Aboveground-belowground linkages and carbon allocation in pasture grasses during climate extremes

Abstract

Predicted increases in climate extremes, such as an increase in the intensity and frequency of drought events and heatwaves, are expected to affect ecosystem functions and services. Pastures and rangelands are particularly sensitive to these changes in climate, with negative consequences for livestock production and associated food security. Knowledge of grass species' responses to climate extremes in terms of their carbon allocation and trait plasticity associated with resource acquisition can inform management decisions for sustainable pasture production in the face of ongoing and projected changes in a global climate. For this, I employed field and growth chamber manipulation experiments and examined the partitioning of primary production to respiration and growth, as well as biomass allocation and root trait plasticity, in response to predicted changes in rainfall patterns (60% reduction in winter and spring rainfall) and atmospheric warming (ambient +3 ?). I specifically tested the following overarching questions in this thesis: i) Are there differences in the root economic spectrum and resistance and resilience strategies between C3 and C4 pasture grasses in response to drought?; ii) Do belowground responses in a common pasture grass facilitate aboveground production during heat and drought?; iii) Does partitioning of primary products of photosynthesis between growth and respiration explain pasture production during heat and drought, and how does clipping influence these relationships? Overall, my research provides insight into several resource allocation and carbon uptake mechanisms behind pasture grasses' responses to drought and warming, both above and belowground. In addition, this work highlights adaptation strategies of pasture species to maintain aboveground production both during exposure to climate stress and for post-stress recovery. In conclusion, this study, in line with ecosystem model projections, demonstrates the heat and drought sensitivity of pasture production and associated implications of declining pasture productivity for the meat, livestock and dairy industries in a future warmer and drier climate. However, findings from my study can also help inform a framework for selecting pasture species and cultivars with traits favoring climate resistance and resilience that will support sustained pasture production under future climates.

Date of Award	2022
Original language	English