Melbourne School of Land and Environment Department of Forest and Ecosystem Science

Measurement of soil respiration (CO₂ efflux)

Soil respiration in the field is measured using Infra-red Gas Analysers (PP Systems or LICOR). These are carried out by manual soil respiration chambers to provide daily, weekly or monthly measurements accounting for the wide spatial variability, or by automated chamber system to provide continuous CO₂ efflux measurements and therefore a good understanding of temporal variability. The laboratory-based RESPICOND enables us to closely control soil moisture, temperature and fertility to investigate their importance upon soil CO₂ efflux in a fully replicated, 96 chamber design.

Measurement of trace gas exchange (N₂O, CH₄ and CO₂ )

Trace gas emissions (N₂O, CO₂) and uptake (CH₄ ) from forest soil systems can be continuously measured using field-based gas chromatograph/Infra-red Gas Analyser linked to ten pneumatically controlled chambers. This analytical system has been van mounted to make it portable and has been applied in various land-use systems throughout Australia. This approach enables us to follow trace gas fluxes in response to individual events (rainfall, fertiliser application) or over seasonal changes to construct annual trace gas budgets. This field-based GC and automated chamber system is applied in a joint collaboration between UniMelb and IMK-IFU, Germany.

Measurement of stable isotopes using the Isotope Ratio Mass Spectrometer (IRMS)

Stable isotopes are important tools in integrated ecosystem research. The LFR Stable Isotope Facility in Creswick is equipped with a GV Instruments IsoPrime IRMS with high temperature elemental analyser and TraceGas system. The IRMS can analyse carbon, nitrogen, oxygen and hydrogen stable isotopes in solid, liquid and gaseous samples. One specific feature of the IRMS is the automated on-line gas pre-concentration and purification of atmospheric trace gases, isolating N₂O, CH₄ and CO₂ from less than 100 ml of atmospheric air. The facility also analyses samples for external clients and a costing structure exists for all sample types.

“Leaf to Landscape” scale analysis of plant and soil chemistry

Analytical chemistry provides valuable insight into ecophysiology and ecosystem processes. We adopt a range of analytical techniques to determine chemical attributes and patterns at a range of scales. These include Carbohydrate (GC and HPLC), polyol (GC) and amino acid analysis (GC and CE), elemental analysis (ICP-OES) and the measurement of stable isotopes (IRMS).

Water transport in trees using the Heat Ratio Method (HRM)

The HRM is a non-destructive and precise technique to evaluate the xylem sap flow rates and with sufficient sampling intensities can be used to evaluate the water consumption of whole forest stands. The fundamental principle of this technique is the measurement of the ratio of the increase in temperature during a fixed time after inducing a pulse of heat. According to the flow rate of the xylem sap, the ratio between the points of measurement will change more or less rapidly.

Chlorophyll fluorescence and gas exchange

These are sensitive tools for probing state variables of the photosynthetic apparatus, for quantifying photosynthetic performances or for studying effects of stress under laboratory conditions or in the field. We measure chlorophyll fluorescence with a Licor LI-6400 (Licor, Lincoln, NE, USA ) with integrated fluorescence chamber head (LI-6400-40) or the OS 30p plant efficiency analyser (OptiScience, Tyngsboro, MA, USA ). Gas exchange measurements are made with one of our three LI-6400.

Terminal-restriction fragment length polymorphism (T-RFLP) for the measurement of soil microbial diversity.

Traditional detection techniques, which require growth of organisms in the laboratory, are severely limited because less than 1% of environmental microorganisms can be cultured. T-RFLP is a molecular technique based on profiling of nucleic acids and gives access to previously unknown parts of soil microbial diversity.

Mechanistic modelling of soil biogeochemistry and forest growth

Several mechanistic computer models are available for simulating forest ecosystem carbon pools and fluxes as well as trace gas emissions (N₂O, CO₂) and uptake (CH₄) from forest soil systems. Various research projects feed into further development and testing of these models. Applications reach from scientific exploration and explanation to policy and decision support using Geographic Information Systems and spatial databases.