Respiratory Ratio Research Articles

Evaluating variation of respiration:photosynthesis ratio in sagebrush species: Implications for carbon flux modeling

AbstractPlant respiration and photosynthesis are the two main processes influencing carbon (C) flux balance at leaf‐to‐ecosystem scales. The ratio of respiration to photosynthesis (R:A) or carbon use efficiency (CUE) is considered an important trait for determining global carbon storage in the near future. One school of thought assumes that R:A is constant in terrestrial productivity models, irrespective of biomass, climate, and species. Others believe it is variable, although within a limited range. Semiarid systems dominated by woody vegetation, such as sagebrush steppe, have been recognized as potentially important C sinks on regional to global scales in the context of future climate scenarios. Therefore, there is a critical need to study R:A over different organizational scales (i.e., at the leaf, whole plant, and ecosystem scales) to use this approach for future C flux predictions under climate change scenarios. The objective of this study was to compare leaf‐, shrub‐, and ecosystem‐scale R:A among three sagebrush (Artemisia spp.) communities, and to determine how R:A varies throughout the growing season (i.e., early, mid‐, and late summer) among these communities. We measured photosynthesis and respiration monthly in three sagebrush communities spanning a 685‐m elevation gradient at the Reynolds Creek Experimental Watershed and Critical Zone Observatory in southwestern Idaho. Consistent with our expectations, we found large seasonal variations in R and A at all scales, but with differences in A among the three sagebrush communities significant only at the leaf scale. The R:A ratio was not significantly different among the three species at all organizational scales. However, the R:A ratio did vary among months at the leaf level and there was a statistical interaction between species and month at both leaf and shrub levels. Our study indicates that the R:A ratio is generally conservative, although not tightly constrained (range: 0.12–0.77) among three sagebrush species. Therefore, approaches that assume conservative R:A ratios in terrestrial productivity models need to be considered carefully to evaluate the impact of projected climatic changes on future C cycling in shrub‐dominated rangeland ecosystems.

Impact of seawater warming and nutrient deprivation on the physiology and energy metabolism of corals

Seawater temperature and the availability of dissolved inorganic nutrients (DINut) have a major influence on the stability of the symbiosis between corals and Symbiodiniaceae. In particular, seawater warming or DINut depletion can lead to coral bleaching, the loss of Symbiodiniaceae from coral tissue. However, the combined effects of heat stress and DINut deficiency on the coral energy metabolism are still understudied. Here, we investigated the physiological and energetic responses of the octocoral Heteroxenia fuscescens and the hexacoral Stylophora pistillata exposed to two levels of inorganic nutrients in seawater (control, depleted) and two temperatures, 25°C (control) and 30°C (high temperature), in a crossed factorial design. Our results show that thermal and DINut stress both decreased the photosynthesis to respiration ratio of the two species and induced bleaching in H. fuscescens. While nutrient deprivation had little effect on the corals’ energy metabolism, heat stress led to higher concentrations of macromolecules such as carbohydrates and lipids, as well as anaerobic metabolism, and decreased ATP production in H. fuscescens. Given that the intensity and frequency of marine heatwaves will significantly increase in the future, there is an urgent need to investigate the processes by which corals can overcome starvation.

Responses of greenhouse gas emissions to increased precipitation events in different ecosystems: A meta-analysis

Changes in precipitation patterns induced by climate change exacerbate the phenomenon by stimulating carbon (C) and nitrogen (N) processes in terrestrial ecosystems, leading to increased emissions of soil greenhouse gases (GHGs). However, the response of soil GHG fluxes across various global ecosystems under conditions of increased precipitation (IP) and extreme precipitation (EP) remains unclear. This study conducted a meta-analysis to examine the effects of IP and EP on soil GHG fluxes, synthesizing data from 49 published studies worldwide, and explored potential influencing factors. The results indicated that (1) IP significantly elevated CO2 emissions by 10.2 % and N2O emissions by 61.7 %, and did not impact CH4 emissions. EP treatment significantly increased N2O emissions by 61.8 %, CO2 emissions by 13.3 %, and CH4 emissions by 3.2 %. (2) Under IP treatment, significant differences in soil GHGs among various ecosystems were observed (P < 0.01). Among the three analyzed ecosystems (grassland, forest, and farmland), the response ratios of CO2 (30.4 %), N2O (61.8 %), and soil respiration (37.5 %, excluding plant respiration) were highest in the forest ecosystem and lowest in the grassland. (3) The response of CO2 flux to precipitation was most affected by soil dissolved organic C (P < 0.001) and microbial biomass C (P < 0.001). The key factor affecting the change in N2O flux was NH4+-N (P < 0.001). These findings provide a new perspective for understanding the effects of IP on soil C and N cycles in the context of global climate change.

Effects of carbon and nitrogen availability on soil microbial respiration and its metabolic response in subtropical plantations.

We examined the metabolic response of microbial respiration to glucose addition with the topsoil (0-10 cm) from five plantation types, including Quercus glauca, Castanopsis kawakamii, Pinus massoniana, Phoebe bournei, and Cinnamomum camphora plantations, in the Sanming Forest Ecosystem National Field Observation and Research Station in Fujian Province. The results showed that glucose addition significantly increased microbial respiration by 82.4%-349.5%, with significant difference among tree species. In the control, microbial respiration significantly correlated with microbial biomass carbon, soil organic carbon, and the fungi/bacteria ratio, indicating that microbial metabolism was regulated by soil organic carbon content and was associated with microbial biomass and community structure in the absence of labile carbon supply. In the glucose addition treatment, microbial respiration positively correlated with soil total nitrogen, dissolved organic nitrogen, and mineral nitrogen, indicating that microbial metabolism was mainly constrained by soil nitrogen content and its availability in the presence of adequate labile carbon supply. The metabolic response of microbial respiration, as indicated by the ratio of microbial respiration in the glucose addition treatment to that in the control, was primarily affected by soil carbon/nitrogen ratio, with a decrease in the ratio leading to an increase in the microbial metabolic response. Additionally, soil pH played an important role in mediating microbial metabolic response. The effect of the content and availability of soil carbon and nitrogen on microbial respiration depended on whether microbes were carbon-limited. Soil carbon content media-ted microbial respiration when microbes were carbon-limited, whereas soil nitrogen content and availability mediated microbial respiration after the alleviation of microbial carbon limitation.

Modeling food web and fisheries dynamics in Lake Baringo, Kenya

AbstractLakes are important in supporting ecosystem services and livelihoods. However, their food webs and ecological functioning are continuously threatened by anthropogenic influences. Food web models have been widely used in studying trophodynamics, fisheries impacts, and ecological functioning of temperate lakes, but less often in Afrotropical lake systems. We used Ecopath mass‐balanced trophic models annually in 1999, 2010, and 2020 to assess trends in ecosystem function, and the impact of fisheries on the Lake Baringo Ecosystem, a shallow freshwater lake in Kenya. Pre‐balance (PREBAL) and Pedigree analyses supplemented Ecopath models. Model input data were from field sampling, published and gray literature. Food web trophic models indicated a bottom‐up grazer and detrital food chains in all 3 years. Odum's ecosystem development indicators (total productivity to total biomass and total respiration ratios; TPP/TB and TPP/TR) showed that the lake was in a low to intermediate developmental stage, with room for bio‐manipulation, and a highly reduced mean transfer efficiency (TE) (6.4%–0.49%) indicated low trophic transfer of internal production. System omnivory (SOI) and connectance (CI) indices that varied among years indicated temporal variation in food web complexity. Indices of system resilience (overhead and ascendency) indicated an increasing potential for the lake to recover from perturbations. The mean trophic level of the catch (MTLc) increased from 1999 to 2010 and decreased in 2020, by fishing down the food chain as fishing pressure increased. Oreochromis niloticus, an endemic cichlid, was the keystone species (KSi &gt;0) controlling community structure, while the lungfish Protopterus aethiopicus, the top predator in the lake, was not a keystone species (KSi &lt;0). We recommend an integrated approach to lake management that incorporates watershed regulations, regulates fishing effort on the keystone species (O. niloticus), and monitors water quality for sustainable management of the Lake Baringo ecosystem.

Minor Effects of Canopy and Understory Nitrogen Addition on Soil Organic Carbon Turnover Time in Moso Bamboo Forests

Increased atmospheric nitrogen (N) deposition has greatly influenced soil organic carbon (SOC) dynamics. Currently, the response of SOC to atmospheric N deposition is generally detected through understory N addition, while canopy processes have been largely ignored. In the present study, canopy N addition (CN) and understory N addition (UN, 50 and 100 kg N ha−1 year−1) were performed in a Moso bamboo forest to compare whether CN and UN addition have consistent effects on SOC and SOC turnover times (τsoil: defined as the ratio of SOC stock and soil heterotrophic respiration) with a local NHx:NOy ratio of 2.08:1. The experimental results showed that after five years, the SOC content of canopy water addition without N addition (CN0) was 82.9 g C kg−1, while it was 79.3, 70.7, 79.5 and 74.5 g C kg−1 for CN50, CN100, UN50 and UN100, respectively, and no significant difference was found for the SOC content between CN and UN. Five-year N addition did not significantly change τsoil, which was 34.5 ± 7.4 (mean ± standard error) for CN0, and it was 24.9 ± 4.8, 22.4 ± 4.9, 30.5 ± 4.0 and 22.1 ± 6.5 years for CN0, CN50, CN100, UN50 and UN100, respectively. Partial least squares structural equation modeling explained 93% of the variance in τsoil, and the results showed that soil enzyme activity was the most important positive factor controlling τsoil. These findings contradicted the previous assumption that UN may overestimate the impacts of N deposition on SOC. Our findings were mainly related to the high N deposition background in the study area, the special forest type of Moso bamboo and the short duration of the experiment. Therefore, our study had significant implications for modeling SOC dynamics to N deposition for high N deposition areas.

Effect of Secondary Paper Sludge on Physiological Traits of Lactuca sativa L. under Heavy-Metal Stress.

To eliminate the negative effect of soil contamination with heavy metals on plant growth and crop yield, different methods and techniques are the subject of discussion and study. In this study, we aimed to evaluate the effect of secondary pulp and paper-mill sludge application to soil on the response of the main physiological processes such as the growth, photosynthesis, and respiration of lettuce (Lactuca sativa L.) plants to soil contamination with Pb. For the pot experiment, Pb was added to sandy loam soil at concentrations of 0, 50, and 250 mg Pb(NO3)2 per kg of the soil, and secondary sludge was added to a 0, 20, or 40% sludge solution during each plant watering. The Pb-mediated change in plant biomass allocation, decrease in the photosynthetic rate, increase in leaf respiration rate, and the degree of light inhibition of respiration were closely associated with increases in both root and shoot Pb content. For the Pb-free soil condition, secondary sludge application contributed to the allocation of plant biomass towards a greater accumulation in the shoots than in the roots. Although stomatal opening was not affected by either Pb or sludge, sludge application increased photosynthetic CO2 assimilation regardless of soil Pb content, which was associated with an increase in the electron-transport rate and carboxylase activity of Rubisco. Soil contamination with Pb significantly increased the ratio of respiration to photosynthesis, reflecting a shift in the carbon balance toward carbon losses in the leaves, but sludge application modified the coupling between the processes with a decrease in the proportion of respiratory carbon losses. The sludge-mediated recovery of the physiological processes of L. sativa reflected an increase in plant tolerance to soil contamination with heavy metals, the formation of which is associated with plant and soil adjustments initiated by secondary sludge application.

Regulatory T cells and bioenergetics of peripheral blood mononuclear cells linked to pediatric obesity.

Obesity-associated inflammation drives the development of insulin resistance and type 2 diabetes. We sought to identify associations of circulating regulatory T cells (Treg) with the degree of obesity (eg, body mass index Z-score [BMIz]), insulin resistance (homeostatic model of insulin resistance [HOMA-IR]), and glycemic control (HbA1c) in children and adolescents. We further sought to examine associations among bioenergetics of peripheral blood mononuclear cells (PBMCs) and CD4 T cells and BMIz, HOMA-IR, and HbA1c. A total of 65 children and adolescents between the ages 5 and 17 years were studied. HbA1c and fasting levels of plasma glucose and insulin were measured. We quantified circulating Tregs (CD3+CD4+CD25+CD127-FoxP3+) by flow cytometry, and measured mitochondrial respiration (oxygen consumption rate [OCR]) and glycolysis (extracellular acidification rate [ECAR]) in PBMCs and isolated CD4 T cells by Seahorse extracellular flux analysis. Tregs (% CD4) are negatively associated with BMIz but positively associated with HOMA-IR. In PBMCs, OCR/ECAR (a ratio of mitochondrial respiration to glycolysis) is positively associated with BMIz but negatively associated with HbA1c. In children, Tregs decrease as body mass index increases; however, the metabolic stress and inflammation associated with insulin resistance may induce a compensatory increase in Tregs. The degree of obesity is also associated with a shift away from glycolysis in PBMCs but as HbA1c declines, metabolism shifts back toward glycolysis. Comprehensive metabolic assessment of the immune system is needed to better understand the implications immune cell metabolic alterations in the progression from a healthy insulin-sensitive state toward glucose intolerance in children. This observational study was registered at the ClinicalTrials.gov (NCT03960333, https://clinicaltrials.gov/study/NCT03960333?term=NCT03960333&rank=1).

Climate change is poised to alter mountain stream ecosystem processes via organismal phenological shifts

Climate change is affecting the phenology of organisms and ecosystem processes across a wide range of environments. However, the links between organismal and ecosystem process change in complex communities remain uncertain. In snow-dominated watersheds, snowmelt in the spring and early summer, followed by a long low-flow period, characterizes the natural flow regime of streams and rivers. Here, we examined how earlier snowmelt will alter the phenology of mountain stream organisms and ecosystem processes via an outdoor mesocosm experiment in stream channels in the Eastern Sierra Nevada, California. The low-flow treatment, simulating a 3- to 6-wk earlier return to summer baseflow conditions projected under climate change scenarios in the region, increased water temperature and reduced biofilm production to respiration ratios by 32%. Additionally, most of the invertebrate species explaining community change (56% and 67% of the benthic and emergent taxa, respectively), changed in phenology as a consequence of the low-flow treatment. Further, emergent flux pulses of the dominant insect group (Chironomidae) almost doubled in magnitude, benefitting a generalist riparian predator. Changes in both invertebrate community structure (composition) and functioning (production) were mostly fine-scale, and response diversity at the community level stabilized seasonally aggregated responses. Our study illustrates how climate change in vulnerable mountain streams at the rain-to-snow transition is poised to alter the dynamics of stream food webs via fine-scale changes in phenology-leading to novel predator-prey "matches" or "mismatches" even when community structure and ecosystem processes appear stable at the annual scale.

Changes in soil oxidase activity induced by microbial life history strategies mediate the soil heterotrophic respiration response to drought and nitrogen enrichment.

Drought and nitrogen deposition are two major climate challenges, which can change the soil microbial community composition and ecological strategy and affect soil heterotrophic respiration (Rh). However, the combined effects of microbial community composition, microbial life strategies, and extracellular enzymes on the dynamics of Rh under drought and nitrogen deposition conditions remain unclear. Here, we experimented with an alpine swamp meadow to simulate drought (50% reduction in precipitation) and multilevel addition of nitrogen to determine the interactive effects of microbial community composition, microbial life strategy, and extracellular enzymes on Rh. The results showed that drought significantly reduced the seasonal mean Rh by 40.07%, and increased the Rh to soil respiration ratio by 22.04%. Drought significantly altered microbial community composition. The ratio of K- to r-selected bacteria (BK:r) and fungi (FK:r) increased by 20 and 91.43%, respectively. Drought increased hydrolase activities but decreased oxidase activities. However, adding N had no significant effect on microbial community composition, BK:r, FK:r, extracellular enzymes, or Rh. A structural equation model showed that the effects of drought and adding nitrogen via microbial community composition, microbial life strategy, and extracellular enzymes explained 84% of the variation in Rh. Oxidase activities decreased with BK:r, but increased with FK:r. Our findings show that drought decreased Rh primarily by inhibiting oxidase activities, which is induced by bacterial shifts from the r-strategy to the K-strategy. Our results highlight that the indirect regulation of drought on the carbon cycle through the dynamic of bacterial and fungal life history strategy should be considered for a better understanding of how terrestrial ecosystems respond to future climate change.

Microbial mediated carbon and nitrogen cycling in the spatially heterogeneous vadose zone: A modeling study

AbstractSpatially distributed properties of the subsurface result in varying water saturation and preferential flow paths, which lead to heterogeneous solute transport patterns and heterogeneous microbial environments. This, in turn, influences the distribution of nutrients and energy gradients, microbial biomass, and activity thereof. By their very nature, current field sampling techniques do not resolve subsampling scale heterogeneities in microbial biomass and activity, resulting in inaccurate estimates of microbially mediated carbon and nitrogen turnover in the heterogeneous subsurface. Thus, in this study, we undertook a numerical modeling approach to study the impact of spatial heterogeneity on microbially mediated carbon and nitrogen turnover in the vadose zone. We adapted an established biogeochemical process network that captures a variety of respiration pathways, carbon decomposition strategies, and microbial life processes to simulate microbially mediated carbon and nitrogen turnover in variably saturated spatially heterogeneous settings, using an established numerical tool (OGS#BRNS). The fractionation of microbial communities into active and inactive states, as well as immobile and mobile states followed could be linked to the bulk average saturation. Lastly, we identified three reactive systems, distinguished by the rate ratio of aerobic respiration and transfer of oxygen from the air to the water phase, to evaluate the impact of spatial heterogeneity on carbon and nitrogen removal in subsurface heterogeneous domains. Specifically, when this ratio is approximately 1, there is no impact on carbon removal, while when this ratio is very high, then carbon removal decreases as the domain tends to be oxygen limited.

Landscape regulation of microbial use of terrestrial carbon in boreal streams

Microbes decomposing leaf litter in aquatic ecosystems are exposed to two major sources of carbon (C), namely, particulate organic C (POC) and dissolved organic C (DOC). The use of DOC relative to POC during litter decomposition likely depends on the availability of DOC, which in turn is regulated by the characteristics of the surrounding landscape, although this extrinsic indirect control of DOC use remains largely unexplored. We have investigated how variations in stream physical and chemical characteristics, distribution of major landscape elements (i.e., forest, mires, and lakes), and riparian vegetation community composition (i.e., relative cover of deciduous vs. coniferous tree species) influence DOC use by leaf-associated microbes (LAM). Specifically, in a boreal stream network of ten first- to third-order streams, we related in-stream characteristics, landscape elements, and riparian vegetation community composition to DOC/POC respiration ratios (i.e., the amount of CO2 produced by LAM respiration of DOC + POC divided by the amount of leaf C mass lost through decomposition). The results showed that DOC/POC respiration ratios were > 1 in most of the study sites, indicating that LAM use a substantial amount of DOC during leaf litter decomposition. This microbial reliance on DOC varied with in-stream DOC and nutrient concentrations, proportional mire and forest cover, and riparian vegetation community composition. In particular, high mire and coniferous cover increased DOC use by LAM. As such, landscape configuration and how it is modified by land use and climate change must be considered in order to understand microbial turnover of terrestrial C in boreal streams.

Ecosystem Characteristics and Trophic Model of the Artificial Reef Ecosystem in the Sea of Oman, Sultanate of Oman

This study aimed to understand the structure and function of the artificial reef ecosystem of the Sea of Oman and its stability and maturity. For this study, the trophic model of the Sea of Oman’s artificial reef ecosystem was described using the Ecopath with Ecosim (EwE) ecosystem modeling software (Version 6.6.7). The essential characteristics of the aquatic system were identified using a total of 38 fish species/functional groups, spread across an area of 140 km2 of artificial reef farm. The mean trophic level of the artificial reef ecosystem of the Sea of Oman was 3.039. Sharks were the keystone species of the studied ecosystem. Heniochus acuminatus and Chaetodon gardneri were the species with the highest niche overlap, whereas Acanthurus sohal and other crustaceans, and Terapon puta and Saurida undosquamis were the species with the lowest niche overlap. It was found that the ratio of total primary production to total respiration of the ecosystem studied was more than one, indicating that the system produces more energy than it uses to respire, and the ecosystem of the Sea of Oman can be regarded as a developing system because of its low degree of stability and maturity. The omnivory index was 0.260, the connectance index was 0.159, the total biomass to total throughput ratio was 0.006, Finn’s cycling index was 5.41, the total primary production to total biomass ratio was 64.895, and the total primary production to total respiration ratio was 4.424. The results indicate that the artificial reef ecosystem in the Sea of Oman can be categorized as immature (in the early developmental stage). Further study is needed to improve the input data and track ecosystem health, as well as exploring other management strategies. Based on the outcomes of the study, it is suggested that environmental management of the reef ecosystem, along with the fish catch data, should be taken into consideration for future research.

Physiological Responses of Cucumber Plants to Sodium Lignosulfonate Application to Sandy Loam Soil

The use of lignosulfonates (LS) to improve soil fertility is currently under study and discussion. The effect of sodium LS application in the sandy loam soil on the accumulation of biomass, photosynthesis, respiration and their coupling in cucumber plants was studied. The LS rate of 10–25 g/kg did not have a significant effect on the studied parameters of the physiological state of plants. However, at a high LS content (50–100 g/kg), the plant growth rate and activity of the photosynthetic apparatus decreased, and the respiration rate increased, which caused the increase in the ratio of respiration to photosynthesis. The negative effect of high concentrations of LS on the physiological state of cucumber plants and their cold resistance is presumably associated with sodium salinization of the soil.

Variation in autotrophic and heterotrophic sponge abundance in a shallow water seagrass system

AbstractSponges are well known to feed heterotrophically through suspension feeding, but their relationships with photosynthetic symbionts mean they also have the potential to utilise or release photosynthetically derived carbon. Here, we determined the nutritional mode of sponges that occurred seagrass meadows at two sites in the Wakatobi National Park (Hoga‐1 and 2), Indonesia from the near‐reef flat (d = 1.9 m), middle‐shore (d = 1.2 m) and high‐shore (d = 0.5 m) zones to assess the role they might play in nutrient fluxes. We measured photosynthetic pigment concentrations and in situ net primary production to dark respiration (P:R) ratios of eight sponge species representing 75%–100% of the total sponge assemblage biomass at the two sites. We found that six of eight sponge species were autotrophic, based on their instantaneous P:R ratios and estimated daily oxygen production/consumption. The proportion of autotrophic sponge biomass in the high and middle shore of the seagrass meadows ranged between 40% and 70%, and accounted for 98% and 81% of the biomass in the near‐flat zones. Our findings that many seagrass sponges are autotrophic challenges the general view that sponges are consumers of organic carbon from the water column.

Microbial P limitation in tropical forest soils could be overestimated: Insight from a sorption experiment and a meta-analysis

The prevailing paradigm for soil microbial activity in tropical forests is that microbial activity is limited by phosphorus (P) availability, and thus exogenous P addition stimulates organic matter decomposition. This idea has been testified by studies demonstrating that experimental P addition accelerates soil respiration. Contrary to this conventional view, we hypothesize that the increased rates of soil microbial respiration could be due to the release of organic material from the surface of soil minerals when P is added, because P competes with organic C for binding sites in soil particles. Here we performed a sorption experiment in a tropical evergreen forest in southern China, where P addition had previously been reported to stimulate soil respiration but suppressed leaf litter decomposition. P addition to soils significantly increased dissolved organic carbon (DOC) content, which was extracted immediately after P addition and under a cold temperature where microbial activity was suppressed. This result can explain why P addition stimulated soil respiration but not litter decomposition in our study site. Namely, P addition abiotically elevated microbially-available C through the release of organic matter from the soil mineral surface. We also conducted a meta-analysis using data obtained in forest ecosystems, demonstrating that previous studies have consistently reported that P addition led to higher response ratios of soil microbial respiration than litter decomposition. Our findings suggest that the prevailing paradigm (i.e., soil microbial activity in tropical forests is limited by P availability) might require re-evaluation.

Interactions between cage fish farms and fishing in Brazilian semiarid reservoirs: An ecosystemic approach

Knowledge of the trophic web structure and control mechanisms in reservoirs of the semiarid tropical regions can enable a better understanding and proper management of these aquatic environments. This paper used an ecosystem approach to two Brazilian semiarid reservoirs and evaluated the interactions between cage fish farms and fishing activity. The trophic web models of the reservoirs were elaborated using Ecopath with Ecosim (EwE) software. Over two years, the data were locally obtained, including information on fish farm, fishing activity, and functional groups (phytoplankton, aquatic macrophytes, benthic fauna, and fish). The modeling results indicated that most of the system energy is derived from the detritivory chain, which was more critical than the herbivory chain, with a Detritivory/Herbivory ratio of approximately 3.0 in both reservoirs. The key group of the ecosystem was the piscivorous fish, with Hoplias malabaricus and Cichla monoculus as the species with the greatest trophic impact, especially on fish at the intermediate trophic level. The benthic community and detritus had positive impacts on almost all other components of the trophic web. The reservoirs were considered immature, with low nutrient cycling and a high Total Primary Production/Total Respiration ratio. Systemic stability was deemed low for both reservoirs, which was indicated by the low overhead values. In both reservoirs, the presence of a well-developed detritus chain supports the trophic web and represents a source of stored energy in aquatic systems. The simulations demonstrated a positive relationship between fish farming and fishing activity, with all communities benefiting from the nutrient input from cage fish farms, with a biomass increase of aquatic organisms, either by direct or indirect effects.

The Effect of Device-Controlled Breathing on the Pulse Arrival Time and the Heart Rate Asymmetry Parameters in Healthy Volunteers

Background: The development of wearables has facilitated the monitoring of biomedical parameters in everyday life. One of the most common sensors of these gadgets is the photoplethysmograph (PPG); hence, the proper processing and interpretation of the PPG signal are essential. Besides pulse rate detection, these devices—together with an ECG—compute the pulse arrival time (PAT), from which the actual beat-to-beat blood pressure can be estimated. The heart rate shows asymmetrical accelerations and decelerations, quantified by the parameters of heart rate asymmetry (HRA). In the present study, we investigated the influences of different breathing-patterns on the PATs and HRA parameters. Methods: The authors evaluated 5 min simultaneous respiratory-, ECG- and PPG-signal recordings of 35 healthy, young volunteers specifically expressing the following breathing patterns: metronome-controlled inspiration, and both inspiration and expiration controlled at 1:1 and 1:2 ratios, respectively. The records were analyzed by HRVScan_Merge v3.2 software. The PAT values were calculated at eight different reference points. The HRA parameters and the PAT values at different breathing patterns were compared using the Friedman test and post hoc Wilcoxon paired-sample test. Results: Porta- and Guzik-indices significantly increased at 1:1 breathing compared to 1:2 and single-paced breathing. PATs increased significantly in dual-paced series compared to single-paced series at each reference point. Conclusion: Based on our results, the increased PATs at dual-paced versus single-paced breathing may indicate the involvement of cognitive functions. The symmetrical respiration ratio increases the heart rate symmetry; however, this effect is not detectable in the periphery through the PATs.

Effect of Photoperiod Duration on Efficiency of Low-Temperature Hardening of &lt;i&gt;Arabidopsis thaliana&lt;/i&gt; Heynh. (L.)

The effect of photoperiod duration on efficiency of low-temperature hardening was investigated in Arabidopsis thaliana (L.) Heynh. plants, ecotype Col-0. Six-week-old plants were exposed to cold acclimation at a temperature of 2С during 1‒5 days at photoperiods of 0, 8, and 16 h (illuminance of 200 mol/(m2 s)). According to survival data and leakage of electrolytes after test freezing (6C, 24 h), the plants exposed to cold acclimation in the dark did not show frost resistance. The plants hardened in the light (irrespective of the length of photoperiod) considerably improved their frost resistance by the end of the cold-acclimation period. Net photosynthesis/dark respiration ratio in these plants was almost two times greater than in control material (without hardening). The plants exposed to a 16-h-long photoperiod surpassed the type of treatment with 8-h-long illumination both in the highest levels of accumulation of sugars (by almost 40%) and in the rate of reaching these levels in daily dynamics of hardening. It was shown that MDA content transiently rose during the first 24 h of hardening in the light and did not change in the dark, which may point to a signal role of lipid peroxidation products upon cold acclimation. It was discovered that the photoperiod duration affected the formation rate of frost resistance in A. thaliana plants. A more prolonged operation of A. thalianas photosynthetic apparatus at 16-h-long photoperiod considerably accelerated the accumulation of sugars upon cold acclimation and, therefore, hastened development of frost resistance as compared with an 8-h-long photoperiod. It was concluded that rapid formation of frost resistance in A. thaliana requires a combination of low above-zero temperature and 16-h-long photoperiod.

Hierarchical stringent response behaviors of activated sludge system to stressed conditions

The stringent response of activated sludge systems to either stressed or harmful environments is important for the stable operation of activated sludge, which is examined by taking copper ion (Cu2+) as a stress model in this study. When weak stress was employed (Cu2+ ≤ 2.5 mg/L), the N-acyl-homoserine lactones (AHLs) of C6-, C8-, and C10-HSL increased by 30 %, 13 %, and 127 %, respectively, while the redox sensor green (RSG) intensity decreased by 28 %. Encountering the increased stress (2.5 mg/L < Cu2+ ≤ 5 mg/L), bacteria concentration in the supernatant increased by 87 %. However, the respiration rates of autotrophic and heterotrophic bacteria (SOURa and SOURh) and adenosine triphosphate decreased by 52 %, 18 %, and 27 %, respectively, and the flocs disintegrated with a diameter decreasing from 57 to 51 μm. When the stress became more serious (Cu2+ > 5 mg/L), the respiration rates continued to decline, but the quasi-endogenous respiration ratio (Rq/t) increased from 31 % to 47 %. Negligible changes occurred in the endogenous respiration rate (SOURe), adenosine diphosphate, and adenosine monophosphate. Based on these results, a hierarchical stringent response model of the activated sludge system to stressed conditions was proposed, and these responses were evaluated by respirogram. The initial response to weak stress was related to the most sensitive signals of quorum sensing and RSG intensity, well described by the quasi-endogenous respiration rate. The adaptive response to increased stress was the proactive migrations of low- and high-nucleic-acid bacteria to the supernatant, causing the looseness and even disintegration of sludge flocs, well described by SOURa, SOURh, and Rq/t. The lethal response to lethal stress was related to endogenous metabolic processes, well described by SOURe. This work provides new insights into understanding the stringent response of activated sludge systems to some stressed conditions. It helps to regulate the stability of activated sludge systems with respirogram technology.