Natural Temporal Variability Research Articles

Sensitivity of dryland plant allometry to climate

Abstract Patterns of plant biomass partitioning are fundamental to estimates of primary productivity and ecosystem process rates. Allometric relationships between above‐ground plant biomass and non‐destructive measures of plant size, such as cover, volume or stem density are widely used in plant ecology. Such size‐biomass allometry is often assumed to be invariant for a given plant species, plant functional group or ecosystem type. Allometric adjustment may be an important component of the short‐ or long‐term response of plants to abiotic conditions. We used 18 years of size‐biomass data describing of 85 plant species to investigate the sensitivity of allometry to precipitation, temperature or drought across two seasons and four ecosystems in central New Mexico, USA. Size‐biomass allometry varied with climate in 65%–70% of plant species. Closely related plant species had similar sensitivities of allometry to natural spatiotemporal variation in precipitation, temperature or drought. Annuals were less sensitive than perennials, and forbs were less sensitive than grasses or shrubs. However, the differences associated with plant life history or functional group were not independent of plant evolutionary history, as supported by the application of phylogenetically independent contrasts. Our results demonstrate that many plant species adjust patterns in the partitioning of above‐ground biomass under different climates and highlight the importance of long‐term data for understanding functional differences among plant species. A free Plain Language Summary can be found within the Supporting Information of this article.

Muscle-specific gene expression and metabolic enzyme activities in Atlantic salmon Salmo salar L. fry reared under different photoperiod regimes.

This study was conducted to characterise the muscle-specific gene expression, energy metabolism level and growth rates of Atlantic salmon Salmo salar L. reared under different photoperiod regimes. The effects of two photoperiod regimes - LD 16:8 (16 h light:8 h dark) and LD 24:0 (24 h light:0 h dark) over a period of 3 months (August to October) on growth, energy metabolism enzyme activities (cytochrome c oxidase, COX; lactate dehydrogenase, LDH; and aldolase) and the gene expression levels of myogenic regulatory factors (MRFs - MyoD1 paralogues (MyoD1a, MyoD1b, MyoD1c), Myf5, MyoG), myostatin paralogues (MSTN-1a, MSTN-1b, MSTN-2a) and the fast skeletal myosin heavy chain (MyHC) in the muscles of Atlantic salmon underyearling fry (0+) were investigated. The experiment was conducted in a fish hatchery with natural variations in water temperature. The results were compared with those obtained in salmon reared under the lighting conditions of a fish hatchery (HL, hatchery lighting). The results revealed that the fry reared under constant light (LD 24:0) grew faster and were bigger at the end of the experiment. Fishes reared within the photoperiod regime LD 16:8 had a lower growth rate. COX activity was lower in fish under the LD 16:8 regime compared with the LD 24:0 group. The LDH and aldolase enzyme activities were higher in the group with constant light in comparison to control in the beginning of September. The expression level for all of the genes studied variated during the duration of the experiment, and MyHC, MyoG, MyoD1a and Myf5 expression depended on the light regime as well. The more noticeable changes in gene expression occurred in October. The MyHC and MyoG mRNA levels increased, accompanied by MyD1c gene expression, in both groups that had additional lighting (LD 16:8 and LD24:0) at the beginning of October and were higher than the HL group. In the HL group, the elevation of MyHC and MyoG mRNA was gradual during October, but there was a sharp increase in Myf5 expression at the beginning of October. MyoD1 paralogues differently expressed during the experiment. The MyoD1a mRNA level was elevated at the end of October along with MyHC and MyoG expression, but MyoD1b and MyoD1c mRNA levels decreased along with Myf5 gene expression. The expression of MSTN paralogues were elevated with increases in MyHC and MRFs transcripts. These findings show that constant light has a positive effect on the growth rate of salmon, affecting the aerobic and anaerobic capacity in their muscles. The alterations in muscle-specific gene expression between the groups with different light indicated that the mechanisms for regulating muscle growth processes in fish depend on photoperiod duration.

The performance of an anaerobic ammonium oxidation upflow anaerobic sludge blanket reactor during natural periodic temperature variations

An anaerobic ammonium oxidation-upflow anaerobic sludge blanket (anammox-UASB) reactor was operated without temperature control during the four seasons and was therefore subjected to natural periodic temperature variations between 9 and 28 ℃. The anammox reactor had a high nitrogen removal ability at intermediate and low temperatures. The total nitrogen (TN) concentration of the influent increased from 200 to 1200 mg/L, the nitrogen removal efficiency was maintained at 90%, and the nitrogen removal rate (NRR) increased to 9.15 ± 0.35 kg N/m3/d. The enrichment of anammox bacteria in the UASB granular sludge reached 53.8%, and the dominant bacteria changed from Candidatus Brocadia to Candidatus Kuenenia after several seasons of cultivation. Dynamics analysis revealed that the maximum reaction rate of the anammox-UASB sludge was 62.5 kg N/m3/d, reflecting the high potential nitrogen removal ability of the reactor.

Temperature coupling of mate attraction signals and female mate preferences in four populations of Enchenopa treehopper (Hemiptera: Membracidae).

Variation in temperature can affect the expression of a variety of important fitness-related behaviours, including those involved with mate attraction and selection, with consequences for the coordination of mating across variable environments. We examined how temperature influences the expression of male mating signals and female mate preferences-as well as the relationship between how male signals and female mate preferences change across temperatures (signal-preference temperature coupling)-in Enchenopa binotata treehoppers. These small plant-feeding insects communicate using plantborne vibrations, and our field surveys indicate they experience significant natural variation in temperature during the mating season. We tested for signal-preference temperature coupling in four populations of E.binotata by manipulating temperature in a controlled laboratory environment. We measured the frequency of male signals-the trait for which females show strongest preference-and female peak preference-the signal frequency most preferred by females-across a range of biologically relevant temperatures (18°C-36°C). We found a strong effect of temperature on both male signals and female preferences, which generated signal-preference temperature coupling within each population. Even in a population in which male signals mismatched female preferences, the temperature coupling reinforces predicted directional selection across all temperatures. Additionally, we found similar thermal sensitivity in signals and preferences across populations even though populations varied in the mean frequency of male signals and female peak preference. Together, these results suggest that temperature variation should not affect the action of sexual selection via female choice, but rather should reinforce stabilizing selection in populations with signal-preference matches, and directional selection in those with signal-preference mismatches. Finally, we do not predict that thermal variation will disrupt the coordination of mating in this species by generating signal-preference mismatches at thermal extremes.

Restoring a Natural Fire Regime Alters the Water Balance of a Sierra Nevada Catchment

AbstractFire suppression in western U.S. mountains has caused dense forests with high water demands to grow. Restoring natural wildfire regimes to these forests could affect hydrology by changing vegetation composition and structure, but the specific effects on water balance are unknown. Mountain watersheds supply water to much of the western United States, so understanding the relationship between fire regime and water yield is essential to inform management. We used a distributed hydrological model to quantify hydrologic response to a restored fire regime in the Illilouette Creek Basin (ICB) within Yosemite National Park, California. Over the past 45 years, as successive fires reduced the ICB's forest cover approximately 25%, model results show that annual streamflow, subsurface water storage, and peak snowpack increased relative to a fire‐suppressed control, while evapotranspiration and climatic water deficit decreased. A second model experiment compared the water balance in the ICB under two vegetation cover scenarios: 2012 vegetation, representing a frequent‐fire landscape, and 1969 vegetation, representing fire suppression. These two model landscapes were run with observed weather data from 1972 to 2017 in order to capture natural variations in precipitation and temperature. This experiment showed that wet years experienced greater fire‐related reductions in evapotranspiration and increases in streamflow, while reductions in climatic water deficit were greater in dry years. Spring snowmelt runoff was higher under burned conditions, while summer baseflow was relatively unaffected. Restoring wildfire to the fire‐suppressed ICB likely increased downstream water availability, shifted streamflows slightly earlier, and reduced water stress to forests.

Thermal Preference and Species Range in Mountaintop Salamanders and Their Widespread Competitors

Temperature tolerance can be a critical factor in determining amphibian species range over both latitudinal and elevational gradients; however, range limits across latitudes and elevations are not always congruent. For some mountaintop endemic and widespread salamanders in the Southern Appalachians, elevational distributions suggest the hypothesis that mountaintop species should be more cold tolerant, whereas latitudinal patterns are consistent with the hypothesis that widespread species should be more cold tolerant or tolerate a wider range of temperatures. We tested these hypotheses with year-round surveys of two mountaintop endemic species, Big Levels salamanders (Plethodon sherando) and Peaks of Otter salamanders (Plethodon hubrichti), at high- and low-elevation sites where they overlap with the widespread Eastern Redback salamander (Plethodon cinereus). We fit hierarchical Bayesian models to salamander surface counts across natural variation in soil temperature and moisture to compare temperatures that maximized surface counts (“peak activity temperature”) and the range of temperatures at which each species was active (“activity window”). We found that P. sherando and P. cinereus showed similar peak activity temperatures in areas of overlap, though P. sherando had a wider activity window as compared to P. cinereus. For P. hubrichti, we found a similar to somewhat higher peak activity temperature compared to P. cinereus, though P. cinereus had a wider activity window. We found no consistent differences in responses to soil moisture across species pairs. Our results suggest that elevational zonation in salamanders can result from a variety of processes and may not always reflect differences in relative temperature preferences.

Detection of the effects of stormwater control measure in streams using a Bayesian BACI power analysis

The unpredictable timing and magnitude of precipitation events and the spatiotemporal variability of constituent concentrations are major complications to effective monitoring of watershed nutrient and sediment loads. Furthermore, detecting small changes in constituent loads in response to implementation of Stormwater control measures (SCMs) against natural variability is a challenge. Nevertheless, regulatory frameworks that direct reductions of pollutants to streams frequently depend on the ability to quantify changes in loads after management interventions. The before-after-control impact (BACI) sampling design is often used to assess the effects of an environmental change made at a known point in time. However, this approach may be complicated to apply to nutrient and sediment loads in streams as the relative impact of SCMs on nutrient concentration conditional on the long term variability of discharges has not been evaluated. Multi-scale monitoring studies that provide estimates of the natural temporal and spatial variability of discharge and concentrations could provide useful information in designing a BACI study. Here we use data from the Baltimore Long Term Ecological Research (LTER) sites and urban restoration sites to develop multiple statistical measures of the effectiveness of a given monitoring scheme in revealing the hypothesized restoration effects in terms of hydrology and nutrient loads. Stratified sampling over baseflow and stormflow and the use of multiple control streams were useful tools to detect long term cumulative reductions in concentrations due to SCMs. Moderate reductions in concentration (20%), however, were not detectable with the design options considered. We emphasize that appropriate pre-planning of monitoring schemes and sampling frequency is essential to determine if the effects on constituent loads resulting from a given watershed restoration activity are measurable.

Anthropogenic and Natural Radiative Forcing: Positive Feedbacks

This article is based on recent work intended to estimate the impact of solar forcing mediated by long-period ocean Rossby waves that are resonantly forced—the ‘Gyral Rossby Waves’ (GRWs). Here, we deduce both the part of the anthropogenic and climate components within the instrumental surface temperature spatial patterns. The natural variations in temperature are estimated from a weighted sum of sea surface temperature anomalies in preselected areas of subtropical gyres representative of long-period GRWs. The temperature response to anthropogenic forcing is deduced by subtracting the climate component from the instrumental temperature. Depending on whether the inland regions are primarily impacted by latent or sensible heat fluxes from the oceans, positive feedbacks occur. This suggests that the lapse rate and the high troposphere cloud cover have a driving role in the amplification effect of anthropogenic climate forcing, while specifying the involved mechanisms.

Temperature sensitivity of soil respiration in a low-latitude forest ecosystem varies by season and habitat but is unaffected by experimental warming

Experimental warming of forest ecosystems typically stimulates soil respiration (CO2 efflux), but most warming experiments have been conducted in northern latitudes (> 40°N) with relatively young soils. We quantified the influence of experimental warming on soil respiration (RT) in two adjacent forest habitats—a mature, closed canopy forest and a gap where trees were manually removed— on highly-weathered Ultisols of the southeastern U.S. (33°N). Using temperature variation, both natural and induced by experimental warming, we also quantified the temperature sensitivity of RT, defined as the activation energy, EA in the Arrhenius equation. Experimental warming (either + 3 °C or + 5 °C above ambient) did not significantly increase soil respiration rate or cumulative CO2 loss over the 3 years of the experiment, and did not influence the temperature sensitivity of soil respiration, once the influence of natural temperature variation was taken into consideration. Despite the absence of an experimental warming effect, we observed that EA varied on monthly time scales, and varied differently in each habitat. Soil moisture and habitat also influenced RT, but the effects were not consistent, and varied by month. Our results suggest that although RT does depend on temperature, the sensitivity of RT to temperature variation is influenced primarily by factors like microclimate and plant phenology that can change on relatively short (< monthly) time scales. Thus, using the temperature sensitivity of RT to predict future CO2 losses due to warming is only reasonable if monthly variation in EA is incorporated into models for lower-latitude subtropical ecosystems with highly weathered soils, such as those in this study. Finally, our results suggest that higher temperatures may not enhance RT in highly-weathered, C-poor soils to the extent that has been reported in prior studies of high-latitude soils, which may constrain ecosystem-atmosphere carbon exchanges and feedbacks to the climate system.

How Data Set Characteristics Influence Ocean Carbon Export Models

AbstractOcean biological processes mediate the transport of roughly 10 petagrams of carbon from the surface to the deep ocean each year and thus play an important role in the global carbon cycle. Even so, the globally integrated rate of carbon export out of the surface ocean remains highly uncertain. Quantifying the processes underlying this biological carbon export requires a synthesis between model predictions and available observations of particulate organic carbon (POC) flux; yet the scale dissimilarities between models and observations make this synthesis difficult. Here we compare carbon export predictions from a mechanistic model with observations of POC fluxes from several data sets compiled from the literature spanning different space, time, and depth scales as well as using different observational methodologies. We optimize model parameters to provide the best match between model‐predicted and observed POC fluxes, explicitly accounting for sources of error associated with each data set. Model‐predicted globally integrated values of POC flux at the base of the euphotic layer range from 3.8 to 5.5 Pg C/year, depending on the data set used to optimize the model. Modeled carbon export pathways also vary depending on the data set used to optimize the model, as well as the satellite net primary production data product used to drive the model. These findings highlight the importance of collecting field data that average over the substantial natural temporal and spatial variability in carbon export fluxes, and advancing satellite algorithms for ocean net primary production, in order to improve predictions of biological carbon export.

Optimal dose of PG600 when given to progestogen-synchronized ewes during anestrus as affected by day of the year and temperature.

The objective of this long-term study was to improve the out-of-season breeding rates for ewes by examining effectiveness of dose levels of PG600, a combination of 80-IU/mL pregnant mare serum gonadotropin and 40-IU/mL human chorionic gonadotropin. Each week, during the anestrous season from 1998 through 2016, mature ewes were inserted with 1 of 2 progestogen devices. After 9 to 13 d, at removal of the device, ewes were injected intramuscularly with a specific dose of PG600. A total of 1,402 ewes were treated in this study, with weekly treatment groups ranging from 3 to 12 ewes. Ewes were assigned randomly in equal numbers to 1 of 2 ram pens with one fertile ram in each pen. Rams were fitted with a marking harness. Between 36 and 48 h after removal of the device, rams were switched. Ewes were checked for crayon marks (indicative of estrus) at 36, 48, and 96 h after removal of synchronizing devices. Rams were removed after 1 wk. Pregnancy status was diagnosed at 90 d of gestation using radiography and verified at 120 d or at lambing. To explore the impact of dose level, daylight, and temperature on pregnancy rate, we formulated an ordered multinomial probit model. The model controls statistically for dose level, synchronization device type, device reuse, and natural variation in minimum daily temperature and day of the year (DOY). Predicted pregnancy rate and type of birth at 90 d of gestation were significantly affected by DOY and temperature as well as dose level. Both observed and predicted pregnancy rates were higher for PG600 dose levels between 2.00 and 3.50 mL than for those below 2.00 mL or above 3.99 mL. By giving optimal amounts of PG600 to anestrous ewes, producers will have a greater number of pregnant ewes at lambing during the out-of-season lambing time.

Maintenance dredging impacts on a highly stressed estuary (Guadalquivir estuary): A BACI approach through oligohaline and polyhaline habitats

Understanding the effects of dredging in estuaries is a hard task due to the difficulty of implementing an adequate environmental diagnosis, as a consequence of the salinity gradient and anthropogenic disturbances. To assess the effects of maintenance dredging work on the Guadalquivir estuary (southwestern Spain), we used a Before-After-Control-Impact (BACI) approach to determine both direct and indirect effects in two salinity ranges. No effects were found on water and sediment physicochemical characteristics. The small impacts on dredged areas were followed by a rapid recovery of opportunistic species. The poor status of the benthos does not permit the detection of significant effects on macrofaunal community structure. The use of stable isotopes analysis to determine impacts on food web structure showed that changes over time seem to be explained by natural temporal variation rather than the dredging works. This paper emphasises the need to define proper management and conservation plans to improve the status of the benthic communities of the Guadalquivir estuary.

Diverse fungal lineages in subtropical ponds are altered by sediment-bound copper

Ponds represent a black box for fungal ecology. Compared to terrestrial environments, the fungal ecology of aquatic environments is rarely studied, and the few published studies have tended to be of lotic habitats in the northern hemisphere. We explored fungal communities and their responses to a gradient of copper in five year old artificial, replicated ponds in Australia. Ponds were subject to natural variations in temperature, precipitation and biotic colonisation. To explore the fungal communities, we amplified the ITS1 region of rDNA from samples of the water column, the sediment and cellulose baits (analogues to leaf fall) alone and in the presence of a gradient of copper. Fungal amplicon data revealed almost 800 fungal species from these habitats within the ponds. Interestingly, no chytrids from the Cladochytriales and Rhizophlyctidales were detected on cellulose baits, instead, putatively novel zoosporic taxa in the Chytridiomycota and the Rozellomycota were observed. Given the keystone role zoosporic fungi are thought to play in aquatic food webs, along with their role as primary decomposers of plant material, improved knowledge of their diversity and distribution is vital for understanding ecosystem function in standing water habitats. In aquatic environments copper tends to be bound to sediment and is not especially mobile in the water phase. The presence of copper in our sediment samples was correlated with repeatable and profound shifts in the fungal community, with chytrid species appearing to be the most sensitive, suggesting that they may be useful indicator organisms. Indirect effects of copper on fungal communities living on leaf analogues and in the water column were also explored.

Data-driven dynamical model indicates that the heat shock response in Chlamydomonas reinhardtii is tailored to handle natural temperature variation.

Global warming exposes plants to severe heat stress, with consequent crop yield reduction. Organisms exposed to high temperature stresses typically protect themselves with a heat shock response (HSR), where accumulation of unfolded proteins initiates the synthesis of heat shock proteins through the heat shock transcription factor HSF1. While the molecular mechanisms are qualitatively well characterized, our quantitative understanding of the underlying dynamics is still very limited. Here, we study the dynamics of HSR in the photosynthetic model organism Chlamydomonas reinhardtii with a data-driven mathematical model of HSR. We based our dynamical model mostly on mass action kinetics, with a few nonlinear terms. The model was parametrized and validated by several independent datasets obtained from the literature. We demonstrate that HSR quantitatively and significantly differs if an increase in temperature of the same magnitude occurs abruptly, as often applied under laboratory conditions, or gradually, which would rather be expected under natural conditions. In contrast to rapid temperature increases, under gradual changes only negligible amounts of misfolded proteins accumulate, indicating that the HSR of C. reinhardtii efficiently avoids the accumulation of misfolded proteins under conditions most likely to prevail in nature. The mathematical model we developed is a flexible tool to simulate the HSR to different conditions and complements the current experimental approaches.

Sparse estimation based monitoring method for damage detection and localization: A case of study

Abstract This paper suggests a Structural Health Monitoring (SHM) method for damage detection and localization in pipeline. The baseline signals, used in SHM, could change due to the variation of environmental and operational conditions (EOCs). Hence, the damage detection method could give rise to false alarm. In this study, this issue is addressed by estimating the current signal using only few reference signals with similar or very close EOCs. Such an operation can be performed by calculating a sparse estimation of the current signal. The estimation error is used as an indication of the presence of damage. Actually, a signal from the damaged pipe will be characterized by a high estimation error compared to that of a signal from the undamaged pipe. The damage location is obtained by calculating the estimation error on a sliding window over the signal from the damaged pipe. This method was tested on signals collected on a 6 m pipeline segment placed in a workshop under natural temperature variations. Results have shown that the created damage was successfully detected and localized.

The thermal dependence of carbon stable isotope incorporation and trophic discrimination in the domestic cricket, Acheta domesticus

Stable isotopes are valuable tools in physiological and ecological research, as they can be used to estimate diet, habitat use, and resource allocation. However, in most cases a priori knowledge of two key properties of stable isotopes is required, namely their rate of incorporation into the body (incorporation rate) and the change of isotope values between consumers and resources that arises during incorporation of the isotopes into the consumer’s tissues (trophic discrimination). Previous studies have quantified these properties across species and tissue types, but little is known about how they vary with temperature, a key driver of many biological rates and times. Here, we explored for the first time how temperature affects both carbon incorporation rate and trophic discrimination via growth rates, using the domestic cricket, Acheta domesticus. We raised crickets at 16 °C, 21 °C, and 26 °C and showed that temperature increased carbon isotope incorporation rate, which was driven by both an increased growth rate and catabolism at higher temperatures. Trophic discrimination of carbon isotopes decreased at higher temperatures, which we attributed to either lower activation energies needed to synthesize non-essential amino acids at higher temperatures or the increased utilization of available resources of consumers at higher temperatures. Our results demonstrate that temperature is a key driver of both carbon isotope incorporation rate and trophic discrimination, via mechanisms that likely persist across all ectotherms. Experiments to determine incorporation rates and trophic discrimination factors in ectotherms must include temperature as a major factor, and natural variation in temperature might have significant effects on these isotopic properties that then can affect inferences made from isotope values.

Ground Source Heat Supply in Moscow Oblast: Temperature Potential and Sustainable Depth of Heat Wells

The paper is devoted to a problem of increasing the efficiency of low-potential geothermal heat in heat pump systems of residential buildings the Moscow oblast of Russia, including Moscow. Estimates of a natural geothermal potential in the Moscow oblast (based on climatological data for the period from 1982 to 2011) are presented and a “Typical climatic year of natural soil temperature variations for the geoclimatic conditions of the Moscow oblast, including the city of Moscow” is proposed. Numerical simulation of the influence of geothermal energy potential and the depth of heat wells on the efficiency of ground source heat pump systems for the heat supply of residential buildings is carried out. Analysis of the numerical simulation showed that the operation of a heat pump system in a house heating mode under the geoclimatic conditions of the Moscow oblast leads to a temperature drop of the heat-exchange medium circulating through heat wells to 5–6°C by the end of the first 10 years of operation, and the process stabilizes by the 15th year of operation, and further changes in the heat-exchange medium temperature do not any longer significantly affect the temperature of the heat-exchange medium in the heat well. In this case, the exact dependence of the heat-exchange medium temperature drop on the depth is not revealed. Data on the economically expedient heat well depth for the conditions of the Moscow oblast ensuring a net present value for the whole residential building life cycle are presented. It is found that the heat well depth of 60 m can be considered as an endpoint for the Moscow oblast, and a further heat well deepening is economically impractical.

Does restoration work? It depends on how we measure success

The restoration of 4 partial stream barriers was evaluated in watersheds of Terra Nova National Park, Newfoundland, Canada from 2009 to 2011. Brook trout (n = 462) were tagged and tracked moving through our study sites using passive‐integrated transponder telemetry and the restoration actions were assessed using 3 different measures: passage success rates; the range of passable flows; and the availability of passable flows. We considered the observed results within a before‐after‐control‐impact (BACI) design that included reference reaches and pre‐restoration observations. The conclusions of BACI analyses were also contrasted with those that would have been obtained from commonly used before‐after (B‐A) or control‐impact (C‐I) study designs. While the restoration actions changed hydrological conditions in a way that should facilitate fish passage, our biological measures indicated that success was variable across culverts and within culverts depending on the measure evaluated. Furthermore, the natural temporal and spatial variability of fish movements often resulted in different conclusions between the more robust BACI design and the more commonly used B‐A and C‐I designs. Our results demonstrate that restoration of partial barriers may not always yield dramatic improvements. Furthermore, without suitable controls, the chances of drawing false conclusions regarding restorations in temporally and spatially dynamic systems are substantial.

The Inuit gut microbiome is dynamic over time and shaped by traditional foods

BackgroundThe human gut microbiome represents a diverse microbial community that varies across individuals and populations, and is influenced by factors such as host genetics and lifestyle. Diet is a major force shaping the gut microbiome, and the effects of dietary choices on microbiome composition are well documented. However, it remains poorly known how natural temporal variation in diet can affect the microbiome. The traditional Inuit diet is primarily based on animal products, which are thought to vary seasonally according to prey availability. We previously investigated the Inuit gut microbiome sampled at a single time point, and found no detectable differences in overall microbiome community composition attributable to the traditional Inuit diet.ResultsTo determine whether seasonal changes in the Inuit diet might induce more pronounced changes in the microbiome, we collected stool and toilet paper samples, and dietary information from Inuit volunteers living in Resolute Bay (Nunavut, Canada), and compared them to individuals of European descent living in Montréal (Québec, Canada) consuming a typical Western diet. We sequenced the V4 region of the 16S rRNA gene to characterize microbiome diversity and composition, and compared samples collected with toilet paper or from stool. Our results show that these sampling methods provide similar, but non-identical portraits of the microbiome. Based on toilet paper samples, we found that much of the variation in microbiome community composition could be explained by individual identity (45–61% of variation explained, depending on the beta diversity metric used), with small but significant variation (3–5%) explained by sex or geography (Nunavut or Montréal). In contrast with our previous study at one time point, sampling over the course of a year revealed that diet explains 11% of variation in community composition across all participants, and 17% of variation specifically among Nunavut participants. However, we observed no clear seasonal shifts in the microbiomes of participants from either Nunavut or Montréal. Within-individual microbial diversity fluctuated more over time in Nunavut than in Montréal, consistent with a more variable and highly individualized diet in Nunavut.ConclusionsTogether, these results shows that the traditional Inuit diet and lifestyle has an impact on the composition, diversity and stability of the Inuit gut microbiome, even if the seasonality of the diet is less pronounced than expected, perhaps due to an increasingly westernized diet.

Analysis of uncertainty for N2O fluxes measured with the closed‐chamber method under field conditions: Calculation method, detection limit, and spatial variability.

AbstractThe search for agricultural practices that mitigate N2O emissions, and the validation and development of models, would benefit if the uncertainty of emission estimates would be reduced relative to current levels. This uncertainty has different sources, such as the error of the flux measurements, the error caused by spatially scaling up measurements to the field or regional level, and the error caused by estimating emissions for the time intervals between measurements by interpolation. This paper focuses on the uncertainty of flux measurements and on flux spatial variability, which is a major cause of error when measured fluxes are scaled up spatially. The analysis focuses on 2415 flux measurements made with the closed chamber method over a monitoring campaign of approximately 3 years.Statistically significant nonlinearities in the changes of N2O concentrations during chamber closure were infrequent (8.3%). Further analysis of significant non‐linear concentration changes indicates that, for positive fluxes, nonlinearity might not always be an artifact caused by chamber placement, but that it can reflect natural temporal variability of the flux during chamber placement in a significant number of cases. The analysis of the coefficients of determination (R2) and of the normalized root mean squared errors (NRMSE) of the linear regressions shows that, below emission rates of 5 g N2O‐N ha−1 d−1, the uncertainty of flux estimates strongly increases. The flux detection limit was 3.5 g N2O‐N ha−1 d−1, which is consistent with the outcome of the analysis of the R2s and NRMSEs. Flux measurements based on less than five N2O concentrations per flux led to estimates with considerably larger confidence intervals. When the number of N2O concentrations per flux was reduced from five to four, the detection limit increased to 7.5 g N2O‐N ha−1 d−1. The individual fluxes of spatially replicated plots show strong dispersion around the mean: the average coefficient of variation for fluxes above 5 g N2O‐N ha−1 d−1 was 54.3% and the data suggest that the spatial variability of fluxes correlates positively with flux magnitude.Our results suggest that, for measurements performed with the closed static chamber method, (1) linear regression might generally lead to the best estimates of the average fluxes during closure time, and that the chamber sampling strategy might be designed accordingly, (2) there is considerable potential to reduce the uncertainty for fluxes lower than 5 g N2O‐N ha−1 d−1 by employing analytical instrumentation with higher precision, (3) flux uncertainty and detection limit are strongly affected by the number of concentrations measured for each flux, and (4) large numbers of replicated chambers could be particularly beneficial if high fluxes are expected.