Martin Lukac

More new carbon in the mineral soil of a poplar plantation under Free Air Carbon Enrichment (POPFACE): Cause of increased priming effect?

[1] In order to establish suitability of forest ecosystems for long-term storage of C, it is necessary to characterize the effects of predicted increased atmospheric CO2 levels on the pools and fluxes of C within these systems. Since most C held in terrestrial ecosystems is in the soil, we assessed the influence of Free Air Carbon Enrichment (FACE) treatment on the total soil C content (C-total) and incorporation of litter derived C (C-new) into soil organic matter (SOM) in a fast growing poplar plantation. C-new was estimated by the C3/C4 stable isotope method. C-total contents increased under control and FACE respectively by 12 and 3%, i.e., 484 and 107 gC/m(2), while 704 and 926 gC/m(2) of new carbon was sequestered under control and FACE during the experiment. We conclude that FACE suppressed the increase of C-total and simultaneously increased C-new. We hypothesize that these opposite effects may be caused by a priming effect of the newly incorporated litter, where priming effect is defined as the stimulation of SOM decomposition caused by the addition of labile substrates.

Responses to Elevated [CO2] of a Short Rotation, Multispecies Poplar Plantation: the POPFACE/EUROFACE Experiment

Forest and agricultural soils present interesting opportunities to conserve and sequester carbon. Soil C pools may be restored and enlarged by managing agricultural and forest soil and by the use of surplus agricultural land for reforestation or high-yield woody crops for biomass and bioenergy. Recently, bioenergy woody crops were reported to have the greatest potential for C mitigation, for their capability to sequester C and, contemporarily, to substitute fossil fuel carbon (Smith et al. 2000).

Root production and turnover in Populus grown under elevated CO2 using a free air enrichment system POPFACE

Rising levels of atmospheric CO 2 may change root production, root turnover and ecosystem carbon balance. In order to quantify these possible alterations over longer time period and at an ecosystem level a novel technique of air CO 2 enrichment was applied to a plantation of three fast growing Populus species. Root production and turnover were measured both by auger and ingrowth coring methods. In two years of this experiment, both methods applied show increased production of fine and coarse roots under elevated CO 2 conditions for all three clones utilised. These results suggest that future levels of atmospheric CO 2 will have to be taken into account when constructing a carbon budget of an ecosystem.