• Introduction
• Background
• Hypotheses
• Experimental Design
• Expectations
• Acknowledgments
• References

Physiology, biochemistry, and biomass production in genetically improved loblolly pine

Mike Aspinwall

Introduction

 

This research will focus on understanding the physiological basis of increased growth with increasing levels of genetic improvement as well as the impact of genetic improvement on ecosystem-level processes. The main physiological and biochemical aspects that will be investigated are: photosynthetic rates, dark respiration, biomass production, resources use efficiencies, and production of carbon-based secondary compounds. The project will incorporate both a single-tree plot study, where physiological and biomass responses will be measured in a plantation setting and a greenhouse study where physiological processes and biomass production will be observed under a controlled environment. The single-tree plot study will then be scaled-up to estimate physiological, biochemical and growth responses at the stand-level.

Background

 

Historically, loblolly pine tree improvement operations have focused on selection of genotypes producing more volume and displaying traits important to product value (Li et al. 1999). In the southern U.S., more than 95% of seedlings planted are genetically improved, dramatically increasing productivity (McKeand et al. 2003). In many plant species, there is an inverse relationship between growth and the production of carbon-based secondary compounds (CBSC), which help defend the plant against disease and insect attack (Herms and Mattson 1992, Booker et al. 1996). Therefore, it is reasonable to expect that the increases in stand productivity are also affecting stand-level secondary biochemistry, suggesting changes in plant defense. These changes may also affect ecosystem-level processes such as nutrient cycling and soil organic C formation.

The physiological basis of increased growth of genetically improved seedlings may provide insight into the reason why intensively selected genotypes are more productive. There could be several reasons, including higher rates of physiological processes, biomass allocation to one plant part more than another or increased resource use efficiency.

 

Hypotheses

 

There are several hypotheses to be tested throughout this research. The first hypothesis to be tested is that increased productivity in genetically improved loblolly pine is the result of more uniform physiological processes and greater resources use efficiency. The second hypothesis to be tested is that the production of CBSC’s will be inversely related to growth. Meaning, more carbon is allocated to biomass production than to biochemical defense. The third hypothesis to be tested is that there will be a shift in biomass partitioning from roots to shoots with increasing genetic improvement. In other words, as genetic improvement increases, stem production increases and root production decreases.

Experimental Design

 

The first study site in this project is the 80,000-acre Hofmann Forest located in both Jones and Onslow counties, North Carolina.  In January 2006, a completely randomized single-tree plot study was planted which included 20 replications of 9 genotypes.  Of the 9 genotypes, 3 are clones, 3 are full-sib families, and 3 are half-sib families.  Growth, physiological and biomass measurements will be collected monthly for testing the hypotheses related to increasing genetic improvement.  Biomass production will be assessed by harvesting above-ground and below-ground plant parts and developing allometric relationships.  The results of this study will also provide data for estimating ecosystem-level processes. 

In addition to the field study, a greenhouse study conducted at the NCSU Horticulture Field Labs will use the same 9 genotypes and 2 levels of nutrition to assess the impact of resource availability.  Detailed physiological measurements will be taken weekly and an entire above-ground and below-ground harvest will be done to assess biomass production.

Expectations

 

The results of this study will provide a comprehensive understanding of the impact of genetic improvement on physiology, biochemistry, and biomass production in loblolly pine.  Also, the implications of this research will be helpful for understanding the impact of genetically improved loblolly pine plantations on ecosystem-level responses such as nutrient cycling and soil C formation.

Acknowledgments

 

I would like to thank my committee members; John King and Steve McKeand for their help and guidance. We also thank the NCSU-CTIP for additional support and funding for this project. Finally, I’d like to thank the faculty, staff and graduate students in the NCSU-CTIP for all their help.

References

 

Booker F.L, S. Anttonen, and A.S. Heagle. 1996. Catechin, proanthocyanidin and lignin contents of loblolly pine (Pinus taeda) needles after chronic exposure to ozone. New Phytol. 132:483-492.

 

Herms D.A. and W.J. Mattson. 1992. The dilemma of plants: to grow or defend. Q. Rev. Biol. 67:283-335.

 

Li, B., S. McKeand, and R. Weir. 1999. Tree Improvement and Sustainable Forestry – impact of two cycles of loblolly pine breeding in the U.S.A. Forest Genetics. 6(4):229-234.

 

McKeand, S., T. Mullin, T. Byram, and T. White. 2003. Deployment of genetically improved loblolly and slash pines in the South. Journal of Forestry. 101(3):32-37(6).