not the case. While the effect of climate extremes on soil nutrient availability is gaining global interest, the importance of maintaining sustainable nutrient management in pasture system to minimise excessive use of mineral fertilisers while still maintaining growth under climate change is a growing concern.

My research objectives are to investigate (1) soil nutrient availability and relative concentration in microbes and plants in response to, and recovery from drought across different species used in Australian pasture system, (2) soil nutrient availability and relative concentration in microbes and plants in response to warming and short-term drought in a grass and legume species and whether arbuscular mycorrhizal (AM) fungi will mediate these response, and (3) how integrated use of conventional fertiliser and organic amendments will improve relative use of nutrients by plants and microbes under drought stress conditions in an Australian pasture system with two different soil types.


Churchill AC, Zhang H, Fuller KJ, Amiji B, Anderson IC, Barton CVM, Carrillo Y, Catunda KLM, Chandregowda MH, Igwenagu C, Jacob V, Kim GW, Macdonald CA, Medlyn BE, Moore BD, Pendall E, Plett JM, Post AK, Powell JR, Tissue DT, Tjoelker MG, Power SA, (2022) 'Pastures and Climate Extremes: Impacts of Cool Season Warming and Drought on the Productivity of Key Pasture Species in a Field Experiment', Frontiers in Plant Science, vol.13, Article no.836968

Zhang H, Powell JR, Plett JM, Churchill AC, Power SA, Macdonald CA, Jacob V, Kim GW, Pendall E, Tissue D, Catunda KM, Igwenagu C, Carrillo Y, Moore BD, Anderson IC, (2021) 'Climate warming negates arbuscular mycorrhizal fungal reductions in soil phosphorus leaching with tall fescue but not lucerne', Soil Biology and Biochemistry, vol.152, Article no.108075

Zhang H, Powell JR, Power SA, Churchill AC, Plett JM, Macdonald CA, Jacob V, Kim GW, Pendall E, Tissue DT, Catunda KLM, Igwenagu C, Carrillo Y, Moore BD, Anderson IC, (2021) 'Arbuscular mycorrhizal fungal-mediated reductions in N2O emissions were not impacted by experimental warming for two common pasture species', Pedobiologia, vol.s 87-88, Article no.150744

Research Supervisors

Dr. Yolima Carrillo and Dr. Catriona Macdonald