SPATIAL AND TEMPORAL FINE-ROOT DISTRIBUTION IN 3 LOUISIANA FOREST SOILS

The distribution of fine plant roots (less-than-or-equal-to 3-mm diam.) in three northern Lousiana forest soils was investigated. Two upland mixed pine-hardwood sites and one bottomland hardwood site were sampled periodically for a year. Fine-root biomass and surface area were determined on root samples extracted using wet sieving of soil corings. Both fine-root biomass and surface area decreased abruptly with increasing depth on all sites, with 60 to 64% of the biomass and 63 to 70% of the fine-root surface area occurring in the top 20 cm of soil. Prolonged soil wetness or dryness during the growing season caused reductions in fine-root-biomass concentrations. A contradictory increase in fine-root surface area occurred, however, during prolonged soil saturation in the bottomland site, suggesting a possible change in fine-root morphology during inundation. Total fine-root biomass was similar on the three sites, averaging 8.4 and 10.5 Mg ha-1 on the two upland sites, and 9.9 Mg ha-1 on the bottomland site. Total fine-root surface area was much higher on the bottomland site, however, averaging 1.48 x 10(5) m2 ha-1 vs. 9.5 x 10(4) and 7.0 x 10(4) m2 ha-1 on the upland sites. These data indicate that fine-root concentrations in these forest soils decrease rapidly in response to unfavorable soil environmental conditions such as prolonged saturation or dying. These data also indicate that maximum root concentrations generally occur in the spring and early summer, with minimums during late summer, fall, and winter.