1,720,986 research outputs found
Is optimal resource partitioning theory applicable to water‐limited mature trees?
No full textOptimal resource partitioning theory predicts that plants should increase the ratio between water absorbing and transpiring surfaces under short water supply. An increase in fine root mass and surface area relative to leaf area has frequently been found in herbaceous plants, but supporting evidence from mature trees is scarce and several results are contradictory. In 12 mature Fagus sylvatica forests across a precipitation gradient (820–540 mm yr−1), we tested several predictions of the theory by analysing the dependence of standing fine root biomass, fine root production and fine root morphology on mean annual precipitation (MAP), the precipitation of the study year, and stand structural and edaphic variables. The water storage capacity of the soil (WSC) was included as a covariable by comparing pairs of stands on sandy (lower WSC) and loam-richer soils (higher WSC). Fine root biomass, total fine root surface area, fine root production and the fine root : leaf biomass production ratio markedly increased with reduced MAP and precipitation in the study year, while WSC was only a secondary factor and stand structure had no effect. The precipitation effect on fine root biomass and production was more pronounced in stands on sandy soil with lower WSC, which had, at equal precipitation, a higher fine root biomass and productivity than stands on loam-richer soil. The high degree of allocational plasticity in mature F. sylvatica trees contrasts with a low morphological plasticity of the fine roots. On the more extreme sandy soils, a significant decrease in mean fine root diameter and increase in specific root area with decreasing precipitation were found; a similar effect was absent on the loam-richer soils. Synthesis. In support of optimal partitioning theory, mature Fagus sylvatica trees showed a remarkable allocational plasticity as a long-term response to significant precipitation reduction with a large increase in the size and productivity of the fine root system, while only minor adaptive modifications occurred in root morphology. More severe summer droughts in a future warmer climate may substantially alter the above-/below-ground C partitioning of this tree species with major implications for the forest C cycle
Functional composition of plant communities determines the spatial and temporal stability of soil microbial properties in a long‐term plant diversity experiment
No full textStable provisioning of ecosystem functions and services is crucial for human well-being in a changing world. Two essential ecological components driving vital ecosystem functions in terrestrial ecosystems are plant diversity and soil microorganisms. In this study, we tracked soil microbial basal respiration and biomass over a time period of 12 years in a grassland biodiversity experiment (the Jena Experiment) and examined the role of plant diversity and plant functional group composition for the spatial and temporal stability of soil microbial properties (basal respiration and biomass) in bulk-soil. Spatial and temporal stability were calculated as the inverse coefficient of variation (CV-1) of soil microbial respiration and biomass measured from soil samples taken over space and time, respectively. We found that 1) plant species richness consistently increased soil microbial properties after a time lag of four years since the establishment of the experimental plots, 2) plant species richness had minor effects on the spatial stability of soil microbial properties, whereas 3) the functional composition of plant communities significantly affected spatial stability of soil microbial properties, with legumes and tall herbs reducing both the spatial stability of microbial respiration and biomass, while grasses increased the latter, and 4) the effect of plant diversity on temporal stability of soil microbial properties turned from being negative to neutral, suggesting that the recovery of soil microbial communities from former arable land-use takes more than a decade. Our results highlight the importance of plant functional group composition for the spatial and temporal stability of soil microbial properties, and hence for microbially-driven ecosystem processes, such as decomposition and element cycling, in temperate semi-natural grassland
Incorporation of mineral nitrogen into the soil food web as affected by plant community composition
No full textWe set up a field experiment in experimental grasslands (Jena Experiment) with different levels of plant species richness (2, 4, 8, and 16 plant species), and plant functional group richness (1, 2, 3, and 4 plant functional groups; legumes, grasses, small herbs, tall herbs). The experimental subplots were labeled with 15N at the beginning of the growing season in 2011 (18- 19th April). The 15N tracer solution (0.01 mol 15NH415NO3/L deionized water; 98 atom %; Cambridge Isotope Laboratories, Tewksbury, MA, USA) was injected into pre-drilled holes of a depth of 7 cm in the soil arranged along gridlines (distance within grid lines 8.7 cm, distance between grid lines 10 cm, resulting in 49 holes per subplot). The tracer solution was injected using a 3 mm thick four-side port needle (2 mL per injection point) connected with a silicon tube to a bottle top dispenser (Socorex Isba SA, Switzerland) on a 1 L glass bottle. We measured incorporation of mineral-derived 15N into soil microorganisms and mesofauna over three months. For measuring the time-integrated incorporation of 15N into soil microorganisms, five sampling campaigns were carried out: 2, 15, 30, 60, and 120 days after labeling, respectively. At each sampling campaign, three soil cores were taken per subplot for microbial biomass (Ø 5 cm, 0-5 cm depth). Microbial biomass N was extracted from soil by chloroform fumigation-extraction (CFE). Two subsamples (10 g soil fresh weight each) were taken from each pre-extracted soil sample. One subsample was fumigated with chloroform vapor for 24 h, the other remained unfumigated. Both subsamples were extracted with 60 ml 0.05 M K2SO4 , the extracts were filtered and frozen at -18°C until further analysis. Before analyzing stable isotope ratios of the subsamples, a fraction of the samples (15 mL) was freeze-dried (VaCo2, Zirbus Technology, Bad Grund, Germany) at -30°C for 3 d and stored in plastic vessels in a desiccator. For referring results of 15N measurements to one gram dry soil, gravimetric soil water content was measured by drying 10 g of fresh soil subsamples of each sample at 105°C for 48 h. For analyses of 15N/14N ratios in microbial biomass N, appropriate amounts of the freeze-dried microbial N extract (60-65 μg) were transferred into tin capsules. Stable isotope ratios were measured with a coupled system of an elemental analyzer (NA 1500, Carlo Erba, Milan, Italy) and a mass spectrometer (MAT 251, Finnigan, Bremen, Germany). Microbial biomass N was calculated as Nmic = EN/kEN, with EN being the difference between total N extracted from fumigated soil and total N extracted from unfumigated soil, and kEN the extractable fraction of microbial biomass N after fumigation. Soil microbial biomass 15N (μg 15N/ g dry soil) was calculated as 15Nmic (μg/ g dry soil) = 15N (μg / g dry soil) of fumigated subsample – 15N (μg /g dry soil) of unfumigated subsample. Atom percent excess (APE, isotopic enrichment) of 15N in microbial biomass N was calculated as the difference in atom% between labelled and natural abundance level of 15N in soil microbial biomass. For measuring the time-integrated incorporation of 15N into soil microorganisms and mesofauna, five sampling campaigns were carried out: 5, 15, 30, 60, and 120 days after labeling, respectively. At each sampling campaign, one soil core per subplot was taken for mesofauna (Ø 20 cm, 0-10 cm depth). The following mesofauna species were used for stable isotope analyses: Tectocepheus velatus sarekensis (Oribatida, primary decomposer), Lepidocyrtus cyaneus, Isotoma viridis, Parisotoma notabilis, Ceratophysella sp. and Stenaphorura denisi (all Collembola, secondary decomposers), as well as Lasioseius berlesei (Gamasina, predator). Tectocepheus velatus sarekensis (Oribatida, primary decomposer), Lepidocyrtus cyaneus, Isotoma viridis, Parisotoma notabilis, Ceratophysella sp. and Stenaphorura denisi (all Collembola, secondary decomposers), as well as Lasioseius berlesei (Gamasina, predator). For analyses of 15N/14N ratios in soil mesofauna, appropriate numbers of animals (10-120 individuals weighing 10-200 μg and containing 1-20 μg N) were transferred into tin capsules. In few cases individuals from the same sampling campaign but different plots with similar plant community composition were pooled. Stable isotope ratios were measured with a coupled system of a micro- elemental analyzer system (Euro-EA 300, Eurovector, Milano, Italy) allowing the analysis of small amounts of animal tissue, and a mass spectrometer (MAT 251, Finnigan, Bremen, Germany). Isotope signatures are expressed using the δ notation with δ15N (‰) = (Rsample/Rstandard -1) x 1000, where R is the molar ratio of heavy to the light isotope (15N/14N). Acetanilide (C8H9NO, Merck, Darmstadt, Germany) was used for internal calibration. As standard for δ15N, atmospheric nitrogen was used. Shifts in 15N/14N ratios in mesofauna species due to labeling with 15NH415NO3 were inspected by calculating the difference between δ15N values of specimens inside and outside the subplots, i.e. Δ values
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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