The effects of live and dead roots on soil fungi in spodosolic soils of the New Jersey Pinelands

The effects of live and dead roots on soil fungi were investigated experimentally in a spodosolic soil of the New Jersey Pinelands. Field mesocosm plots were constructed to have a layer of either C- and N-rich organic soil or a vermiculite substitute overlying a layer of sandy mineral soil with a very low organic content. The plots were also supplied with live pitch pine and blueberry roots or dead pitch pine roots in varying quantities based on naturally occurring densities (half, same, and double the ambient quantities). All plots were sampled 1 year after construction (June 1991), and-three more times in two subsequent years (November 1991, June 1992, June 1993). In the presence of live roots, fluorescein diacetate-determined (FDA-active) fungal hyphae, total fungal hyphae, and soil moisture decreased significantly in the organic material, while no change was associated with the dead roots. The FDA-active fungal length in the live-root plots ranged from 40 to 165 m g-1 soil, and from 55 to 335 mg-1 soil in the dead-root plots. While the total fungal length in live-root plots remained constant over time (approximately 3000 mg-1 soil), the total fungal length in the dead-root plots increased from an initial value of 3000 to >4000 m g-1 soil at the conclusion of the study. Fungal lengths in mineral soil were higher under organic material than under the vermiculite substitute. Soil moisture was higher in the presence of live roots in mineral soils, but this did not increase the fungal abundance. Inputs of dead roots did not alter the fungal abundance. Overall, we demonstrated that live and dead roots had different effects on fungal abundance in soils with contrasting qualities, and in a spodosolic forest soil, roots could have ecosystem effects very different from those in agricultural soils.