Southern pine plantations cover a large geographic area and supply a large proportion of the nations wood products. Research on management strategies designed to maximize wood production while also optimizing nutrient use efficiency and soil C sequestration is needed. Understanding the influence of soil management on root dynamics may be particularly important because periodic replacement of fine roots consumes a substantial proportion of NPP and root turnover is a key valve for transferring atmospheric C into soil pools. We used minirhizotrons to quantify the effects of logging residue incorporation on fine root standing crop, production, and mortality in two loblolly pine clones of contrasting ideotypes. Clone 93 is known to allocate more C to stem growth while clone 32 allocates less C to stems and more to leaves. The relative allocation by these clones to support fine root turnover is unknown.

Results/Conclusions   Clone 32 generally produced and maintained more fine roots for the first 1.5 years after planting while production for the next 0.5 yr was generally greater in clone 93. Fine root standing crop in plots amended with logging residue was initially higher than control plots but by the end of the experiment standing crop in control plots had exceeded that in residue amended plots. A significant treatment x clone x depth interaction was observed for fine root mortality. As expected, turnover rate of fine roots was greater in shallow (0-25 cm) compared to deeper (25-50 cm) soil. Rates of fine root turnover were similar in both clones. Significantly higher turnover rate in plots amended with logging residue, however, indicated a negative effect of soil organic matter on fine root longevity. Preliminary analyses suggested that incorporation of logging residue into soil may increase very early production and standing crop of fine roots but this effect is quickly reversed by opposite effects on fine root longevity.