Ecosystem function in a changing climate

The climate is changing across the globe as a result of human activities1. Atmospheric concentration of greenhouse gases such as carbon dioxide (CO2) are increasing, which has led to an increase in the global mean temperature over the last 100 years1. Climate change also increases the likelihood of extreme weather events1. However, how will various ecosystems respond to these changes? This was the focus of Associate Professor Sally Power, from the Hawkesbury Institute for the Environment (UWS), at her seminar at Macquarie University.

Assoc Prof Sally Power is an ecosystem ecologist, previously working in the United Kingdom on nitrogen deposition and cycling, tropospheric ozone, nitrogen and ozone interactions with drought, and the effects of drought on plant diversity4. She was also involved in the DIRECT Experiment (Diversity Rainfall and Elemental Cycling in a Terrestrial ecosystem), which looked at extreme rainfall events on a mesic grassland in southern England4. She arrived at the Hawkesbury Institute two years ago and has been working on two projects: the DRI-Grass project, and the EucFACE project (Eucalyptus Free Air CO2 Experiment)4.

The DIRECT Experiment

Grasslands provide various ecosystem services (such as carbon storage) but are threatened by climate change, particularly due to changes in rainfall patterns2. For example, in southern England, there is expected to be an overall decrease in annual rainfall, with rainfall occurring in more extreme events2. As discussed by Assoc Prof Power, the DIRECT experiment looks at the responses of a mesic grassland to different rainfall regimes to predict how they will be affected in the future4.

 DIRECT experiment

 DIRECT Experiment – controlling rainfall regimes. Image retrieved from


Plant species will vary in their resistance to climate change due to their varying functional traits2. Functional traits include features such as root depth, growth rates, the amount of nitrogen in their leaves, and how quickly they can photosynthesise2. The DIRECT experiment divided plants into 3 distinctive groups:

–          Group 1: Perennial forbs and grasses2,4

–          Group 2: Caespitose (tufted) grasses2,4

–          Group 3: Annual herbs, grasses and some legumes2, 4

The experiment found that perennial plants (which are very important for ecosystem functioning) are quite sensitive to climate change, particularly during times of water stress2. According to Assoc Prof Power, reduced frequency of rainfall events has a large effect on perennial plant species. Hence, annual plants will be required to maintain ecosystem function during drought periods2.

DRI-Grass Experiment

A similar type of experiment is currently being conducted by Assoc Prof Power at the Hawkesbury Institute. This experiment is looking at how changing rainfall regimes will affect grassland ecosystems and root herbivory in western Sydney4.

As stated by Assoc Prof Power, early results indicate that different rainfall regimes have led to changes in soil moisture4. Furthermore, Assoc Prof Power has found species composition changes, such as an increase in the weed Eragrostis curvula (African lovegrass) in wetter environments, a decrease in the weed Setaria sp. (Pigeon Grass) during dry treatments, and summer drought plots solely dominated by the weed Cynodon dactylon (Couch). Although early in the experiment, it is evident that species composition changes in western Sydney grasslands should be expected under climate change in the future.

EucFACE Experiment

Currently there is a major uncertainty of how forests will be affected by an increase in carbon dioxide3. At the leaf level, it is known that an increase in CO2 will lead to increased photosynthesis and reduced water loss3 – but what about at the ecosystem level? This is the focus of the EucFACE experiment at the Hawkesbury Institute – a realistic, long term experiment5 to determine effects of elevated CO2 on an intact Cumberland Plain Woodland System4.

 EucFace experiment

EucFACE Experiment. Image retrieved from


Assoc Prof Power is focussing her research on the effects of soil nutrient cycling in a higher CO2 world, and according to Reich, Hungate & Luo (2006), evidence for Carbon (C) and Nitrogen (N) interactions are rare. This experiment can be looked at as highly significant as C and N play a major role in the metabolism of plants, herbivores and microbes5. According to Assoc Prof Power, increased CO2 could lead to increased nutrient cycling, but it may also cause the down-regulation of nitrogen uptake. Assoc Prof Power’s early results indicate increased CO2 is causing very rapid phosphate releases, which requires further investigation in the near future.

 CO2 output following rain Data from the EucFACE Experiment: After a prolonged period of drought, the CO2 output shows the forest “breathing”. Image retrieved from,_breathe_out_eucface_and_the_forest_breathing


Concluding Points

  • Ecosystems are complex! Their reactions to climate change will vary, and this will change depending on the ecosystem in focus.
  • More research is required into responses of ecosystem functioning with increased CO2, temperature and extreme rainfall events.


  1. Cubasch, U., D. Wuebbles, D. Chen, M.C. Facchini, D. Frame, N. Mahowald, and J.-G. Winther (2013). Introduction. In Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung … and P.M. Midgley (Eds.). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
  1. Fry, E. L., Manning, P., Allen, D. G., Hurst, A., Everwand, G., Rimmler, M., & Power, S. A. (2013). Plant functional group composition modifies the effects of precipitation change on grassland ecosystem function. PloS one, 8(2), e57027. doi: 10.1371/journal.pone.0057027
  1. Kauwe, M. G., Medlyn, B. E., Zaehle, S., Walker, A. P., Dietze, M. C., Hickler, T., … & Norby, R. J. (2013). Forest water use and water use efficiency at elevated CO2: a model‐data intercomparison at two contrasting temperate forest FACE sites. Global change biology, 19(6), 1759-1779. doi: 10.1111/gcb.12164
  1. Power, S. (2014, May 14). Drought, deluge and elevated CO2 – a two hemisphere look at ecosystem responses to climate change. BioSeminar. Conducted from Macquarie University, North Ryde, NSW.
  1. Reich, P. B., Hungate, B. A., & Luo, Y. (2006). Carbon-nitrogen interactions in terrestrial ecosystems in response to rising atmospheric carbon dioxide. Annu. Rev. Ecol. Evol. Syst., 37, 611-636. doi: 10.1146/annurev.ecolsys.37.091305.110039



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