Author's personal copy Review and model-based analysis of factors influencing soil carbon sequestration under hybrid poplar5

The potential for soil carbon (C) sequestration under short-rotation woody crops, like hybrid poplar (Populus spp.), is a significant uncertainty in our understanding of how managed tree plantations might be used to partially offset increasing atmospheric CO2 concentrations. Through development of amulti-compartmentmodel,we reviewed information fromstudies on hybrid poplar and analyzed the potential impact of changes in plant traits and nitrogen (N) fertilizationonsoilC storage. Forahypothetical setting in thesoutheasternU.S.A., andstarting from soils that are relatively depleted in organicmatter (2.5 kg Cm ), themodel predicted an increase in mineral soil C stocks (1.7 kg C m ) over four 7-year rotations of hybrid poplar. However, at the endof the fourth rotation, bothcumulative soilC gains andannual rates of soil C accrual (23e93gCm 2 yr ) variedwidely depending on fertilization rate, biomass yield, and rates of dead root decomposition (three factors thatwere examined in a factorialmodel-based experiment). Our analysis indicated that processes linked to genetically modifiable poplar traits (aboveground biomass production, belowground C allocation, root decomposition) are potential controls on soil C sequestration. Keymeasures ofmodel performancewere sensitive to how aboveground biomass production responded to N fertilization. Site specific properties thatwere independentofplant traitswerealso important topredicted soilCaccumulationand point to possible genotype x site interactions that may explain contradictory data from both empirical and theoretical studies of C sequestration under hybrid poplar plantations. a 2010 Elsevier Ltd. All rights reserved.