Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are considered as the key drivers of global nitrogen (N) biogeochemical cycling. Responses of the associated microorganisms to global changes remain ...unclear. This study was to determine if there was a shift in soil AOB and AOA abundances and community structures under free-air carbon dioxide (CO
2) enrichment (FACE) and N fertilization in Duke Forest of North Carolina, by using DNA-based molecular techniques, i.e., quantitative PCR, restriction fragment length polymorphism (RFLP) and clone library. The N fertilization alone increased the abundance of bacterial
amoA gene, but this effect was not observed under elevated CO
2 condition. There was no significant effect of the N fertilization on the thaumarchaeal
amoA gene abundance in the ambient CO
2 treatments, while such effect increased significantly under elevated CO
2. A total of 690 positive clones for AOA and 607 for AOB were selected for RFLP analysis. Analysis of molecular variance (AMOVA) indicated that effects of CO
2 enrichment and N fertilization on the community structure of AOA and AOB were not significant. Canonical correspondence analysis also showed that soil pH rather than elevated CO
2 or N fertilization shaped the distribution of AOB and AOA genotypes. A negative linear relationship between the δ
13C and archaeal
amoA gene abundance indicated a positive effect of elevated CO
2 on the growth ammonia oxidizing archaea. On the other hand, the community structures of AOB and AOA are determined by the soil niche properties rather than elevated CO
2 and N fertilization.
► N fertilization increased AOB abundance under ambient CO
2 but not elevated CO
2. ► N fertilization increased AOA abundance under elevated CO
2 but not ambient CO
2. ► Elevated CO
2 and N fertilization did not affect AOA and AOB structure. ► Soil properties rather than elevated CO
2 or N shaped the AOB and AOA genotypes.
While multiple experiments have demonstrated that trees exposed to elevated CO₂can stimulate microbes to release nutrients from soil organic matter, the importance of root‐ versus mycorrhizal‐induced ...changes in soil processes are presently unknown. We analyzed the contribution of roots and mycorrhizal activities to carbon (C) and nitrogen (N) turnover in a loblolly pine (Pinus taeda) forest exposed to elevated CO₂by measuring extracellular enzyme activities at soil microsites accessed via root windows. Specifically, we quantified enzyme activity from soil adjacent to root tips (rhizosphere), soil adjacent to hyphal tips (hyphosphere), and bulk soil. During the peak growing season, CO₂enrichment induced a greater increase of N‐releasing enzymes in the rhizosphere (215% increase) than in the hyphosphere (36% increase), but a greater increase of recalcitrant C‐degrading enzymes in the hyphosphere (118%) than in the rhizosphere (19%). Nitrogen fertilization influenced the magnitude of CO₂effects on enzyme activities in the rhizosphere only. At the ecosystem scale, the rhizosphere accounted for c. 50% and 40% of the total activity of N‐ and C‐releasing enzymes, respectively. Collectively, our results suggest that root exudates may contribute more to accelerated N cycling under elevated CO₂at this site, while mycorrhizal fungi may contribute more to soil C degradation.
•Extra stored soil carbon was lost again seven years after FACE termination.•Increased soil carbon during FACE stimulated the decomposition of old soil carbon.•Large transfer of nitrogen from deeper ...soil layers upon increasing plant demand.•Soil carbon and nitrogen pools in this ecosystem are highly dynamic.
The response of soil carbon to global climate change remains one of the largest uncertainties for future climate projection. In this study, we re-sampled the soil in a long-term, field-scale, multi-factorial climate experiment, CLIMAITE (Free Air CO2Enrichment (FACE), warming and drought in all combinations in a Danish heathland ecosystem) in 2020, seven years after the experiment was terminated. We aimed to study the dynamics of the soil carbon after the cessation of long-term multi-factorial climate manipulation, with special attention to the fate of the additional soil carbon (19% increase) that was sequestered in plots exposed to elevated CO2 concentrations (eCO2). Soil carbon pools in former eCO2 plots, as well as in drought and warming plots, had normalized again by 2020. However, the difference in soil isotopic composition between ambient and former eCO2 plots remained, indicating similar loss fractions from older and newer soil carbon pools in the eCO2 plots as well as stimulation of the decomposition of old soil carbon via priming. Throughout the study period, soil nitrogen dynamics tracked the changes in soil carbon, suggesting that nitrogen from deeper soil layers was transported upwards to meet increasing plant demand during eCO2 but was lost again from the topsoil after termination of the FACE treatment. Our findings show that the soil carbon and nitrogen pools in this ecosystem are highly dynamic and may respond strongly and rapidly to changes in major ecosystem drivers, and that revisiting climate experiments after the cessation of treatments may provide valuable insights into the dynamics, stability and resilience of major element pools in ecosystems.
Free-air carbon dioxide (CO2) enrichment (FACE) experiments provide an opportunity to test models of heat and water flow under novel, controlled situations and eventually allow use of these models ...for hypothesis evaluation. This study assesses whether the United States Department of Agriculture SHAW (Simultaneous Heat and Water) numerical model of vertical one-dimensional soil water flow across the soil-plant-atmosphere continuum is able to adequately represent and explain the effects of increasing atmospheric CO2 on soil moisture dynamics in temperate grasslands. Observations in a FACE experiment, the BioCON (Biodiversity, CO2, and Nitrogen) experiment, in Minnesota, USA, were compared with results of vertical soil moisture distribution. Three scenarios represented by different plots were assessed: bare, vegetated with ambient CO2, and similarly vegetated with high CO2. From the simulations, the bare plot soil was generally the wettest, followed by a drier high-CO2 vegetated plot, and the ambient CO2 plot was the driest. The SHAW simulations adequately reproduced the expected behavior and showed that vegetation and atmospheric CO2 concentration significantly affected soil moisture dynamics. The differences in modeled soil moisture amongst the plots were largely due to transpiration, which was low with high CO2. However, the modeled soil moisture only modestly reproduced the observations. Thus, while SHAW is able to replicate and help broadly explain soil moisture dynamics in a FACE experiment, its application for point- and time-specific simulations of soil moisture needs further scrutiny. The typical design of a FACE experiment makes the experimental observations challenging to model with a one-dimensional distributed model. In addition, FACE instrumentation and monitoring will need improvement in order to be a useful platform for robust model testing. Only after this can we recommend that models such as SHAW are adequate for process interpretation of datasets from FACE experiments or for hypothesis testing.
•We investigated holistic processing during mother’s face perception using the composite face experiment in 5- to 8-month-old infants.•There is a developmental difference in the composite face effect ...between 5- to 6-month and 7- to 8-month-old infants.•Infants older than 7 months are able to process mothers’ faces holistically.
In this study, we created composite faces using mothers’ faces to examine holistic face processing in infants aged 5–8 months. The composite-face effect occurred only in infants aged 7–8 months, suggesting that infants older than 7 months are able to process familiar faces holistically.
During the first six years of atmospheric CO2 enrichment at the Duke Forest free‐air CO2 enrichment (FACE) experiment, an additional sink of 52 ± 16 g C·m−2·yr−1 accumulated in the forest floor ...(O‐horizon) of the elevated CO2 treatment relative to the ambient CO2 control in an aggrading loblolly pine (Pinus taeda L.) forest near Chapel Hill, North Carolina, USA. The experiment maintained an atmospheric CO2 concentration 200 μL/L above ambient levels in replicated (n = 3) FACE rings throughout the six‐year period. This CO2‐induced C sink was associated with greater inputs of organic matter in litterfall and fine‐root turnover. There was no evidence that microbial decomposition was altered by the elevated CO2 treatment. Consistent with ecosystem recovery following decades of intensive agriculture, the C and N content of the mineral soil increased under both the elevated CO2 treatment and the ambient CO2 control during the six‐year period. This increase is attributed to accumulation of plant residues derived from fine roots with relatively high turnover rates rather than accumulation of refractory or physically protected soil organic matter (SOM). The elevated CO2 treatment produced no detectable effect on the C and N content of the bulk mineral soils or of any particulate organic matter size fraction. Because the fumigation gas was strongly depleted in 13C, the incorporation of new C could be traced within the ecosystem. Significant decreases in δ13C of soil organic carbon (SOC) under the elevated CO2 treatment were used to estimate the mean residence times of intra‐aggregate particulate organic matter and mineral‐associated organic matter as well as the annual C inputs required to produce the observed changes in δ13C. Our results indicate that forest soils such as these will not significantly mitigate anthropogenic C inputs to the atmosphere. The organic matter pools receiving large annual C inputs have short mean residence times, while those with slow turnover rates receive small annual inputs.
The present study focused on the quality traits of durum wheat grains (protein and content, gluten content, yellow pigment content), semolina (gluten index and yellow index) and pasta (firmness, ...yellow index, cooking time) obtained from 12 durum wheat genotypes grown under elevated atmospheric CO2 concentration in an open field Free Air CO2 Enrichment (FACE) experiment. The aims were to evaluate the impact of elevated CO2 on durum wheat pasta making related traits as well as investigate genetic differences existing in a panel of old and modern cultivars. The protein content showed a not significant decrease (7%), the GC decreased significantly (13.3%), while the GI showed an increasing significant tendency (14%). The overall pasta quality (firmness and weight) worsened in ELE. Correlation between all traits and pasta firmness demonstrated that the decrease in pasta firmness under ELE was correlated with GPC and GC while it was not with the GI. All varieties, although to different extent, showed lower pasta firmness values compared to the ambient condition. Among the varieties tested, some were more sensitive than others to the increased atmospheric CO2 concentration, a finding that can be exploited by breeding for designing novel genotypes with lower sensitivity to increased atmospheric CO2.
•12 durum wheat genotypes under ELE in a FACE experiment were evaluated.•Under ELE, gluten content decreased significantly while protein content unchanged.•The gluten index showed an increasing tendency under elevated CO2 conditions of about 14%.•The overall pasta quality (firmness and weight) worsened in ELE.•The genotypes variability helps designing novel varieties with lower sensitivity to ELE.
When planning sampling in an experiment where soil organic carbon (SOC) content is expected to change, it is necessary to know how many samples will need to be taken to demonstrate a change in SOC ...and after how long this change will be detectable. Much has been published on the number of samples required to demonstrate the minimum detectable difference in SOC, but less on how long it takes for this change to be detectable. In this paper, a model of SOC dynamics is used to estimate the minimum time taken for a change in total SOC content to become measurable under different carbon inputs, land uses and soil types.
For free air carbon dioxide enrichment (FACE), and other experiments in which SOC is expected to increase, relationships between the percentage change in C inputs and the time taken to measure a change in SOC are presented, for two levels of sampling intensity corresponding to the maximum that is practically possible in most experiments (∼100 samples) and that used regularly in field experiments (10–20 samples).
In FACE experiments, where C inputs increase by a maximum of about 20–25%, SOC change could be detected with 90% confidence after about 6–10 years if a sampling regime allowing 3% change in background SOC level (probably requiring a very large number of samples) were used, but could not be detected at all if a sampling regime were used that allowed only a 15% change in background SOC to be detected. If increases in C inputs are much below 15%, it might not be possible to detect a change in soil C without an enormous number of samples. Relationships between the change in C inputs and the time taken to measure a change in SOC are robust over a range of soil types and land uses.
The results demonstrate how models of SOC dynamics can be used to complement statistical power analyses for planning when, and how intensively, to sample soils during experiments. An advantage of the modelling approach demonstrated here is that estimates of the minimum time taken for a change in soil carbon to become detectable can be made, even before any detailed soil samples are taken, simply from estimates of the likely increase in carbon inputs to the soil (via expected changes in net primary production).
The impact of rising atmospheric carbon dioxide (CO2) may be mitigated, in part, by enhanced rates of net primary production and greater C storage in plant biomass and soil organic matter (SOM). ...However, C sequestration in forest soils may be offset by other environmental changes such as increasing tropospheric ozone (O3) or vary based on species-specific growth responses to elevated CO2. To understand how projected increases in atmospheric CO2 and O3 alter SOM formation, we used physical fractionation to characterize soil C and N at the Rhinelander Free Air CO2–O3 Enrichment (FACE) experiment. Tracer amounts of 15NH4+ were applied to the forest floor of Populus tremuloides, P. tremuloides–Betula papyrifera and P. tremuloides–Acer saccharum communities exposed to factorial CO2 and O3 treatments. The 15N tracer and strongly depleted 13C–CO2 were traced into SOM fractions over four years. Over time, C and N increased in coarse particulate organic matter (cPOM) and decreased in mineral-associated organic matter (MAOM) under elevated CO2 relative to ambient CO2. As main effects, neither CO2 nor O3 significantly altered 15N recovery in SOM. Elevated CO2 significantly increased new C in all SOM fractions, and significantly decreased old C in fine POM (fPOM) and MAOM over the duration of our study. Overall, our observations indicate that elevated CO2 has altered SOM cycling at this site to favor C and N accumulation in less stable pools, with more rapid turnover. Elevated O3 had the opposite effect, significantly reducing cPOM N by 15% and significantly increasing the C:N ratio by 7%. Our results demonstrate that CO2 can enhance SOM turnover, potentially limiting long-term C sequestration in terrestrial ecosystems; plant community composition is an important determinant of the magnitude of this response.
► We measure CO2, O3 and plant community effects on SOM formation ► Elevated CO2 increased formation of new SOM and mineralization of old SOM. ► Elevated O3 reduced N stocks and increased the C:N ratio of cPOM. ► SOM dynamics under elevated CO2 vary with O3 and plant species.
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