Agricultural production is under threat of water scarcity
due to increasingly frequent and severe drought events under climate change.
Whether a change in cropping systems can be used as an effective ...adaptation
strategy against drought is still unclear. We investigated how plant water
uptake patterns of a field-grown pea–barley (Pisum sativum L. and Hordeum vulgare L.) mixture, an
important fodder intercrop, responded to experimental drought under four
cropping systems, i.e. organic intensive tillage, conventional intensive
tillage, conventional no tillage, and organic reduced tillage. Drought was
simulated after crop establishment using rain shelters. Proportional
contributions to plant water uptake from different soil layers were
estimated based on stable water isotopes using Bayesian mixing models. Pea
plants always took up proportionally more water from shallower depths than
barley plants. Water uptake patterns of neither species were affected by
cropping systems. Both species showed similar responses to the drought
simulation and increased their proportional water uptake from the shallow soil
layer (0–20 cm) in all cropping systems. Our results highlight the impact of
drought on plant water uptake patterns for two important crop species and
suggest that cropping systems might not be as successful as adaptation
strategies against drought as previously thought.
Climate models predict decreasing amounts of precipitation for future summers in Switzerland. Since grasslands cover about one quarter of the area, severe consequences might be expected for Swiss ...agriculture, ranging from loss of grassland productivity to changes in vegetation composition. Since stressed ecosystems are also more susceptible to invasion, future drier conditions might favour the emergence of weeds. However, the response of temperate grasslands to drought has not been investigated in great detail so far. Using transparent rain shelters, we simulated extreme summer drought conditions in intensively managed temperate grassland in the Swiss lowlands at 400
m (Chamau, located near the city of Lucerne) and studied the drought response of
Rumex obtusifolius, one of the most troublesome weeds for forage production. We quantified above-ground biomass and assessed the resource use in terms of carbon, nitrogen and water.
R. obtusifolius increased its above-ground biomass production in response to drought, comprising up to 80% of the total community biomass in 2006. Within the drought plots, highest pre-dawn leaf water potentials, high values for midday leaf water potentials, stomatal conductance and assimilation clearly indicated that
R. obtusifolius was much less affected by drought than other plant species. In general, no significant differences were found for these variables between drought and control
R. obtusifolius plants, in contrast to the other plant species. Higher water use efficiency together with a change in N acquisition patterns resulted in a competitive advantage of
R. obtusifolius over other species, favouring the spread of this weed. Thus, our results suggest a potential increase of weed pressure by
R. obtusifolius under future climatic conditions, demanding additional management measures to limit its success.
Abstract
Aims
To evaluate if ticagrelor, an effective platelet inhibitor without known non-responders, could inhibit growth of small abdominal aortic aneurysms (AAAs).
Methods and results
In this ...multi-centre randomized controlled trial, double-blinded for ticagrelor and placebo, acetylic salicylic acid naïve patients with AAA and with a maximum aortic diameter 35–49 mm were included. The primary outcome was mean reduction in log-transformed AAA volume growth rate (%) measured with magnetic resonance imaging (MRI) at 12 months compared with baseline. Secondary outcomes include AAA-diameter growth rate and intraluminal thrombus (ILT) volume enlargement rate. A total of 144 patients from eight Swedish centres were randomized (72 in each group). MRI AAA volume increase was 9.1% for the ticagrelor group and 7.5% for the placebo group (P = 0.205) based on intention-to-treat analysis, and 8.5% vs. 7.4% in a per-protocol analysis (P = 0.372). MRI diameter change was 2.5 mm vs. 1.8 mm (P = 0.113), US diameter change 2.3 mm vs. 2.2 mm (P = 0.778), and ILT volume change 12.9% vs. 10.4% (P = 0.590).
Conclusion
In this RCT, platelet inhibition with ticagrelor did not reduce growth of small AAAs. Whether the ILT has an important pathophysiological role for AAA growth cannot be determined based on this study due to the observed lack of thrombus modulating effect of ticagrelor.
Trial registration
The TicAAA trial is registered at the US National Institutes of Health (ClinicalTrials.gov) #NCT02070653.
BACKGROUND:A general abdominal aortic aneurysm (AAA) screening program, targeting 65-year-old men, has gradually been introduced in Sweden since 2006 and reached nationwide coverage in 2015. The aim ...of this study was to determine the outcome of this program.
METHODS:Data on the number of invited and examined men, screening-detected AAAs, AAAs operated on, and surgical outcome were retrieved from all 21 Swedish counties for the years 2006 through 2014. AAA-specific mortality data were retrieved from the Swedish Cause of Death Registry. A linear regression analysis was used to estimate the effect on AAA-specific mortality among all men ≥65 years of age for the observed time period. The long-term effects were projected by using a validated Markov model.
RESULTS:Of 302 957 men aged 65 years invited, 84% attended. The prevalence of screening-detected AAA was 1.5%. After a mean of 4.5 years, 29% of patients with AAA had been operated on, with a 30-day mortality rate of 0.9% (1.3% after open repair and 0.3% after endovascular repair, P<0.001). The introduction of screening was associated with a significant reduction in AAA-specific mortality (mean, 4.0% per year of screening, P=0.020). The number needed to screen and the number needed to operate on to prevent 1 premature death were 667 and 1.5, respectively. With a total population of 9.5 million, the Swedish national AAA-screening program was predicted to annually prevent 90 premature deaths from AAA and to gain 577 quality-adjusted life-years. The incremental cost-efficiency ratio was estimated to be 7770 per quality-adjusted life-years.
CONCLUSIONS:Screening 65-year-old men for AAA is an effective preventive health measure and is highly cost-effective in a contemporary setting. These findings confirm the results from earlier randomized controlled trials and model studies in a large population-based setting of the importance for future healthcare decision making.
Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation ...events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta‐analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.
Future changes in precipitation will strongly impact ecosystem functioning and services through changes in plant growth. Here, we synthesize 83 precipitation experiments to look at responses of above and belowground plant growth (ANPP and BNPP) across climatic gradients and levels of precipitation change extremity. Overall, we found that (1) ANPP was more responsive to precipitation increases than decreases, and this was especially evident in dry ecosystems; (2) BNPP responses were similar under precipitation increases vs. decreases; (3) under extreme wet conditions, NPP responses leveled off, creating a saturating function of NPP response vs. the magnitude of precipitation change. Based on these findings, we suggest that future research focus on BNPP and plant responses to extreme precipitation change.
Extreme events such as drought and heatwaves are among the biggest challenges to agricultural production and food security. However, the effects of cropping systems on drought resistance of arable ...crops via their hydraulic behaviour remain unclear. We investigated how hydraulic traits of a field‐grown pea‐barley (Pisum sativum L. and Hordeum vulgare L.) mixture were affected by different cropping systems, that is, organic and conventional farming with intensive or conservation tillage. Xylem vulnerability to cavitation of both species was estimated by measuring the pressure inducing 50% loss of hydraulic conductivity (P50), while the water stress plants experienced in the field were assessed using native percentage loss of hydraulic conductivity (nPLC). Pea and barley showed contrasting hydraulic behaviours: pea was less vulnerable to xylem cavitation and less stressed than barley; cropping systems affected the xylem vulnerability of barley, but not of pea. Barley grown under conventional farming with no tillage was more vulnerable and stressed than under organic farming with intensive tillage. nPLC proved to be a valuable indicator for plant water stress. Our results highlight the impact of cropping systems on crop xylem vulnerability and drought resistance, thus plant hydraulic traits, for protecting food security under future climate.
Effects of cropping systems on drought resistance of arable crops were investigated for a field‐grown Pisum sativum/Hordeum vulgare mixture. Pea was less vulnerable to xylem cavitation and less stressed than barley. Cropping systems only affected xylem vulnerability of barley, but not of pea.
Temperate C₃-grasslands are of high agricultural and ecological importance in Central Europe. Plant growth and consequently grassland yields depend strongly on water supply during the growing season, ...which is projected to change in the future. We therefore investigated the effect of summer drought on the water uptake of an intensively managed lowland and an extensively managed sub-alpine grassland in Switzerland. Summer drought was simulated by using transparent shelters. Standing above- and belowground biomass was sampled during three growing seasons. Soil and plant xylem waters were analyzed for oxygen (and hydrogen) stable isotope ratios, and the depths of plant water uptake were estimated by two different approaches: (1) linear interpolation method and (2) Bayesian calibrated mixing model. Relative to the control, aboveground biomass was reduced under drought conditions. In contrast to our expectations, lowland grassland plants subjected to summer drought were more likely (43–68 %) to rely on water in the topsoil (0–10 cm), whereas control plants relied less on the topsoil (4–37 %) and shifted to deeper soil layers (20–35 cm) during the drought period (29–48 %). Sub-alpine grassland plants did not differ significantly in uptake depth between drought and control plots during the drought period. Both approaches yielded similar results and showed that the drought treatment in the two grasslands did not induce a shift to deeper uptake depths, but rather continued or shifted water uptake to even more shallower soil depths. These findings illustrate the importance of shallow soil depths for plant performance under drought conditions.
In Switzerland, the traditional three-stage grassland farming system consists of grazed or cut grasslands along a gradient from lowland to alpine elevations. We measured carbon dioxide (CO₂) fluxes ...at three grassland sites (400, 1000, and 2000m elevation) and estimated carbon sequestration for two different but exceptionally warm years (2006 and 2007). Grasslands at higher elevations (>1000m), managed at lower intensities, exhibited a larger net CO₂ uptake compared to intensively managed grasslands at lower elevations (400m). Taking into account harvest outputs as well as manure inputs, we calculated the carbon stocks and their changes for grasslands at 400m and 1000m during two years. Similar to the cumulative net ecosystem CO₂ fluxes, the seasonal course of carbon stock changes were strongly driven by management intensity, in particular by timing and amount of manure applications. Despite differences in environmental and management conditions with elevation, both grassland sites were carbon sinks during 2006 and 2007 (between 25 and 150gCm⁻² yr⁻¹).
Future sea ice retreat in the Arctic
in summer and autumn is expected to affect both natural and anthropogenic
aerosol emissions: sea ice acts as a barrier between the ocean and the
atmosphere, and ...reducing it increases dimethyl sulfide and sea salt
emissions. Additionally, a decrease in the area and thickness of sea ice
could lead to enhanced Arctic ship traffic, for example due to shorter routes
of cargo ships. Changes in the emissions of aerosol particles can then
influence cloud properties, precipitation, surface albedo, and radiation.
Next to changes in aerosol emissions, clouds will also be affected by
increases in Arctic temperatures and humidities. In this study, we quantify
how future aerosol radiative forcings and cloud radiative effects might
change in the Arctic in late summer (July–August) and early autumn
(September–October). Simulations were conducted for the years 2004 and 2050 with the global
aerosol–climate model ECHAM6-HAM2. For 2050, simulations with and without
additional ship emissions in the Arctic were carried out to quantify the
impact of these emissions on the Arctic climate. In the future, sea salt as well as dimethyl sulfide emissions and burdens
will increase in the Arctic. The increase in cloud condensation nuclei, which
is due to changes in aerosol particles and meteorology, will enhance cloud
droplet number concentrations over the Arctic Ocean (+10 % in late summer
and +29 % in early autumn; in-cloud values averaged between 75 and
90∘ N). Furthermore, both liquid and total water path will increase
(+10 % and +8 % in late summer; +34 % and +26 % in early
autumn) since the specific humidity will be enhanced due to higher
temperatures and the exposure of the ocean's surface. Changes in both aerosol radiative forcings and cloud radiative effects at the
top of the atmosphere will not be dominated by the aerosol particles and
clouds themselves but by the decrease in surface albedo (and by the increase
in surface temperature for the longwave cloud radiative effect in early
autumn). Mainly due to the reduction in sea ice, the aerosol radiative
forcing will become less positive (decreasing from 0.53 to 0.36 W m−2
in late summer and from 0.15 to 0.11 W m−2 in early autumn). The
decrease in sea ice is also mainly responsible for changes in the net cloud
radiative effect, which will become more negative in late summer (changing
from −36 to −46 W m−2). Therefore, the cooling component of both
aerosols and clouds will gain importance in the future. We found that future Arctic ship emissions related to transport and oil and
gas extraction (Peters et al., 2011) will not have a large impact on clouds and
radiation: changes in aerosols only become
significant when we increase these
ship emissions by a factor of 10. However, even with 10-fold ship emissions,
the net aerosol radiative forcing shows no significant changes. Enhanced
black carbon deposition on snow leads to a locally significant but very small
increase in radiative forcing over the central Arctic Ocean in early autumn
(no significant increase for average between 75 and 90∘ N).
Furthermore, the 10-fold higher ship emissions increase the optical thickness
and lifetime of clouds in late summer (net cloud radiative effect changing
from −48 to −52 W m−2). These aerosol–cloud effects have a
considerably larger influence on the radiative forcing than the direct
effects of particles (both aerosol particles in the atmosphere and particles
deposited on snow). In summary, future ship emissions of aerosols and their
precursor gases might have a net cooling effect, which is small compared to
other changes in future Arctic climate such as those caused by the decrease
in surface albedo.
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