Decomposition of nitrogen-15 labeled hoop pine harvest residues in subtropical Australia

Information on decomposition of harvest residues may assist in the maintenance of soil fertility in second rotation (2R) hoop pine plantations (Araucaria cunninghamii Aiton ex A. Cunn.) of subtropical Australia. The experiment was undertaken to determine the dynamics of residue decomposition and fate of residue-derived N. We used N-15-labeled hoop pine foliage, branch, and stem material in microplots, over a 30-mo period following harvesting. We examined the decomposition of each component both singly and combined, and used C-13 cross-polarization and magic-angle spinning nuclear magnetic resonance (C-13 CPMAS NMR) to chart C transformations in decomposing foliage. Residue-derived N-15 was immobilized in the 0- to 5-cm soil layer, with approximately 40% N-15 recovery in the soil from the combined residues by the end of the 30-mo period. Total recovery of N-15 in residues and soil varied between 60 and 80% for the combined-residue microplots, with 20 to 40% of the residue N-15 apparently lost. When residues were combined within microplots the rate of foliage decomposition decreased by 30% while the rate of branch and stem decomposition increased by 50 and 40% compared with rates for these components when decomposed separately. Residue decomposition studies should include a combined-residue treatment. Based on C-15 CPMAS NMR spectra for decomposing foliage, we obtained good correlations for methoxyl C, aryl C, carbohydrate C and phenolic C with residue mass, N-15 enrichment, and total N. The ratio of carbohydrate C to methoxyl C may be useful as an indicator of harvest residue decomposition in hoop pine plantations.

Correlations, integration and Hansen-Jagannathan Bounds

Recent studies have documented the growing economic and financial integration between countries. Among other things, this has led to the argument that greater integration results in higher bilateral correlations between returns on national stock markets. This study endeavours to link the two issues by utilizing the assumption that if countries are integrated, they would have to display a minimum level of correlation. This is achieved by constructing a bound on the level of the bilateral correlation, as originally developed by Kasa (1995). In contrast to Kasa, the present studies demonstrate that the correlation bound may not be downward sloping in all cases and careful interpretation of the results is required.