Non‐linear plant‐plant interactions modulate impact of extreme drought and recovery on a Mediterranean ecosystem

Interaction effects of different stressors, such as extreme drought and plant invasion, can have detrimental effects on ecosystem functioning and recovery after drought. With ongoing climate change and increasing plant invasion, there is an urgent need to predict the short- and long-term interaction impacts of these stressors on ecosystems. We established a combined precipitation exclusion and shrub invasion (Cistus ladanifer) experiment in a Mediterranean cork oak (Quercus suber) ecosystem with four treatments: (1) Q. suber control; (2) Q. suber with rain exclusion; (3) Q. suber invaded by shrubs; and (4) Q. suber with rain exclusion In an average precipitation year, the interaction effects of both stressors were neutral. However, the combination of imposed drought and shrub invasion led to amplifying interaction effects during an extreme drought by strongly reducing tree transpiration. Contrarily, the imposed drought reduced the competitiveness of the shrubs in the following recovery period, which buffered the negative effects of shrub invasion on Q. suber. Our results demonstrate the highly dynamic and nonlinear effects of interacting stressors on ecosystems and urges for further investigations on biotic interactions in a context of climate change pressures

Drought reduces tree growing season lenght but increases nitrogen resorption efficiency in a Mediterranean ecosystem

Mediterranean ecosystems are hotspots for climate change, as the highest impacts are forecasted for the Mediterranean region, mainly by more frequent and intense severe droughts. Plant phenology is a good indicator of species’ responses to climate change. In this study, we compared the spring phenology of cork oak trees (Quercus suber), an evergreen species, over 2 contrasting years, a mild year (2004) and a dry year (2005), which was the most severe drought since records exist. We evaluated the timing of occurrence, duration, and intensity of bud development, budburst, shoot elongation, trunk growth, and leaf senescence (phenophases) and assessed the nitrogen resorption efficiency from senescent to green leaves. The temperature was the main driver of budburst. Nevertheless, water had the main role of constraining all the other phenophases by strongly reducing the growing season length (48 %) and consequently the tree growth. Basal area increment was the most affected growth variable (36 %), although it occurred at a similar rate in the 2 years. Shoot elongation was also reduced (21 %), yet elongation occurred at a higher rate in the dry year compared to the mild year. Leaf senescence during the bulk period was higher in the dry year, in which leaves were shed at the same rate over a longer period. Nitrogen concentrations in green and senescent leaves were affected by drought and nitrogen resorption efficiency increased remarkably (C22 %). Our results highlight the importance of studying different phenological metrics to improve our understanding of the ecosystem’s responses to climate change. The faster dynamics observed in shoot elongation, while all other phenophases developed at the same rate, indicate that leaf area development is privileged in cork oak. Water availability was the main driver of spring growth in this Mediterranean ecosystem; however, growth may be affected by complex interplays between precipitation and temperature, such as higher temperatures during dry winters or heatwaves during spring, that are likely to result in water stress. Longer studies are needed to disentangle those interplays. Finally, a higher nitrogen resorption efficiency in response to drought appears to be an adaptive trait that mitigates the limitation in nitrogen uptake by the roots during drought and contributes to improving tree fitness in the short term but will probably exert a negative feedback on the nitrogen cycle in the long term, which might affect the ecosystem functioning under the forecasted droughtsinfo:eu-repo/semantics/publishedVersio

Litterfall, litter stock and water holding capacity in post-mining forest restoration ecosystems, Eastern Amazon

The objective of this study was to evaluate the litterfall deposition, the decomposition rate (KL) and the water holding capacity (WHC) of litter stored in the soil in two areas degraded by mining submitted to different methods of forest restoration: induction of natural regeneration (NR) and planting seedlings of native forest species (PS) with a forest fragment (FF) used as reference. The litterfall deposition was collected monthly over 12 months in collectors of 0.25 m2. The KL was estimated by the relation between annual litter production and litter stock in the soil surface. WHC was determined in the rainy and dry period. The litterfall deposition was lower in PS with values of 6.61 ± 0.20, 10.75 ± 0.52 and 11.83 ± 0.72 Mg ha-1 yr-1 for PS, NR and FF respectively. The KL and WHC were significantly lower in PS when compared to NR and FF, and WHC decreased significantly from the rainy season to the dry season. The induction of natural regeneration was the more effective restoration method for degraded areas regarding litterfall deposition, decomposition and water retention capacity, surpassing planting native tree species and approaching a native forest fragmentinfo:eu-repo/semantics/publishedVersio

Comparison of static chambers to measure CH4 emissions from soils

The static chamber method (non-flow-through-non-steady-state chambers) is the most common method to measure fluxes of methane (CH4) from soils. Laboratory comparisons to quantify errors resulting from chamber design, operation and flux calculation methods are rare. We tested fifteen chambers against four flux levels (FL) ranging from 200 to 2300 g CH4m−2 h−1. The measurements were conducted on a calibration tank using three quartz sand types with soil porosities of 53% (dry fine sand, S1), 47% (dry coarse sand, S2), and 33% (wetted fine sand, S3). The chambers tested ranged from 0.06 to 1.8 m in height, and 0.02 to 0.195 m3 in volume, 7 of them were equipped with a fan, and 1 with a vent-tube. We applied linear and exponential flux calculation methods to the chamber data and compared these chamber fluxes to the reference fluxes from the calibration tank. The chambers underestimated the reference fluxes by on average 33% by the linear flux calculation method (Rlin), whereas the chamber fluxes calculated by the exponential flux calculation method (Rexp) did not significantly differ from the reference fluxes (p < 0.05). The flux under- or overestimations were chamber specific and independent of flux level. Increasing chamber height, area and volume significantly reduced the flux underestimation (p < 0.05). Also, the use of non-linear flux calculation method significantly improved the flux estimation; however, simultaneously the uncertainty in the fluxes was increased. We provide correction factors, which can be used to correct the under- or overestimation of the fluxes by the chambers in the experiment.Peer reviewe

Estratégias de intervenção na morbimortalidade da fibrilação atrial no pós-operatório de cirurgias cardíacas / Intervention strategies in the morbimortality of atrial fibrillation in the postoperative heart surgery

O presente estudo almejou descrever quais intervenções apresentam melhor desfecho na Fibrilação Atrial Pós-Operatório (FAPO) de cirurgia cardíaca em adultos. Sabe-se que a Fibrilação Atrial (FA) é a manifestação arrítmica mais comum no pós-operatório de cirurgias cardíacas. Acredita-se que seu desenvolvimento esteja atrelado ao fato da manipulação direta ou indireta do miocárdio poder estimular a remodelação das câmaras cardíacas, e quando feita de maneira inapropriada poder resultar em eventos arrítmicos. A fisiopatologia da FA no pós-operatório ainda não é bem descrita, entretanto, considera-se que seja oriunda de uma alteração eletrofisiológica preexistente, associada com a ativação do sistema simpático e liberação de catecolaminas, resposta inflamatória da cirurgia. Embora seja uma condição que pode se resolver espontaneamente, também está relacionada diretamente com o aumento da morbimortalidade dos pacientes. Alguns estudos constataram que determinadas intervenções como o uso profilático de antiarrítmicos, como Amiodarona; e o uso profilático de betabloqueadores, dentre eles destacando-se o Sotalol, mostraram benefícios na profilaxia da FAPO. Mediante o exposto, fica evidente a relevância do tema e o conhecimento dele por parte dos profissionais para que os pacientes possam se beneficiar do não desenvolvimento dessa patologia

After more than a decade of soil moisture deficit, tropical rainforest trees maintain photosynthetic capacity, despite increased leaf respiration

Determining climate change feedbacks from tropical rainforests requires an understanding of how carbon gain through photosynthesis and loss through respiration will be altered. One of the key changes that tropical rainforests may experience under future climate change scenarios is reduced soil moisture availability. In this study we examine if and how both leaf photosynthesis and leaf dark respiration acclimate following more than 12 years of experimental soil moisture deficit, via a through-fall exclusion experiment (TFE) in an eastern Amazonian rainforest. We find that experimentally drought-stressed trees and taxa maintain the same maximum leaf photosynthetic capacity as trees in corresponding control forest, independent of their susceptibility to drought-induced mortality. We hypothesize that photosynthetic capacity is maintained across all treatments and taxa to take advantage of short-lived periods of high moisture availability, when stomatal conductance (gs) and photosynthesis can increase rapidly, potentially compensating for reduced assimilate supply at other times. Average leaf dark respiration (Rd) was elevated in the TFE-treated forest trees relative to the control by 28.2 ± 2.8% (mean ± one standard error). This mean Rd value was dominated by a 48.5 ± 3.6% increase in the Rd of drought-sensitive taxa, and likely reflects the need for additional metabolic support required for stress-related repair, and hydraulic or osmotic maintenance processes. Following soil moisture deficit that is maintained for several years, our data suggest that changes in respiration drive greater shifts in the canopy carbon balance, than changes in photosynthetic capacity.</p

Impacts of experimentally imposed drought on leaf respiration and morphology in an Amazon rain forest

1. The Amazon region may experience increasing moisture limitation over this century. Leaf dark respiration (R) is a key component of the Amazon rain forest carbon (C) cycle, but relatively little is known about its sensitivity to drought. 2. Here, we present measurements of R standardized to 25 C and leaf morphology from different canopy heights over 5 years at a rain forest subject to a large-scale through-fall reduction (TFR) experiment, and nearby, unmodified Control forest, at the Caxiuana˜ reserve in the eastern Amazon. 3. In all five post-treatment measurement campaigns, mean R at 25 C was elevated in the TFR forest compared to the Control forest experiencing normal rainfall. After 5 years of the TFR treatment, R per unit leaf area and mass had increased by 65% and 42%, respectively, relative to pre-treatment means. In contrast, leaf area index (L) in the TFR forest was consistently lower than the Control, falling by 23% compared to the pre-treatment mean, largely because of a decline in specific leaf area (S). 4. The consistent and significant effects of the TFR treatment on R, L and S suggest that severe drought events in the Amazon, of the kind that may occur more frequently in future, could cause a substantial increase in canopy carbon dioxide emissions from this ecosystem to the atmosphere

Shifts in plant respiration and carbon use efficiency at a large-scale drought experiment in the eastern Amazon

The effects of drought on the Amazon rainforest are potentially large but remain poorly understood. Here, carbon (C) cycling after 5 yr of a large-scale through-fall exclusion (TFE) experiment excluding about 50% of incident rainfall from an eastern Amazon rainforest was compared with a nearby control plot. • Principal C stocks and fluxes were intensively measured in 2005. Additional minor components were either quantified in later site measurements or derived from the available literature. • Total ecosystem respiration (Reco) and total plant C expenditure (PCE, the sum of net primary productivity (NPP) and autotrophic respiration (Rauto)), were elevated on the TFE plot relative to the control. The increase in PCE and Reco was mainly caused by a rise in Rauto from foliage and roots. Heterotrophic respiration did not differ substantially between plots. NPP was 2.4 ± 1.4 t C ha)1 yr)1 lower on the TFE than the control. Ecosystem carbon use efficiency, the proportion of PCE invested in NPP, was lower in the TFE plot (0.24 ± 0.04) than in the control (0.32 ± 0.04). • Drought caused by the TFE treatment appeared to drive fundamental shifts in ecosystem C cycling with potentially important consequences for long-term forest C storage

Assimilação do carbono pelas árvores de uma floresta tropical húmida da Amazónia: sazonalidade, variação inter-anual e o impacto de secura induzida

As florestas tropicais húmidas constituem importantes ecossistemas terrestres. Os períodos de seca sazonal afectam o ciclo do carbono e prevê-se que aumentem no futuro, principalmente na Amazónia oriental. Um ensaio de exclusão de chuva foi conduzido numa floresta tropical húmida da Amazónia de modo a estudar as respostas da floresta a uma redução da precipitação (cerca de 50%). Foram realizados estudos fisiológicos ao nível da folha durante cinco estações consecutivas (seca/húmida). Observaram-se variações inter-anuais e sazonais e efeitos da exclusão de chuva na assimilação do carbono e na condutância estomática, que foram mais significativos nas estações secas. Não se observaram alterações nos parâmetros bioquímicos, sugerindo que a principal limitação na assimilação do carbono, em condições de secura induzida, foi estomática. A respiração foliar aumentou em resposta a reduzida disponibilidade hídrica. Os baixos valores na assimilação do carbono sugerem que o fósforo poderá estar a limitar o potencial fotossintético desta floresta; SUMMARY:Tropical rain forests are important terrestrial ecosystems. Seasonal drought affects the global carbon cycle and is predicted to increase in the future, particularly in the eastern Amazon. A ‘through fall exclusion’ experiment (TFE) was conducted to promote drought stress in an Amazonian rain forest plot to investigate the forest responses to 50% through fall exclusion from the soil. Leaf-level measurements were performed in a Control and a TFE plots for five consecutive seasons (dry/wet). Inter-annual and imposed seasonal variations were observed in carbon assimilation and stomatal conductance, which were reduced in the TFE plot particularly in the dry seasons. No alterations were observed in biochemical parameters, suggesting that the main limitation to carbon assimilation under reduced water availability was stomatal. Leaf dark respiration increased in response to reduced water availability. The low values of carbon assimilation indicate that phosphorus may be limiting the photosynthetic potential of this forest