Coppicing shifts CO stimulation of poplar productivity to above-ground pools: a synthesis of leaf to stand level results from the POP/EUROFACE experiment

摘要

A poplar short rotation coppice (SRC) grown for the production of bioenergy can combine carbon (C) storage with fossil fuel substitution. Here, we summarize the responses of a poplar (Populus) plantation to 6 yr of free air CO enrichment (POP/EUROFACE consisting of two rotation cycles). We show that a poplar plantation growing in nonlimiting light, nutrient and water conditions will significantly increase its productivity in elevated CO concentrations ([CO]). Increased biomass yield resulted from an early growth enhancement and photosynthesis did not acclimate to elevated [CO]. Sufficient nutrient availability, increased nitrogen use efficiency (NUE) and the large sink capacity of poplars contributed to the sustained increase in C uptake over 6 yr. Additional C taken up in high [CO] was mainly invested into woody biomass pools. Coppicing increased yield by 66% and partly shifted the extra C uptake in elevated [CO] to above-ground pools, as fine root biomass declined and its [CO] stimulation disappeared. Mineral soil C increased equally in ambient and elevated [CO] during the 6 yr experiment. However, elevated [CO] increased the stabilization of C in the mineral soil. Increased productivity of a poplar SRC in elevated [CO] may allow shorter rotation cycles, enhancing the viability of SRC for biofuel production.