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Project A.1: Belowground carbon dynamicsProject Leader: Dr Roger Gifford (Email) The group is working in Adelaide, Brisbane, Canberra, and Perth. Work is carried out in laboratories in those cities and in field sites in each of the States involved. Cooperative activities within the group and with other CRC Projects will continue to foster coordination of the work within CRC objectives.
Research objectives
StrategyA major area of uncertainty in the national C-account (carbon inventory) is the flux of carbon into, and out of, the soil in relation to direct human activities (e.g. Land use change, land management) and to changes in the environment (e.g. changing atmospheric CO2 concentration, global warming, climate variability, salinisation, wildfire ec.). The below-ground carbon stocks (C-stocks) comprise organic matter pools with a wide range of turnover times. On the time-scale of current political concern for modifying net fluxes
of CO2 to the atmosphere, the faster turnover pools
are the most important because they can be accumulated faster than slow
pools and are also more at risk of oxidation to CO2
if not managed to be conserved. Hence the faster pools and the inputs
to these pools, by fine root and litter turnover, will receive more attention
than the slower pools. However, to model the whole system, all pools must
be understood better including the mechanisms of stabilisation of soil
organic matter in the creation of the slower-turnover pools.
ThemesLitter input and decay Root turnover with respect to CO2 & temperature: Track fine root production and turnover of field phalaris swards as a function of atmospheric CO2 concentration, atmospheric warming, and day/night temperature differential during the first year of sward establishment using Temperature Gradient Tunnel and mini-rhizotron technologies. Litter and root decomposition: Commence long-term incubation under optimal temperature and moisture conditions to examine the decomposition kinetics of a wide range of litter and roots relevant to land use change in Queensland. Changes in the chemical composition of the litter and roots will be monitored during the incubation period )Litter and root decay on mulga site: Use the information for mulga site collected in Burrows' Project for baseline data and add value to woodland thickening studies. Preliminary experiments set up on litter and soil carbon studies on the mulga site. Assist in soil sampling buffel grass and crop sites for root-length density and biomass estimates. Incubation study of litter input: Commence incubation study to examine the effect of rising saline water table through the soil profile on the decomposition/breakdown of organic matter, gaseous losses (CO2, CH4) and measure movement of soil carbon after interaction with saline water through the soil profile.
Impact of burning on d13C (delta13): Changes in d13C will be determined on a range of plant materials, mostly C4 grasses, as well as charcoals and ashes produced from them. Chars and ashes from C4 grasses recovered from the field show a substantial d13C shift towards that of C3 vegetation. To be able to accurately proportion C3 and C4 contributions to soil OM, an understanding and quantification of this change in d13C must be gained. This work is an important preliminary step in the collaborative projects on woodland thickening and mulga conversion. Incubations: Incubation experiments designed to define the role of soil water content on the rates of C mineralisation during the decomposition of labile OM will be continued and expanded to examine the role of soil texture and mineralogy. Labelled Plant Materials: A range of 13C/15N-labelled plant materials (a C4 tropical grass, a C3 temperate grass and a woody eucalypt) that exhibit a range of litter quality will be grown in a closed canopy system under different nutrient regimes. These materials will be used in future litter quality and influence of matrix work. Changing Factors: Quantifying the effects of moisture (aerobic-equivalent to 60% of WHC and anaerobic-saturated prevalent under saline environments) on turnover of C fractions to other pools through laboratory incubation studies. Land use change (LUC) /management effects on soil C stocks Forest/grassland
changes in soil C: Investigate
the role of above-ground litter and fine root production, death, decomposition
and turnover in determining the change in soil C stocks under grasslands
and under forests.
Woodland thickening: Commence and finalise (if weather conditions for soil core extraction permit) collection of field samples. Catalogue, pre-process (dry, determine soil BD's) & forward collected samples to Adelaide. Commence sample preparation (saturated salt/acid wash/grinding etc) for chemical analyses. Carry out some preliminary analyses on initial samples. Effects of land use change on soil C stocks and fluxes. Changes in the amounts of C input from litter and roots, C fluxes as CO2 into the atmosphere and total C stocks and pools in light and heavy fractions of soil organic matter following land use change (land clearing, crop/pasture systems) will be quantified (Brisbane). Effect of agricultural management on soil C stocks and fluxes. Quantify the effects of agricultural practices (tillage vs. no-tillage, N fertilization vs no N fertiliser, and stubble retention vs stubble burned) on C stocks and fluxes. Carbon dynamics in soil aggregates. Study C dynamics through CO2 fluxes following soil aggregate breakdown in tilled and no-tilled cropping systems (in collaboration with the University of Queensland). Soil carbon turnover in tropical landscapes. Changes in C stocks and pools in the Eastern Australian landscapes under different vegetation, using fractionation, NMR and d13C tracing techniques (in collaboration with the University of Queensland). Field survey: A field survey that will encompass salinity gradients, soil types, environmental conditions and landscape history will lead us to an understanding of the variability in soil carbon stocks and fluxes under salt affected land.
Write papers for publication:
Review and synthesis: Analyse and synthesise the data on nitrous oxide emissions from the Australian agricultural soils. Write soil carbon dynamics experimental work done in years 1-3. Review of the literature on the effects of acidity and Al on soil carbon turnover. RelevanceSoil organic carbon (SOC) is a major part of the ecosystem C-stock containing about twice as much C as found aboveground in forests and many times as much C as found aboveground in crops and pastures. It is therefore a major fraction of the store of terrestrial C (total land-based carbon). It may also be a major potential sink for more C in managed agricultural and forest systems. For this reason SOC was identified in Article 3.4 of the Kyoto Protocol as a potential sink under the category of "additional activities". The Australian methodology for the current National Greenhouse Gas Inventory (1999 inventory released in 2001) adopts general rules of thumb to estimate soil C change under land use change, rules which have little or no Australian data underpinning them quantitatively. Thus, this research is relevant to the creation of soil C accounting procedures that are more soundly data-related. Change in the stock of C in soil is determined by the difference between the C input from plant litter (root as well as shoot) and the C output primarily from decomposition. There is much to be learnt about the processes involved in both those aspects under various environmental and management changes but it has been recognised that the biggest data deficiency of all is the rate of fine root input into the soil pools. Thus years 3 to 5 of the CRC's operations will increase the emphasis on that area.
Outputs
Outcomes
©
CRC for GA 2001-2003
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