Changes in species richness and composition in European acidic grasslands over the past 70 years: the contribution of cumulative atmospheric nitrogen deposition

Our study investigates the negative impact of nitrogen (N) deposition on species richness in acidic grasslands, based on a temporal comparison of vegetation data spanning a period of almost 70 years. We compiled a large data base of plots assigned to the Violion caninae grassland type, composed of managed, but unfertilized semi-natural grasslands on nutrient-poor, acidic soils. In total 1114 plots, mainly from Great Britain, the Netherlands and Germany, were compiled, dating back to 1939. Environmental site information included geographical and soil (mean Ellenberg values) variables as well as estimates of cumulative N and sulphur (S) deposition since 1939. Statistical analyses were carried out separately for the data subsets from the three regions. In all regions, the vegetation differentiation was mainly related to soil acidity and nutrient availability, as well as to the year of sampling and the cumulative amounts of N and S deposition. Plot-species richness of vascular plants and bryophytes (analysed for Great Britain only) decreased with time and analyses suggest these are affected by various factors, notably soil pH, but also latitude and cumulative N deposition. The latter explained more of the variation in species number than the year of sampling and cumulative S deposition, which supports the interpretation that the decline in species richness is mainly caused by increasing N availability and less by altered management and soil acidification. For Great Britain and Germany, cumulative N deposition showed a strong negative relationship with several biodiversity measures, especially the proportion of dicots, whereas it was positively related to the proportion of grass species. In general, our results give temporal evidence for the negative effect of N deposition on species richness in semi-natural vegetation.     

Alternative modes of leaf dissection in monocotyledons

Although a majority of monocotyledons have simple leaves, pinnately or palmately dissected blades are found in four orders, the Alismatales, Pandanales, Dioscoreales and Arecales. Independent evolutionary origins of leaf dissection are indicated by phylogenetic analyses and are reflected in the diversity of mechanisms employed during leaf development. The mechanism of blastozone fractionation through localized enhancement and suppression of growth of the free margin of the leaf primordium occurs in the Araceae and Dioscoreaceae. By contrast, the corrugated, dissected leaves of palms (Arecaceae) develop through a two-step process: first, plications are formed through intercalary growth in a submarginal position and, second, the initially simple leaf blade is dissected through an abscission-like process of leaflet separation. A third mechanism, perforation formation, is employed in Monstera and five related genera of the Araceae. In this mode, discrete patches of cells undergo programmed cell death during lamina development, resulting in formation of open perforations. When perforations are positioned near the leaf margin, mechanical disruption of the thin bridges of marginal tissue results in a deeply pinnatisect blade. Whereas blastozone fractionation defines the early primary morphogenesis phase of leaf development, the other two modes occur later, during the secondary morphogenesis/histogenesis phase. Evolution of these mechanisms presumably has involved recruitment of other developmental programmes into the development of dissected leaves.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 25–44.     

Meiotic Chromosome Pairing, Isozyme Analyses and Ferritin Expression in a Red Clover Mutant Capable of Somatic Embryogenesis

Red clover genotypes capable of regenerating plantletsin vitrofromnon-meristem-derived callus are rare. A previous study identifieda pair of near isogenic lines which were derived from a singleseed but differed in regenerative ability. The callus-derivedplants of this clone were highly regenerative when reintroducedto culture whereas the epicotyl-derived plants produced non-regenerativecallus cultures. The objective of the present study was to observemeiotic chromosome pairing and to compare isozyme profiles andferritin gene expression in regenerative and non-regenerativeplants and cultures from the clone. Meiotic cells exhibitednormal homologous chromosome pairing. Starch gel zymograms fromglasshouse-grown regenerative (F49R) and non-regenerative (F49M)plants failed to show somaclonal variation for alcohol dehydrogenase,glutamate dehydrogenase, esterase or peroxidase. Isoelectricfocusing of callus cultures from regenerative and non-regenerativeplants revealed that regeneration was accompanied by a reductionin staining intensity and numbers of peroxidase bands comparedto non-regenerative cultures. A unique cathodic peroxidase band(pI 7.6) was associated with non-regenerative cultures. Ferritinexpression was greater in callus than in fresh petiole tissue.Ferritin expression remained high in non-regenerative calluscultures but declined in regenerative cultures as regenerationprogressed.Copyright 1999 Annals of Botany Company Trifolium pratenseL., red clover, ferritin, isozymes, meiosis, peroxidase, somatic embryogenesis.     

Effects of Radiotransmitter Necklaces on Behaviors of Adult Male Western Burrowing Owls

Abstract: We studied the behavioral effects of necklace-style radiotransmitters on breeding male western burrowing owls (Athene cunicularia hypugaea) in 2 areas of northwestern Texas, USA, in 2004 and 2005. We tested the hypothesis that transmittered owls would spend time interacting with their necklaces and as a result spend less time in vigilance and resting activities than would nontransmittered owls. Nontransmittered owls (n = 6) spent significantly more time being vigilant (P = 0.007) than did transmittered owls (n = 3) in 2004, who spent significant amounts of time interacting with their necklaces. In 2005, behaviors of transmittered owls (n = 8) were significantly different (P < 0.001) from control individuals (n = 4), but behaviors did not vary consistently by treatment period (prenecklace vs. necklace vs. postnecklace periods). Behavioral activity budgets varied considerably among individuals. Although the owls spent a significant amount of time interacting with their necklaces, they appeared to habituate to the presence of the transmitters within a relatively short period (<1week), and necklaces did not affect survivorship or fitness in the short-term.     

Thresholds and Multiple Stable States in Coral Reef Community Dynamics

Multiple stable states occur when more than one type of communitycan stably persist in a single environmental regime. Simpletheoretical analyses predict multiple stable states for (1)single species dynamics via the Allee effect, (2) two-speciescompetitive interactions characterized by unstable coexistence,(3) some predator-prey interactions, and (4) some systems combiningpredation and competition. Potential examples of transitionsbetween stable states on reefs include the failure of Diademaantillarum and Acropora cervicornis to recover following catastrophicmortality, and the replacement of microalgal turf by unpalatablemacroalgae after rapid increase in the amount of substratumavailable for colonization by algae. Subtidal marine ecosystemsin general, and reefs in particular, have several attributeswhich favor the existence of multiple stable states. Studiesof transitions between states often need to rely upon poorlycontrolled, unreplicated natural "experiments," as transitionstypically require pulses of disturbance over very large spatialscales. The stability of a state must often be inferred fromanalyses of the dynamics of participants at that state, as generationtimes and the potential for further extrinsic disturbance precludethe use of persistence as an indicator of stability. The potentialfor multiple stable states strongly influences our interpretationof variability in space and time and our ability to predictreef responses to natural and man-made environmental change.     

The Excystment Process in the Ciliate Euplotes muscicola: An Integrated Light and Scanning Electron Microscopic Study1

Resting cysts and the excystment process in the freshwater ciliate Euplotes muscicola were studied by both light and scanning electron microscopy. Groups of distinctly crested resting cysts adhere to the substrate. Silver-stained preparations reveal surface conservation of dorsal kinetosomes and dorsal argyrome while ventral organelles are directed inward. Excystment involves the development of an expanding excystment vacuole concurrent with a localized thinning on the dorsal cyst wall surface. Cells exit through the pre-formed ostiole, mid-dorsal region first, initially by the force of cytoplasmic streaming, but later aided by cirral movement. Newly emerged cells retain the excystment vacuole and show no dorsal ridging. As the cell expels its excystment vacuole and partially unfolds, normal trophont morphology is re-established. Both cyst structure and cyst typology have implications for hypotrich taxonomy.     

A Sensitive and Specific DNA Probe for the Oyster Pathogen Haplosporidium nelsoni

ABSTRACT. Haplosporidium nelsoni is a pathogen of the eastern oyster, Crassostrea virginica , along the middle Atlantic coast of the U.S. Genomic DNA was extracted from H. nelsoni plasmodia and small subunit (SSU) rDNA was amplified by PCR, cloned and sequenced. The sequence of H. nelsoni SSU rDNA was aligned with that of another haplosporidian, Minchinia teredinis , and with SSU rDNA data of C. virginica and various protists in GenBank. A 21-base oligonucleotide unique to H. nelsoni , designated MSX1347, was commercially synthesized and tested for sensitivity and specificity. In dot blot hybridizations the probe detected 100 pg of cloned H. nelsoni rDNA and the presence of H. nelsoni in 1 μg of genomic DNA from an infected oyster. It did not hybridize with 1 μg of genomic DNA from uninfected C. virginica or with cloned SSU rDNA of M. teredinis. The probe was further tested for specificity with in situ hybridizations on AFA-fixed, paraffin-embedded tissue sections. The probe hybridized well with H. nelsoni plasmodia and immature spores, but poorly with mature spores. The probe did not hybridize with oyster tissue, with other common oyster parasites such as P. marinus or Nematopsis sp., or with the haplosporidians Haplosporidium louisiana from mud crabs ( Panopeus spp.), Haplosporidium costale from C. virginica or M. teredinis from shipworms ( Teredo spp.).     

Heterophylly in Ranunculus flabellaris: The Effect of Abscisic Acid on Leaf Anatomy

Ranunculus flabellaris Raf., the yellow water crowfoot, exhibitsstriking heterophylly between submerged and terrestrial leaves.Leaves produced under water are highly divided with numerousnarrow lobes and deep sinuses, whereas terrestrial leaves havefew broad lobes and shallow sinuses. When plants are submergedin a 25 µM solution of ABA, the typical transition fromterrestrial to submerged leaves is completely suppressed and,instead, terrestrial-like leaves are produced. Image analysistechniques show that, in addition to this modification of leafmorphology, leaves produced under ABA treatment possess surfaceand internal features characteristic of terrestrial leaf anatomy.This study provides evidence that the environmental factorsthat influence the morphological and anatomical expression ofheterophylly may act through endogenous ABA. Ranunculus flabellaris, yellow water crowfoot, ABA, heterophylly, leaf anatomy