The role of nitrogen availability, hydroperiod and litter quality in root decomposition along a barrier island chronosequence

The decomposition of organic matter regulates carbon and nutrient flux between biotic and abiotic pools. Traditional research emphasizes aboveground decomposition processes and, by inference, extends these findings to belowground systems. The study, conducted along a southeastern Atlantic Coast barrier island dune and swale chronosequence (Virginia Coast Reserve Long Term Ecological Research site), addressed how hydroperiod, litter quality and nitrogen availability influenced belowground root decay in response to gradients associated with site age and topographic position and in the context of a nitrogen limited ecosystem. Effects on rates of mass loss and nitrogen and phosphorus dynamics during decomposition of a common root type (Spartina patens) and native roots are discussed.; Spartina patens roots decayed slower and lost more phosphorus in seasonally saturated swale soils than in well drained dune soils. Variation in hydroperiod between swales did not result in different rates of Spartina patens root decay, but more nitrogen was lost under greater flooding frequency. Nitrogen availability influenced dune root litter quality and subsequent decay. Higher nitrogen content and faster decay occurred in older dune roots. Decomposing native dune roots rapidly lost phosphorus. Brief periods of nitrogen immobilization occurred during dune root decay and were attributed to low nitrogen content and lignin-nitrogen interactions. Root litter quality among swales was determined by dominant vegetation. Myrica cerifera, a woody nitrogen-fixing shrub, occurred in older (36 and 120 year) swales, produced roots high in nitrogen and immobilized nitrogen during decay. Highly lignified woody 36 year swale roots exhibited the slowest rate of decay and immobilized phosphorus. Nitrogen amendment in dunes increased decay on younger, more nitrogen limited sites and increased nitrogen immobilization potential.; Herbaceous roots were nitrogen poor and higher nitrogen immobilization potentials were expected based on aboveground models. Rapid decay and net nitrogen and phosphorus mineralization contributes to open, leaky nutrient cycles typical of barrier island ecosystems. Decreased decay in swales increases soil carbon reserves and nutrient capital. The introduction of a woody nitrogen fixing species increases the availability of nitrogen on older landscape units.