Seasonal Fine Root Carbohydrate Relations of Plantation Loblolly Pine After Thinning
Loblolly pine (Pinus taeda L.) occurs naturally on soils that are frequently low in fertility and water availability (Allen et al., 1990; Schultz 1997). Despite these limitations, this species maintains a high level of productivity on most sites (Schultz, 1997). Knowledge of plantation loblolly pine root system growth and physiology is needed to understand how this species is adapted to soil resource limitations, and how management can be used to favor root system function. The fine root dynamics of mature conifers is modal with a distinct surge of growth in spring, and the variable occurrence of a second flux of growth in fall (Gholz et al., 1986; Santantonio and Santantonio, 1987). We found that the new root growth of plantation loblolly pine peaked in May through July, and continued at a reduced rate in fall without a second surge of growth (Sword et al., 1998a, b). We are conducting intensive research in a loblolly pine plantation to identify the physiological mechanisms that control root growth, and determine how silvicultural treatments affect these mechanisms. As a component of this research, the objectives of the present study were to simultaneously document the seasonal root growth and carbohydrate concentrations of thinned and non-thinned loblolly pine, and use these results together with canopy information to propose the sources of energy for root growth.