Effects of elevated CO2 on the reproductive performance and early life fitness of long-lived woody plant species

Abstract

Atmospheric concentrations of CO2 have risen considerably since the industrial revolution due to human activity. Without extreme intervention, climate forecasts indicate that atmospheric CO2 concentrations will continue to rise. Plant growth and productivity in response to elevated CO2 has been studied extensively, however, few studies explore how reproduction will be affected under future CO2 concentration; particularly for long-lived woody plant species. This study is undertaken within the EucFACE facility in Western Sydney (Australia), with naturally growing populations, on nutrient limited soils, which form part of the remnant Cumberland Plains Woodland. The effects of elevated CO2 on vegetative growth in this ecosystem have previously been demonstrated to be absent due to phosphorous limitation despite maintaining higher photosynthetic rates. Little is known how reproductive performance of long-lived woody plants species will respond to increased CO2 concentrations in this environment. The main objective of this thesis is to explore direct effects of elevated CO2 on the reproductive performance of a dominant tree, Eucalyptus tereticornis, and a perennial shrub, Hakea sericea, in addition to the subsequent maternal effects on early-life fitness of H. sericea. It is the first study to assess the reproductive performance of mature dominant evergreen angiosperm (E. tereticornis) in response to rising CO2 concentration. Several experiments were undertaken to determine how reproductive performance and subsequent early-life fitness is affected by elevated CO2; (i) The impacts on reproductive effort and output through quantifying the proportion of biomass invested into floral buds, fruit and seeds for E. tereticornis and H. sericea. (ii) Seed quality was assessed through conducting germination experiments for E. tereticornis and H. sericea. (iii) Seed sourced from maternal H. sericea plants grown in ambient and elevated CO2 conditions were propagated into growth chambers simulating pre-industrial, ambient, and future CO2 concentrations to assess early-life fitness through measurements of biomass, photosynthesis, and functional traits. Key findings from these experiments were; (i) Reproductive effort for E. tereticornis is increased for plants growing in elevated CO2, however, there is great interannual variability which will require further exploration, (ii) Germination success is differentially affected by elevated CO2, with H. sericea (large seeded species) seeing greater benefits than E. tereticornis (small seeded species), (iii) Despite having lower biomass, seedlings with maternal plants grown in ambient CO2 conditions had greater photosynthetic capacity than seedlings with maternal plants grown in elevated CO2, and (iv) Photosynthesis was down-regulated in response to long-term exposure of elevated CO2 only for seedlings 7 with maternal plants grown in elevated CO2 indicating acclimation may occur across generations but not necessarily within a generation. Differential responses between species may have profound impacts on vegetation community composition, thereby altering ecosystem structure and function.

Date of Award	2019
Original language	English