Summary
The ‘assimilates inhibition hypothesis’ posits that accumulation of nonstructural carbohydrates (NSCs) in leaves reduces leaf net photosynthetic rate, thus internally regulating ...photosynthesis. Experimental work provides equivocal support mostly under controlled conditions without identifying a particular NSC as involved in the regulation.
We combined 3‐yr in situ leaf gas exchange observations (natural dynamics) in the upper crown of mature Betula pendula simultaneously with measurements of concentrations of sucrose, hexoses (glucose and fructose), and starch, and similar measurements during several one‐day shoot girdling (perturbation dynamics). Leaf water potential and water and nitrogen content were measured to account for their possible contribution to photosynthesis regulation.
Leaf photosynthetic capacity (A/Ci) was temporally negatively correlated with NSC accumulation under both natural and perturbation states. For developed leaves, leaf hexose concentration explained A/Ci variation better than environmental variables (temperature history and daylength); the opposite was observed for developing leaves.
The weaker correlations between NSCs and A/Ci in developing leaves may reflect their strong internal sink strength for carbohydrates. By contrast, the strong decline in photosynthetic capacity with NSCs accumulation in mature leaves, observed most clearly with hexose, and even more tightly with its constituents, provides support for the role of assimilates in regulating photosynthesis under natural conditions.
For decades, the effect of surfactants in the sea-surface microlayer (SML) on gas transfer velocity (k) has been recognized; however, it has not been quantified under natural conditions due to ...missing coherent data on in situ k of carbon dioxide (CO₂) and characterization of the SML. Moreover, a sea-surface phenomenon of wave-dampening, known as slicks, has been observed frequently in the ocean and potentially reduces the transfer of climate-relevant gases between the ocean and atmosphere. Therefore, this study aims to quantify the effect of natural surfactant and slicks on the in situ k of CO₂. A catamaran, Sea Surface Scanner (S³), was deployed to sample the SML and corresponding underlying water, and a drifting buoy with a floating chamber was deployed to measure the in situ k of CO₂. We found a significant 23% reduction of k above surfactant concentrations of 200 μg Teq l−1, which were common in the SML except for the Western Pacific. We conclude that an error of approximately 20% in CO₂ fluxes for the Western Pacific is induced by applying wind-based parametrization not developed in low surfactant regimes. Furthermore, we observed an additional 62% reduction in natural slicks, reducing global CO₂ fluxes by 19% considering known frequency of slick coverage. From our observation, we identified surfactant concentrations with two different end-members which lead to an error in global CO₂ flux estimation if ignored.
OBJECTIVES:PaO2/FIO2 is used commonly for diagnosis of lung injury (acute respiratory distress syndrome and transfusion-related acute lung injury), for assessment of pulmonary disease course and ...therapy, and in pulmonary transplantation for evaluation of donor lungs and clinical outcome. It was developed for convenience, without formal mathematical and graphic assessment to validate its suitability for these purposes.
DESIGN:We examined, mathematically and graphically, the relationship of PaO2/FIO2 to FIO2 at constant normal and several degrees of increased intrapulmonary shunting (QS/QT), assessing the impact of intra- and extrapulmonary factors on the relationship and thus the reliability of PaO2/FIO2.
MEASUREMENTS AND MAIN RESULTS:The relationship of PaO2/FIO2 varies at all shunt fractions but most with QS/QT from 0.1 to 0.3 with FIO2 approximately greater than 0.4. At higher QS/QT, the relationship is more constant and changes less with FIO2 more than 0.4. Hemoglobin concentration and arterial-venous oxygen content difference have large effects that can confound interpretation of PaO2/FIO2. Barometric pressure has a substantial effect; PCO2, base excess, and respiratory quotient have small effects.
CONCLUSIONS:At high QS/QT with FIO2 more than 0.4, the relationship of PaO2/FIO2 to FIO2 is relatively constant. However, with QS/QT of 0.1–0.3, PaO2/FIO2 changes substantially with FIO2. Understanding the important effects of nonpulmonary factors (especially hemoglobin concentration and arterial-venous oxygen content difference) should enhance appropriate clinical use, interpretation of PaO2/FIO2, and interpretation of previous publications and future studies (especially those seeking to assess effects of anemia or transfusion on lung function). The ratio of PaO2/FIO2 is a good tool for some, but not many clinical circumstances, and is insufficiently robust for most research applications.
Premise
Water is the most limiting factor in dryland ecosystems, and plants are adapted to cope with this constraint. Particularly vulnerable are phreatophytic plants from groundwater‐dependent ...ecosystems (GDEs) in regions that have to face water regime alterations due to the impacts of climate and land‐use changes.
Methods
We investigated two aspects related to the water‐use strategy of a keystone species that dominates one of the few terrestrial GDEs in European drylands (Ziziphus lotus): where it obtains water and how it regulates its use. We (1) evaluated plants’ water sources and use patterns using a multiple‐isotope approach (δ2H, δ18O, and Δ13C); (2) assessed the regulation of plant water potential by characterizing the species on an isohydric–anisohydric continuum; and (3) evaluated plants’ response to increasing water stress along a depth‐to‐groundwater (DTGW) gradient by measuring foliar gas exchange and nutrient concentrations.
Results
Ziziphus lotus behaves as a facultative or partial phreatophyte with extreme anisohydric stomatal regulation. However, as DTGW increased, Z. lotus (1) reduced the use of groundwater, (2) reduced total water uptake, and (3) limited transpiration water loss while increasing water‐use efficiency. We also found a physiological threshold at 14 m depth to groundwater, which could indicate maximum rooting length beyond which optimal plant function could not be sustained.
Conclusions
Species such as Z. lotus survive by squandering water in drylands because of a substantial groundwater uptake. However, the identification of DTGW thresholds indicates that drawdowns in groundwater level would jeopardize the functioning of the GDE.
The origin of low frequency cerebral hemodynamic fluctuations (CHF) in the resting state remains unknown. Breath-by breath O.sub.2 -CO.sub.2 exchange ratio (bER) has been reported to correlate with ...the cerebrovascular response to brief breath hold challenge at the frequency range of 0.008-0.03Hz in healthy adults. bER is defined as the ratio of the change in the partial pressure of oxygen (DELTAPO.sub.2) to that of carbon dioxide (DELTAPCO.sub.2) between end inspiration and end expiration. In this study, we aimed to investigate the contribution of respiratory gas exchange (RGE) metrics (bER, DELTAPO.sub.2 and DELTAPCO.sub.2) to low frequency CHF during spontaneous breathing. Twenty-two healthy adults were included. We used transcranial Doppler sonography to evaluate CHF by measuring the changes in cerebral blood flow velocity (DELTACBFv) in bilateral middle cerebral arteries. The regional CHF were mapped with blood oxygenation level dependent (DELTABOLD) signal changes using functional magnetic resonance imaging. Temporal features and frequency characteristics of RGE metrics during spontaneous breathing were examined, and the simultaneous measurements of RGE metrics and CHF (DELTACBFv and DELTABOLD) were studied for their correlation. We found that the time courses of DELTAPO.sub.2 and DELTAPCO.sub.2 were interdependent but not redundant. The oscillations of RGE metrics were coherent with resting state CHF at the frequency range of 0.008-0.03Hz. Both bER and DELTAPO.sub.2 were superior to DELTAPCO.sub.2 in association with CHF while CHF could correlate more strongly with bER than with DELTAPO.sub.2 in some brain regions. Brain regions with the strongest coupling between bER and DELTABOLD overlapped with many areas of default mode network including precuneus and posterior cingulate. Although the physiological mechanisms underlying the strong correlation between bER and CHF are unclear, our findings suggest the contribution of bER to low frequency resting state CHF, providing a novel insight of brain-body interaction via CHF and oscillations of RGE metrics.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Extracorporeal Membrane Oxygenation
In article 2302708, Tong Li, Song Zhao, and co‐workers develop an asymmetric triple‐functional Janus membrane for extracorporeal membrane oxygenation (ECMO) ...system. The PSBMA‐PAD@PDMS membrane exhibits sufficient gas exchange capacity for blood oxygenation under the premise of preventing thrombus formation and plasma leakage, and thus provides novel insights for the advancement of oxygenation membranes.
Radiotherapy is a mainstay for the treatment of lung cancer that can induce pneumonitis or pulmonary fibrosis. The matricellular protein connective tissue growth factor (CTGF) is a central mediator ...of tissue remodeling.
A radiation-induced mouse model of pulmonary fibrosis was used to determine if transient administration of a human antibody to CTGF (FG-3019) started at different times before or after 20 Gy thoracic irradiation reduced acute and chronic radiation toxicity. Mice (25 mice/group; 10 mice/group in a confirmation study) were examined by computed tomography, histology, gene expression changes, and for survival. In vitro experiments were performed to directly study the interaction of CTGF blockade and radiation. All statistical tests were two-sided.
Administration of FG-3019 prevented (∼50%-80%) or reversed (∼50%) lung remodeling, improved lung function, improved mouse health, and rescued mice from lethal irradiation ( P < .01). Importantly, when antibody treatment was initiated at 16 weeks after thoracic irradiation, FG-3019 reversed established lung remodeling and restored lung function. CTGF blockade abrogated M2 polarized macrophage influx, normalized radiation-induced gene expression changes, and reduced myofibroblast abundance and Osteopontin expression.
These results indicate that blocking CTGF attenuates radiation-induced pulmonary remodeling and can reverse the process after initiation. CTGF has a central role in radiation-induced fibrogenesis, and FG-3019 may benefit patients with radiation-induced pulmonary fibrosis or patients with other forms or origin of chronic fibrotic diseases.
In addition to buffering plants from water stress during severe droughts, plant water storage (PWS) alters many features of the spatio-temporal dynamics of water movement in the soil–plant system. ...How PWS impacts water dynamics and drought resilience is explored using a multi-layer porous media model.
The model numerically resolves soil–plant hydrodynamics by coupling them to leaf-level gas exchange and soil–root interfacial layers. Novel features of the model are the considerations of a coordinated relationship between stomatal aperture variation and whole-system hydraulics and of the effects of PWS and nocturnal transpiration (F
e;night) on hydraulic redistribution (HR) in the soil.
The model results suggest that daytime PWS usage and F
e;night generate a residual water potential gradient (Δψp;night) along the plant vascular system overnight. This Δψp;night represents a non-negligible competing sink strength that diminishes the significance of HR.
Considering the co-occurrence of PWS usage and HR during a single extended dry-down, a wide range of plant attributes and environmental/soil conditions selected to enhance or suppress plant drought resilience is discussed. When compared with HR, model calculations suggest that increased root water influx into plant conducting-tissues overnight maintains a more favorable water status at the leaf, thereby delaying the onset of drought stress.
New Findings
What is the central question of this study?
Breath‐by‐breath gas exchange analysis during treadmill exercise can be disturbed by different breathing patterns depending on cadence, and ...the flow sensor might be subjected to variable mechanical stress. It is still unclear whether the outcomes of the gas exchange algorithms can be affected by running at different speeds.
What is the main finding and its importance?
Practically, the three investigated breath‐by‐breath algorithms (‘Wessel’, ‘expiration‐only’ and ‘independent breath’) provided similar average gas exchange values for steady‐state conditions. The ‘independent breath’ algorithm showed the lowest breath‐by‐breath fluctuations in the gas exchange data compared with the other investigated algorithms, both at steady state and during incremental exercise.
Recently, a new breath‐by‐breath gas exchange calculation algorithm (called ‘independent breath’) was proposed. In the present work, we aimed to compare the breath‐by‐breath O2 uptake (V̇O2) values assessed in healthy subjects undergoing a running protocol, as calculated applying the ‘independent breath’ algorithm or two other commonly used algorithms. The traces of respiratory flow, O2 and CO2 fractions, used by the calculation algorithms, were acquired at the mouth on 17 volunteers at rest, during running on a treadmill at 6.5 and 9.5 km h−1, and thereafter up to volitional fatigue. Within‐subject averages and standard deviations of breath‐by‐breath V̇O2 were calculated for steady‐state conditions; the V̇O2 data of the incremental phase were analysed by means of linear regression, and their root mean square was assumed to be an index of the breath‐by‐breath fluctuations. The average values obtained with the different algorithms were significantly different (P < 0.001); nevertheless, from a practical point of view the difference could be considered ‘small’ in all the investigated conditions (effect size <0.3). The standard deviations were significantly lower for the ‘independent breath’ algorithm (post hoc contrasts, P < 0.001), and the slopes of the relationships with the corresponding data yielded by the other algorithms were <0.70. The root mean squares of the linear regressions calculated for the incremental phase were also significantly lower for the ‘independent breath’ algorithm, and the slopes of the regression lines with the corresponding values obtained with the other algorithms were <0.84. In conclusion, the ‘independent breath’ algorithm yielded the least breath‐by‐breath O2 uptake fluctuation, both during steady‐state exercise and during incremental running.
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