Fine root production and turnover across a complex edaphic gradient of a Pinus palustris-Aristida stricta savanna ecosystem
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Fine root dynamics significantly affect plant performance through soil resource capture, and ecosystem function through soil carbon and nitrogen cycling. The responses of fine roots to natural gradients in resource availability, however, are poorly understood. We assessed fine root dynamics across a soil texture gradient in Pinus palustris Mill.-Aristida stricta Michx. savannas. These savannas are currently the subject of considerable conservation and restoration efforts in the southeastern US. Fine root dynamics were determined for two growing seasons in three soil types with minirhizotrons. The soils were characterized as: shallow, loamy soils; intermediate depth sandy soils; and deep, sandy soils. Although soil moisture was not quantified in this study, increasing drainage capacity and clear shifts to xerophytic vegetation strongly suggest increasing soil moisture limitation from shallow to deep soils. Potential net N mineralization, microbial biomass and annual overstory litterfall were also characterized across the gradient. Consistent with increasing soil moisture limitation, fine root production increased and diameters decreased from shallow to deep sands, as did the amount of deep root production. Litterfall also declined across this gradient. In contrast, fine root turnover rates were highest in the intermediate soils where nitrogen availability was highest. These results suggest that fine root turnover rate may vary independently of annual fine root production and these components may differentially respond to multiple limiting resources. 2003 Elsevier B.V. All rights reserved.
