Program B: Anticipating Changes in the Carbon Cycle

An Overview of the 2001- 2002 Research Year and Prospects

This year saw Program B nearly fully operational, with research efforts from fundamental subcellular processes up to landscape and continental spatial scales. Projects also examine processes from daily up to annual and decadal levels. As the projects mature, there has been increase in collaboration between them, for synthesis and comparison.

One feature that impacts several of the projects, is nutrient limitation. Experiments in controlled environments enable the effect of rising atmospheric CO2 to be examined with respect to growth with limited nitrogen and/or phosphorus. Specifically, we have examined the interaction with symbiotic nitrogen fixation by clover, or with maize plants infected with mycorrhizae growing in compact soil. Over an annual cycle in open topped chambers in the field, the interacting effect of rising atmospheric CO2 with nitrogen nutrition has been investigated with snowgum seedlings. Theoretical modelling of nitrogen distribution through plant canopies has been developed to enable leaf level processes to be scaled and applied at the canopy level. These elements are required to build continental scale models for Net Primary Production (NPP), one of which also uses nitrogen and phosphorus to constrain the estimates.

While it might be hoped to derive generalisations from our experimental work, this is not always the case. Unexpected results are sometimes revealed. For example, the work on snowgums revealed substantially greater susceptibility to frost damage of plants grown under elevated atmospheric CO2 in both the Autumn and Spring. In an attempt to define the underlying mechanisms involved, a Free Air Temperature Increase system has also been installed in the field and should enhance our ability to investigate subtle, but cumulative temperature effects. The importance of continuing fundamental experimental work on the effects of elevated atmospheric CO2, have been borne out with the Marrakech accords raising the possibility of having to factor out the effects of CO2.

The issues of importance change as the spatial scale increases. Several landscapes are being parameterised in order to drive models that allow the investigation the effects of a mosaic of disturbance over time. In the Victorian central highlands, a Eucalyptus regnans forest has been intensively studied, complemented with additional data collected from trees up to 4 centuries old in Tasmania. In the Fitzroy basin in Queensland, land-use change in the last three decades up to 2000 has been assembled. This then allows the investigation of the consequences of spatial and temporal complexity on the carbon cycle.

Within Program B, there are 3 independent models for modelling NPP at the continental scale – VAST, RFBN and BIOS. These were compared with others at a Program C workshop and the differences between them will be used to work out which approaches and features work best under different circumstances. A comprehensive survey of Australian sandy soils has been completed which will provide valuable constraints on the running of these models. Given the large proportion of terrestrial carbon that resides in the soil and the long time periods over which pools of soil carbon change, models are a powerful way of improving our understanding of the potential impact of human actions.