Interaction Between the Hydrological and Carbon Cycles at a Global Scale

Principal Investigator

Jon Lloyd

Environmental Biology Group

Research School of Biological Sciences

A new model of global plant productivity has been developed based on plant physiological principles usually used at the canopy or stand scale. The model runs at 1X1 degree resolution and required temperature, humidity and radiation and NDVI as the monthly varying inputs. A multi-layered soil hydrological model is employed and soil water deficit effects on canopy gas exchange and energy partitioning are realistically represented. C4 photosynthesis in tropical grasslands and savannas is also implicitly taken into account. Gross primary productivity predicted by the model is significantly less than is usually inferred by ecologists; about 8 Pmol yr-1, with over 25% by C4 plants. Both plant and soil respiration are represented in the model with the seasonality of plant respiration dependent on the simulated monthly plant growth rate and standing biomass as well as temperature and soil moisture. The seasonality of litter fall is also simulated and this exerts an effect on the seasonality of soil respiration which is also dependent on temperature and soil moisture status.

Co-Investigators

Rachel Law

Co-operative Research Centre for Southern Hemipshere Meteorology

Monash University

Frank Kelliher

Landcare Reserach

Chritchchurch, New Zealand

Ian Enting

CSIRO Division of Atmospheric Research


Projects

s53 - VPP

What the results to date and the future of the work?

The monthly net ecosystem productivitites have seen used as source inputs to allow comparisons between two atmospheric tracer transport models; the Melbourne University Transport Model and a model derived from the NCAR MATCH tracer transport model (CRC-MATCH) and predictions of the seasonal cycle of CO2 by the ANU model are markedly superior to previously published simulations.

The extent of the covariance between the seasonality of terrestrial gas exchange and atmospheric transport has been investigated by looking at the annual mean gradient in CO2 predicted by both transport models. The inter-hemispheric difference was 0.27 ppm for the MUTM model

- Appendix A



and 0.77 ppm for the CRC-MATCH model emphasising the possible importance of PBL dynamics in Global CBL simulations.

What computational techniques are used?

Soil water budgets and the simultaneous solutions of a canopy energy balance consistent with optimal stomatal behaviour and biochemical constraints is achieved using NAG minimisation routines.

Publications

Schulze, E.D., Kelliher, F.M., Koerner, Ch., LLoyd, J., Hollinger, D.Y. and Vyodskaya, N.N. (1996) The role of vegetation in controlling carbon dioxide and water exchange between land surface and the atmopshere. In Global Change and Terrestrial Ecosystems (Ed. B. Walker and W. Steffen). IGBP Book Series. Cambridge University Press, Cambridge.