Nitrogen mineralization in epiphytic soils of an old-growth Fitzroya cupressoides forest, southern Chile

Epiphytic soils derive from organic matter accumulation on trunks and canopy branches of large trees. We compared chemical and physical properties, rates of net N mineralization, and bacterial biomass carbon associated with epiphytic soils and the forest floor of an old-growth, temperate forest dominated by the long-lived Fitzroya capressoides (Cupressaceae) in Chiloe Island, southern Chile. Epiphytic soils had lower density, higher moisture content, higher total carbon and nitrogen contents, and lower pH than forest floor; however, these differences were only slight. Microbial biomass and soil C/N ratios did not differ between soil types. We estimated similar N mineralization rates in epiphytic soil and in the forest floor, but there was a significant interaction between time of the year and soil type, resulting from higher N production in epiphytic soils in some months. Microbial net N mineralization in the epiphytic layer contributed ca 6% of the internal N circulation. Fitzroya trees may access these nutrients via adventitious root uptake and leaching to the forest floor, thus exploiting an alternative path of nutrient circulation in old-growth forests.