Effects of free atmospheric CO<sub>2</sub> enrichment (FACE), N fertilization and poplar genotype on the physical protection of carbon in the mineral soil of a polar plantation after five years

Abstract

Abstract. Free air CO 2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO 2 . However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro-and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the small macro-aggregate and free micro-aggregate weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed microaggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions, although not significantly. This study reveals that FACE did not affect the formation of aggregates. We did, however, observe a trend of increased stabilization and protection of soil C in micro-aggregates formed within macroaggregates under FACE. Moreover, the largest effect on aggregate formation was due to differences in species, i.e. poplar genotype. P. euramericana increased the formation of free micro-aggregates which means that more newly inCorrespondence to: M. R. Hoosbeek (marcel.hoosbeek@wur.nl) corporated soil C was stabilized and protected. The choice of species in a plantation, or the effect of global change on species diversity, may therefore affect the stabilization and protection of C in soils.

Surface soil carbon size–density fractions altered by loblolly pine families and forest management intensity for a Spodosol in the southeastern US

“…However, these studies did not report changes in soil carbon, which may or may not change in the same way as the above ground biomass. The study most similar to our work was that by Hoosbeek et al (2006), who reported that Populus euramericana showed 31% higher C in the 250 to 1,000-μm soil fraction, than two other poplar species at age 5; differences were presumably due to greater SOC protection through formation of microaggregates.…”

Effects of increased residue biomass under elevated CO2 on carbon and nitrogen in soil aggregate size classes (rice-wheat rotation system, China)

“…However, the dynamic behaviour of biological binding agents was only partly explained by the initial quality of the organic materials . Other studies by physical fractionation of soil samples collected after 5 yr of treatment at the POP-EuroFACE experiment revealed that the effect on aggregate formation due to FACE was dependent on plant species, and FACE increased the micro-aggregates within macro-aggregates (iM-microaggregate) weight and C fractions (Hoosbeek et al 2006), which was similar to our results. Recently, the primary effects of litter added to soil on the decomposition of original organic matter in soil and macro-aggregate dispersal have also been the focus of attention (Hoosbeek and Scarascia-Mugnozza 2009).…”

Coppicing shifts CO2 stimulation of poplar productivity to above‐ground pools: a synthesis of leaf to stand level results from the POP/EUROFACE experiment

“…Tellingly, the choice of species may strongly affect the C sequestration capacity of a forest ecosystem (Hoosbeek et al ., 2006b; Hyvönen et al ., 2007). The three poplar species planted at the POP/EUROFACE experiment performed equally well when growing in an abundance of nutrients, sunlight and water, and produced very large amounts of woody biomass for potential use as biofuel.…”