1,720,979 research outputs found
Tackling local ecological homogeneity. Finding intraspecific trait variability in local populations of Mediterranean plants
Full text linkLocal homogeneity, in ecology, is the often undisclosed assumption that variability within populations is negligible or mostly distributed evenly. In large areas, this can lead to the aggregation of different populations without regard for their unique needs and characteristics, such as drought sensitivity and functional trait distributions. Here, we discuss whether this assumption can be justified, and we hypothesize that discerning the source of variation between plasticity and adaptation could be a feasible approach to formulate an informed decision. We test this hypothesis on plants, resorting to a common garden experiment to determine the source of variation of several plant functional traits at a local scale (~60 km) of three wild species: Quercus ilex, Pistacia lentiscus, and Cistus salviifolius. Individuals of each species were sourced from three key sites chosen along a local aridity gradient. Our approach led to the rejection of the local homogeneity assumption for Q. ilex and C. salviifolius at this scale due to the adaptive divergence observed among neighboring populations. This case study provides evidence that addressing local homogeneity can highlight diverging populations in a relatively simple way. We conclude that gathering empirical evidence on intraspecific variability is a feasible approach that can provide researchers with solid bases to decide whether to adopt the local homogeneity assumption or not
Diachronic adjustments of functional traits scaling relationships to track environmental changes. Revisiting Cistus species leaf cohort classification
No full textLeaf functional traits and their relationships can differ between leaf flushes, particularly for species characterized by an extended growing season such as Mediterranean ones. Among them, Cistus spp. are generally reported to display two different leaf cohorts (i.e. summer and winter leaves) during the same growing season. We tested the generality of such leaf cohort classification by analyzing the diachronic adjustments of relationships between different leaf functional traits in 3 Cistus spp. Traits included were: leaf mass per area (LMA), leaf thickness (LT), leaf dry matter content (LDMC) and net photosynthesis on a mass basis (Am). The slopes of the relationships between morphological traits were then regressed against climate variables. The slopes were also regressed against leaf production rate (LPR) and the scores of the positioning as Competitors (%C), Stress tolerators (%S) and Ruderals (%R) in the tertiary CSR scheme. The different leaf flushes reshaped the well-known trait covariation patterns thus reflecting shifts in leaf-level resource-acquisition and -use strategies. This was achieved through an opposite response of the relationships LMA–LT and LMA–LDMC to temperature changes. In fact, the relationship LMA–LT was better modulated in leaves produced at different temperatures, while the LMA–LDMC one was possibly constrained due to the tighter negative relationship LDMC–Am (i.e. higher costs in terms of carbon assimilation). Accordingly, changes in LMA–LDMC coordination were significantly related to %C. Our results provide an evidence that while Cistus spp. leaf cohort classification generally holds, it does not necessarily capture the entire seasonal spectrum of traits covariation. We propose to move forward from the generally accepted winter–summer leaf classification shown in literature providing a new framework that can better describe Cistus species potential response to environmental changes
Climatic variations along an aridity gradient drive significant trait intraspecific variability in Mediterranean plant species
Full text linkDrought represents one of the main sources of stress for plants in the Mediterranean region, and climate change is further escalating this stress. Plants can employ several response strategies to cope with stress, reflected in the adoption of specific Plant Functional Traits (PFTs). Trait-based approaches commonly meet three issues: they may overlook Intraspecific Variability (ITV), they could focus on large spatial scales, or they could focus on few traits. Here we present evidence that it's possible to observe ITV in morphological and anatomical trait syndromes between three local populations of Phillyrea latifolia, Pistacia lentiscus, and Quercus ilex, distributed along an aridity gradient. Thicker, physiologically expensive leaves and lower heights found in the drier sites mainly conform to drought-resistance strategies, while trait spectra from Cistus salviifolius were found not to vary significantly across sites. Thus, the amount of ITV observable at a local scale varies between species. We conclude that climate can easily drive a significant amount of ITV for several species, reflected in their trait spectra, among plant populations that are geographically close to each other. This highlights the importance of local environmental variability and implies that different populations hailing from nearby sites might respond differently to climate change
Thermal requirements for seed germination of three invasive alien species (IAS).
No full textInvasive alien species (IAS) have been introduced
outside their native sites by humans and
becoming part of local flora. The IAS number is
strongly increased worldwide during the past two
centuries, redefining the classical biogeography
boundaries, affecting ecosystem functioning,
human health and economies. IAS represent
one of the main threats to biodiversity and
interconnected ecosystem services.
This work aimed to investigate thermal
requirements for seed germination of Ailanthus
altissima (Mill.) Swingle, Robinia pseudoacacia L.
and Phytolacca americana L. Germination tests
were carried out at the Germplasm Bank (Botanical
Garden of Rome). Seeds were incubated in the
dark, and in the light (12 h light/12 h darkness)
at three range temperatures (15/6, 20/10 and
30/20 °C). For A. altissima and P. americana cold
stratification (4 °C, for 1 month) was investigated
as potential factor improving seed germination.
Differently, no cold stratification was applied to R.
pseudoacacia, which shows pronounced physical
dormancy due to an impermeable seed coat. In
this case a seed piercing to determine a higher
germination was applied.
A. altissima and P. americana showed a higher
germination rate at 30/20 °C than at 20/10 and 15/6
°C. R. pseudoacacia showed a high germination
rate after piercing at 15/6 °C and 20/10 °C, whereas
at 30/20 °C a high seed mortality was observed.
Expanding knowledge on IAS seed germination
is crucial to better understand the invasiveness
process. This information can help to find and
apply incisive and more appropriate actions to
limit the establishment and survival of IAS, whose
invasiveness could benefit from climate change in
progress.Invazivne tujerodne vrste so na območja zunaj
domorodnih območij vnesli ljudje in postajajo del
lokalne flore. Število invazivnih tujerodnih vrst je
v zadnjih dveh stoletjih močno naraslo po vsem
svetu, zaradi česar se na novo določajo klasične
biogeografske meje, to pa vpliva na delovanje
ekosistemov, zdravje ljudi in gospodarstvo.
Invazivne tujerodne vrste so ena od glavnih groženj
biotski raznovrstnosti in povezanim ekosistemskim
storitvam.
Cilj te študije je raziskati toplotne zahteve za klitje
semen vrst Ailanthus altissima ((Mill.) Swingle),
Robinia pseudoacacia L. in Phytolacca americana
L. Testi kalivosti so bili izvedeni v semenski banki
(Botanični vrt v Rimu). Semena so bila inkubirana v
temi in na svetlobi (12 ur na svetlobi/12 ur v temi)
pri treh temperaturnih razponih (15/6, 20/10 in
30/20 °C). Za vrsti A. altissima in P. americana je bila
kot potencialni dejavnik izboljšanja kalivosti semen
raziskana hladna stratifikacija (4 °C, 1 mesec). Za vrsto
R. pseudoacacia, ki ima izrazito fizično dormanco
zaradi nepropustne semenske ovojnice, pa hladna
stratifikacija, nasprotno, ni bila uporabljena. Pri tej
vrsti je bila za določanje večje kalivosti uporabljena
perforacija semen.
Pri vrstah A. altissima in P. americana je bila pri
temperaturnem razponu 30/20 °C ugotovljena večja
kalivost kot pri temperaturnih razponih 20/10 in
15/6 °C. Pri vrsti R. pseudoacacia je bila ugotovljena
večja kalivost po perforaciji pri temperaturnih
razponih 15/6 °C in 20/10 °C, pri temperaturnem
razponu 30/20 °C pa je bila ugotovljena velika
smrtnost semen. Razvijanje znanja o kalivosti
semen invazivnih tujerodnih vrst je ključno za boljše
razumevanje procesa invazivnosti. Te informacije
lahko pomagajo pri iskanju in uvedbi učinkovitih
in primernejših ukrepov za omejitev naselitve
in preživetja invazivnih tujerodnih vrst, saj lahko
na njihovo invazivnost ugodno vplivajo trenutne
podnebne spremembe
Carbon sequestration capability provided by different types of green areas in Rome
No full textCarbon dioxide (CO2) has been recognized as a major driver of climate change accounting for over 80% of all greenhouse gas emissions in the European Union. In particular, urban green areas represent a sink of CO2 due to plants capacity to fix carbon via photosynthesis and store the carbon excess as biomass. However, the plant CO2 sequestration capability occurs at different rates depending on plant species, the relative growth rate and the photosynthetic capability. Rome is among the largest European cities, with a surface area of 1285 Km2, where the green areas represent 35.3% of the total surface. In such context, the main objective of this research was to quantify the plant CO2 sequestration capability (CS, Mg CO2 ha-1 y-1) by green areas of different size, location and vegetation types in Rome. In particular, four historical residences (Villa Pamphjli, 184 ha, Villa Ada Savoia, 160 ha, Villa Borghese, 74 ha, and Villa Torlonia, 14 ha), the Botanical Garden of Rome (12 ha) and the Campus of the Sapienza University of Rome (20.3 ha) were analyzed. The CS of the four historical residences were 780, 998, 664 and 756 Mg CO2 ha-1 y-1 respectively, the Botanical Garden 809 Mg CO2 ha-1 y-1, and the Campus 43.4 Mg CO2 ha-1 y-1. The results highlight the importance of green areas in cities in order to mitigate the atmospheric CO2 concentration increasing. Our data concerning CS capability by green areas might be incorporated in a geographic information system allowing the monitoring of CO2 concentration variations over time, implement strategies to maximize the urban vegetation ecological function and the management practices to fully realize the benefits of the services that green areas can provide
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Leaf rolling as indicator of water stress in Cistus incanus from different provenances
Full text linkLeaf movements such as leaf rolling affect plant physiological performance by reducing light capture. The relationship between leaf rolling and physiological traits under imposed water stress conditions was analyzed in two population of Cistus incanus. We tested the hypothesis that leaf rolling reflected physiological changes occurring during water stress irrespective of the different acclimation in order to cope with water stress. On the whole, our results confirmed our hypothesis since leaf rolling significantly reflected physiological activity changes. Moreover, leaf rolling might be involved in protecting the PSII complex under water stress during the progressive inhibition of photosynthetic metabolism. Thus, leaf rolling could be part of C. incanus adaptive strategy to cope with water stress by sustaining leaf turgor. As such, leaf rolling may be used as a morphological index to evaluate the progressive inhibition of photosynthesis irrespective of the different acclimation to cope with water stress
Variations on the Author
Full text link“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
Full text linkWe 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
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