In 2018, Central Europe experienced one of the most severe and long-lasting summer drought and heat wave ever recorded. Before 2018, the 2003 millennial drought was often invoked as the example of a “hotter drought”, and was classified as the most severe event in Europe for the last 500 years. First insights now confirm that the 2018 drought event was climatically more extreme and had a greater impact on forest ecosystems of Austria, Germany and Switzerland than the 2003 drought. Across this region, mean growing season air temperature from April to October was more than 3.3°C above the long-term average, and 1.2°C warmer than in 2003. Here, we present a first impact assessment of the severe 2018 summer drought and heatwave on Central European forests. In response to the 2018 event, most ecologically and economically important tree species in temperate forests of Austria, Germany and Switzerland showed severe signs of drought stress. These symptoms included exceptionally low foliar water potentials crossing the threshold for xylem hydraulic failure in many species and observations of widespread leaf discoloration and premature leaf shedding. As a result of the extreme drought stress, the 2018 event caused unprecedented drought-induced tree mortality in many species throughout the region. Moreover, unexpectedly strong drought-legacy effects were detected in 2019. This implies that the physiological recovery of trees was impaired after the 2018 drought event, leaving them highly vulnerable to secondary drought impacts such as insect or fungal pathogen attacks. As a consequence, mortality of trees triggered by the 2018 events is likely to continue for several years. Our assessment indicates that many common temperate European forest tree species are more vulnerable to extreme summer drought and heat waves than previously thought. As drought and heat events are likely to occur more frequently with the progression of climate change, temperate European forests might approach the point for a substantial ecological and economic transition. Our assessment also highlights the urgent need for a pan-European ground-based monitoring network suited to track individual tree mortality, supported by remote sensing products with high spatial and temporal resolution to track, analyse and forecast these transitions. 相似文献
Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegetation and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately represented for accurately modeling the coupled biosphere–atmosphere–climate earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. We describe the diurnal and seasonal variation in isoprene, monoterpene, and methanol fluxes from a temperate forest ecosystem before, during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were dominated by isoprene, which attained high emission rates of up to 35.4 mg m?2 h?1 at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which highlights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Nevertheless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout the season, confirming the complex processes driving biogenic methanol fluxes. The fraction of daytime (7–17 h) assimilated carbon released back to the atmosphere combining the three BVOCs measured was 2% of gross primary productivity (GPP) and 4.9% of net ecosystem exchange (NEE) on average for our whole measurement campaign, while exceeding 5% of GPP and 10% of NEE just before the strongest drought phase. The megan v2.1 model correctly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research is needed to address model BVOC fluxes during drought events. 相似文献
Heat waves and droughts are predicted to increase in frequency and intensity with climate change. However, we lack a mechanistic understanding of the independent and interactive effects of severe heat and water stress for most ecosystems. In a mesic tallgrass prairie ecosystem, we used a factorial experimental approach to assess ecophysiological and productivity responses of two dominant C4 grasses, Andropogon gerardii and Sorghastrum nutans, to a season-long drought and a mid-summer heat wave at four intensities. We hypothesized that drought would have greater impacts than heat waves, that combined effects would be greater than either factor alone, and that the dominant grasses would differ in their responses to heat and water heat stress. We detected significant reductions in photosynthesis, leaf water potential, and productivity with drought but few direct responses to the heat waves. Surprisingly, there was no additive effect of heat and water stress on any plant response. However, S. nutans was more sensitive than A. gerardii to drought. In this grassland, water stress will likely dominate photosynthetic and productivity responses caused by discrete drought and heat wave events, rather than direct or additive effects of heat stress, with differential sensitivity in these grasses altering future ecosystem structure and function. 相似文献
Plants emit a substantial amount of biogenic volatile organic compounds (BVOCs) into the atmosphere. These BVOCs represent a large carbon loss and can be up to approximately 10% of that fixed by photosynthesis under stressful conditions and up to 100gCm(-2) per year in some tropical ecosystems. Among a variety of proven and unproven BVOC functions in plants and roles in atmospheric processes, recent data intriguingly link emission of these compounds to climate. Ongoing research demonstrates that BVOCs could protect plants against high temperatures. BVOC emissions are probably increasing with warming and with other factors associated to global change, including changes in land cover. These increases in BVOC emissions could contribute in a significant way (via negative and positive feedback) to the complex processes associated with global warming. 相似文献
Within their natural habitat, crops are often subjected to drought and heat stress, which suppress crop growth and decrease
crop production. Causing overaccumulation of glycinebetaine (GB) has been used to enhance the crop yield under stress. Here,
we investigated the response of wheat (Triticum aestivum L.) photosynthesis to drought, heat stress and their combination with a transgenic wheat line (T6) overaccumulating GB and
its wild-type (WT) Shi4185. Drought stress (DS) was imposed by controlling irrigation until the relative water content (RWC)
of the flag leaves decreased to between 78 and 82%. Heat stress (HS) was applied by exposing wheat plants to 40°C for 4 h.
A combination of drought and heat stress was applied by subjecting the drought-stressed plants to a heat stress as above.
The results indicated that all stresses decreased photosynthesis, but the combination of drought and heat stress exacerbated
the negative effects on photosynthesis more than exposure to drought or heat stress alone. Drought stress decreased the transpiration
rate (Tr), stomatal conductance (Gs) and intercellular CO2 concentration (Ci), while heat stress increased all of these; the deprivation of water was greater under drought stress than
heat stress, but heat stress decreased the antioxidant enzyme activity to a greater extent. Overaccumulated GB could alleviate
the decrease of photosynthesis caused by all stresses tested. These suggest that GB induces an increase of osmotic adjustments
for drought tolerance, while its improvement of the antioxidative defense system including antioxidative enzymes and antioxidants
may be more important for heat tolerance. 相似文献
Heat waves, which are projected to be more frequent and intense in a warmer climate, could become a serious threat to plants that rely on water surplus availability, such as bryophytes. Here, I take the advantage of the European summer 2003 climate anomaly to assess the impact of an extreme heat wave on peat mosses of the genus Sphagnum, a group of bryophytes forming the bulk of living and dead biomass in peatlands. With this aim, 20 selected bogs in the Italian Alps were checked for Sphagnum survival in the years following the heat wave. Over the study area, the period May–September 2003 was characterized by higher mean monthly air temperature (13.5 °C) and lower mean monthly precipitation (87 mm) compared with normal climatic conditions (11.5 °C and 117 mm, respectively) so that the heat wave coincided with a drought spell. As a consequence of the unusual water stress, I documented an increased mortality of peat mosses forming high hummocks. In particular, at habitat scale, the distribution of desiccated peat mosses was restricted to the hummock face receiving the greatest amount of solar irradiation. However, at regional scale, the present study identified a climatic threshold, simply defined by the ratio of precipitation to temperature (P : T), which triggered an irreversible desiccation of peat mosses when mean monthly P : T dropped below 6.5 (mm : °C) during May–September 2003. The absence of any sign of recovery after 4 years since the drought must be seen as a harbinger of the deleterious effects of extreme heat waves on organisms not adapted to cope with abrupt climate anomaly. 相似文献
Boreal and subarctic peatlands have been extensively studied for their major role in the global carbon balance. However, study
efforts have so far neglected the contribution of these ecosystems to the non-methane biogenic volatile organic compound (BVOC)
emissions, which are important in the atmospheric chemistry and feedbacks on climate change. We aimed at estimating the BVOC
emissions from a subarctic peatland in northern Finland. Furthermore, our aim was to assess how these emissions are affected
by enhanced UV-B radiation, the amount of which has increased especially at high latitudes as a result of stratospheric ozone
depletion. The contribution of BVOC emissions to the total net carbon exchange and correlations between the emission of different
BVOCs and net ecosystem CO2 exchange, CH4 emission, total green leaf area, and abiotic factors were also studied. The UV-B exposure, simulating a 20% depletion of
stratospheric ozone, was started in 2003, and measurements were performed during the growing seasons of 2006 and 2008. The
subarctic peatland proved to be a small source of BVOCs and the dominant moss, Warnstorfia exannulata, emitted a diverse compound spectrum. The water table level exerted a major influence on the BVOC emissions surpassing the
effect of enhanced UV-B. In fact, no overall UV-B effect was established on the BVOC emissions, apart from toluene and 1-octene,
emissions of which were doubled and tripled by enhanced UV-B in 2008, respectively. The contribution of BVOCs to the total
net carbon exchange was below 1%. 相似文献
The effects of the 2003 European heat wave on a freshwater plankton assemblage and its fatty acid (FA) composition were investigated. Composition and FA profiles of four size categories of planktonic organisms collected in 2003 were compared to those of the colder year 2002. 相似文献
Rising temperature and altered precipitation regimes will lead to severe droughts and concomitant extreme events in the future. Forest ecosystems have shown to be especially prone to climate change. In assessing climate change impacts, many studies focus on high altitude or ecological edge populations where a climate signal is supposedly most pronounced. While these studies represent only a fraction of the forest ecosystems throughout Europe, findings on climate sensitivity of lowland core populations remain comparatively underrepresented.By using tree-ring widths of a large region-wide network of European beech and Scots pine populations along a precipitation gradient in northeastern Germany, we identify main climatic drivers and spatio-temporal patterns in climate sensitivity. Further, we analyze the resistance of tree growth towards drought. Detailed data on soil characteristics was used to interpret climate-growth relationships.Beech was found to be most sensitive to summer drought during early summer at dry sites, whereas pine displayed highest sensitivity for winter temperature at wet sites. The resistance to extreme drought was lower for beech. By splitting the observation period (1964–2017) into an early and late period, we found non-stationary climate-growth relationships for both study species with beech showing an increase in drought sensitivity and pine in winter temperature sensitivity.Overall, beech populations seem to be especially endangered by prospective climate changes, whereas climate-growth relationships of pine seem more ambiguous with a possible trade-off between enhanced photosynthetic activity caused by early photosynthesis in late winter and reduced activity due to summer drought. 相似文献
Arctic ecosystems are known to be extremely vulnerable to climate change. As the Intergovernmental Panel on Climate Change scenarios project extreme climate events to increase in frequency and severity, we exposed High Arctic tundra plots during 8 days in summer to a temperature rise of approximately 9°C, induced by infrared irradiation, followed by a recovery period. Increased plant growth rates during the heat wave, increased green cover at the end of the heat wave and higher chlorophyll concentrations of all four predominating species (Salix arctica Pall., Arctagrostis latifolia Griseb., Carex bigelowii Torr. ex Schwein and Polygonum viviparum L.) after the recovery period, indicated stimulation of vegetative growth. Improved plant performance during the heat wave was confirmed at plant level by higher leaf photochemical efficiency (Fv/Fm) and at ecosystem level by increased gross canopy photosynthesis. However, in the aftermath of the temperature extreme, the heated plants were more stressed than the unheated plants, probably because they acclimated to warmer conditions and experienced the return to (low) ambient as stressful. We also calculated the impact of the heat wave on the carbon balance of this tundra ecosystem. Below‐ and aboveground respiration were stimulated by the instantaneous warmer soil and canopy, respectively, outweighing the increased gross photosynthesis. As a result, during the heat wave, the heated plots were a smaller sink compared with their unheated counterparts, whereas afterwards the balance was not affected. If other High Arctic tundra ecosystems react similarly, more frequent extreme temperature events in a future climate may shift this biome towards a source. It is uncertain, however, whether these short‐term effects will hold when C exchange rates acclimate to higher average temperatures. 相似文献
Climatic change is predicted to alter rates of soil respiration and assimilation of carbon by plants. Net loss of carbon from ecosystems would form a positive feedback enhancing anthropogenic global warming. We tested the effect of increased heat input, one of the most certain impacts of global warming, on net ecosystem carbon exchange in a Rocky Mountain montane meadow. Overhead heaters were used to increase the radiative heat flux into plots spanning a moisture and vegetation gradient. We measured net whole-ecosystem CO2 fluxes using a closed-path chamber system, relatively nondisturbing bases, and a simple model to compensate for both slow chamber leaks and the CO2 concentration-dependence of photosynthetic uptake, in 1993 and 1994. In 1994, we also measured soil respiration separately. The heating treatment altered the timing and magnitude of net carbon fluxes into the dry zone of the plots in 1993 (reducing uptake by ≈100 g carbon m–2), but had an undetectable effect on carbon fluxes into the moist zone. During a strong drought year (1994), heating altered the timing, but did not significantly alter the cumulative magnitude, of net carbon uptake in the dry zone. Soil respiration measurements showed that when differences were detected in dry zone carbon fluxes, they were caused by changes in carbon input from photosynthesis, not by temperature-driven changes in carbon output from soil respiration. When differences were detected in dry-zone carbon fluxes, they were caused by changes in carbon input from photosynthesis, not by a temperature-driven changes in carbon output from soil respiration. Regression analysis suggested that the reduction in carbon inputs from plants was due to a combination of two soil moisture effects: a direct physiological response to decreased soil moisture, and a shift in plant community composition from high-productivity species to low-productivity species that are more drought tolerant. These results partially support predictions that warming may cause net carbon losses from some terrestrial ecosystems. They also suggest, however, that changes in soil moisture caused by global warming may be as important in driving ecosystem response as the direct effects of increased soil temperature. 相似文献
Longer and more intense heat and drought stresses will occur in terrestrial ecosystems in the future. Although the effects of individual heat or drought stress on wheat plants have been largely explored, the regulatory effect of nitrogen (N) on winter wheat under heat, drought, and combined stresses and whether N alleviates damage to wheat plants caused by these stresses remain unclear. Therefore, the objective of the present study was to investigate the growth, photosynthesis, antioxidant enzyme and N metabolism-related enzyme activity, cell membrane system, osmoregulatory substance, and yield responses to heat, drought, and combined stresses in wheat plants and to clarify the regulatory effects of N on the growth, physiological and biochemical characteristics, and yield of wheat plants under stress conditions. The results showed that wheat plant exposure to individual heat or drought stress reduced photosynthesis and N metabolism-related enzyme activities and increased antioxidant enzyme activities, electrolyte leakage (EL), and the contents of MDA (malondialdehyde) and O2? (superoxide anion). The above parameters showed typical superposition effects under combined stress. Under individual heat or drought stress, wheat plants treated with a medium (N2) or high (N3) N supply maintained higher photosynthesis and N metabolism-related enzyme activities than did those treated with a low N supply (N1). Enhanced heat and drought tolerance in wheat plants under an appropriate N supply may be attributed to improved antioxidant capacity, as exemplified by increased activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione reductase (GR) and ascorbate peroxidase (APX), and to enhanced osmoregulation capacity, as signified by increased contents of soluble sugar (SS), soluble protein (SP), and proline (Pro). Variable importance in projection (VIP) analysis indicated that efficient SOD, POD, CAT, and GR activities and an increased Pro content had superior potential to alleviate heat, drought, and combined stress stresses in wheat plants, and the improvements in growth and grain yield in wheat plants further confirmed the oxidative stress alleviation and stress tolerance enhancement. However, positive effects of N on wheat growth and grain yield under combined stress were usually observed under a low N supply. These results may facilitate future research on the effects of N fertilizer on the stress resistance of winter wheat.