title: Successional changes in soil nitrogen availability, non-symbiotic nitrogen fixation and carbon/nitrogen ratios in southern Chilean forest ecosystems.
abstract: Vast areas of southern Chile are now covered by second-growth forests because of fire and logging. To study successional patterns after moderate-intensity, anthropogenic fire disturbance, we assessed differences in soil properties and N fluxes across a chronosequence of seven successional stands (2-130 years old). We examined current predictions of successional theory concerning changes in the N cycle in forest ecosystems. Seasonal fluctuations of net N mineralization (N(min)) in surface soil and N availability (N(a); N(a)=NH4+-N+NO3--N) in upper and deep soil horizons were positively correlated with monthly precipitation. In accordance with theoretical predictions, stand age was positively, but weakly related to both N(a) ( r(2)=0.282, P<0.001) and total N (N(tot); r(2)=0.192, P<0.01), and negatively related to soil C/N ratios ( r(2)=0.187, P<0.01) in surface soils. A weak linear increase in soil N(min) (upper plus deep soil horizons) was found across the chronosequence ( r(2)=0.124, P<0.022). N(min) occurred at modest rates in early successional stands, suggesting that soil disturbance did not impair microbial processes. The relationship between N fixation (N(fix)) in the litter layer and stand age best fitted a quadratic model ( r(2)=0.228, P<0.01). In contrast to documented successional trends for most temperate, tropical and Mediterranean forests, non-symbiotic N(fix) in the litter layer is a steady N input to unpolluted southern temperate forests during mid and late succession, which may compensate for hydrological losses of organic N from old-growth ecosystems.
authors.affiliation: Centre for Advanced Studies in Ecology and Biodiversity, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, CP6513677, Chile. cperez@bio.puc.cl
authors.forename: Cecilia A
authors.initials: CA
authors.lastname: Pérez
authors.forename: Martín R
authors.initials: MR
authors.lastname: Carmona
authors.forename: Juan C
authors.initials: JC
authors.lastname: Aravena
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Armesto
mesh_terms: D000367:Age Factors; D002244:Carbon / Q000032:analysis; D002677:Chile; D017753:Ecosystem; D008954:Models, Biological; D009584:Nitrogen / Q000032:analysis*; D009586:Nitrogen Fixation / Q000502:physiology; D011891:Rain; D012044:Regression Analysis; D012621:Seasons; D012987:Soil / Q000032:analysis*; D014197:Trees / Q000502:physiology*
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen