Recurring weather extremes alter the flowering phenology of two common temperate shrubs.

The aim of this study is to explore the effects of heavy rain and drought on the flowering phenology of two shrub species Genista tinctoria and Calluna vulgaris. We conducted a field experiment over five consecutive years in Central Europe, applying annually recurring extreme drought and heavy rain events on constructed shrubland communities and recorded the flowering status. Further, we correlated spring temperature and precipitation with the onset of flowering. Both species showed a response to extreme weather events: drought delayed the mid flowering date of Genista tinctoria in 3 of 5 years by about 1 month and in 1 year advanced the mid flowering date by 10 days, but did not affect the length of flowering. Mid flowering date of Calluna vulgaris was not affected by drought, but the length of flowering was extended in 2 years by 6 and 10 days. For C. vulgaris the closer the drought occurred to the time of flowering, the larger the impact on the flowering length. Heavy rainfall advanced mid flowering date and reduced the length of flowering of Genista tinctoria by about 2 months in 1 year. Mid flowering date of Calluna vulgaris was not affected by heavy rain, but the length of flowering was reduced in 1 year by 4 days. Our data suggest that extreme weather events, including alterations to the precipitation regime, induce phenological shifts of plant species of a substantial magnitude. Thus, the impacts of climate extremes on plant life cycles may be as influential as gradual warming. Particularly, the variability in the timing of precipitation events appears to have a greater influence on flowering dynamics than the magnitude of the precipitation.

Stochastic trajectories of succession initiated by extreme climatic events.

Deterministic or rule-based succession is expected under homogeneous biotic and abiotic starting conditions. Effects of extreme climatic events such as drought, however, may alter these assembly rules by adding stochastic elements. We monitored the succession of species composition of 30 twin grassland communities with identical biotic and abiotic starting conditions in an initially sown diversity gradient between 1 and 16 species over 13 years. The stochasticity of succession, measured as the synchrony in the development of the species compositions of the twin plots, was strongly altered by the extreme warm and dry summer of 2003. Moreover, it was independent from past and present plant diversity and neighbourhood species compositions. Extreme climatic events can induce stochastic effects in community development and therefore impair predictability even under homogeneous abiotic conditions. Stochastic events may result in lasting shifts of community composition, as well as adverse and unforeseeable effects on the stability of ecological services.

15N natural abundance during early and late succession in a middle-European dry acidic grassland.

delta(15)N and total nitrogen content of above- and belowground tissues of 13 plant species from two successional stages (open pioneer community and ruderal grass stage) of a dry acidic grassland in Southern Germany were analysed, in order to evaluate whether resource use partitioning by niche separation and N input by N(2)-fixing legumes are potential determinants for species coexistence and successional changes. Within each stage, plants from plots with different legume cover were compared. Soil inorganic N content, total plant biomass and delta(15)N values of bulk plant material were significantly lower in the pioneer stage than in the ruderal grass community. The observed delta(15)N differences were rather species- than site-specific. Within both stages, there were also species-specific differences in isotopic composition between above- and belowground plant dry matter. Species-specific delta(15)N signatures may theoretically be explained by (i) isotopic fractionation during microbial-mediated soil N transformations; (ii) isotopic fractionation during plant N uptake or fractionation during plant-mycorrhiza transfer processes; (iii) differences in metabolic pathways and isotopic fractionation within the plant; or (iv) partitioning of available N resources (or pools) among plant groups or differential use of the same resources by different species, which seems to be the most probable route in the present case. A significant influence of N(2)-fixing legumes on the N balance of the surrounding plant community was not detectable. This was confirmed by the results of an independent in situ removal experiment, showing that after 3 years there were no measurable differences in the frequency distribution between plots with and without N(2)-fixing legumes.

Invasion windows for a global legume invader are revealed after joint examination of abiotic and biotic filters.

Successful alien plant invasion is influenced by both climate change and plant-plant interactions. We estimate the single and interactive effects of competition and extreme weather events on the performance of the global legume invader Lupinus polyphyllus (Lindl.). In three experimental studies we assessed (i) the stress tolerance of seedling and adult L. polyphyllus plants against extreme weather events (drought, fluctuating precipitation, late frost), (ii) the competitive effects of L. polyphyllus on native grassland species and vice versa, and (iii) the interactive effects of extreme weather events and competition on the performance of L. polyphyllus. Drought reduced growth and led to early senescence of L. polyphyllus but did not reduce adult survival. Fluctuating precipitation events and late frost reduced the length of inflorescences. Under control conditions, interspecific competition reduced photosynthetic activity and growth of L. polyphyllus. When subjected to competition during drought, L. polyphyllus conserved water while simultaneously maintaining high assimilation rates, demonstrating increased water use efficiency. Meanwhile, native species had reduced performance under drought. In summary, the invader gained an advantage under drought conditions through a smaller reduction in performance relative to its native competitors but was competitively inferior under control conditions. This provides evidence for a possible invasion window for this species. While regions of high elevation or latitude with regular severe late frost events might remain inaccessible for L. polyphyllus, further spread across Europe seems probable as the predicted increase in drought events may favour this non-native legume over native species.

Factors influencing seedling emergence of three global invaders in greenhouses representing major eco-regions of the world.

Successful germination and seedling emergence in new environments are crucial first steps in the life history of global plant invaders and thus play a key role in processes of range expansion. We examined the germination and seedling emergence success of three global plant invaders - Lupinus polyphyllus, Senecio inaequidens and Verbascum thapsus - in greenhouses and climate chambers under climate regimes corresponding to seven eco-regions. Seed materials were collected from one non-native population for L. polyphyllus and S. inaequidens, and from 12 populations for V. thapsus (six natives and six non-natives). Experimental climates had significant effects on species responses. No species germinated in the dry (humidity ≤ 50%) and cool (≤ 5 °C) experimental climates. But all species germinated and emerged in two moderately cool (12-19 °C) and in three warm (24-27 °C) experimental climates. In general, V. thapsus showed higher fitness than S. inaequidens and L. polyphyllus. The climate of the seed source region influenced responses of native and non-native populations of V. thapsus. Non-native populations of V. thapsus, originating from the warmer seed source, showed higher performance in warm experimental climates and lower performance in moderately cool experimental climates compared to native populations. Responses of V. thapsus populations were also related to precipitation of the seed source region in moderately dry experimental climates. The warm, semi-arid and humid experimental climates are suitable for the crucial first steps of invasion success for L. polyphyllus, S. inaequidens and V. thapsus. The species adaptation to its source region modified the responses of our studied plants under different experimental climates representing major eco-regions of the world.

Effects of extreme weather events and legume presence on mycorrhization of Plantago lanceolata and Holcus lanatus in the field.

Little is known about direct and indirect effects of extreme weather events on arbuscular mycorrhizal fungi (AMF) under field conditions. In a field experiment, we investigated the response of mycorrhization to drought and heavy rain in grassland communities. We quantified AMF biomass in soil, mycorrhization of roots of the grass Holcus lanatus and the forb Plantago lanceolata, as well as plant performance. Plants were grown in four-species communities with or without a legume. We hypothesised that drought increases and heavy rain decreases mycorrhization, and that higher mycorrhization will be linked to improved stress resistance and higher biomass production. Soil AMF biomass increased under both weather extremes. Heavy rain generally benefitted plants and increased arbuscules in P. lanceolata. Drought neither reduced plant performance nor root mycorrhization. Arbuscules increased in H. lanatus several weeks after drought, and in P. lanceolata several weeks after heavy rain spells. These long-lasting effects of weather events on mycorrhization highlight the indirect influence of climate on AMF via their host plant. Legume presence increased plant community biomass, but had only minor effects on mycorrhization. Arbuscule colonisation was negatively correlated with senescence during the dry summer. Mycorrhization and biomass production in P. lanceolata were positively related. However, increased mycorrhization was related to less biomass in the grass. AMF mycelium in soil might generally increase under extreme events, root colonisation, however, is host species specific. This might amplify community shifts in grassland under climate change by further increasing stress resistance of species that already benefit from changed precipitation.

Holocene re-colonisation, central-marginal distribution and habitat specialisation shape population genetic patterns within an Atlantic European grass species.

Corynephorus canescens (L.) P.Beauv. is an outbreeding, short-lived and wind-dispersed grass species, highly specialised on scattered and disturbance-dependent habitats of open sandy sites. Its distribution ranges from the Iberian Peninsula over Atlantic regions of Western and Central Europe, but excludes the two other classical European glacial refuge regions on the Apennine and Balkan Peninsulas. To investigate genetic patterns of this uncommon combination of ecological and biogeographic species characteristics, we analysed AFLP variation among 49 populations throughout the European distribution range, expecting (i) patterns of SW European glacial refugia and post-glacial expansion to the NE; (ii) decreasing genetic diversity from central to marginal populations; and (iii) interacting effects of high gene flow and disturbance-driven genetic drift. Decreasing genetic diversity from SW to NE and distinct gene pool clustering imply refugia on the Iberian Peninsula and in western France, from where range expansion originated towards the NE. High genetic diversity within and moderate genetic differentiation among populations, and a significant pattern of isolation-by-distance indicate a gene flow drift equilibrium within C. canescens, probably due to its restriction to scattered and dynamic habitats and limited dispersal distances. These features, as well as the re-colonisation history, were found to affect genetic diversity gradients from central to marginal populations. Our study emphasises the need for including the specific ecology into analyses of species (re-)colonisation histories and range centre-margin analyses. To account for discontinuous distributions, new indices of marginality were tested for their suitability in studies of centre-periphery gradients.

Weak magnetic fields change extinction of a conditioned reaction and daytime melatonin levels in the rat.

Altogether 100 albino rats were conditioned to flee after an acoustic stimulus (1000 Hz). During the following retention period (extinction of the reaction), half of the animals (test group) were exposed to a vertically directed, weak and extremely low-frequency magnetic field (10 Hz, 10(-4) T). Under the field's influence, the animals showed an increased retention of conditioned reactions and had an elevated level of serum melatonin compared with the animals of the control group. These effects disappeared when the investigation was performed in the dark.

The influence of a weak artificial magnetic 10 Hz field on the extinction of a conditioned flight reaction in rats.

36 three to four months old albino rats were conditioned to flee after the onset of an acoustic stimulus (1000 Hz). During the period of extinction of the flight reaction half of the animals were exposed to an alternating magnetic field (10 Hz, 0.03 mT peak to peak) for the time of investigation. These animals showed a significantly higher number of flight reactions than the control animals investigated without magnetic field, on the 4th, 5th, and 6th day of exposure (p less than 0.05).

Behaviour of heart rate and electrical muscle activity in the simultaneous dynamic action of larger and smaller sets of muscles in the permanent performance threshold range.

This study was undertaken to assess more comprehensively and with greater differentiation the reduction in the absolute electrical muscle activity (aEA) determined by different investigations in the permanent performance threshold range of the cardiovascular system (HKS) by means of the behaviour of the aEA of the highly stressed leg muscles and little stressed forearm muscles. Six healthy, untrained male subjects operated a hand ergograph alone in one test, and, in four more tests, in combination with a constant bicycle ergometer load of 40, 60, 80, and 100 W, respectively. As a result of these tests, a relative reduction in aEA for the leg muscles and an absolute reduction in aEA for the forearm muscles could be identified in the permanent performance threshold range of the HKS. Therefore, aEA is also considered to be an indicator of general stress that can define the permanent performance threshold range of the HKS more completely. The reduction in aEA is probably an expression of a negative feedback from the cardiovascular system to the neuromuscular system induced by the central nervous system.

[Visualization of symmetric striopallidodentate calcinosis by using high-resolution susceptibility-weighted MR imaging. An account of the impact of different diagnostic methods of M. Fahr]. / Visualisierung der symmetrischen Stammganglienverkalkung mittels räumlich hochaufgelöster suszeptibilitätsgewichteter MR-Bildgebung. Bedeutung diverser diagnostischer Verfahren zur Diagnosestellung eines M. Fahr.

Bilateral striopallidodentate calcinosis, also known as Fahr's disease, is characterized by symmetric calcifications of the basal ganglia, thalami, dentate nuclei of the cerebellum and white matter of the cerebral hemispheres. Besides the common idiopathic etiology of bilateral intracerebral calcinosis, alterations of calcium metabolism are present in rare cases, which are especially caused by hormonal dysfunction of the parathyroids. Advanced imaging techniques, such as CT and MRI, demonstrate increasing relevance regarding diagnosis of bilateral striopallidodentate calcinosis. Intracranial calcifications are routinely observed with high sensitivity by CT. On MR images calcifications exhibit different signal intensities, which depend on the stage of the disease, differences in calcium metabolism and the compound of these calcifications. Application of a new high-resolution, susceptibility-weighted MR sequence allows detailed visualization of the intracerebral calcifications in Fahr's disease. Further diagnostic methods and important aspects regarding clinical manifestation of bilateral striopallidodentate calcinosis are also discussed.

Pulmonary 15NO uptake in man.

Nitric oxide (NO) is commonly thought to reveal more precise values of pulmonary gas uptake through alveolar-capillary membranes (DL) than the normally used carbon monoxide (CO). Since such measurements are influenced by a significant endogenous NO delivery within human airways, we propose the use of the naturally occurring (15)N-labelled stable nitric oxide isotope (15)NO. It occurs with a relative abundance of 0.37% of the dominating isotope (14)NO. Therefore, the endogenous (15)NO production can be neglected. In the present pilot study we demonstrate the workability of (15)NO in determining DL in healthy individuals. In seven female and 15 male volunteers, averaged values of DL increase with increasing mean alveolar volume as well as individual body height ( P=0.000001). Due to the very high significance level obtained from the multiple regression analysis, we conclude that the application of (15)NO establishes a novel approach to calculate standard values of DL. Such calculations can be employed to predict a reference for patients who suffer from pulmonary diffusion limitation.