Biogeosciences Discuss., 6, 9891-9944, 2009
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A global model of carbon, nitrogen and phosphorus cycles for the terrestrial biosphere
Y. P. Wang, R. M. Law, and B. Pak
CSIRO Marine and Atmospheric Research, Centre for Australian Weather and Climate Research, PMB #1, Aspendale, Victoria 3195, Australia

Abstract. Carbon storage by many terrestrial ecosystems can be limited by nutrients, predominantly nitrogen (N) and phosphorous (P), in additional to other environmental constraints, water, light and temperature. However the spatial distribution and the extent of both N and P limitation at global scale have not been quantified. Here we have developed a global model of carbon (C), nitrogen (N) and phosphorus (P) cycles for the terrestrial biosphere. Model estimates of steady state C and N pool sizes and major fluxes between plant, litter and soil pools, under present climate conditions, agree well with various independent estimates. The total amount of C in the terrestrial biosphere is 2526 Gt C, and the C fractions in plant, litter and soil organic matter are 21, 6 and 73%. The total amount of N is 124 Gt N, with about 94% stored in the soil, 5% in the plant live biomass, and 1% in litter. We found that the estimates of total soil P and its partitioning into different pools in soil are quite sensitive to biochemical P mineralization that has not been included in any other global models previously. The total amount of P is 26 Gt P in the terrestrial biosphere, 17% of which is stored in the soil organic matter if biochemical P mineralization is modelled, or 40 Gt P, with 60% in soil organic matter, otherwise.

This model was used to derive the global distribution of N or P limitation on the productivity of terrestrial ecosystems. Our model predicts that the net primary productivity of most tropical evergreen broadleaf forests and tropical savannahs is reduced by about 20% on average by P limitation, and most of the remaining biomes are N limited; N limitation is strongest in high latitude deciduous needle leaf forests, and reduces its net primary productivity by up to 40% under present conditions.

Citation: Wang, Y. P., Law, R. M., and Pak, B.: A global model of carbon, nitrogen and phosphorus cycles for the terrestrial biosphere, Biogeosciences Discuss., 6, 9891-9944, doi:10.5194/bgd-6-9891-2009, 2009.
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