Browsing by Author "Carmona, MR"

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    Litterfall dynamics and nitrogen use efficiency in two evergreen temperate rainforests of southern Chile
    (2003) Pérez, CA; Armesto, JJ; Torrealba, C; Carmona, MR
    In unpolluted regions, where inorganic nitrogen (N) inputs from the atmosphere are minimal, such as remote locations in southern South America, litterfall dynamics and N use efficiency of tree species should be coupled to the internal N cycle of forest ecosystems. This hypothesis was examined in two evergreen temperate forests in southern Chile (42degrees30'S), a mixed broad-leaved forest (MBF) and a conifer forest (CF). Although these forests grow under the same climate and on the same parental material, they differ greatly in floristic structure and canopy dynamics (slower in the CF). In both forests, biomass, N flux, and C/N ratios of fine litterfall were measured monthly from May 1995 to March 1999. There was a continuous litter flux over the annual cycle in both forests, with a peak during autumn in the CF. In the MBF, litterfall decreased during spring. In both forests, the C/N ratios of litterfall varied over the annual cycle with a maximum in autumn. Annual litterfall biomass flux (Mean +/- SD = 3.3 +/- 0.5 vs 2.0 +/- 0.5 Mg ha(-1)) and N return (34.8 +/- 16 vs 9.1 +/- 2.8 kg N ha(-1)) were higher in the MBF than in the CF. At the ecosystem level, litterfall C/N was lower in the MBF (mean C/N ratio = 60.1 +/- 15, n = 3 years) suggesting decreased N use efficiency compared with CF (mean C/N ratio = 103 +/- 19.6, n = 3 years). At the species level, subordinated (subcanopy) tree species in the MBF had significantly lower C/N ratios (<50) of litterfall than the dominant trees in the CF and MBF (>85). The litterfall C/N ratio and percentage N retranslocated were significantly correlated and were lower in the MBF. The higher net N mineralization in soils of the MBF is related to a lower N use efficiency at the ecosystem and species level.
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    Nitrogen mineralization in epiphytic soils of an old-growth Fitzroya cupressoides forest, southern Chile
    (2005) Pérez, CA; Guevara, R; Carmona, MR; Armesto, JJ
    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.
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    Successional changes in soil nitrogen availability, non-symbiotic nitrogen fixation and carbon/nitrogen ratios in southern Chilean forest ecosystems
    (2004) Pérez, CA; Carmona, MR; Aravena, JC; Armesto, JJ
    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.