Fine root carbon allocation and fates in longleaf pine forests

Abstract

The patterns and mechanistic controls of fine root production and mortality in a 19-year-old longleaf pine (Pinus palustris Miller) plantation were assessed using minirhizotrons in a complete factorial design experiment that manipulated root carbon source and sink strengths. Carbon source strength to roots was manipulated through foliar scorching, carbon sink strength in roots was altered via nitrogen fertilization, and carbon transfer from roots to the soil organic matter pool was impacted using a general soil pesticide to distinguish between root mortality via herbivory and senescence. Fertilization significantly increased fine root nitrogen concentrations and mortality rates in the nonscorched plots across the last four sample intervals. Scorching significantly reduced fine root biomass. The influence of soil herbivores on fine root carbon allocation and fates could not be assessed in this study because the soil pesticide had no measurable effect on herbivorous nematode and insect larvae populations. The results of this study suggest that nitrogen increases fine root mortality via an increase in fine root carbon sink strength rather than a decrease in carbon allocation to fine roots. These findings support the constant allocation hypothesis regarding nitrogen controls on fine root carbon allocation and transfers in forest ecosystems.