Revista Chilena de Historia Natural 81 (2): 267-278, 2008
RESEARCH ARTICLE
Effects of labile phosphorous and carbon on non-symbiotic N2 fixation in logged and unlogged
evergreen forests in Chiloé Island, Chile
SANDRA E. PÉREZ, CECILIA A. PÉREZ , MARTÍN R. CARMONA, JOSÉ M. FARIÑA & JUAN J.
Nitrogen input to evergreen temperate forests of Chiloé Island, Chile occurs
predominantly via non-symbiotic fixation (NSF). Because this is a bacterial-mediated process (diazotrophs), in addition to
environmental factors (e.g., temperature and moisture), phosphorous availability and energy supply from carbon in the substrate may
influence the rates of N fixation. Our hypothesis is that if both phosphorous and carbon are limiting NSF, this limitation would be greater
in logged forests, where additions of labile P and C would stimulate microbial activity. Our objectives are to assess the effects of
inorganic phosphorus and labile carbon (as glucose) additions (0 mmol P/L, 0.645 mmol P/L, 3.23 mmol P/L y 6.45 mmol P/L and 0
mmol P/L, 23.3 mmol C/L, 46.6 mmol C/L y 70 mmol C/L, respectively) on the rates of NSF measured in the litter layer of each forest
in laboratory assays, under controlled temperature and moisture and using homogeneous litter samples. We studied lowland
evergreen rainforests (100-200 m of altitude), located in the Chonchi district, in Chiloé Island. Two forest stands were logged,
subjected to industrial and non-industrial selective logging, and the third stand was unlogged (control). The NSF of nitrogen was
assessed by the acetylene reduction assay. Two-way ANOVAs showed that phosphorous addition had no effect on acetylene
reduction rates (ARR) in the litter of logged or unlogged forests, but the addition of labile carbon in the form of glucose negatively
affected ARR when applied at the maximum level to the litter of unlogged forest. In all treatments the factor forest accounted for the
differences in ARR, which was higher in unlogged forest. These differences were not explained by any of the variables experimentally
manipulated in this study. The main difference among forests was floristic composition of litterfall, but litter did not differ among forests
in its C/N ratio or total P and N contents.
logging effects,
Laureliopsis philippiana, acetylene reduction assay, microbial activity
