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Lolium perenne Grasslands May Function as a Sink for Atmospheric Carbon Dioxide

DLO-Research Inst. for Agrobiology and Soil Fertility (AB-DLO), Dep. of Soil Ecology, P.O. Box 14, 6700 AA Wageningen, the Netherlands.

^* Corresponding author. (j.h.vanginkel{at}ab.dlo.nl) (for more details about the model contact andy.whitmore{at}bbsrc.ac.uk)

ABSTRACT

Model calculations and scenario studies suggest the existence of a considerable positive feedback between temperature and CO₂ levels in the atmosphere. Rising temperatures are supposed to increase decomposition of soil organic C leading to increased production of CO₂ and this extra CO₂ induces a positive feedback by raising the temperature still further. Evidence was found that negative feedback mechanisms also exist: more primary production is allocated to roots as atmospheric CO₂ rises and these roots decompose more slowly than roots grown at ambient CO₂ levels. Experimental data partly obtained with ¹⁴C-techniques were applied in a grassland C model. The model results show that at an atmospheric CO₂ concentration of 700 µL L^–1 increased belowground C storage will be more than sufficient to balance the increased decomposition of soil organic C in a ryegrass (Lolium perenne L.) grassland soil. Once a doubling of the present atmospheric CO₂ concentration has been reached, C equivalent to 55% of the annual CO₂ increase above 1 ha ryegrass can be withdrawn from the atmosphere. This indicates that grassland soils represent a significant sink for rising atmospheric CO₂.

A.P. Whitmore, current address: Silsoe Research Inst., Wrest Park, Silsoe, MK45 4HS, UK.

Received for publication November 4, 1998.