Effects of resource availability on carbon utilization in Pinus taeda L. and Pinus ponderosa Dougl. ex Laws. seedlings

The growth and development of tree seedlings is often regulated by the availability of resources such as atmospheric CO{dollar}sb2{dollar} and soil nitrogen. Our ability to predict the effects of resource availability on plant growth is limited by our poor understanding of the control of carbon flow during plant growth and development. Traditionally, biomass has been used to describe carbon and energy allocation; yet, the reduction state of carbon in this biomass may be more informative.; I analyzed data from the primary literature to characterize the range, mean and amount of variation in construction cost; the amount of glucose required to provide carbon skeletons, reductant and ATP for biosynthesis. Resources that are actively taken up (i.e. nitrogen) require the construction and maintenance of expensive biochemical machinery, increasing construction cost. Carbon uptake requires energetically expensive machinery but can lead to the formation of inexpensive carbohydrates, diluting construction cost.; I manipulated CO{dollar}sb2{dollar} and nitrogen resource availability in a phytotron to examine the nature of carbon and nitrogen interactions in loblolly and ponderosa pine seedlings. Oxygen bomb calorimetery was used to determine construction cost. The relationships between resource availability and construction cost were mechanistically analyzed by comparing cost with photosynthesis, respiration, leaf carbon-, nitrogen-, soluble sugar-, starch- and total nonstructural carbohydrate-concentration, leaf mass, leaf area, specific leaf mass, total plant mass and carbon allocation. A sensitivity analysis of the response of construction cost to changes in the biochemical fractionation of pine leaves was performed with a simple model and supported the empirical results.; Over a wide range of carbon and nitrogen availabilities small differences were found in leaf construction costs. Elevated CO{dollar}sb2{dollar} decreased, and elevated N increased leaf construction cost (g glucose g{dollar}sp{lcub}-1{rcub}{dollar}). Carbon and nitrogen resources were interactive, reflecting whole plant source-sink relationships. CO{dollar}sb2{dollar} effects on construction cost were correlated with increased nonstructural carbohydrates, and N effects were correlated with leaf N (protein). The response of leaf construction cost is consistent with our understanding of basic plant response to resource availability, yet the absolute differences observed were small, suggesting that carbon partitioning and allocation are controlling plant energy dynamics.