Paperbark tree to reveal how climate change has affected rainfall in the past. Tree leaves preserved in ancient wetlands could be used to reconstruct past rainfall activity and cast light on the impact of global warming.
From Griffith University
Synonymous with the Australian landscape, the paperbark tree is most recognised for its distinctive bark, but it is the leaves that have found themselves at the centre of research which could provide crucial insights into climate change.
The research, completed by a consortium of researchers including Griffith University School of Engineering Professor Margaret Greenway, found Melaleuca leaves preserved in ancient wetlands could be used to reconstruct past rainfall activity.
The field study was conducted in Melaleuca wetlands in south-east Queensland, including the Carbrook Wetlands.
Professor Greenway, whose research interests are the ecological and hydrological processes of Melaleuca wetlands, said the findings were significant because of the potential they offered to tell the story of tropical and subtropical rainfall history.
She said obtaining that data was crucial if climate change was going to be properly understood.
Prof Greenway said researchers captured a huge data bank of material as part of the study, which monitored rainfall, fluctuations in water levels and water quality, as well as the seasonal patterns of leaf production in wetlands.
Each month over 11 years Professor Greenway collected plant components in litter traps placed below paperbark trees.
Other researchers in the team then analysed the leaves for carbon isotope discrimination to understand the degree of moisture stress experienced by the plants.
In doing so the researchers found the relationship between leaf carbon isotope ratios and rainfall can be used as a proxy to infer changes in climate.
The project was funded by the Australian Research Council and the University of Adelaide.
Quantitative reconstructions of terrestrial climate are highly sought after but rare, particularly in Australia. Carbon isotope discrimination in plant leaves (Δleaf) is an established indicator of past hydroclimate because the fractionation of carbon isotopes during photosynthesis is strongly influenced by water stress. Leaves of the evergreen tree Melaleuca quinquenervia have been recovered from the sediments of some perched lakes on North Stradbroke and Fraser Islands, south-east Queensland, eastern Australia. Here, we examine the potential for using M. quinquenervia ∆leaf as a tracer of past rainfall by analysing carbon isotope ratios (δ13C) of modern leaves. We firstly assess Δleaf variation at the leaf and stand scale and find no systematic pattern within leaves or between leaves due to their position on the tree. We then examine the relationships between climate and Δleaf for a 11-year time series of leaves collected in a litter tray. M. quinquenervia retains its leaves for 1–4 years; thus, cumulative average climate data are used. There is a significant relationship between annual mean ∆leaf and mean annual rainfall of the hydrological year for 1–4 years (i.e. 365–1460 days) prior to leaf fall (r2 = 0.64, P = 0.003, n = 11). This relationship is marginally improved by accounting for the effect of pCO2 on discrimination (r2 = 0.67, P = 0.002, n = 11). The correlation between rainfall and Δleaf, and the natural distribution of Melaleuca quinquenervia around wetlands of eastern Australia, Papua New Guinea and New Caledonia offers significant potential to infer past rainfall on a wide range of spatial and temporal scales.
John Tibby, Cameron Barr, Francesca A. Mcinerney, Andrew C. G. Henderson, Melanie J. Leng, Margaret Greenway, Jonathan C. Marshall, GLenn B. McGregor, Jonathan J. Tyler and Vivienne McNeil; Quantifying past sub-tropical rainfall using leaf from the common paperbark tree, Melaleuca quinquenervia; Global Change Biology,.
Griffith University news release.