Soil water availability mediates woody plant seedling growth to elevated CO2 in a model grassland system

Anthony Manea
Macquarie University

Received the Australian Flora Foundation Young Scientist Award for his talk at EcoTas13, a joint conference between the Ecological Society of Australia and the New Zealand Ecological Society, held at The Aotea Centre, Auckland from 24-29 November 2013.:

Anthony Manea1 and Michelle Leishman1
1Macquarie University

The expansion of woody plants into grasslands has been observed worldwide and is a major threat to the integrity of these systems. It has been proposed that the expansion of woody plants into grasslands is linked to the increases in atmospheric CO2 levels that have occurred over the last 200 years. The cover of adult woody plants in grasslands is most limited by seedling
establishment. This suggests that rising atmospheric CO2 levels should enhance the establishment success of woody plant seedlings in grasslands. In this study we examined the effect of CO2 concentration on the competitive interactions between C4 grasses and C3 woody plant seedlings by growing C3 woody plant seedlings in mesocosms together with C4 grasses under four competition treatments (no competition, root competition only, shoot competition only and complete competition) under ambient and elevated CO2. We found that woody plant seedling biomass was suppressed by competition from grasses with root and shoot competition having the same competitive effect on the woody plant seedlings. Woody plant seedling biomass in the complete competition treatment was significantly higher under ambient CO2 compared to elevated CO2. This result was due to less competition from the grasses for belowground space and water under ambient CO2. Our results suggest that the establishment success of woody plant seedlings and the subsequent expansion of woody plants into grasslands in the future will likely be strongly coupled to the CO2 response of the grasses within those systems.

Anthony Manea is a PhD candidate in the Plant Invasion and Restoration Ecology Laboratory at Macquarie University. His research interests include grass/woody plant competitive interactions, grassland responses to extreme drought and grassland flammability under elevated CO2.