Root Inputs in Podzol Soils: Effects on Nutrient Cycling and Connections between Soil Horizons

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Ehrenfeld and Parmelee have shown in greenhouse microcosm studies that live roots stimulate a rhizosphere effect proportional to the amount of root input in the nutrient-poor mineral soil of the pitch pine forests in the New Jersey Pinelands but have no such effect in the organic forest floor. Because this finding has important implications for nutrient cycling in forest ecosystems, field experimentation is required. The investigators propose to test their results in a field experiment in which decomposition, N mineralization rate, fungal and microfaunal abundance and soil leachate chemistry are followed for 2 years in plots of each soil horizon, into which varying quantities of live and dead roots are introduced. In undisturbed forests, the organic and mineral soil horizons are contiguous, however, and pathways of nutrient connection must exist. Connections between horizons include fungal growth and translocation, leachate, and root growth, and these may influence nutrient cycling rates in an adjacent horizon. Amounts of nutrient transferred from one horizon to the other may be modified by roots and by faunal grazing. Therefore, Ehrenfeld and Parmelee proposed to conduct additional field and microcosm studies to identify which pathways are most important in linking horizons, which response variables are sensitive to the presence of connections, and how the connections are affected by root inputs. They will use microcosms with reconstructed soil profiles to investigate how connections originating in organic horizon influence nutrient cycling rates in mineral soil. They will use biocides and removal of leachate to determine relative importance of fungi and leachate as connections, and to determine how soil fauna affect the magnitude of these connections. The same response variables as in the field experiment will be measured. In the field they will quantify rate of fungal growth between horizons and flux of N (15N) between horizons through fungi. They will also determine the influence of fauna on the nutrient quality of leachate. The institutional support for this research is excellent. The investigators are highly qualified productive research scientists.