Program B Student Profiles

1. Lucas Cernusak
2. Sara Hely
3. Alex Lee
4. Karim Sabetraftar
5. Danny Siegenthaler

Lucas Cernusak

Interpreting variation in the stable isotope composition of plant organic material

Supervisor: Prof Graham Farquhar

Aims: To understand and quantify the fractionation of stable carbon and oxygen isotopes that occurs during the incorporation of these elements into plant biomass. Specifically, I am interested in the extent to which the evaporative enrichment of oxygen isotopes in leaf water is reflected in the oxygen isotope ratio of dried plant material, and in how the stable isotope ratio of photosynthetically captured carbon changes during conversion of the initial products of photosynthesis to leaves and wood.

Background: A small amount of the carbon and oxygen in the atmosphere exists as stable isotopes containing one or more extra neutrons; one in the case of carbon (13C) and two for oxygen (18O). During the exchange of carbon dioxide between the atmosphere and the biosphere, the ratios of these isotopes to their more abundant counterparts (12C and 16O) are altered. The extent of fractionation can provide information about the environmental conditions under which photosynthesis occurred, and about the magnitude of carbon dioxide fluxes between plants and the atmosphere. However, successful interpretation of carbon and oxygen isotope ratios requires a sound understanding of the biological fractionation events causing variation.

Description of research: I am studying how the evaporative enrichment of oxygen isotopes in leaf water is related to both environmental conditions and the physiological status of the plant, and how the leaf water signal in turn relates to the oxygen isotope ratio of sugars exported from leaves for growth in other parts of the plant. This has involved isotopic analysis of phloem sap collected from plants such as lupin, blue gum, and castor bean, grown both in the glasshouse and in the field. I have also analyzed the carbon isotope ratio of sugars in the phloem sap, and related that to the ratio theoretically expected from gas exchange measurements made on the photosynthesizing leaves.

Sara Hely

The effects of elevated CO2 and water limitation on growth and below-ground responses of C4 grassland invader Erogrostis Curvula and C3 grassland native Austrodanthonia racemosa

Supervisors: Dr Roger Gifford (CSIRO Canberra), Asso. Prof. Ross McMurtrie (UNSW), Dr. Terry Bolger (CSIRO Canberra)

Aims:

1. To study the effect of elevated CO2 on growth and below ground competitive interactions of C4 and C3 grasses under water-limited conditions.
2. To Establish how these responses impact soil carbon

Background:

• BSc- Resource and Environmental Science (University of Canberra)
• BSc.Hons- Climate Change Ecology (Department of Geography- Australian National university)
• Technical Officer 4 years (CSIRO Plant Industry Canberra)

Description of research: Controlled environment experiment using elevated and ambient CO2 conditions Looks at responses of selected plants to water limited and water non-limited conditions Competition design experiment using an example of a C4 invasive spp (Erogrostis curvula) and a C3 Native species (Austrodanthonia racemosa) Focus on below ground root turnover and soil carbon

Outcomes: Insight into competitive interactions of a C4 grassland invader and a C3 native under elevated CO2 and water limited and non water limited conditions. An indication of whether competitive interactions has an effect on below ground responses. Whether the these responses ultimately effect soil carbon.

Alex Lee

Application of lidar and other optical data to quantification of forest structure and composition in Australia

Karim Sabetraftar

The hydrological flux of organic carbon and its significance to terrestrial carbon accounting

Danny Siegenthaler

Transitional Vegetation Response to Global Warming: Implications for Carbon Sequestration

Supervisors:

Overview of Research: The landscape of south-eastern New South Wales, particularly around the Canberra region has historically been under considerable pressure from settlers clearing native Eucalypt Woodlands and forests to accommodate grazing of sheep and cattle. Broad scale clearing leaves only scattered remnants of the original vegetation, resulting in the conversion of relatively continuous ecosystems, such as forests, into islands of natural habitat surrounded by a matrix of agriculture and urban development (Jules, 1998). Impacts of such clearing are usually considered in terms of local species, environmental degradation such as soil erosion and salinity problems (Brack, 2001) and these factors in turn impact carbon stocks. Vegetation loss, fragmentation and degradation alter microclimatic regimes thus influencing vegetation regeneration processes and adversely affecting carbon sequestration (Chen et al. 1999).

Impacts of land clearing on Carbon Carrying Capacity (CCC) and Net Biome Productivity (NBP) are calculated over time periods of ten to hundreds of years. The accelerated greenhouse effect is predicted to significantly alter climatic regimes such that ecosystem response is in disequilibrium. Thus, in calculating CCC and NBP in response to greenhouse forced climate change it will be necessary to simulate the transitional (non-equilibrium) response of vegetation systems to changing climatic regimes. This requires the capacity to model potential plant response on a species-by-species and spatially explicit basis. In landscapes that have been subject to vegetation loss, fragmentation and degradation, the transitional vegetation responses will reflect the altered micro climatic regimes and how these influence regeneration processes

This project aims to investigate the effects of forest fragmentation on vegetation regeneration processes and to integrate these relationships into a landscape-based, vegetation succession model. This vegetation model will in turn be coupled to a carbon accounting model.

There will be three main studies:

1. Analysis of existing forest fragments to determine spatial patterns in regeneration
2. Experimental analysis of seedling growth in relation to microclimatic conditions caused by forest fragmentation and how these processes relate to patterns in vegetation
3. Development of a simulation model, calibrated with existing and newly generated field data, to explore potential expansion of fragments given certain micro-, meso- and macro-climatic conditions. The model will enable changes in carbon stocks to be estimated on a landscape-wide basis.

Objectives of Study:

• To link micro- with landscape-scaled processes, and to integrate biotic and abiotic processes into vegetation simulation models for assessment of effects of transitional vegetation change on carbon sequestration,
• To identify critical microclimate variables favouring seedling establishment and survival around forest fragments,
• To understand processes affecting directional forest patch expansion and its relationships with microclimate and topography and
• To further develop agent based vegetation succession simulation modelling and its application to carbon accounting.

Relevance and Significance to CRC GA: My project will form a link between two major CRC Research Programs, namely, B1 (Interaction of elevated CO2 and water, temperature, nutrient & soil stresses on carbon sequestration) and B3 (Ecosystem Vulnerability to Chang). Specifically, I plan to use a combination of field-based experiment and modelling to understand how variation in microclimate relates to expansion of forest fragments. My project will link the two programs by explicit incorporation of temperature-dependent effects on resource acquisition, seedling establishment and growth into a transitional vegetation model to assess carbon sequestration.