Loblolly pine needle decomposition and nutrient dynamics as affected by irrigation, fertilization, and substrate quality

This study examined the effects of initial litter quality and irrigation an d fertilization treatments on litter decomposition rates and nutrient dynam ics (N, Ca, K, Mg, and P) of loblolly (Pinus taeda L.) pine needles in the North Carolina Sand Hills over 3 years. Litter quality was based on the ini tial ON ratios, with the high-quality litter having a significantly (P < 0. 001) lower CIN ratio (143 +/- 2.5) compared with the low quality litter (17 2 +/- 1.3). Initial litter quality and the irrigation treatment did not sig nificantly affect decomposition rates but the fertilization treatment effec ts were significant. Low quality needles on fertilized plots had higher dec omposition rates (k = 0.36 +/- 0.01 year(-1) for the fertilized and irrigat ed + fertilized plots) than on unfertilized plots (k = 0.26 +/- 0.01 and 0. 28 +/- 0.01 year(-1) for the control and irrigated plots, respectively). Th e decomposing litter was a net sink for P and N and a net source of Mg, Ca, and especially K. Whereas initial substrate quality did not affect decompo sition rates, it did affect the rate of release. Compared to the low qualit y litter, the high quality litter released K at a higher rate, released Mg at a lower rate, and accumulated N at a higher rate. Fertilization decrease d the rate of release of Mg and K in high-quality litter and Mg and Ca in l ow quality litter. In addition, fertilization increased the rate of accumul ation of P in both. (C) 2001 Elsevier Science B.V. All rights reserved.