European beech dieback after premature leaf senescence during the 2018 drought in northern Switzerland.

During the particularly severe hot summer drought in 2018, widespread premature leaf senescence was observed in several broadleaved tree species in Central Europe, particularly in European beech (Fagus sylvatica L.). For beech, it is yet unknown whether the drought evoked a decline towards tree mortality or whether trees can recover in the longer term. In this study, we monitored crown dieback, tree mortality and secondary drought damage symptoms in 963 initially live beech trees that exhibited either premature or normal leaf senescence in 2018 in three regions in northern Switzerland from 2018 to 2021. We related the observed damage to multiple climate- and stand-related parameters. Cumulative tree mortality continuously increased up to 7.2% and 1.3% in 2021 for trees with premature and normal leaf senescence in 2018, respectively. Mean crown dieback in surviving trees peaked at 29.2% in 2020 and 8.1% in 2019 for trees with premature and normal leaf senescence, respectively. Thereafter, trees showed first signs of recovery. Crown damage was more pronounced and recovery was slower for trees that showed premature leaf senescence in 2018, for trees growing on drier sites, and for larger trees. The presence of bleeding cankers peaked at 24.6% in 2019 and 10.7% in 2020 for trees with premature and normal leaf senescence, respectively. The presence of bark beetle holes peaked at 22.8% and 14.8% in 2021 for trees with premature and normal leaf senescence, respectively. Both secondary damage symptoms occurred more frequently in trees that had higher proportions of crown dieback and/or showed premature senescence in 2018. Our findings demonstrate context-specific differences in beech mortality and recovery reflecting the importance of regional and local climate and soil conditions. Adapting management to increase forest resilience is gaining importance, given the expected further beech decline on dry sites in northern Switzerland.

Long-term soil water limitation and previous tree vigor drive local variability of drought-induced crown dieback in Fagus sylvatica.

Ongoing climate warming is increasing evapotranspiration, a process that reduces plant-available water and aggravates the impact of extreme droughts during the growing season. Such an exceptional hot drought occurred in Central Europe in 2018 and caused widespread defoliation in mid-summer in European beech (Fagus sylvatica L.) forests. Here, we recorded crown damage in 2021 in nine mature even-aged beech-dominated stands in northwestern Switzerland along a crown damage severity gradient (low, medium, high) and analyzed tree-ring widths of 21 mature trees per stand. We aimed at identifying predisposing factors responsible for differences in crown damage across and within stands such as tree growth characteristics (average growth rates and year-to-year variability) and site-level variables (mean canopy height, soil properties). We found that stand-level crown damage severity was strongly related to soil water availability, inferred from tree canopy height and plant available soil water storage capacity (AWC). Trees were shorter in drier stands, had higher year-to-year variability in radial growth, and showed higher growth sensitivity to moisture conditions of previous late summer than trees growing on soils with sufficient AWC, indicating that radial growth in these forests is principally limited by soil water availability. Within-stand variation of post-drought crown damage corresponded to growth rate and tree size (diameter at breast height, DBH), i.e., smaller and slower-growing trees that face more competition, were associated with increased crown damage after the 2018 drought. These findings point to tree vigor before the extreme 2018 drought (long-term relative growth rate) as an important driver of damage severity within and across stands. Our results suggest that European beech is less likely to be able to cope with future climate change-induced extreme droughts on shallow soils with limited water retention capacity.

Soil net nitrogen mineralisation across global grasslands.

Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net Nmin) varies with soil properties and climate. However, because most global-scale assessments of net Nmin are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We find that realised Nmin is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised Nmin, but contributes to explain realised net Nmin when combined with soil and climatic variables. We provide novel insights of global realised soil net Nmin and show that potential soil net Nmin data available in the literature could be parameterised with soil and climate data to better predict realised Nmin.

Temperature and moisture are minor drivers of regional-scale soil organic carbon dynamics.

Storing large amounts of organic carbon, soils are a key but uncertain component of the global carbon cycle, and accordingly, of Earth System Models (ESMs). Soil organic carbon (SOC) dynamics are regulated by a complex interplay of drivers. Climate, generally represented by temperature and moisture, is regarded as one of the fundamental controls. Here, we use 54 forest sites in Switzerland, systematically selected to span near-independent gradients in temperature and moisture, to disentangle the effects of climate, soil properties, and landform on SOC dynamics. We estimated two SOC turnover times, based on bulk soil 14C measurements (τ14C) and on a 6-month laboratory soil incubation (τi). In addition, upon incubation, we measured the 14C signature of the CO2 evolved and quantified the cumulated production of dissolved organic carbon (DOC). Our results demonstrate that τi and τ14C capture the dynamics of contrasting fractions of the SOC continuum. The 14C-based τ14C primarily reflects the dynamics of an older, stabilised pool, whereas the incubation-based τi mainly captures fresh readily available SOC. Mean site temperature did not raise as a critical driver of SOC dynamics, and site moisture was only significant for τi. However, soil pH emerged as a key control of both turnover times. The production of DOC was independent of τi and not driven by climate, but primarily by the content of clay and, secondarily by the slope of the site. At the regional scale, soil physicochemical properties and landform appear to override the effect of climate on SOC dynamics.

Experimental soil warming and cooling alters the partitioning of recent assimilates: evidence from a (14)C-labelling study at the alpine treeline.

Despite concerns about climate change effects on ecosystems functioning, little is known on how plant assimilate partitioning changes with temperature. Particularly, large temperature effects might occur in cold ecosystems where critical processes are at their temperature limit. In this study, we tested temperature effects on carbon (C) assimilate partitioning in a field experiment at the alpine treeline. We warmed and cooled soils of microcosms planted with Pinus mugo or Leucanthemopsis alpina, achieving daily mean soil temperatures (3-10 cm depth) around 5.8, 12.7 and 19.2 °C in cooled, control and warmed soils. We pulse-labelled these systems with (14)CO2 for one photoperiod and traced (14)C over the successive 4 days. Plant net (14)C uptake increased steadily with soil temperature. However, (14)C amounts in fungal hyphae, soil microbial biomass, soil organic matter, and soil respiration showed a non-linear response to temperature. This non-linear pattern was particularly pronounced in P. mugo, with five times higher (14)C activities in cooled compared to control soils, but no difference between warmed and control soil. Autoradiographic analysis of the spatial distribution of (14)C in soils indicated that temperature effects on the vertical label distribution within soils depended on plant species. Our results show that plant growth, in particular root metabolism, is limited by low soil temperature. As a consequence, positive temperature effects on net C uptake may not be paralleled by similar changes in rhizodeposition. This has important implications for predictions of soil C storage, because rhizodeposits and plant biomass vary strongly in their residence times.

Monoamines tissue content analysis reveals restricted and site-specific correlations in brain regions involved in cognition.

The dopamine (DA), noradrenalin (NA) and serotonin (5-HT) monoaminergic systems are deeply involved in cognitive processes via their influence on cortical and subcortical regions. The widespread distribution of these monoaminergic networks is one of the main difficulties in analyzing their functions and interactions. To address this complexity, we assessed whether inter-individual differences in monoamine tissue contents of various brain areas could provide information about their functional relationships. We used a sensitive biochemical approach to map endogenous monoamine tissue content in 20 rat brain areas involved in cognition, including 10 cortical areas and examined correlations within and between the monoaminergic systems. Whereas DA content and its respective metabolite largely varied across brain regions, the NA and 5-HT contents were relatively homogenous. As expected, the tissue content varied among individuals. Our analyses revealed a few specific relationships (10%) between the tissue content of each monoamine in paired brain regions and even between monoamines in paired brain regions. The tissue contents of NA, 5-HT and DA were inter-correlated with a high incidence when looking at a specific brain region. Most correlations found between cortical areas were positive while some cortico-subcortical relationships regarding the DA, NA and 5-HT tissue contents were negative, in particular for DA content. In conclusion, this work provides a useful database of the monoamine tissue content in numerous brain regions. It suggests that the regulation of these neuromodulatory systems is achieved mainly at the terminals, and that each of these systems contributes to the regulation of the other two.

Hyperactivity in the rat is associated with spontaneous low level of n-3 polyunsaturated fatty acids in the frontal cortex.

Inattention, hyperactivity and impulsiveness are the main symptoms of the heterogeneous attention-deficit/hyperactivity disorder (ADHD). It has been suggested that ADHD is associated with an imbalance in polyunsaturated fatty acid (PUFA) composition, with abnormal low levels of the main n-3 PUFA, DHA (22: 6n-3). DHA is highly accumulated in nervous tissue membranes and is implicated in neural function. Animal studies have shown that diet-induced lack of DHA in the brain leads to alterations in cognitive processes, but the relationship between DHA and hyperactivity is unclear. We examined the membrane phospholipid fatty acid profile in frontal cortex of rats characterized for attention, impulsiveness and motricity in various environmental contexts to determine the relationship between brain PUFA composition and the symptoms of ADHD. The amounts of n-3 PUFA in the PE were significantly correlated with nocturnal locomotor activity and the locomotor response to novelty: hyperactive individuals had less n-3 PUFA than hypoactive ones. We conclude that spontaneous hyperactivity in rats is the symptom of ADHD that best predicts the n-3 PUFA content of the frontal cortex. This differential model in rats should help to better understand the role of PUFA in several psychopathologies in which PUFA composition is modified.

Spontaneous individual differences in cognitive performances of young adult rats predict locomotor response to amphetamine.

Inter-individual differences in cognitive capacities of young adult rats have largely been ignored. To explore this variability and its neurobiological bases, the relationships between individual differences in working memory and locomotor responses to novelty and to amphetamine were investigated in SD rats. Groups of good and poor learners were isolated, the latter demonstrating a markedly slower learning of the task compared to performant rats, with more perseverations independently to motivational state. They also presented a much higher increase in amphetamine-induced locomotion that remained significant for more than 1h after the injection. These results provide evidence that variability in cognitive capacities can be used to reveal their neurobiological substrates. They open new perspectives to study a possible cognitive origin of addictive behaviors and to investigate the involvement of these inter-individual differences on those observed later in life.

Impulsivity in youth predicts early age-related cognitive deficits in rats.

Impulsivity is a feature of psychiatric disorders such as mania, addictive behaviors or attention deficit-hyperactivity disorder (ADHD), which has recently been related to complaints of forgetfulness in adults. We investigated whether impulsiveness exerts a long-term influence on cognitive function in rats in a longitudinal study. Impulsivity, assessed by the ability to complete a sequence of presses to obtain food (conditioning box), spatial working memory (8-arm radial maze) assessed with varying degree of attentional load and recognition memory (Y-maze) were tested at different ages. Marked individual differences in impulsivity were observed at youth and remained stable at middle-age despite a general decline in the trait. Working memory scores of impulsive and non-impulsive rats did not differ in youth, whereas by middle-age the impulsive group had impaired working memory and was more sensitive to a higher attentional demand. Thus, impulsiveness in youth predicts cognitive performance in middle-age. These findings may help refine the search for early biological substrates of successful aging and for preventive follow-up of subjects at risk of impaired cognitive aging.

The effect of sympatholytics on uncontrolled hemorrhage.

OBJECTIVE: To assess the possible benefits of sympatholytics on uncontrolled hemorrhage in unanesthetized rats. DESIGN: A randomized laboratory study using rats to test the effects of sympatholytics on uncontrolled hemorrhage. SETTING: Research laboratory. SUBJECTS: Forty female Sprague-Dawley rats, randomly assigned into four groups according to the treatment: untreated (Control); alpha-adrenergic blockade with phenoxybenzamine (Alpha); beta-adrenergic blockade with propranolol (Beta); and a combined alpha- and beta-adrenergic blockade by phenoxybenzamine and propranolol (Alpha/Beta). INTERVENTION: After cannulation under light ether, the rats were allowed to awaken. A baseline blood sample was withdrawn. The uncontrolled hemorrhage was initiated by tail resection and allowed to continue without intervention for the duration of the experiment. After 15 mins, 80 mL/kg isotonic saline fluid was infused at 4.4 mL/min. At 60 mins, another blood sample was drawn; changes in mean arterial pressure, hematocrit, blood loss, and mortality were observed for up to 180 mins. MAIN OUTCOME MEASURE: Survival, mortality, blood loss (amount, prevalence, and rate), and hemodynamic variables (mean arterial pressure, pulse rate, hematocrit). RESULTS: In the Alpha group, there was a reduction in spontaneous blood loss compared with the control group (2.9 vs. 10.6 mL/kg, respectively) and 100% survival. In contrast, the Beta group exhibited an increase in tail blood loss (21.1 mL) and a decreased survival (10%). Despite the enhanced hemorrhage in the Alpha/Beta group (17.0 mL/kg) compared with controls, the survival rate in both of these groups was 60%. In all groups, no significant increase in tail blood loss was observed after 60 mins. CONCLUSIONS: An alpha-adrenergic blockade increased survival in uncontrolled hemorrhage by significantly reducing spontaneous blood loss. Conversely, a beta-adrenergic blockade significantly decreased survival and increased blood loss, whereas a combined blockade significantly increased blood loss without affecting survival.

The effects of varying fluid volume and rate of resuscitation during uncontrolled hemorrhage.

BACKGROUND: The role of rate and volume of infusion in survival from experimental uncontrolled hemorrhage was evaluated. METHODS: Hemorrhage was initiated using tail resection in 43 female rats assigned to the following five groups: nonresuscitated; resuscitated with moderate volume, slower rate; resuscitated with moderate volume, faster rate; resuscitated with high volume, slower rate; and resuscitated with high volume, faster rate. RESULTS: A trend toward improved survival was noted with faster rate of infusion (60 vs. 33.3% survival rate with moderate volume and 28.6 vs. 12.5% with high volume, compared with 16.7% in the nonresuscitated animals). CONCLUSION: Rapid infusion of moderate volume of isotonic saline improved survival in uncontrolled hemorrhage. Extreme volumes, infused rapidly, also resulted in higher survival rates compared with those observed in nonresuscitated rats.

Early isotonic saline resuscitation from uncontrolled hemorrhage in rats.

BACKGROUND: Attempts to modify traditional fluid resuscitation have been based on animal models that evaluate several variables including anesthesia. This study presents the effects of early saline resuscitation from severe uncontrolled hemorrhage unanesthetized rats. METHODS: Sixty-three female Sprague-Dawley rats were equally divided into three groups: group A, nonresuscitated; and groups B and C, resuscitated ;with isotonic saline (40 and 80 mL/kg, respectively). Hemodynamics, blood loss, survival time, and mortality were recorded for 360 minutes after the hemorrhage, which was initiated by 75% resection of the tail. RESULTS: In group C, 80 mL/kg of saline significantly lowered mortality (24% vs 76% and 71% for groups A and B, respectively) with concomitant increases in mean survival time (241 +/- 103 min vs 146 +/- 108 and 175 +/- 92 min for groups A and B, respectively). There were no statistically significant differences in blood loss, hematocrit, or hemodynamic parameters among the groups. CONCLUSIONS: Early and adequate isotonic saline resuscitation of unanesthetized rats improved outcome despite continuing hemorrhage. The significantly lower mortality rate and increased survival time were not a result of transiently improved arterial pressure and did not correlate with blood loss. No significant bleeding increases were noted in the resuscitated groups.

Effects of isotonic saline solution resuscitation on blood coagulation in uncontrolled hemorrhage.

BACKGROUND: It has been suggested that fluid resuscitation before surgical control of hemorrhage may lead to increased bleeding because of the elevated blood pressures and clotting factor dilution. This study was designed to assess the effects of isotonic saline solution resuscitation on blood coagulation during uncontrolled hemorrhage. METHODS: Twenty-four female Sprague-Dawley rats were randomized into four groups with different resuscitation regimens: group A, no resuscitation; group B, 40 ml/kg in 4 minutes; group C, 80 ml/kg in 4 minutes; and group D, 80 ml/kg in 1 minute. Baseline blood samples were collected just before a sharp resection of 75% of the tail to initiate the hemorrhage; 15 minutes later the resuscitation began. Additional blood samples were obtained at 60 minutes after resection. The blood was analyzed for platelets, fibrinogen, prothrombin time, and activated partial thromboplastin time. RESULTS: The largest differences between time 0 and 60 minutes were observed in group D with platelets decreasing 43.36% +/- 7.86%, fibrinogen decreasing 57.10% +/- 16.88%, and prothrombin time increasing from an average 16.5 to 19.2 seconds. These differences was statistiacally significant (p <0.05) with the Student's test. CONCLUSIONS: The results suggested that even though the volume of resuscitation fluid did not appear to affect clotting time when compared with that of nonresuscitated animals, the rate of extremely large volume infusions may play an important role in the cessation of bleeding and consequently in the management of uncontrolled hemorrhagic shock.