Document: JUA-3-63-14

Nitrogen mineralization in epiphytic soil in old-growth Fitzroya cupressoides forest, southern Chile.

ARMESTO, J.J.*, C.PEREZ, M.CARMONA and R.GUEVARA

Universidad de Chile, Santiago, Chile ¹

Abstract:
Epiphytic soil is made up of organic matter accumulated under the epiphytic plant cover on branches and trunks of large, long-lived trees. The possibility of an "epiphytic shortcut", where nutrients from epiphytic soil are taken up directly by the host tree, via adventitious roots, or are leached onto the forest floor, makes it relevant to assess the contribution of nutrients from epiphytic soil to the internal ecosystem cycle. We assessed the seasonal patterns and rates of nitrogen mineralization under the epiphytic mat in large Fitzroya cupressoides (Cupressaceae) trees (mean age=400 years) and in the forest floor. We incubated in parallel epiphytic and forest floor soil samples both in the laboratory and in the field. Ammonium and nitrate were extracted from samples by microkjeldahl distillation. The rate of mineralization was estimated as the slope (k) of the relation of accumulated nitrogen versus time. Mineralization rates varied seasonally, but k values were comparable for epiphytic and forest floor soils. Nitrate and ammonium production ranged between 0.3-3.5 g N/g/day for both soils. Net production was high in epiphytic soil at times when forest floor soil had negative mineralization. Microbial activity in epiphytic soil can contribute importantly to the internal cycling of N in old-growth ecosystems.

Keywords: Net N mineralization, Epiphytic soil, Southern temperate forests

This abstract is being presented at: 9:45 AM in session:
Oral Session #41: N Dynamics: Additions, Retention and Transformations.