Severe droughts have the potential to reduce forest productivity and trigger tree mortality. Most trees face several drought events during their life and therefore resilience to dry conditions may be ...crucial to long-term survival. We assessed how growth resilience to severe droughts, including its components resistance and recovery, is related to the ability to survive future droughts by using a tree-ring database of surviving and now-dead trees from 118 sites (22 species, >3,500 trees). We found that, across the variety of regions and species sampled, trees that died during water shortages were less resilient to previous non-lethal droughts, relative to coexisting surviving trees of the same species. In angiosperms, drought-related mortality risk is associated with lower resistance (low capacity to reduce impact of the initial drought), while it is related to reduced recovery (low capacity to attain pre-drought growth rates) in gymnosperms. The different resilience strategies in these two taxonomic groups open new avenues to improve our understanding and prediction of drought-induced mortality.
•Understory trees showed climatic sensitivity and were affected by drought.•Tree growth showed releases associated with the openings due to canopy mortality.•Understory tree growth increased over ...time, and an upward growth trend is projected.•Drought affects and releases understory trees, providing both vulnerability and opportunity.
Hotter droughts have become important drivers of change in the structure of forest canopy, and the role of structural loss of overstory trees is gaining attention as an important factor that would trigger changes in understory behavior. The projection of understory individuals, allows us to analyze the potential future of the forests. Through a dendroecological approach, we evaluated growth responses in understory Austrocedrus chilensis trees growing underneath canopy that experienced tree mortality as a consequence of severe droughts occurred in Patagonia Argentina. We analyze the climatic response, tree growth patterns and drought resilience of understory components in three A. chilensis mixed forests. Tree growth was significantly reduced by drought, highlighting the climatic sensitivity of understory individuals; but indirectly, tree growth also showed releases associated with the openings due to canopy mortality. Thus, we found that understory tree growth increased over time. Our results demonstrated that growth performance of understory A. chilensis trees become largely modeled by a combination of the releases associated with changes of the canopy and their ability to withstand adverse weather conditions. We were able to show a clear capacity of understory A. chilensis to cope with drought events by increasing its growth, taking advantage of the disturbance in the upper layers of the canopy, while resisting successive dry years. However, the shadier environment underneath canopy did not buffered drought conditions, and understory A. chilensis trees suffers the effects of droughts. Considering an increase in drought frequency and intensity in climate predictions, with the consequent openings due to overstory tree mortality, understory species behavior will result as a complex interaction among a potential increase in understory vulnerability to more severe droughts, and the opportunity of canopy ascension.
The spectrum of structural response in drought-induced mortality (degree of partial crown mortality) could play a key role in pervasive changes in plant composition, as individual openings could ...reset self-replacement dynamics or trigger shifts in vegetation. Here we capture the community pattern 17 years after a drought episode over a range of canopy responses in Nothofagus dombeyi forests. We applied a widespread demographic approach to address evidence of species shifts vs. self-replacement and to relate partial dieback to understory structure and composition. Assuming that the outcome of growth release of the understory components can be observed 17 years after canopy loss, this study reveals evidence of self-replacement in N. dombeyi forests heavily affected by drought. Alternatively, when the co-dominant species A. chilensis is widely present in the understory and large gaps are opened, a compositional shift may be possible, with a potential change in forest functionality. Individual partial openings do not favor more shrubby communities or a shift toward a new community. Thus, partial crown dieback contributes to self-replacement mechanisms by hampering strong growth release in understory shrubs, as evident in plots with high mortality, and by facilitating the growth of dominant tree species.
Celotno besedilo
Dostopno za:
BF, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
1. The understanding of the impacts of climate anomalies on demographic processes involved in forest dynamics is becoming a major global change research objective, as climate-driven demographic ...changes have the potential to alter ecological processes and change the composition of existing communities. 2. Here, we test whether the effects of climatic variability on Nothofagus dombeyi forest dynamics differ along the W-E precipitation gradient of northern Patagonia, Argentina, due to different controlling factors along the gradient. 3. Using a dendroecological approach, we sampled six N. dombeyi stands along the gradient. Tree death, growth release and sapling birth dates were obtained and used to reconstruct stand mortality, canopy disturbance and establishment patterns in each stand. Discrete extreme climatic events were obtained by applying thresholds to meteorological time series. Bivariate event analysis was performed to examine the temporal relationships between climate events and forest demographic and canopy disturbance patterns. 4. In the xeric region, forest dynamics is driven by drought/heat and humid events. Following drought/heat events we observed standing-dead tree mortality, releases in growth, and tree establishment episodes. Regional synchrony of these events was coincident with droughts registered for northern Patagonia. However, successful establishment was related to wet periods that occurred after drought events, showing the dependence on favourable periods for growth. For wet regions, demographic patterns showed a temporally uniform pattern but with synchronies at the regional and local scales. Canopy openings produced by fallen trees, and consequent release in growth and establishment, were related to both drought and snowy/windy years. The effect of drought in wet region forests was related mainly to the extreme 1998-99 drought in northern Patagonia. 5. Synthesis. Climate in northern Patagonia influences N. dombeyi forest dynamics differentially along a precipitation gradient. In xeric forests, strong but relatively short climatic fluctuations impact forest structure through direct effects on tree demography. In wet forests, climatic-induced mechanical disturbance prevails, driving mortality and subsequent growth and establishment. Considering that recent extreme droughts have the strongest negative impact on N. dombeyi populations at the eastern distributional limits, a change in distribution of this species as a consequence of projected climate change is expected.
Tree mortality is a key driver of forest dynamics and its occurrence is projected to increase in the future due to climate change. Despite recent advances in our understanding of the physiological ...mechanisms leading to death, we still lack robust indicators of mortality risk that could be applied at the individual tree scale. Here, we build on a previous contribution exploring the differences in growth level between trees that died and survived a given mortality event to assess whether changes in temporal autocorrelation, variance, and synchrony in time-series of annual radial growth data can be used as early warning signals of mortality risk. Taking advantage of a unique global ring-width database of 3065 dead trees and 4389 living trees growing together at 198 sites (belonging to 36 gymnosperm and angiosperm species), we analyzed temporal changes in autocorrelation, variance, and synchrony before tree death (diachronic analysis), and also compared these metrics between trees that died and trees that survived a given mortality event (synchronic analysis). Changes in autocorrelation were a poor indicator of mortality risk. However, we found a gradual increase in inter-annual growth variability and a decrease in growth synchrony in the last ∼20 years before mortality of gymnosperms, irrespective of the cause of mortality. These changes could be associated with drought-induced alterations in carbon economy and allocation patterns. In angiosperms, we did not find any consistent changes in any metric. Such lack of any signal might be explained by the relatively high capacity of angiosperms to recover after a stress-induced growth decline. Our analysis provides a robust method for estimating early-warning signals of tree mortality based on annual growth data. In addition to the frequently reported decrease in growth rates, an increase in inter-annual growth variability and a decrease in growth synchrony may be powerful predictors of gymnosperm mortality risk, but not necessarily so for angiosperms.
Key message
Recent variations in climate appear to induce similarities in the responses of
N. dombeyi
growth along its entire distribution, supporting global convergence in tree growth responses to ...climate changes.
Understanding forest responses to climate variations is urgently needed for anticipating changes in forest composition and biodiversity. We use twelve tree-ring chronologies from
Nothofagus dombeyi
, the dominant tree at mesic-to-humid sites, to characterize climate–growth relationships along the west-to-east precipitation gradient in Nahuel Huapi National Park, Argentina. A principal components analysis indicates that a large proportion of common variance in tree growth reflects regional-scale influences of climate. Correlation functions between climate and tree-ring indexes show that the critical factor regulating tree growth is spring–summer water deficit induced by above-average temperature and reduced precipitation during the growing season. At high elevations, however, tree growth appears to be less sensitive to water deficit but comparatively more sensitive to warmer conditions. Temporal trends in climate–tree growth relationships supported the occurrence of a dominant large-scale climatic response, but also identify changes in climate–growth relationships over time, primarily at wet and high-elevation sites. These variations in climate–growth relationships are interpreted as a convergence process to similar patterns in tree growth across the entire precipitation gradient, as wet–cool conditions at high-elevation sites turned to be less frequent due to drier and warmer years during the late twentieth century. Sampling along environmental gradients provides a comprehensive view of the potential range of responses of tree growth to climate which is not recorded using traditional dendrochronological sampling at marginal, more climate-sensitive sites. The recent changes in the relationships between climate and growth highlight the vulnerability of
N. dombeyi
to climate changes across its entire range of distribution in Argentina.
Specific T cell responses against SARS-CoV-2 provided an overview of acquired immunity during the pandemic. Anti-SARS-CoV-2 immunity determines the severity of acute illness, but also might be ...related to the possible persistence of symptoms (long COVID). We retrospectively analyzed ex vivo longitudinal CD8+ T cell responses in 26 COVID-19 patients diagnosed with severe disease, initially (1 month) and long-term (10 months), and in a cohort of 32 vaccinated healthcare workers without previous SARS-CoV-2 infection. We used peptide-human leukocyte antigen (pHLA) dextramers recognizing 26 SARS-CoV-2-derived epitopes of viral and other non-structural proteins. Most patients responded to at least one of the peptides studied, mainly derived from non-structural ORF1ab proteins. After 10 months follow-up, CD8+ T cell responses were maintained at long term and reaction against certain epitopes (A*01:01-ORF1ab1637) was still detected and functional, showing a memory-like phenotype (CD127+ PD-1+). The total number of SARS-CoV-2-specific CD8+ T cells was significantly associated with protection against long COVID in these patients. Compared with vaccination, infected patients showed a less effective immune response to spike protein-derived peptides restricted by HLA. So, the A*01:01-S865 and A*24:02-S1208 dextramers were only recognized in vaccinated individuals. We conclude that initial SARS-CoV-2-specific CD8+ T cell response could be used as a marker to understand the evolution of severe disease and post-acute sequelae after SARS-CoV-2 infection.
Targeting epigenetic mechanisms has emerged as a potential therapeutic approach for the treatment of kidney diseases. Specifically, inhibiting the bromodomain and extra-terminal (BET) domain proteins ...using the small molecule inhibitor JQ1 has shown promise in preclinical models of acute kidney injury (AKI) and chronic kidney disease (CKD). However, its clinical translation faces challenges due to issues with poor pharmacokinetics and side effects. Here, we developed engineered liposomes loaded with JQ1 with the aim of enhancing kidney drug delivery and reducing the required minimum effective dose by leveraging cargo protection. These liposomes efficiently encapsulated JQ1 in both the membrane and core, demonstrating superior therapeutic efficacy compared to freely delivered JQ1 in a mouse model of kidney ischemia-reperfusion injury. JQ1-loaded liposomes (JQ1-NPs) effectively targeted the kidneys and only one administration, one-hour after injury, was enough to decrease the immune cell (neutrophils and monocytes) infiltration to the kidney—an early and pivotal step to prevent damage progression. By inhibiting BRD4, JQ1-NPs suppress the transcription of pro-inflammatory genes, such as cytokines (il-6) and chemokines (ccl2, ccl5). This success not only improved early the kidney function, as evidenced by decreased serum levels of BUN and creatinine in JQ1-NPs-treated mice, along with reduced tissue expression of the damage marker, NGAL, but also halted the production of extracellular matrix proteins (Fsp-1, Fn-1, α-SMA and Col1a1) and the fibrosis development. In summary, this work presents a promising nanotherapeutic strategy for AKI treatment and its progression and provides new insights into renal drug delivery.
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•JQ1-NPs circumvent its poor pharmacokinetics and severe side effects of this inhibitor.•JQ1-NPs reach efficiently the kidney of mice with acute kidney injury (AKI).•Administration of JQ1-NPs avoid the AKI induced by bilateral kidney IRI.•JQ1-NPs significantly reduce the recruitment of neutrophils and monocytes to the damaged kidney.•The renal fibrosis development and CKD progression is halted by JQ1-NPs treatment.
To develop the first evidence-based Pan American League of Associations for Rheumatology (PANLAR) guidelines for the treatment of Takayasu arteritis (TAK).
A panel of vasculitis experts developed a ...series of clinically meaningful questions addressing the treatment of TAK patients in the PICO (population/intervention/comparator/outcome) format. A systematic literature review was performed by a team of methodologists. The evidence quality was assessed according to the GRADE (Grading of Recommendations/Assessment/Development/Evaluation) methodology. The panel of vasculitis experts voted each PICO question and made recommendations, which required ≥70% agreement among the voting members.
Eleven recommendations were developed. Oral glucocorticoids are conditionally recommended for newly diagnosed and relapsing TAK patients. The addition of nontargeted synthetic immunosuppressants (e.g., methotrexate, leflunomide, azathioprine, or mycophenolate mofetil) is recommended for patients with newly diagnosed or relapsing disease that is not organ- or life-threatening. For organ- or life-threatening disease, we conditionally recommend tumor necrosis factor inhibitors (e.g., infliximab or adalimumab) or tocilizumab with consideration for short courses of cyclophosphamide as an alternative in case of restricted access to biologics. For patients relapsing despite nontargeted synthetic immunosuppressants, we conditionally recommend to switch from one nontargeted synthetic immunosuppressant to another or to add tumor necrosis factor inhibitors or tocilizumab. We conditionally recommend low-dose aspirin for patients with involvement of cranial or coronary arteries to prevent ischemic complications. We strongly recommend performing surgical vascular interventions during periods of remission whenever possible.
The first PANLAR treatment guidelines for TAK provide evidence-based guidance for the treatment of TAK patients in Latin American countries.
Sulphated polysaccharides (SP) extracted from seaweeds have antiviral properties and are much less cytotoxic than conventional drugs, but little is known about their mode of action. Combination ...antiviral chemotherapy may offer advantages over single agent therapy, increasing efficiency, potency and delaying the emergence of resistant virus. The paramyxoviridae family includes pathogens causing morbidity and mortality worldwide in humans and animals, such as the Newcastle Disease Virus (NDV) in poultry. This study aims at determining the antiviral activity and mechanism of action in vitro of an ulvan (SP from the green seaweed Ulva clathrata), and of its mixture with a fucoidan (SP from Cladosiphon okamuranus), against La Sota NDV strain. The ulvan antiviral activity was tested using syncytia formation, exhibiting an IC50 of 0.1 μg/mL; ulvan had a better anti cell-cell spread effect than that previously shown for fucoidan, and inhibited cell-cell fusion via a direct effect on the F0 protein, but did not show any virucidal effect. The mixture of ulvan and fucoidan showed a greater anti-spread effect than SPs alone, but ulvan antagonizes the effect of fucoidan on the viral attachment/entry. Both SPs may be promising antivirals against paramyxovirus infection but their mixture has no clear synergistic advantage.
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