Contrasting genotypes, soil amendments, and their interactive effects on short-term total soil CO2 efflux in a 3-year-old Pinus taeda L. plantation

• Total soil CO2 efflux (FS) was different among genotypes during the growing season.
• Microbial respiration (RH) was different among genotypes during the growing season.
• Soil amendment treatments effected microbial respiration, but not FS.
• Cumulative C loss from the soil surface differed among our genotypes by 11%.

Intensively managed pine forests in the southeastern United States are considered an important C sink and may play a critical role in offsetting increased global CO2 emissions. The combination of improved silvicultural methods and the use of superior genotypes are estimated to result in future volume gains of up to 60 percent. However to date, no work has looked at whether selection of elite genotypes could influence soil C dynamics, which could decrease the time necessary for the stand to function as a C sink. We evaluated the effects of contrasting loblolly pine genotypes on total soil surface CO2 efflux (FS) and heterotrophic respiration (RH) under two soil amendment treatments: 1.) fertilization and 2.) logging residue (LR) incorporation. We found an immediate and sustained difference in FS (p = 0.05) and RH (p < 0.01) among our two genotypes throughout the first two years of stand development. Our soil amendment treatments did not significantly change FS, but did influence RH. LR increased (p = 0.05) RH while N and P fertilization induced a slight (p = 0.06) decrease throughout the study. Our genotypes differed (p = 0.05) in their temperature response of FS, which resulted in an 11% difference in total cumulative C loss from the soil over the duration of the study. We hypothesize that observed treatment effects in FS and RH are largely due to differences in belowground C allocation among genotypes, which is supported by others that have looked at fine-root standing crop and turnover on these same genotypes. This work underscores the importance of accounting for differences among genotypes when developing stand-level C estimates.