Environmental variability promotes plant invasion

Global environmental change not only entails changes in mean environmental conditions but also in their variability. Changes in climate variability are often associated with altered disturbance regimes and temporal patterns of resource availability. Here we show that increased variability of soil nutrients strongly promotes another key process of global change, plant invasion. In experimental plant communities, the success of one of the world's most invasive plants, Japanese knotweed, is two- to four-fold increased if extra nutrients are not supplied uniformly, but in a single large pulse, or in multiple pulses of different magnitudes. The superior ability to take advantage of variable environments may be a key mechanism of knotweed dominance, and possibly many other plant invaders. Our study demonstrates that increased nutrient variability can promote plant invasion, and that changes in environmental variability may interact with other global change processes and thereby substantially accelerate ecological change

Reconstructing Disturbances and Their Biogeochemical Consequences over Multiple Timescales

Ongoing changes in disturbance regimes are predicted to cause acute changes in ecosystem structure and function in the coming decades, but many aspects of these predictions are uncertain. A key challenge is to improve the predictability of postdisturbance biogeochemical trajectories at the ecosystem level. Ecosystem ecologists and paleoecologists have generated complementary data sets about disturbance (type, severity, frequency) and ecosystem response (net primary productivity, nutrient cycling) spanning decadal to millennial timescales. Here, we take the first steps toward a full integration of these data sets by reviewing how disturbances are reconstructed using dendrochronological and sedimentary archives and by summarizing the conceptual frameworks for carbon, nitrogen, and hydrologic responses to disturbances. Key research priorities include further development of paleoecological techniques that reconstruct both disturbances and terrestrial ecosystem dynamics. In addition, mechanistic detail from disturbance experiments, long-term observations, and chronosequences can help increase the understanding of ecosystem resilience.

Influence of experimental soil disturbances on the diversity of plants in agricultural grasslands

Aims and Methods Disturbance is supposed to play an important role for biodiversity and ecosystem stability as described by the intermediate disturbance hypothesis (IDH), which predicts highest species richness at intermediate levels of disturbances. In this study, we tested the effects of artificial soil disturbances on diversity of annual and perennial vascular plants and bryophytes in a field experiment in 86 agricultural grasslands differing in land use in two regions of Germany. On each grassland, we implemented four treatments: three treatments differing in application time of soil disturbances and one control. One year after experimental disturbance, we recorded vegetation and measured biomass productivity and bare ground. We analysed the disturbance response taking effects of region and land-use-accompanied disturbance regimes into account.Important Findings Region and land-use type strongly determined plant species richness. Experimental disturbances had small positive effects on the species richness of annuals, but none on perennials or bryophytes. Bare ground was positively related to species richness of bryophytes. However, exceeding the creation of 12% bare ground further disturbance had a detrimental effect on bryophyte species richness, which corresponds to the IDH. As biomass productivity was unaffected by disturbance our results indicate that the disturbance effect on species richness of annuals was not due to decreased overall productivity, but rather due to short-term lowered inter- and intraspecific competition at the newly created microsites.Generally, our results highlight the importance of soil disturbances for species richness of annual plants and bryophytes in agricultural grasslands. However, most grasslands were disturbed naturally or by land-use practices and our additional experimental soil disturbances only had a small short-term effect. Overall, total plant diversity in grasslands seemed to be more limited by the availability of propagules rather than by suitable microsites for germination. Thus, nature conservation efforts to increase grassland diversity should focus on overcoming propagule limitation, for instance by additional sowing of seeds, while the creation of additional open patches by disturbance might only be appropriate where natural disturbances are scarce.

Sleep disturbance impairs stroke recovery in the rat

There is a lack of experimental evidence to support the hypothesis that sleep may modulate stroke outcome as suggested by clinical observations. We have previously shown that sleep disturbance (SDis) over 3 days aggravates brain damage in a rat model of focal cerebral ischemia. The aim of this study is to further investigate effects of SDis on long-term stroke recovery and neuroplasticity as assessed by axonal sprouting, neurogenesis, and angiogenesis.

Visual disturbance following sclerotherapy for varicose veins, reticular veins and telangiectasias: a systematic literature review

The objective of the study was to review the literature reporting visual disturbance (VD) following sclerotherapy for varicose veins. Underlying mechanisms will be discussed. A literature search of the databases Medline and Google Scholar was performed. Original articles including randomized trials, case series and case reports reporting VD in humans following sclerotherapy for varicose veins were included. Additional references were also obtained if they had been referenced in related publications. The search yielded 4948 results of which 25 reports were found to meet the inclusion criteria. In larger series with at least 500 included patients the prevalence of VD following sclerotherapy ranges from 0.09% to 2%. In most reports foam sclerotherapy was associated with VD (19); exclusive use of liquid sclerosant was reported in two cases, some reports included foam and liquid sclerosant (4). There were no persistent visual disorders reported. VD occurred with polidocanol and sodium tetradecyl sulphate in different concentrations (0.25-3%). Various forms of foam preparation including various ways of foam production and the liquid - air ratio (1 or 2 parts of liquid mixed with 3, 4 or 5 parts of air) were reported in association with the occurrence of VD. VDs following sclerotherapy for varicose veins are rare and all reported events were transient. Bubble embolism or any kind of embolism seems unlikely to be the only underlying mechanism. A systemic inflammatory response following sclerotherapy has been suggested. Further research to clarify the mechanism of action of sclerosants is required.

Sleep disturbance, norepinephrine, and D-dimer are all related in elderly caregivers of people with Alzheimer disease

STUDY OBJECTIVE: Caregiving for a relative with Alzheimer disease has been associated with sympathoadrenal medullary arousal and morbidity and mortality. In this study, we examined if sleep disturbance of elderly caregivers was associated with physiologic markers of cardiovascular risk, including plasma norepinephrine, epinephrine, and the hemostasis marker D-dimer. DESIGN: Cross-sectional. SETTING: Community-based sample of elderly caregivers of spouses with Alzheimer disease assessed within their homes. PARTICIPANTS: A sample of 40 elderly spousal caregivers of patients with Alzheimer disease. MEASUREMENTS AND RESULTS: Participants underwent in-home full-night polysomnography and had plasma assayed for norepinephrine and epinephrine. Using multiple regression analyses and controlling for a number of cardiovascular risk factors (e.g., age, sex, blood pressure, body mass index), increased wake after sleep onset was positively associated with norepinephrine levels (beta = .35; t = 2.45, df = 32, p = .020) and plasma D-dimer (beta = .31; t = 2.18, df = 29, p = .038). Further, plasma norepinephrine was significantly associated with D-dimer (beta = .34; t = 2.11, df = 29, p = .044). Additional analyses indicated that norepinephrine accounted for 28% of the relationship between wake after sleep onset and D-dimer. No association was observed between sleep variables and epinephrine. CONCLUSIONS: These findings provide preliminary evidence that sleep disturbance may contribute to morbidity in caregivers through sympathoadrenal medullary arousal and downstream physiologic effects such as altering the hemostasis environment.