186,337 research outputs found
Biomass production of Lolio-Cynosuretum grassland is not increased by plant-species richness
No full textIn experimental grasslands, a positive relationship between biomass production and plant diversity has often been found. Here, we compared a moderately species‐rich old sward with its grass‐dominated counterpart (12 vs. 8 species per 2.5 m2, or 8.3 vs. 0.7% yield proportion of dicots at the start of the experiment) established by herbicide application. We hypothesized an increased N, P and K uptake in the diverse sward related to a higher colonization rate with arbuscular mycorrhizal fungi (AMF), the presence of legumes, and complementary nutrient use of plant species. Phosphorus or N fertilizer application (according to contributions of AMF or legumes) were expected to balance the assumed smaller biomass production of the grass compared to the diverse sward. In two experimental years, N, P and K uptake, biomass production, N2 fixation, and intra‐ and extraradical AMF colonization were investigated in an untreated control and plots that were fertilized with P and N in a low (P1: 20 kg P ha−1; N1: 50 kg N ha−1) or a high dose (P2: 100 kg P ha−1; N2: 500 kg N ha−1) in both swards. Biomass production was larger in the grass compared to the diverse sward. The N, P and K uptake, accumulated over three harvests (or 1.5 years), was also larger in the grass sward. The biomass production ranged from 5.3 to 10.0 t ha−1 and accumulated nutrient uptake from 82 to191 kg N ha−1, 19 to 31 kg P ha−1 and 112 to 221 kg K ha−1. Small legume proportions resulted in an accumulated N2 fixation between 0 and 3 kg ha−1. In the second year, the root length colonized with AMF structures was larger in the diverse compared to the grass sward, and the root length colonized with arbuscules and coils was larger in the N2 treatment compared to the control in the diverse sward. There were hints to higher AMF abundance under conditions of limited P availability (low soil P content, high N:P ratio in plant biomass). We conclude that in semi‐natural grassland of moderate species richness several factors may affect the relationship between plant diversity and productivity, i.e., management, plant species identity, and the number of the plant species of the low‐diversity level
On the origin of nitrous oxide and its oxygen
No full textLachgas (N2O) is een broeikasgas dat bijdraagt aan de opwarming van de aarde en de afbraak van ozon in de stratosfeer. Om emissies van N2O terug te dringen zullen we moeten begrijpen hoe en waar het ontstaat. Er is echter veel onduidelijkheid over de verschillende manieren waarop N2O wordt gevormd, en hoe deze processen worden beïnvloed door de omgeving. Wereldwijd vormen bodems de grootste bron van lachgas naar de atmosfeer. Met mijn onderzoek probeer ik daarom een beter inzicht te krijgen in de productie van N2O in bodems. Mijn hoofddoel was om de bijdrage van ‘nitrifier denitrification’ als afzonderlijk proces te bestuderen. In dit proces wordt nitriet (NO2-) omgezet in N2O door ammonia oxiderende bacteriën (AOB), die normaliter juist NO2- vormen vanuit ammonia (NH3). Het reducerende proces tot N2O wordt normaal gesproken voornamelijk toegeschreven aan andere organismen, de denitrificeerders
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Phosphorus, Plant Biodiversity and Climate Change
No full textPhosphorus (P) is a major plant nutrient. Its increasing use as a fertilizer has helped to raise crop and fodder production. However, the global reserves and resources of P are finite, demanding an efficient use of P. Under natural conditions, it is often in limited supply. Plants have developed adaptations to small soil P concentrations. Increased P levels can have unwanted side effects like eutrophication and algal blooms. Besides, P concentrations in the soil have often been found to be negatively correlated with plant diversity. For sustainable agriculture, it is essential to understand 1) adaptations of plants to small P concentrations in soils to maintain production with decreasing P reserves, 2) influences of P on phytodiversity to minimize unwanted effects, and 3) future developments of P and phytodiversity in relation to climate change to adjust agricultural practices. P is essential for the energy and sugar metabolism of plants. As it moves in soils by diffusion only, the geometry of the root system is essential for its uptake. Plants have developed different adaptations for P uptake: e.g., localized or overall increases in the number of roots, the development of cluster roots that increase the root surface area by up to 140 times, exudation of different phosphatases and organic acids in reaction to specific forms of P, or symbiosis with mycorrhiza that may be responsible for up to 75% of the P acquired by plants. Gradual differences in these adaptations decrease interspecific competition and facilitate coexistence. Low P concen trations increase plant diversity by favoring stress-tolerant rather than ruderal species or by restricting the growth of competitive grasses more than that of forbs. According to the niche dimension hypothesis, more limiting resources lead to more coexisting species. Worldwide, P limitation is as relevant for plant production as nitrogen (N) limitation. Thus, P could regulate the size of ecological niches by being the main growth-limiting factor or by being coupled to other limiting resources. Global climate change influences soil P availability. Increasing temperatures tend to increase P mineralization of litter. Furthermore, temperature increases by 5 _ºC have been found to double the colonization of roots by mycorrhiza. Nitrogen mineralization was enhanced by on average 48% by temperature increases of between 0.3 and 6.0 _C. Larger amounts of N stimulate phosphatase exudation and plant P uptake. This could result in increased soil P availability, which is further enhanced by increased P mobilization due to human activities. Such a development would reduce phytodiversity and promote the growth of ruderal, fast-growing species. In the long run, this could cause mining of soil P, which would then again increase plant diversity. However, diversity needs a long time to recover from P additions. Therefore, in sustainable agriculture, increases in soil P relative to other factors limiting plant growth have to be prevented to guarantee large phytodiversity
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
No full textWe 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
Dr. Edward P. Wimberly, ITC, July 2011
No full textThis video is a conversation with Dr. Edward P. Wimberly. Dr. Wimberly talks about his book, "No Shame in Wesley's Gospel: A Twenty-First Century Pastoral Gospel". Brad Ost, AUC Woodruff Library, is the interviewer
Author Rights and Scholarly Publishing
No full textOriginally posted at
http://blog.library.gsu.edu/2014/10/24/author-rights-and-scholarly-publishing/</p
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