Decomposition and nutrient release from radiata pine (Pinus radiata) coarse woody debris
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The dynamics of decomposition of thinning slash and nutrient release were studied in a radiata pine (Pinus radiata D Don) plantation forest in New Zealand. This study examined decomposition of coarse woody debris (CWD) components (log-wood, log-bark, and side branches) originating from stands thinned between 1 and 13 years previously. Changes in component density were used to estimate the decay rates. Both chemical analyses and 13C nuclear magnetic resonance (NMR) spectroscopy were conducted to investigate relationships between decomposition and chemical composition. The rate of decomposition was the fastest for log-wood followed by log-bark, which in turn decomposed faster than side-branch material. After 13 years, log-wood, log-bark and side branches lost 59, 55 and 24% of their initial mass, respectively. Single exponential model analysis indicated that the half-life of total thinning slash (sum of log-wood, log-bark and side branches) was 13.25 years. Proximate analyses showed that the faster rate of decomposition of log-wood was mainly due to greater carbohydrate concentration, while greater concentrations of polyphenol and lignin were responsible for the slower decomposition rate of log-bark. The slow rate of decomposition of side branches was due to unfavorable micro-climate (most of the side branches were not in contact with soil even after 9 years of decomposition) as well as greater lignin and polyphenol concentrations. Carbon-13 NMR analysis revealed that during decomposition the relative proportions of O-alkyl and acetal C, which represent carbohydrates, decreased while N-alkyl, aromatic, and phenolic C, which represent tannins and acid insoluble compounds including lignin, increased in all thinning slash components. Net release of nutrients (N, P, K, Ca and Mg) occurred during thinning slash decomposition, in contrast to earlier studies, although the concentrations of most nutrients increased with time. Nutrient release was attributed to the nature of the thinning slash materials and the high proportion of bark material in particular. Although there was a net release, the rate of release of C and the majority of nutrients from thinning slash was slow making it an important C sink and long-term source of nutrients. 2003 Elsevier B.V. All rights reserved.