Belowground C Allocation Varies Among Clones of Loblolly Pine.

Clonal forestry is becoming an increasing reality in the Southeastern United States due to recent improvements in somatic embryogenesis for loblolly pine.  Differences in belowground C allocation between individual genotypes could have significant implications for C sequestration and cycling in these clonal plantations.  Allocation to coarse, fine, and taproots, and to root exudates may vary between clones and in response to common silvicultural practices, such as fertilization.  An understanding of this variability is necessary given the relatively large acreages that will likely be put into clonal plantations in the coming decades.  Our research objective was to determine the range of biomass partitioning due to fertilization in clones of loblolly pine.  A split plot experimental design was installed in the Virginia Piedmont, with the whole plots being two levels of fertilization (with or without) and the split plot factor being 25 clones.  Whole plot treatments were blocked and replicated four times.  Trees were planted in May 2003, with fertilizer (224 kg ha^-1 DAP and 184 kg ha^-1 ammonium nitrate) applied in May 2004, May 2006, and July 2008.  Root exudates from 4 clones (n = 30) were assessed in July 2009 using XAD-7 resin capsules placed in situ on a single fine root for 9 days.  Ten clones (n = 75) from the trial were destructively harvested both above and belowground at age 6 in February 2009.  Preliminary results indicate that both root exudates and allocation to coarse and tap roots varied between clones.  The implications of genotypic variability on soil C processes in plantations must be incorporated into future C accounting systems to ensure accurate assessment of belowground C sequestration.