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Forest, Range & Wildlands Soils

Litter Quality and Climate Decouple Nitrogen Mineralization and Productivity in Chilean Temperate Rainforests

Dep. of Earth and Environmental Science, The Univ. of Pennsylvania. 240 S. 33rd St., Philadelphia, PA 19104

^* Corresponding author (drvann{at}sas.upenn.edu)

We measured litter quality, N mineralization, air and soil temperatures, soil moisture, and aboveground net primary production (ANPP) at 18 plots in three forest types typical of full-stature forests found on western slopes of the Cordillera de Piuchué (CP) on Isla de Chiloé in southern Chile. The primary objectives were to examine the range of net N mineralization across forest types that have different vegetation and litter composition, assess probable controls on mineral N production and leaching, and to determine if the relationship between N mineralization and ANPP was similar to that observed in cool temperate northern hemisphere forests. Average annual litter lignin/N ratios were high in the evergreen montane broadleaf forest plots (50:1) and very high in the montane conifer plots (80:1). Net N mineralization during the summer months was correspondingly low (1.2 and 2.2 kg ha^–1, respectively). The high litter lignin content and associated low rate of N mineralization can explain the extremely low concentrations of mineral N in soils and upland streams of this region. In the broadleaf evergreen coastal forest plots, lignin/N ratio was lower (23:1) and N mineralized was considerably greater over the same measurement period than in the montane forest plots (14 kg ha^–1). In contrast to findings in many cool temperate northern hemisphere forests, ANNP in the broadleaf forest type was high (average 11.1 Mg ha^–1 yr^–1) in spite of the low net N mineralization rates, and ANPP and net N mineralized were not correlated. Net N mineralization was best correlated with litter quality, soil temperature, and soil moisture content, and ANPP was best correlated with growing degree days.

Abbreviations: ANPP, aboveground primary production • CB, coastal mixed broadleaf • CP, Cordillera de Piuchué • DBH, diameter-at-breast-height (1.4 m) • GSDD, growing season degree days • MB, montane mixed broadleaf • MC, montane conifer forests • PMA, phenylmercuric acetate