Genetics by Nutrient Availability Interactions on Short-term Carbon Pools and Fluxes in Young Pinus taeda Plantations

The objective of this research was to determine how genetics and nutrient availability influence C cycling in intensively managed southern pine forests. This work consisted of a two year field and a complimentary one year greenhouse study each split into above- and below-ground pools and fluxes. Both the greenhouse and field experiment showed differences between contrasting genotypes in gas exchange parameters and C partitioning patterns, but genetic by nutrient availability interactions were only observed in the field. In the field study, some genotypes were better able to tolerate nutrient limitations due to more favorable canopy architecture and lower N demand. Our results clearly show that contrasting ideotypes have the potential to respond differently to differences in nutrient availability in terms of biomass partitioning, leaf physiology, and leaf biochemistry (Chapter 3).

Both experiments showed short-term improvements to soil physical and chemical properties, which have been shown to correlate with higher site quality. In both the greenhouse and field experiment, we concluded that increased C loss by way of total soil CO₂ efflux (FS) made up only a small percent total C incorporated as LR. Short-term results led us to conclude that combining LR treatments and planting of genotypes with low nutrient demand or high nutrient use efficiency may increase soil organic matter (SOM) while avoiding loss of stem volume from nutrient immobilization. Data from our field study showed a strong genotype by soil amendment interaction for FS over all sampling dates with the relative importance of contributing factors (heterotrophic or root respiration) also changing (Chapter 5).

Overall, logging residue incorporation increased total system C gain per ha more than did fertilization alone, but there were differences between genotypes planted (Chapter 6). Data from the field experiment show that although LR incorporation did not decrease overall net primary productivity, it did decrease biomass partitioning to merchantable products (main stem) depending on genotype. These data underline the importance of matching appropriate genotypes to specific site conditions and silvicultural prescriptions.