Unraveling microbial processes involved in carbon and nitrogen cycling and greenhouse gas emissions in rewetted peatlands by molecular biology

Restoration of drained peatlands through rewetting has recently emerged as a prevailing strategy to mitigate excessive greenhouse gas emissions and re-establish the vital carbon sequestration capacity of peatlands. Rewetting can help to restore vegetation communities and biodiversity, while still allowing for extensive agricultural management such as paludiculture. Belowground processes governing carbon fluxes and greenhouse gas dynamics are mediated by a complex network of microbial communities and processes. Our understanding of this complexity and its multi-factorial controls in rewetted peatlands is limited. Here, we summarize the research regarding the role of soil microbial communities and functions in driving carbon and nutrient cycling in rewetted peatlands including the use of molecular biology techniques in understanding biogeochemical processes linked to greenhouse gas fluxes. We emphasize that rapidly advancing molecular biology approaches, such as high-throughput sequencing, are powerful tools helping to elucidate the dynamics of key biogeochemical processes when combined with isotope tracing and greenhouse gas measuring techniques. Insights gained from the gathered studies can help inform efficient monitoring practices for rewetted peatlands and the development of climate-smart restoration and management strategies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10533-024-01122-6.

Non-negligible N2O emission hotspots: Rivers impacted by ion-adsorption rare earth mining

Rare earth mining causes severe riverine nitrogen pollution, but its effect on nitrous oxide (N2O) emissions and the associated nitrogen transformation processes remain unclear. Here, we characterized N2O fluxes from China's largest ion-adsorption rare earth mining watershed and elucidated the mechanisms that drove N2O production and consumption using advanced isotope mapping and molecular biology techniques. Compared to the undisturbed river, the mining-affected river exhibited higher N2O fluxes (7.96 ± 10.18 mmol m-2d-1 vs. 2.88 ± 8.27 mmol m-2d-1, P = 0.002), confirming that mining-affected rivers are N2O emission hotspots. Flux variations scaled with high nitrogen supply (resulting from mining activities), and were mainly attributed to changes in water chemistry (i.e., pH, and metal concentrations), sediment property (i.e., particle size), and hydrogeomorphic factors (e.g., river order and slope). Coupled nitrification-denitrification and N2O reduction were the dominant processes controlling the N2O dynamics. Of these, the contribution of incomplete denitrification to N2O production was greater than that of nitrification, especially in the heavily mining-affected reaches. Co-occurrence network analysis identified Thiomonas and Rhodanobacter as the key genus closely associated with N2O production, suggesting their potential roles for denitrification. This is the first study to elucidate N2O emission and influential mechanisms in mining-affected rivers using combined isotopic and molecular techniques. The discovery of this study enhances our understanding of the distinctive processes driving N2O production and consumption in highly anthropogenically disturbed aquatic systems, and also provides the foundation for accurate assessment of N2O emissions from mining-affected rivers on regional and global scales.

Cost effectiveness, nitrogen, and phosphorus removal in field-based woodchip bioreactors treating agricultural drainage water

Nitrogen (N) and phosphorus (P) losses to surface and coastal waters are still critically high across Europe and globally. Measures to mitigate and reduce these losses are being implemented both at the cultivated land surface and at the edge-of-fields. Woodchip bioreactors represent a new alternative in Denmark for treating agricultural drainage water, and the present study-based on two years of data from five Danish field-based bioreactors-determined N removal rates varying from 1.49 to 5.37 g N m^-3 d^-1 and a mean across all bioreactors and years of 2.90 g N m^-3 d^-1. The loss of phosphorus was relatively high the first year after bioreactor establishment with rates varying from 298.4 to 890.8 mg P m^-3 d^-1, but in the second year, the rates ranged from 12.2 to 77.2 mg P m^-3 d^-1. The investments and the costs of the bioreactors were larger than expected based on Danish standard investments. The cost efficiency analysis found the key issues to be the need for larger investments in the bioreactor itself combined with higher advisory costs. For the four woodchip bioreactors considered in the cost efficiency analysis, the N removal cost was around DKK 350 per kg N ($50 per kg N), which is ca. 50% higher than the standard costs defined by the Danish authorities. Based on the estimated costs of the four bioreactor facilities included in this analysis, a bioreactor is one of the most expensive nitrogen reduction measures compared to other mitigation tools.

Pollution caused by mining reshaped the structure and function of bacterial communities in China's largest ion-adsorption rare earth mine watershed

Ion-adsorption rare earth mining results in the production of high levels of nitrogen, multiple metals, and strong acidic mine drainage (AMD), the impacts of which on microbial assembly and ecological functions remain unclear. To address this knowledge gap, we collected river sediments from the watershed of China's largest ion-adsorption rare earth mine and analyzed the bacterial community's structure, function, and assembly mechanisms. Results showed that bacterial community assembly was weakly affected by spatial dispersion, and dispersal limitation and homogeneous selection were the dominant ecological processes, with the latter increasing with pollution gradients. Bacterial alpha diversity decreased with pollution, which was mainly influenced by lead (Pb), pH, rare earth elements (REEs), and electrical conductivity (EC). However, bacteria developed survival strategies (i.e., enhanced acid tolerance and interspecific competition) to adapt to extreme environments, sustaining species diversity and community stability. Community structure and function showed a consistent response to the polluted environment (r = 0.662, P = 0.001). Enhanced environmental selection reshaped key microbial-mediated biogeochemical processes in the mining area, in particular weakening the potential for microbial denitrification. These findings provide new insights into the ecological response of microbes to compound pollution and offer theoretical support for proposing effective remediation and management strategies for polluted areas.

Small artificial waterbodies are widespread and persistent emitters of methane and carbon dioxide

Inland waters play an active role in the global carbon cycle and emit large volumes of the greenhouse gases (GHGs), methane (CH₄ ) and carbon dioxide (CO₂ ). A considerable body of research has improved emissions estimates from lakes, reservoirs and rivers but recent attention has been drawn to the importance of small, artificial waterbodies as poorly quantified but potentially important emission hotspots. Of particular interest are emissions from drainage ditches and constructed ponds. These waterbody types are prevalent in many landscapes and their cumulative surface areas can be substantial. Furthermore, GHG emissions from constructed waterbodies are anthropogenic in origin and form part of national emissions reporting, whereas emissions from natural waterbodies do not (according to Intergovernmental Panel on Climate Change guidelines). Here, we present GHG data from two complementary studies covering a range of land uses. In the first, we measured emissions from nine ponds and seven ditches over a full year. Annual emissions varied considerably: 0.1-44.3 g CH₄  m^-2  year^-1 and -36-4421 g CO₂  m^-2  year^-1 . In the second, we measured GHG concentrations in 96 ponds and 64 ditches across seven countries, covering subtropical, temperate and sub-arctic biomes. When CH₄ emissions were converted to CO₂  equivalents, 93% of waterbodies were GHG sources. In both studies, GHGs were positively related to nutrient status (C, N, P), and pond GHG concentrations were highest in smallest waterbodies. Ditch and pond emissions were larger per unit area when compared to equivalent natural systems (streams, natural ponds). We show that GHG emissions from natural systems should not be used as proxies for those from artificial waterbodies, and that artificial waterbodies have the potential to make a substantial but largely unquantified contribution to emissions from the Agriculture, Forestry and Other Land Use sector, and the global carbon cycle.

Microbiome Structure and Function in Woodchip Bioreactors for Nitrate Removal in Agricultural Drainage Water

Woodchip bioreactors are increasingly used to remove nitrate (NO₃^–) from agricultural drainage water in order to protect aquatic ecosystems from excess nitrogen. Nitrate removal in woodchip bioreactors is based on microbial processes, but the microbiomes and their role in bioreactor efficiency are generally poorly characterized. Using metagenomic analyses, we characterized the microbiomes from 3 full-scale bioreactors in Denmark, which had been operating for 4–7 years. The microbiomes were dominated by Proteobacteria and especially the genus Pseudomonas, which is consistent with heterotrophic denitrification as the main pathway of NO₃^– reduction. This was supported by functional gene analyses, showing the presence of the full suite of denitrification genes from NO₃^– reductases to nitrous oxide reductases. Genes encoding for dissimilatory NO₃^– reduction to ammonium were found only in minor proportions. In addition to NO₃^– reducers, the bioreactors harbored distinct functional groups, such as lignocellulose degrading fungi and bacteria, dissimilatory sulfate reducers and methanogens. Further, all bioreactors harbored genera of heterotrophic iron reducers and anaerobic iron oxidizers (Acidovorax) indicating a potential for iron-mediated denitrification. Ecological indices of species diversity showed high similarity between the bioreactors and between the different positions along the flow path, indicating that the woodchip resource niche was important in shaping the microbiome. This trait may be favorable for the development of common microbiological strategies to increase the NO₃^– removal from agricultural drainage water.

Warming and eutrophication interactively drive changes in the methane-oxidizing community of shallow lakes

Freshwater ecosystems are the largest natural source of the greenhouse gas methane (CH4), with shallow lakes a particular hot spot. Eutrophication and warming generally increase lake CH4 emissions but their impacts on the sole biological methane sink-methane oxidation-and methane-oxidizer community dynamics are poorly understood. We used the world's longest-running freshwater climate-change mesocosm experiment to determine how methane-oxidizing bacterial (MOB) abundance and composition, and methane oxidation potential in the sediment respond to eutrophication, short-term nitrogen addition and warming. After nitrogen addition, MOB abundance and methane oxidation potential increased, while warming increased MOB abundance without altering methane oxidation potential. MOB community composition was driven by both temperature and nutrient availability. Eutrophication increased relative abundance of type I MOB Methyloparacoccus. Warming favoured type II MOB Methylocystis over type I MOB Methylomonadaceae, shifting the MOB community from type I dominance to type I and II co-dominance, thereby altering MOB community traits involved in growth and stress-responses. This shift to slower-growing MOB may explain why higher MOB abundance in warmed mesocosms did not coincide with higher methane oxidation potential. Overall, we show that eutrophication and warming differentially change the MOB community, resulting in an altered ability to mitigate CH4 emissions from shallow lakes.

Nitrogen removal and greenhouse gas fluxes from integrated buffer zones treating agricultural drainage water

Integrated buffer zones (IBZ) are novel mitigation measures designed to decrease the loading of nitrogen (N) transported by subsurface drainage systems from agricultural fields to streams. In IBZ, drainage water flows into a pond with free water surface followed by an inundated, vegetated filterbed. This design provides an environment favorable for denitrification and thus a decrease in nitrate concentration is expected as water flow through the IBZ. However, due to the establishment of anaerobic conditions, there is a risk for increasing emissions of the greenhouse gases nitrous oxide (N₂O) and methane (CH₄). In this year-long study, we evaluated the N removal efficiency along with the risk of N₂O and CH₄ emissions from two pilot-scale IBZs (IBZ1 and 2). The two IBZs had very different yearly removal efficiencies, amounting to 29% and 71% of the total N load at IBZ1 and 2, respectively. This was probably due to differences in infiltration rates to the filterbed, which was 22% and 81% of the incoming water at IBZ1 and 2, respectively. The site (IBZ2) with the highest removal efficiency was a net N₂O sink, while 0.9% of the removed nitrate was emitted as N₂O at IBZ1. Both IBZs were net sources of CH₄ but with different pathways of emission. In IBZ1 CH₄ was mainly lost directly to the atmosphere, while waterborne losses dominated in IBZ2. In conclusion, the IBZs were effective in removing N three years after establishment, and although the IBZs acted as greenhouse gas sources, especially due to CH₄, the emissions were comparable to those of natural wetlands and other drainage transport mitigation measures.

Influence of plant habitats on denitrification in lowland agricultural streams

The aim of this study was to assess potential differences in denitrification in contrasting stream habitats in agricultural lowland streams located in Denmark. The study focused on three types of habitats i) vegetated habitats with emergent plants, ii) vegetated habitats with submerged plants, iii) bare sediments. Denitrification rates were measured in situ using denitrification chambers and nitrogen isotope pairing technique three times during a growing season. Denitrification rates across all habitats and samplings were 73 ± 116 μmol N m^-2 h^-1 (mean ± sd) with greater denitrification rates in vegetated habitats compared to bare sediments. Habitats with emergent plants had significantly higher denitrification rates than habitats with submerged plants. The habitats exhibited differences in oxygen and carbon availability probably connected to differences in flow velocity and physical effect of the vegetation (if present) which likely acted as a trap for finer organic-rich particles. Placing these results in the context of stream and river restoration highlights the potential of in-stream vegetation to mitigate nitrogen pollution, especially by restoring plant habitats in degraded and channelized streams to sustain vegetation promoting higher denitrification rates.

Efficiency of mitigation measures targeting nutrient losses from agricultural drainage systems: A review

Diffusive losses of nitrogen and phosphorus from agricultural areas have detrimental effects on freshwater and marine ecosystems. Mitigation measures treating drainage water before it enters streams hold a high potential for reducing nitrogen and phosphorus losses from agricultural areas. To achieve a better understanding of the opportunities and challenges characterising current and new drainage mitigation measures in oceanic and continental climates, we reviewed the nitrate and total phosphorus removal efficiency of: (i) free water surface constructed wetlands, (ii) denitrifying bioreactors, (iii) controlled drainage, (iv) saturated buffer zones and (v) integrated buffer zones. Our data analysis showed that the load of nitrate was substantially reduced by all five drainage mitigation measures, while they mainly acted as sinks of total phosphorus, but occasionally, also as sources. The various factors influencing performance, such as design, runoff characteristics and hydrology, differed in the studies, resulting in large variation in the reported removal efficiencies.

Wetland buffer zones for nitrogen and phosphorus retention: Impacts of soil type, hydrology and vegetation

Wetland buffer zones (WBZs) are riparian areas that form a transition between terrestrial and aquatic environments and are well-known to remove agricultural water pollutants such as nitrogen (N) and phosphorus (P). This review attempts to merge and compare data on the nutrient load, nutrient loss and nutrient removal and/or retention from multiple studies of various WBZs termed as riparian mineral soil wetlands, groundwater-charged peatlands (i.e. fens) and floodplains. Two different soil types ('organic' and 'mineral'), four different main water sources ('groundwater', 'precipitation', 'surface runoff/drain discharge', and 'river inundation') and three different vegetation classes ('arboraceous', 'herbaceous' and 'aerenchymous') were considered separately for data analysis. The studied WBZs are situated within the temperate and continental climatic regions that are commonly found in northern-central Europe, northern USA and Canada. Surprisingly, only weak differences for the nutrient removal/retention capability were found if the three WBZ types were directly compared. The results of our study reveal that for example the nitrate retention efficiency of organic soils (53 ± 28%; mean ± sd) is only slightly higher than that of mineral soils (50 ± 32%). Variance in load had a stronger influence than soil type on the N retention in WBZs. However, organic soils in fens tend to be sources of dissolved organic N and soluble reactive P, particularly when the fens have become degraded due to drainage and past agricultural usage. The detailed consideration of water sources indicated that average nitrate removal efficiencies were highest for ground water (76 ± 25%) and lowest for river water (35 ± 24%). No significant pattern for P retention emerged; however, the highest absolute removal appeared if the P source was river water. The harvesting of vegetation will minimise potential P loss from rewetted WBZs and plant biomass yield may promote circular economy value chains and provide compensation to land owners for restored land now unsuitable for conventional farming.

Forest streams are important sources for nitrous oxide emissions

Streams and river networks are increasingly recognized as significant sources for the greenhouse gas nitrous oxide (N₂ O). N₂ O is a transformation product of nitrogenous compounds in soil, sediment and water. Agricultural areas are considered a particular hotspot for emissions because of the large input of nitrogen (N) fertilizers applied on arable land. However, there is little information on N₂ O emissions from forest streams although they constitute a major part of the total stream network globally. Here, we compiled N₂ O concentration data from low-order streams (~1,000 observations from 172 stream sites) covering a large geographical gradient in Sweden from the temperate to the boreal zone and representing catchments with various degrees of agriculture and forest coverage. Our results showed that agricultural and forest streams had comparable N₂ O concentrations of 1.6 ± 2.1 and 1.3 ± 1.8 µg N/L, respectively (mean ± SD) despite higher total N (TN) concentrations in agricultural streams (1,520 ± 1,640 vs. 780 ± 600 µg N/L). Although clear patterns linking N₂ O concentrations and environmental variables were difficult to discern, the percent saturation of N₂ O in the streams was positively correlated with stream concentration of TN and negatively correlated with pH. We speculate that the apparent contradiction between lower TN concentration but similar N₂ O concentrations in forest streams than in agricultural streams is due to the low pH (<6) in forest soils and streams which affects denitrification and yields higher N₂ O emissions. An estimate of the N₂ O emission from low-order streams at the national scale revealed that ~1.8 × 10⁹  g N₂ O-N are emitted annually in Sweden, with forest streams contributing about 80% of the total stream emission. Hence, our results provide evidence that forest streams can act as substantial N₂ O sources in the landscape with 800 × 10⁹  g CO₂ -eq emitted annually in Sweden, equivalent to 25% of the total N₂ O emissions from the Swedish agricultural sector.

Nitrogen and phosphorus retention in Danish restored wetlands

Wetland restoration is considered an effective mitigation method for decreasing nitrogen (N) losses from agricultural land. However, when former cropland becomes rewetted, there is a risk that phosphorus (P) accumulated in soils will be released downstream. Here, we evaluate N and P retention in eight restored wetlands in Denmark monitored for 1 year using a mass balance approach. The wetlands represented different types, for instance, lakes and wet meadows, and ages (3-13 years). We also show the results from a long-term monitoring station established in 1973, located downstream a lake that was re-established in 2006. All restored wetlands removed total N (42-305 kg N ha^-1 year^-1), while some wetlands acted as source of total P and others as a sink (- 2.8 to 10 kg P ha^-1 year^-1). Our study confirms that restored wetlands are effective at removing N, whereas P can be released for several years after restoration.

An Assessment of the Multifunctionality of Integrated Buffer Zones in Northwestern Europe

Integrated buffer zones (IBZs) have recently been introduced in the Northwestern Europe temperate zone to improve delivery of ecosystem services compared with the services associated with long-established vegetated buffer zones. A common feature of all the studied IBZ sites is that tile drainage, which previously discharged directly into the streams, is now intercepted within the IBZ. Specifically, the design of IBZs combines a pond, where soil particles present in drain water or surface runoff can be deposited, and a planted subsurface flow infiltration zone. Together, these two components should provide an optimum environment for microbial processes and plant uptake of nutrients. Nutrient reduction capacities, biodiversity enhancement, and biomass production functions were assessed with different emphasis across 11 IBZ sites located in Denmark, Great Britain, and Sweden. Despite the small size of the buffer zones (250-800 m) and thus the small proportion of the drained catchment (mostly <1%), these studies cumulatively suggest that IBZs are effective enhancements to traditional buffer zones, as they (i) reduce total N and P loads to small streams and rivers, (ii) act as valuable improved habitats for aquatic and amphibian species, and (iii) offer economic benefits by producing fast-growing wetland plant biomass. Based on our assessment of the pilot sites, guidance is provided on the implementation and management of IBZs within agricultural landscapes.

The interplay between total mercury, methylmercury and dissolved organic matter in fluvial systems: A latitudinal study across Europe

Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64 °N. THg concentrations (0.06-2.78 ng L^-1) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8-159 pg L^-1) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, autochthonous DOM (aquatically produced) and the availability of electron acceptors for Hg methylating microorganisms (e.g. sulfate) drive %MeHg and potentially MeHg concentration. Overall, these results highlight the large spatial variability in THg and MeHg concentrations at the European scale, and underscore the importance of DOM composition on mercury cycling in fluvial systems.

Nitrogen and Phosphorus Removal from Agricultural Runoff in Integrated Buffer Zones

Integrated buffer zones (IBZs) represent a novel form of edge-of-field technology in Northwest Europe. Contrary to the common riparian buffer strips, IBZs collect tile drainage water from agricultural fields by combining a ditch-like pond (POND), where soil particles can settle, and a flow-through filter bed (FILTERBED) planted with Alnus glutinosa (L.), a European alder (black alder). The first experimental IBZ facility was constructed and thoroughly tested in Denmark for its capability to retain various nitrogen (N) and phosphorus (P) species within the first three years after construction. We calculated the water and nutrient budget for the total IBZ and for the two compartments, POND and FILTERBED, separately. Furthermore, a tracer experiment using sodium bromide was conducted in order to trace the water flow and estimate the hydraulic residence time in the FILTERBEDs. The monthly average removal efficiency amounted to 10-67% for total N and 31-69% for total P, with performance being highest during the warm season. Accordingly, we suggest that IBZs may be a valuable modification of dry buffer strips in order to mitigate the adverse impacts of high nutrient loading from agricultural fields on the aquatic environment.

Eutrophication effects on greenhouse gas fluxes from shallow-lake mesocosms override those of climate warming

Fresh waters make a disproportionately large contribution to greenhouse gas (GHG) emissions, with shallow lakes being particular hot spots. Given their global prevalence, how GHG fluxes from shallow lakes are altered by climate change may have profound implications for the global carbon cycle. Empirical evidence for the temperature dependence of the processes controlling GHG production in natural systems is largely based on the correlation between seasonal temperature variation and seasonal change in GHG fluxes. However, ecosystem-level GHG fluxes could be influenced by factors, which while varying seasonally with temperature are actually either indirectly related (e.g. primary producer biomass) or largely unrelated to temperature, for instance nutrient loading. Here, we present results from the longest running shallow-lake mesocosm experiment which demonstrate that nutrient concentrations override temperature as a control of both the total and individual GHG flux. Furthermore, testing for temperature treatment effects at low and high nutrient levels separately showed only one, rather weak, positive effect of temperature (CH4 flux at high nutrients). In contrast, at low nutrients, the CO2 efflux was lower in the elevated temperature treatments, with no significant effect on CH4 or N2 O fluxes. Further analysis identified possible indirect effects of temperature treatment. For example, at low nutrient levels, increased macrophyte abundance was associated with significantly reduced fluxes of both CH4 and CO2 for both total annual flux and monthly observation data. As macrophyte abundance was positively related to temperature treatment, this suggests the possibility of indirect temperature effects, via macrophyte abundance, on CH4 and CO2 flux. These findings indicate that fluxes of GHGs from shallow lakes may be controlled more by factors indirectly related to temperature, in this case nutrient concentration and the abundance of primary producers. Thus, at ecosystem scale, response to climate change may not follow predictions based on the temperature dependence of metabolic processes.

Phosphorus load to surface water from bank erosion in a Danish lowland river basin

Phosphorus loss from bank erosion was studied in the catchment of River Odense, a lowland Danish river basin, with the aim of testing the hypothesis of whether stream banks act as major diffuse phosphorus (P) sources at catchment scale. Furthermore, the study aimed at analyzing the impact of different factors influencing bank erosion and P loss such as stream order, anthropogenic disturbances, width of uncultivated buffer strips, and the vegetation of buffer strips. A random stratified procedure in geographical information system (GIS) was used to select two replicate stream reaches covering different stream orders, channelized vs. naturally meandering channels, width of uncultivated buffer strips (≤ 2 m and ≥ 10 m), and buffer strips with different vegetation types. Thirty-six 100-m stream reaches with 180 bank plots and a total of 3000 erosion pins were established in autumn 2006, and readings were conducted during a 3-yr period (2006-2009). The results show that neither stream size nor stream disturbance measured as channelization of channel or the width of uncultivated buffer strip had any significant ( < 0.05) influence on bank erosion and P losses during each of the 3 yr studied. In buffer strips with natural trees bank erosion was significantly ( < 0.05) lower than in buffer strips dominated by grass and herbs. Gross and net P input from bank erosion amounted to 13.8 to 16.5 and 2.4 to 6.3 t P, respectively, in the River Odense catchment during the three study years. The net P input from bank erosion equaled 17 to 29% of the annual total P export and 21 to 62% of the annual export of P from diffuse sources from the River Odense catchment. Most of the exported total P was found to be bioavailable (71.7%) based on a P speciation of monthly suspended sediment samples collected at the outlet of the river basin. The results found in this study have a great importance for managers working with P mitigation and modeling at catchment scale.

Cell cycle distribution of primitive haematopoietic cells stimulated in vitro and in vivo

A novel approach is used to study the proliferating behaviour of primitive haematopoietic cell populations in response to different stimuli. A mathematical model based on the average proportion of apoptotic, dividing and quiescent cells in primitive haematopoietic cell populations is developed to describe the mitotic history of 5- (and 6-) carboxyfluorescein diacetate succinimidyl ester-labelled cells. The cell cycle distributions in different cytokine-supplemented cultures of primitive human and mouse bone marrow cells are determined and compared with those found in vivo. The results indicate that a combination of flt-3 ligand, Steel factor and interleukin-11 or hyper-interleukin-6 provide a level of mitogenic stimulation similar to that existing in vivo after a myeloablative radiation dose. The comparison of the cell cycle distribution obtained for different cultures of human bone marrow CD34(+)(45RA/71)(-) cells demonstrates that the addition of flt-3 ligand in these cultures decreases apoptosis significantly but does not reduce quiescence. In addition, in vivo and in vitro, it was found that more than 3 days of stimulation are required to recruit a maximum number of quiescent cells into active cell cycle. These kinetics of cell cycle activation are found to be similar to those identified for the haematopoietic stem cells compartment in the same cultures. This mathematical analysis provides a useful tool for the development of haematopoietic stem cell culture processes for clinical applications.

Characterization of human hematopoietic cells with short-lived in vivo repopulating activity

Recent studies with purified hematopoietic stem cells in vitro support a model of stem cell self-renewal control that involves distinct mechanisms regulating permissiveness to and execution of lineage restriction. Such a model predicts the existence of phenotypically separable populations of hematopoietic cells that are pluripotent and either capable or incapable of extensive self-renewal. Such populations have been previously described in the mouse. We describe here the first evidence that such cells can now be identified in humans using different types of immunodeficient mice as hosts.

Distinct role of gp130 activation in promoting self-renewal divisions by mitogenically stimulated murine hematopoietic stem cells

Previous studies have demonstrated hematopoietic stem cell amplification in vitro after the activation of three cell-surface receptors: flt3/flk2, c-kit, and gp130. We now show flt3-ligand and Steel factor alone will stimulate >85% of c-kit(+)Sca-1(+)lin(-) adult mouse bone marrow cells to proliferate in single-cell serum-free cultures, but concomitant retention of their stem cell activity requires additional exposure to a ligand that will activate gp130. Moreover, this response is restricted to a narrow range of gp130-activating ligand concentrations, above and below which hematopoietic stem cell activity is lost. These findings indicate a unique contribution of gp130 signaling to the maintenance of hematopoietic stem cell function when these cells are stimulated to divide with additional differential effects dictated by the intensity of gp130 activation.

High-resolution tracking of cell division suggests similar cell cycle kinetics of hematopoietic stem cells stimulated in vitro and in vivo

The kinetics of proliferation of primitive murine bone marrow (BM) cells stimulated either in vitro with growth factors (fetal liver tyrosine kinase ligand 3 [FL], Steel factor [SF], and interleukin-11 [IL-11], or hyper-IL-6) or in vivo by factors active in myeloablated recipients were examined. Cells were first labeled with 5- and 6-carboxyfluorescein diacetate succinimidyl ester (CFSE) and then incubated overnight prior to isolating CFSE(+) cells. After 2 more days in culture, more than 90% of the in vivo lymphomyeloid repopulating activity was associated with the most fluorescent CFSE(+) cells (ie, cells that had not yet divided), although this accounted for only 25% of the repopulating stem cells measured in the CFSE(+) "start" population. After a total of 4 days in culture (1 day later), 15-fold more stem cells were detected (ie, 4-fold more than the day 1 input number), and these had become (and thereafter remained) exclusively associated with cells that had divided at least once in vitro. Flow cytometric analysis of CFSE(+) cells recovered from the BM of transplanted mice indicated that these cells proliferated slightly faster (up to 5 divisions completed within 2 days and up to 8 divisions completed within 3 days in vivo versus 5 and 7 divisions, respectively, in vitro). FL, SF, and ligands which activate gp130 are thus efficient stimulators of transplantable stem cell self-renewal divisions in vitro. The accompanying failure of these cells to accumulate rapidly indicates important changes in their engraftment potential independent of accompanying changes in their differentiation status.

Relations of diabetes intrusiveness and personal control to symptoms of depression among adults with diabetes

The generalizability of a model linking illness characteristics to psychosocial well-being was tested in a cross-sectional study of 237 adults with type 2 diabetes. It was hypothesized that diabetic complications increase illness intrusiveness, which in turn increases depressive symptomatology either directly or indirectly by reducing personal control over health outcomes. Illness intrusiveness was defined as the result of disruptions of valued activities and interests due to constraints imposed by the illness. An excellent fit of this model to the data was found using structural equation modeling. The model explained 65% of the variance in depressive symptomatology. Assessment of an alternative model excluding personal control suggested that the extent to which diabetes intrudes in life, rather than diabetic complications per se or personal control, is a key factor in relation to depressive symptomatology in individuals with diabetes.

Relations of diabetes intrusiveness and personal control to symptoms of depression among adults with diabetes

The generalizability of a model linking illness characteristics to psychosocial well-being was tested in a cross-sectional study of 237 adults with type 2 diabetes. It was hypothesized that diabetic complications increase illness intrusiveness, which in turn increases depressive symptomatology either directly or indirectly by reducing personal control over health outcomes. Illness intrusiveness was defined as the result of disruptions of valued activities and interests due to constraints imposed by the illness. An excellent fit of this model to the data was found using structural equation modeling. The model explained 65% of the variance in depressive symptomatology. Assessment of an alternative model excluding personal control suggested that the extent to which diabetes intrudes in life, rather than diabetic complications per se or personal control, is a key factor in relation to depressive symptomatology in individuals with diabetes.

Introduction to stem cell biology in vitro. Threshold to the future

Transplantable hematopoietic cells with multilineage reconstituting ability can be quantitated in suspensions of human or murine cells using similar assay procedures. The incorporation into these assays of stringently defined functional endpoints ensures a high degree of specificity for the cells detected. Application of these assays to stem cell-containing suspensions after they have been stimulated for several days with defined cytokines in vitro, or by a mixture of defined and/or undefined factors in vivo, has shown that net amplifications in these populations can be obtained under both circumstances. Such studies have allowed cytokine conditions that support stem cell self-renewal divisions to be identified and have also provided evidence that stem cell regeneration can be manipulated both in vitro and in vivo by altering the molecular milieu of the responding cells. These observations pave the way to future delineation of mechanisms that control the normal behavior, pathology and future clinical exploitation of hematopoietic stem cell populations.

Cell division tracking and expansion of hematopoietic long-term repopulating cells

The combined use of rigorous assays for quantitating transplantable stem cell numbers and precise cell labeling and tracking procedures have provided definitive evidence that stem cell self-renewal divisions can occur in vitro in the absence of stromal feeder layers. These findings set the stage for defining conditions that may alter the ability of these cells to maintain their primitive status when mitogenically activated.

Advances in hematopoietic stem cell culture

Recent advances in our understanding of the earliest stages of hematopoietic cell differentiation, and how these may be manipulated under defined conditions in vitro, have set the stage for the development of robust bioprocess technology applicable to hematopoietic cells. Sensitive and specific assays now exist for measuring the frequency of hematopoietic stem cells with long-term in vivo repopulating activity from human as well as murine sources. The production of natural or engineered ligands through recombinant DNA and/or combinatorial chemistry strategies is providing new reagents for enhancing the productivity of hematopoietic cell cultures. Multifactorial and dose-response analyses have yielded new insight into the different types and concentrations of factors required to optimize the rate and the extent of amplification of specific subpopulations of primitive hematopoietic cells. In addition, the rate of cytokine depletion from the medium has also been found to be dependent on the types of cell present. The discovery of these cell-type-specific parameters affecting cytokine concentrations and responses has introduced a new level of complexity into the design of optimized hematopoietic bioprocess systems.

The assessment of diabetes-related cognitive and social factors: the Multidimensional Diabetes Questionnaire

The purpose of this study was to examine the psychometric properties of the recently developed Multidimensional Diabetes Questionnaire (MDQ). The MDQ, which is theoretically linked to a social learning perspective of diabetes, was designed to provide a comprehensive assessment of diabetes-related cognitive and social factors. It includes 41 items grouped into three sections: (1) perceptions related to diabetes and related social support, (2) positive and misguided reinforcing behaviors related to self-care activities, and (3) self-efficacy and outcome expectancies. Confirmatory factor analyses, conducted on a sample of 249 patients with non-insulin-dependent diabetes mellitus, supported the construct validity of the MDQ. Adequate internal consistency and significant demographic, psychological, behavioral, and disease-related correlates were found. The MDQ may prove valuable in understanding individual differences in adjustment to diabetes.

Structural and in vivo mechanical characterization of canine patellar cartilage: a closed chondromalacia patellae model

The purpose of this project was to study the relationship between the structure of the patellar cartilage and its response to static compressive loading with a closed chondromalacia patellae model. An animal model was used to induce degeneration of the patella that was monitored quantitatively and qualitatively as a function of time. Ten adult mongrel dogs had their left patellofemoral groove replaced by a customized metallic implant covered with a thin film of polyethylene for periods of 3 months (five dogs) and 6 months (five dogs). An indenter was designed to perform mechanical indentation testing on the patellar cartilage in situ. The animals were anesthetized and the response of patellar cartilage to a static compressive load of 4.5 MPa was monitored for 20 min and its relaxation after load removal for 20 min. Indentation tests were performed every 3 months of the implantation period. At the end of the implantation period, the patellae were processed for histology, and sections were stained with Safranin-O indicative of the proteoglycans content. Macroscopically, no apparent degeneration or fibrillation of the patellar surfaces was observed after 3 or 6 months of implantation. However, the patellar surface showed a change in coloration after 6 months. A 17 +/- 3% and 37 +/- 8% deformation of the cartilage were calculated for the 3-month and 6-month specimens, respectively. Histologically, a progressive loss of proteoglycans was observed in the matrix as a function of implantation time. These results indicated that an increase in cartilage compliance is associated with an intrinsic remodeling of the cartilage matrix and that these changes might occur without external signs of degeneration and can be quantified.

Rheological properties of the human lumbar spine ligaments

The purpose of this study is to provide a better understanding of the rheological properties of the lumbar spinal ligaments under subfailure physiological loads. Non-destructive tests including an hysteresis experiment, stress-relaxation and stepwise load-relaxation tests were used to investigate the time-dependent properties of the interspinous-supraspinous ligament complex. Using a reduced relaxation function, the viscoelastic behaviour over the experimental time-scale was described by a linear function of the logarithm of time. Internal damping of ligament substance dissipates about 36% of the mechanical energy applied during physiological loading. Local elastic stiffness is found to be two to four times global stiffness of the bone-ligament-bone complex. These physical parameters (stiffness, energy dissipation, hysteresis, relaxation, etc) can be used to improve computer models of the lumbar spinal column.

Microwave thermography--characteristics of waveguide applicators and signatures of thermal structures

In this paper, we study the problem of the interpretation of the signals provided by microwave thermography, which allows the detection of the thermal gradients in living tissues. These signals correspond to the thermal noise measured by a radiometer when the probe scans the surface of the tissues (passive process). We describe how these signals can be computed by means of a new method based on the antenna reciprocity principle. This process requires a knowledge of the electrical field distribution in the lossy medium when the applicator is radiating a microwave signal (active process). Examples of computations of the thermal signals and experimental verifications are presented. Then, we introduce a new concept of 'thermal signature' and show how it is possible to reach a quantitative interpretation of the thermal signals such as those obtained in clinical investigations (thermal pattern recognition).

Evidence that reduced growth hormone secretion observed in monosodium glutamate-treated rats is the result of a deficiency in growth hormone-releasing factor

The present experiments were designed to examine various aspects of GH secretion in adult male rats given monosodium glutamate (MSG; 4 mg/g BW, sc) during the neonatal period. MSG-treated animals sustained lesions localized to the hypothalamic arcuate nuclei (ARC) and had reduced nasal-anal lengths and body weights. Anterior pituitary (AP) weights were decreased, but AP concentrations of GH and PRL were not significantly altered. Analysis of pulsatile GH secretion showed depressed GH pulses and prolonged GH trough periods. Mean 5-h plasma GH levels were reduced, whereas PRL levels were not affected. Morphine sulfate (MS) at doses of 0.01, 0.1, 1.0, and 3.0 mg/kg induced a prompt rise in GH during the 45 min after drug administration in controls. MSG-treated animals showed a significant rise in GH only with 1.0 and 3.0 mg/kg MS. A significant elevation in PRL was found in both control and MSG-treated animals after 1.0 and 3.0 mg/kg MS. The pentobarbital-induced rise in GH was also blunted in MSG-treated animals. MSG-treated animals which were administered antisomatostatin serum showed elevated GH trough and mean GH levels, with no apparent effect on GH peak levels. In view of the mechanisms by which MS and pentobarbital act to increase GH secretion, the present data suggest that the GH regulatory deficit observed in MSG-treated rats is due to a relative loss of GH-releasing factor secondary to ARC damage.

Electrical characteristics of waveguide applicators for medical applications

This work concerns the electrical properties of waveguide applicators consisting of flanged rectangular waveguides filled with a dielectric, used in medical applications (microwave thermography and local hyperthermia). The reflection coefficient and the near field configuration in lossy materials were obtained in some cases analytically and in some other cases numerically. The validity of these methods was verified experimentally. The study shows that the matching of the applicator and the penetration depth in a lossy material, such as a living tissue, depend not only on the tissue characteristics but also on the characteristics of the applicator itself.

Neuropharmacological regulation of episodic growth hormone and prolactin secretion in the rat

The effects on GH and PRL secretion of several pharmacological agents known to modify central neurotransmitter action were determined in unanesthetized male rats. Phenoxybenzamine, an alpha-adrenergic blocker (5 mg/kg iv), abolished episodic GH secretion and caused elevation of serum PRL levels. Propranolol, a beta-adrenergic blocker (5 mg/kg iv), had no effect on GH secretion and caused a small but significant depression in PRL levels. Parachlorophenylalanine methyl ester, an inhibitor of tryptophan hydroxylase (300-350 mg/kg ip), resulted in significant inhibition of GH pulsatile secretion and suppressed PRL levels. Methysergide hydrogen maleinate (25 mg/kg iv), a serotonin receptor antagonist, also inhibited GH secretion, but produced a transient stimulation in PRL levels. Atropine sulfate (2 mg/kg iv) caused significant suppression in GH secretion, but had no effect on PRL. Picrotoxin, a gamma-aminobutyric acid antagonist, in a subconvulsive dose of 1-3 mg/kg iv, also depressed GH episodic secretion but did not affect PRL levels. These results indicate that several neurotransmitters, i.e., norepinephrine, serotonin, acetylcholine, and gamma-aminobutyric acid, found in high concentration in the hypothalamus, influence GH and PRL secretion.

Haemodynamic changes due to clamping of the abdominal aorta

Haemodynamic changes due to aortic cross-clamping were examined in 18 patients. It has been shown that the distal occlusion of the abdominal aorta induces an increased impedance to ejection. Because the mechanisms controlling the auto-regulation of cardiac output and the circulatory reflexes are damped by anaesthesia, the augmentation of resistance is not followed by any increase in contractility or vasomotor tone and thus the cardiac output falls. Patients with chronic obstructive disease (Leriche) did not differ significantly from subjects with more acute obstruction (aneurysm), though the latter have a tendency to show more important changes in their haemodynamic response.

Physiologic secretion of growth hormone and prolactin in male and female rats

Growth hormone and prolactin are secreted episodically in man and experimental animals. To investigate physiologic mechanisms of GH and PRL secretion, a series of experiments were performed in individual, unanaesthetized male and female rats. GH secretion in the male rat is characterized by intermittent surges that occur approximately every 3 h and are entrained to the light-dark cycle. Peaks reach 200--400 ng/ml and troughs are unmeasurable. PRL is secreted in more frequent episodes with a pattern distinct from GH. In the female rat, GH surges occur more frequently--approximately once each hour. PRL levels are low (less than 15 ng/ml) except on the afternoon of pro-oestrous when they surge to levels of 100--300 ng/ml. Prolactin rises 4--6 h before delivery. Levels decline rapidly at the onset of parturition and surge with each episode of suckling in the post-partum period. Growth hormone and corticosterone rise during delivery and remain elevated for several hours after delivery. Reinstitution of suckling after removal of pups causes an immediate rise in PRL and GH. The PRL response is sustained for 3--4 h, whereas the GH response is brief with return to baseline within 1 h. The time courses of the two responses are clearly independent. Stress in the male rat causes a rapid rise in PRL and suppression in GH. The PRL surge to stress is brief with return to baseline by 1 h. GH pulses are suppressed for up to 5 h after stress. These studies indicate that separate neuroendocrine control mechanisms exist for regulation of the episodic release of GH and PRL in the rat.

Dynamic studies of growth hormone and prolactin secretion in the female rat

Blood samples were removed via chronic intra-atrial cannulae every 15 min in female rats during the estrous cycle, the last week of pregnancy, parturition and suckling. Growth hormone (GH) secretion during the estrous cycle is characterized by episodic release, occurring approximately once hourly. The surges in GH increase during the last 3-4 days of gestation, and rise to high levels during delivery and with suckling. Prolactin (PRL) shows minimal fluctuations during the estrous cycle, except for a prominent pulsatile surge during proestrus. PRL rises 4-6 h prior to parturition and declines during delivery. These studies provide a basis for further studies on the dynamics of GH and PRL secretion in the female rat.

Physiological changes associated with unilateral pulmonary ventilation during operations on the lung

No important changes in the respiratory parameters were observed during one-lung anaesthesia. However, this kind of thoracic intervention can be accompanied by a dramatic fall in arterial oxygen tension. Methods to avoid tissue hypoxia have been described. In our series no complications whatever occurred in the operative and post-operative periods which could be related to the oxygenation of the patient.

Effects of somatostatin and hypothalamic ventromedial lesions on GH release induced by morphine

Morphine in intravenous doses ranging from 10 mug/kg to 8 mg/kg was shown to be effective in stimulating GH release in the unanesthetized rat. The response to the log of the dose was linear over a range of 10 to 1000 mug/kg. Somatostatin (GH-release inhibiting factor) administered SC in a dose of 200 mug/kg 5 min before morphine prevented the GH rise. Neither inhibitors of catecholamine or serotonin synthesis nor blockage of alpha and beta-adrenergic receptors had any effect on the response. The response was partially blocked in animals with large hypothalamic ventromedial (VMN) lesions. Such lesions completely abolished the GH response to pentobarbital. These results indicate that morphine is a remarkably potent agent for stimulation of GH release but the precise mechanism and site of action of the drug remain to be determined.