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Canopy soil greenhouse gas dynamics in response to indirect fertilization across an elevation gradient of tropical montane forests
No full textNitrogen cycling in canopy soils of tropical montane forests responds rapidly to indirect N and P fertilization
No full textSoil trace gas fluxes along orthogonal precipitation and soil fertility gradients in tropical lowland forests of Panama
Get PDFAbstract. Tropical lowland forest soils are significant sources and sinks of trace gases. In order to model soil trace gas flux for future climate scenarios, it is necessary to be able to predict changes in soil trace gas fluxes along natural gradients of soil fertility and climatic characteristics. We quantified trace gas fluxes in lowland forest soils at five locations in Panama, which encompassed orthogonal precipitation and soil fertility gradients. Soil trace gas fluxes were measured monthly for 1 (NO) or 2 (CO2, CH4, N2O) years (2010–2012) using vented dynamic (for NO only) or static chambers with permanent bases. Across the five sites, annual fluxes ranged from 8.0 to 10.2 Mg CO2-C, −2.0 to −0.3 kg CH4-C, 0.4 to 1.3 kg N2O-N and −0.82 to −0.03 kg NO-N ha−1 yr−1. Soil CO2 emissions did not differ across sites, but they did exhibit clear seasonal differences and a parabolic pattern with soil moisture across sites. All sites were CH4 sinks; within-site fluxes were largely controlled by soil moisture, whereas fluxes across sites were positively correlated with an integrated index of soil fertility. Soil N2O fluxes were low throughout the measurement years, but the highest emissions occurred at a mid-precipitation site with high soil N availability. Net negative NO fluxes at the soil surface occurred at all sites, with the most negative fluxes at the low-precipitation site closest to Panama City; this was likely due to high ambient NO concentrations from anthropogenic sources. Our study highlights the importance of both short-term (climatic) and long-term (soil and site characteristics) factors in predicting soil trace gas fluxes.
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Free-living nitrogen fixation responds to elevated nutrient inputs in tropical montane forest floor and canopy soils of southern Ecuador
No full textSoil N2O fluxes along an elevation gradient of tropical montane forests under experimental nitrogen and phosphorus addition
No full textNutrient deposition to tropical forests is increasing, which could affect soil fluxes of nitrous oxide (N2O), a powerful greenhouse gas. We assessed the effects of 35-56 months of moderate nitrogen (N) and phosphorus (P) additions on soil N2O fluxes and net soil N-cycling rates, and quantified the relative contributions of nitrification and denitrification to N2O fluxes. In 2008, a nutrient manipulation experiment was established along an elevation gradient (1000, 2000 and 3000 m) of montane forests in southern Ecuador. Treatments included control, N, P and N+P addition (with additions of 50 kg N ha−1 yr-1 and 10 kg P ha−1 yr-1). Nitrous oxide fluxes were measured using static, vented chambers and N cycling was determined using the buried bag method. Measurements showed that denitrification was the main N2O source at all elevations, but that annual N2O emissions from control plots were low, and decreased along the elevation gradient (0.57 ± 0.26 to 0.05 ± 0.04 kg N2O-N ha-1 yr-1). We attributed the low fluxes to our sites’ conservative soil N cycling as well as gaseous N losses possibly being dominated by N2. Contrary to the first 21 months of the experiment, N addition did not affect N2O fluxes during the 35-56 month period, possibly due to low soil moisture contents during this time. With P addition, N2O fluxes and mineral N concentrations decreased during Months 35-56, presumably because plant P limitations were alleviated, increasing plant N uptake. Nitrogen plus phosphorus addition showed similar trends to N addition, but less pronounced given the counteracting effects of P addition. The combined results from this study (Months 1-21 and 35-56) showed that effects of N and P addition on soil N2O fluxes were not linear with time of exposure, highlighting the importance of long-term studies
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Conversion of tropical forests to smallholder rubber and oil palm plantations impacts nutrient leaching losses and nutrient retention efficiency in highly weathered soils
No full textConversion of forest to rubber
and oil palm plantations is widespread in Sumatra, Indonesia, and it is
largely unknown how such land-use conversion affects nutrient leaching
losses. Our study aimed to quantify nutrient leaching and nutrient retention
efficiency in the soil after land-use conversion to smallholder rubber and
oil palm plantations. In Jambi province, Indonesia, we selected two
landscapes on highly weathered Acrisol soils that mainly differed in texture:
loam and clay. Within each soil type, we compared two reference land uses,
lowland forest and jungle rubber (defined as rubber trees interspersed in
secondary forest), with two converted land uses: smallholder rubber and oil
palm plantations. Within each soil type, the first three land uses were
represented by 4 replicate sites and the oil palm by three sites, totaling
30 sites. We measured leaching losses using suction cup lysimeters
sampled biweekly to monthly from February to December 2013. Forests and
jungle rubber had low solute concentrations in drainage water, suggesting low
internal inputs of rock-derived nutrients and efficient internal cycling of
nutrients. These reference land uses on the clay Acrisol soils had lower
leaching of dissolved N and base cations (P =  0.01–0.06) and higher N and
base cation retention efficiency (P < 0.01–0.07) than those on
the loam Acrisols. In the converted land uses, particularly on the loam
Acrisol, the fertilized area of oil palm plantations showed higher leaching
of dissolved N, organic C, and base cations (P < 0.01–0.08) and
lower N and base cation retention efficiency compared to all the other land
uses (P < 0.01–0.06). The unfertilized rubber plantations,
particularly on the loam Acrisol, showed lower leaching of dissolved P (P = 0.08) and organic C (P < 0.01) compared to forest or jungle
rubber, reflecting decreases in soil P stocks and C inputs to the soil. Our
results suggest that land-use conversion to rubber and oil palm causes
disruption of initially efficient nutrient cycling, which decreases nutrient
availability. Over time, smallholders will likely be increasingly reliant on
fertilization, with the risk of diminishing water quality due to increased
nutrient leaching. Thus, there is a need to develop management practices to
minimize leaching while sustaining productivity.</p
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