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Incidence of Phytophthora species in oak forests in Austria and their possible involvement in oak decline

FOREST PATHOLOGY, Issue 3 2003
Y. Balci
Summary A survey on the occurrence of Phytophthora species in oak ecosystems in Austria was conducted from April to May 1999 and in June 2000. The investigations were carried out at 35 study sites distributed throughout the zone of oak forests in eastern Austria. Four oak species, including Quercus robur, Q. petraea, Q. cerris and Q. pubescens were considered in the survey. Rhizosphere soil samples were taken from sample trees, which consisted of healthy and declining trees as indicated by their crown transparency. Young oak leaflets were used as baits to recover Phytophthora species. The assemblage of Phytophthora spp. detected in Austrian oak forests consisted of five species, including Phytophthora quercina, P. citricola, P. gonapodyides, P. europaea and P. syringae. P. quercina and P. citricola were isolated from 11 and seven sites, respectively, and were thus the most common and most widely distributed species. The three other species were recovered only sporadically. P. citricola could be separated into two morphologically and genetically well-characterized types (A and B). Phytophthora species, in particular the common P. quercina and P. citricola occurred on sites showing a wide variety of soil types, soil textures and moisture classes. There was mild evidence for connection between deteriorating crown status and the presence of Phytophthora spp. Furthermore, significant differences in contents of magnesium, as well as calcium, aluminium, nitrogen and carbon at different soil depths (0,10, 10,20 and 20,40 cm) were detected between Phytophthora -infested and Phytophthora -free sites. The results of the present study provide circumstantial evidence that Phytophthora species are involved in oak decline at certain sites in Austria. Résumé Une prospection des espèces de Phytophthora dans les écosystèmes de chênaie a été réalisée en Autriche en avril-mai 1999 et en juin 2000. Les recherches ont été conduites dans 35 sites répartis dans l'ensemble des chênaies de l'est de l'Autriche. Quatre espèces de chênes ont été prises en considération: Quercus robur, Q. petraea, Q. cerris et Q. pubescens. Des échantillons de sol rhizosphérique ont été prélevés au pied d'arbres sains ou dépérissants, jugés d'après la transparence de leur houppier. De jeunes feuilles de chênes ont été utilisées comme piège. Les Phytophthora spp. détectés dans les chênaies autrichiennes appartenaient à cinq espèces : P. quercina, P. citricola, P. gonapodyides, P. europaea et P. syringae. Phytophthora quercina et P. citricola ont été isolés dans 11 et 7 sites respectivement; ils étaient les plus fréquents et les plus largement répandus. Les trois autres espèces n'ont été trouvées que sporadiquement. Chez P. citricola, deux types (A et B) ont pu être distingués, morphologiquement et génétiquement différents. Les espèces de Phytophthora, en particulier P. quercina et P. citricola,étaient présents dans des sites très variés pour les types de sol, leur texture et l'humidité. Phythophthora spp. tendaient àêtre plus fréquemment présents en lien avec la détérioration des houppiers. Par ailleurs, des différences significatives ont été trouvées entre les sites avec ou sans Phytophthora, pour les teneurs en magnésium ainsi qu'en calcium, aluminium, azote et carbone à différentes profondeurs du sol (0,10, 10,20 et 20,40 cm). Les résultats montrent que des espèces de Phytophthora sont impliquées dans le dépérissement des chênes dans certains sites en Autriche. Zusammenfassung Im Rahmen einer breit angelegten Erhebung wurde im April und Mai 1999 sowie im Juni 2000 das Auftreten von Phytophthora -Arten in Eichenwaldökosystemen in Österreich untersucht. Die Erhebungen wurden an 35 Standorten durchgeführt, die über das gesamte natürliche Eichenwaldvorkommen in Ostösterreich verteilt waren. In die Untersuchung wurden die vier Eichenarten Quercus robur, Q. petraea, Q. cerris und Q. pubescens einbezogen. Von jeder , anhand ihres Kronenzustands als gesund bzw. krank eingestuften , Eiche wurden Bodenproben entnommen und aus diesen mittels ,Eichenblatt'-Ködermethode die Phytophthora -Arten isoliert. Das Spektrum der in Österreich isolierten Phytophthora -Arten umfasste die 5 Arten Phytophthora quercina, P. citricola, P. gonapodyides, P. europaea und P. syringae. P. quercina und P. citricola wurden von 11 bzw. 7 der untersuchten Standorte isoliert und waren somit die häufigsten und am weitesten verbreiteten Arten. Die drei anderen Phytophthora -Arten traten hingegen nur sporadisch auf. Innerhalb von P. citricola konnten anhand morphologischer und genetischer Merkmale 2 Typen (Typ A und Typ B) unterschieden werden. Phytophthora -Arten, insbesondere die häufig nachgewiesenen Arten P. quercina und P. citricola wurden an Standorten mit den unterschiedlichsten Bodentypen, -textur und -feuchteklassen nachgewissen. Es wurde ein schwach signifikanter Zusammenhang zwischen dem sich verschlechternden Kronenzustand und dem Vorhandensein von Phytophthora nachgewissen. Darüber hinaus unterschieden sich Phytophthora -infizierte und Phytophthora -freie Standorte in verschiedenen Bodentiefen (0,10, 10,20 und 20,40 cm) signifikant in ihren Magnesium, Kalzium, Aluminium, Stickstoff und Kohlenstoff-Gehalten. Die Ergebnisse der vorliegenden Studie lassen den Schluss zu, dass Phytophthora -Arten an einigen Untersuchungsstandorten in Österreich am Eichensterben beteiligt sind. [source]

Development of a stable isotope index to assess decadal-scale vegetation change and application to woodlands of the Burdekin catchment, Australia

GLOBAL CHANGE BIOLOGY, Issue 7 2007
EVELYN KRULL
Abstract Forty-four study sites were established in remnant woodland in the Burdekin River catchment in tropical north-east Queensland, Australia, to assess recent (decadal) vegetation change. The aim of this study was further to evaluate whether wide-scale vegetation ,thickening' (proliferation of woody plants in formerly more open woodlands) had occurred during the last century, coinciding with significant changes in land management. Soil samples from several depth intervals were size separated into different soil organic carbon (SOC) fractions, which differed from one another by chemical composition and turnover times. Tropical (C4) grasses dominate in the Burdekin catchment, and thus ,13C analyses of SOC fractions with different turnover times can be used to assess whether the relative proportion of trees (C3) and grasses (C4) had changed over time. However, a method was required to permit standardized assessment of the ,13C data for the individual sites within the 13 Mha catchment, which varied in soil and vegetation characteristics. Thus, an index was developed using data from three detailed study sites and global literature to standardize individual isotopic data from different soil depths and SOC fractions to reflect only the changed proportion of trees (C3) to grasses (C4) over decadal timescales. When applied to the 44 individual sites distributed throughout the Burdekin catchment, 64% of the sites were shown to have experienced decadal vegetation thickening, while 29% had remained stable and the remaining 7% had thinned. Thus, the development of this index enabled regional scale assessment and comparison of decadal vegetation patterns without having to rely on prior knowledge of vegetation changes or aerial photography. [source]

Land-use impact on ecosystem functioning in eastern Colorado, USA

GLOBAL CHANGE BIOLOGY, Issue 6 2001
J. M. Paruelo
Abstract Land-cover change associated with agriculture has had an enormous effect on the structure and functioning of temperate ecosystems. However, the empirical evidence for the impact of land use on ecosystem functioning at the regional scale is scarce. Most of our knowledge on land-use impact has been derived from simulation studies or from small plot experiments. In this article we studied the effects of land use on (i) the seasonal dynamics and (ii) the interannual variability of the Normalized Difference Vegetation Index (NDVI), a variable linearly related to the fraction of the photosynthetically active radiation (PAR) intercepted by the canopy. We also analysed the relative importance of environmental factors and land use on the spatial patterns of NDVI. We compared three cultivated land-cover types against native grasslands. The seasonal dynamics of NDVI was used as a descriptor of ecosystem functioning. In order to reduce the dimensionality of our data we analysed the annual integral (NDVI-I), the date of maximum NDVI (DMAX) and the quarterly average NDVI. These attributes were studied for 7 years and for 346 sites distributed across eastern Colorado (USA). Land use did modify ecosystem functioning at the regional level in eastern Colorado. The seasonal dynamics of NDVI, a surrogate for the fraction of PAR intercepted by the canopy, were significantly altered by agricultural practices. Land use modified both the NDVI integral and the seasonal dynamics of this spectral index. Despite the variability within land-cover categories, land use was the most important factor in explaining regional differences of the NDVI attributes analysed. Within the range of environmental conditions found in eastern Colorado, land use was more important than mean annual precipitation, mean annual temperature and soil texture in determining the seasonal dynamics of NDVI. [source]

Development of a historical ice database for the study of climate change in Canada

HYDROLOGICAL PROCESSES, Issue 18 2002
Frédéric Lenormand
Abstract The Canadian government has been compiling various observations on freshwater and coastal sea ice conditions for many years. However, the records are not easily accessible and are dispersed within different government departments. Given this, a major effort was undertaken in order to gather all available observations into a common database,the Canadian Ice Database (CID). This database will respond to the needs for climate monitoring in Canada, the validation and improvement of numerical ice models and the development of new remote-sensing methods. Indeed, several studies have shown that freshwater ice and sea ice are good proxy indicators of climate variability and change. The first version of CID contains in situ observations from 757 sites distributed across Canada, which were originally kept on digital or paper records at the Meteorological Service of Canada Headquarters and the Canadian Ice Service (CIS). The CID holds 63 546 records covering the period from ice season 1822,23 to 2000,01. An analysis of the database allows one to trace the temporal evolution of the ice networks. The freeze-up/break-up network of 2000,01 only represents 4% of what it was in 1985,86. A drastic decline of the ice thickness and the snow on ice network is also observable. In 1997,98, it represented only 10% of the network that existed in 1984,85. The major budget cuts in Canadian government agencies during the late 1980s and the 1990s offer the most plausible explanation for the drastic decline in the ice observation networks. Weekly ice coverage determination on large lakes from satellite imagery by the CIS and the national volunteer ice monitoring program, IceWatch, may provide a means of reviving, at least, the freeze-up/break-up network. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Temperature reconstructions and comparisons with instrumental data from a tree-ring network for the European Alps

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2005
David Frank
Abstract Ring-width and maximum latewood density data from a network of high-elevation sites distributed across the European Alps are used to reconstruct regional temperatures. The network integrates 53 ring-width and 31 density chronologies from stands of four species all located above 1500 m a.s.l. The development and basic climatic response patterns of this network are described elsewhere (Frank and Esper, 2005). The common temperature signal over the study region allowed regional reconstructions to be developed using principal component regression models for average June,August (1600,1988) and April,September (1650,1987) temperatures from ring-width and density records, respectively. Similar climatic histories are derived for both seasons, but with the ring-width and density-based reconstructions seemingly weighted toward carrying more of their variance in the lower and higher frequency domains, respectively. Distinct warm decades are the 1940s, 1860s, 1800s, 1730s, 1660s and the 1610s, and cold decades, the 1910s, 1810s, 1710s, 1700s and the 1690s. Because of the model fitting and the shorter time spans involved, comparisons between the reconstructions with high-elevation instrumental data during the majority of the 1864,1972 calibration period show good agreement. Yet, prior to this period, from which only a few low elevation temperature records are available, a trend divergence between tree-ring and instrumental records is observed. We present evidence that this divergence may be explained by the ring-width data carrying more of an annual rather than warm-season signal in the lower frequency domain. Other factors such as noise, tree-ring standardization, or the more uncertain nature of low-frequency trends in early instrumental records and their homogenization, might help explain this divergence as well. Copyright © 2005 Royal Meteorological Society. [source]

Assessing river biotic condition at a continental scale: a European approach using functional metrics and fish assemblages

JOURNAL OF APPLIED ECOLOGY, Issue 1 2006
D. PONT
Summary 1The need for sensitive biological measures of aquatic ecosystem integrity applicable at large spatial scales has been highlighted by the implementation of the European Water Framework Directive. Using fish communities as indicators of habitat quality in rivers, we developed a multi-metric index to test our capacity to (i) correctly model a variety of metrics based on assemblage structure and functions, and (ii) discriminate between the effects of natural vs. human-induced environmental variability at a continental scale. 2Information was collected for 5252 sites distributed among 1843 European rivers. Data included variables on fish assemblage structure, local environmental variables, sampling strategy and a river basin classification based on native fish fauna similarities accounting for regional effects on local assemblage structure. Fifty-eight metrics reflecting different aspects of fish assemblage structure and function were selected from the available literature and tested for their potential to indicate habitat degradation. 3To quantify possible deviation from a ,reference condition' for any given site, we first established and validated statistical models describing metric responses to natural environmental variability in the absence of any significant human disturbance. We considered that the residual distributions of these models described the response range of each metric, whatever the natural environmental variability. After testing the sensitivity of these residuals to a gradient of human disturbance, we finally selected 10 metrics that were combined to obtain a European fish assemblage index. We demonstrated that (i) when considering only minimally disturbed sites the index remains invariant, regardless of environmental variability, and (ii) the index shows a significant negative linear response to a gradient of human disturbance. 4Synthesis and applications. In this reference condition modelling approach, by including a more complete description of environmental variability at both local and regional scales it was possible to develop a novel fish biotic index transferable between catchments at the European scale. The use of functional metrics based on biological attributes of species instead of metrics based on species themselves reduced the index sensitivity to the variability of fish fauna across different biogeographical areas. [source]

Common use of sleeping sites by two primate species in Tana River, Kenya

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2001
Geoffrey M. Wahungu
Abstract Choice of sleeping sites by two species of primates sharing two adjacent patches of gallery forest in Tana River, Kenya, was studied between August 1992 and February 1993. One group each of the Tana crested mangabey, Cercocebus galeritus galeritus Peters, and yellow baboon, Papio cynocephalus cynocephalus L., interchangeably shared nine sleeping sites distributed among four tree species, Acacia robusta Burch., Ficus sycomorus L., Abizzia gummifera (J. F. Gmel.) E. A. Sm. and Pachystela msolo (Engl.) Engl. The trees used by both species as sleeping sites were mainly tall trees with canopy level or emergent crowns. The trees had relatively larger crowns and lower percentage canopy cover compared to other trees at the site and were characterized by poor to moderate accessibility. Overlap in use of sleeping sites was never simultaneous and baboons occasionally supplanted mangabeys. Site choice by these two primates appeared to be influenced by predation risk, the feeding area used in the late afternoon, daily range and the availability of trees with the preferred structural characteristics. Sleeping sites appeared to be limited during and immediately after the wet season, when the frequency of supplantings increased. This observation is attributed to an increase in percentage canopy cover. Résumé Entre août 92 et février 93, on a étudié le choix des lieux de sommeil par des primates qui partageaient deux portions adjacentes de la galerie forestière de la rivière Tana, au Kenya. Un groupe de cercocèbes à crête, Cercocebus galeritus galeritus Peters, et un de babouins olive, Papio cynocephalus cynocephalus L., partageaient pour y dormir, de façon interchangeable, neuf emplacements répartis parmi quatre espèces d'arbres, Acacia robusta Burch., Ficus sycomorus L., Abizzia gummifera (J.F. Gmel) E.A. Sm. Et Pachystela msolo (Engl) Engl. Les arbres qui servent aux deux espèces comme sites de sommeil étaient principalement des arbres élevés, avec une canopée ou une couronne émergentes. Les arbres avaient une couronne relativement plus large et une couverture de la canopée dont le pourcentage était relativement plus bas que celui des autres arbres de l'endroit, et ils se caractérisaient par une accessibilité médiocre à modérée. Le recouvrement entre les sites de sommeil n'étaient jamais simultanés, et à l'occasion, les babouins supplantaient les cercocèbes. Le choix des sites par ces deux primates semblait influencé par les risques de prédation, par l'aire de nourrissage fréquentée en fin d'après midi, par le déplacement de la journée et par la disponibilité d'arbres qui présentaient les caractéristiques structurelles souhaitées. Les sites de sommeil semblent être limités à la saison des pluies et juste après, lorsque la fréquence d'évictions augmentait. Cette observation a été attribuée à une augmentation du pourcentage du couvert de la canopée. [source]

Genetic discontinuities and disequilibria in recently established populations of the plant pathogenic fungus Mycosphaerella fijiensis

MOLECULAR ECOLOGY, Issue 18 2010
F. HALKETT
Abstract Dispersal processes of fungal plant pathogens can be inferred from analysis of spatial genetic structures resulting from recent range expansion. The relative importance of long-distance dispersal (LDD) events vs. gradual dispersal in shaping population structures depends on the geographical scale considered. The fungus Mycosphaerella fijiensis, pathogenic on banana, is an example of a recent worldwide epidemic. Founder effects in this species were detected at both global and continental scale, suggesting stochastic spread of the disease through LDD events. In this study, we analysed the structure of M. fijiensis populations in two recently (,1979,1980) colonized areas in Costa Rica and Cameroon. Isolates collected in 10,15 sites distributed along a ,250- to 300- km-long transect in each country were analysed using 19 microsatellite markers. We detected low-to-moderate genetic differentiation among populations in both countries and isolation by distance in Cameroon. Combined with historical data, these observations suggest continuous range expansion at the scale of banana-production area through gradual dispersal of spores. However, both countries displayed specific additional signatures of colonization: a sharp discontinuity in gene frequencies was observed along the Cameroon transect, while the Costa Rican populations seemed not yet to have reached genetic equilibrium. These differences in the genetic characteristics of M. fijiensis populations in two recently colonized areas are discussed in the light of historical data on disease spread and ecological data on landscape features. [source]

A structural basis for processivity

PROTEIN SCIENCE, Issue 9 2001
Wendy A. Breyer
Abstract The structures of a number of processive enzymes have been determined recently. These proteins remain attached to their polymeric substrates and may perform thousands of rounds of catalysis before dissociating. Based on the degree of enclosure of the substrate, the structures fall into two broad categories. In one group, the substrate is partially enclosed, while in the other class, enclosure is complete. In the latter case, enclosure is achieved by way of an asymmetric structure for some enzymes while others use a symmetrical toroid. In those cases where the protein completely encloses its polymeric substrate, the two are topologically linked and an immediate explanation for processivity is provided. In cases where there is only partial enclosure, the structural basis for processivity is less obvious. There are, for example, pairs of proteins that have quite similar structures but differ substantially in their processivity. It does appear, however, that the enzymes that are processive tend to be those that more completely enclose their substrates. In general terms, proteins that do not use topological restraint appear to achieve processivity by using a large interaction surface. This allows the enzyme to bind with moderate affinity at a multitude of adjacent sites distributed along its polymeric substrate. At the same time, the use of a large interaction surface minimizes the possibility that the enzyme might bind at a small number of sites with much higher affinity, which would interfere with sliding. Proteins that can both slide along a polymeric substrate, and, as well, recognize highly specific sites (e.g., some site-specific DNA-binding proteins) appear to undergo a conformational change between the cognate and noncognate-binding modes. [source]