Isolation of Methylococcus Strain Resistant to Abnormal Climate Change to Reduce Methane Emissions from the Iranian Salt Lake

Abstract

An increase in the atmospheric concentration of methane greenhouse gas results in an increase in global warming, surface water evaporation, and amount of the solutes in relevant areas besides, it also causes climate change. In these situations, methanotrophs that are resistant to climate change and deserted conditions could be applied. Methylococcus, as one of the most extensively studied methanotrophs is highly resistant to salinity, a strain of which was isolated in this study from Hoz-e Soltan Salt Lake in Iran as an example influenced by climate change. Isolated strain was identified. To determine the ability of the bacteria for decrease of methane gas, the culture medium was analyzed by gas chromatography. Results showed that isolated strain is able to grow in salt proportion of 3.3% and acidic pH of 3.5 in vitro, reducing more than 75% of total methane gas within 10?days. In addition to nitrogen fixation ability of the strain, positive results obtained regarding drought tolerance and heat shock in this study confirmed that Methylococcus strains may be able to withstand environmental conditions of foreseeable future. Thus, to prevent methane emission in regions such as Hoz-e Soltan Salt Lake in Iran, more compatible methanotroph strains need to be identified and used.     

Peatland restoration: A brief assessment with special reference to Sphagnum bogs

Recent literature on peatland restorationindicates as a general goal repairing orrebuilding ecosystems by restoringecosystem structure, trophic organization,biodiversity, and functions to thosecharacteristic of the type of peatland towhich the damaged ecosystem belonged, or atleast to an earlier successional stage.Attainment requires provision of anappropriate hydrological regime,manipulating surface topography, improvingmicroclimate, adding appropriate diaspores,manipulating base status where necessary,fertilizing in some cases, excludinginappropriate invaders, adaptively managingthrough at least one flood/drought cycle toensure sustainability, and monitoring on ascale of decades. Several matchingconditions favoring or opposing restorationare suggested.In the restoration of peatlands, successeshave generally been those of short-termrepair. Periods of restoration have beenmuch too short to ensure progression to, oreven well toward, a fully functionalpeatland reasonably compatible with thepristine state of similar peatlandselsewhere, although with altered surfacepatterns.Long-term monitoring ofpeatland-restoration projects is essentialfor a better understanding of how to carryout such restoration successfully.Paleoecology is suggested as anunderutilized tool in peatlandrestoration.     

Methane flux from rice/wheat agroecosystem as affected by crop phenology, fertilization and water level

Methane flux was measured for a rice/wheat agroecosystem of Gangetic Plains, with and without application of chemical fertilizer and wheat straw (WS). Three treatments of control, fertilizer application and fertilizer + WS application, were established in a completely randomized block design and measurements were made for two consecutive years (1993 and 1994). CH₄ measurements during growth of the rice crop period showed that there were significant difference in flux rates during the two years. Maximum emission occurred at the time of anthesis and minimum at the seedling stage. The flux rates were significantly higher for fertilizer or fertilizer + WS treatments. The effects of the treatments were similar across phenological stages and years. In the subsequent wheat crop and fallow period, the soils consumed CH₄. There were significant differences in CH₄ uptake rates between the two years. Fertilizer treatments reduced CH₄ uptake in both the years. The results suggested that tropical agroecosystems may consume substantial amounts of CH₄ and that the methane output can be reduced by lowering the submergence level in rice paddies.     

Methanotrophic Activity,Abundance, and Diversity in Forested Swamp Pools: Spatiotemporal Dynamics and Influences on Methane Fluxes

Methane oxidation (methanotrophy) in the water column and sediments of forested swamp pools likely control seasonal and annual emission of CH₄ from these systems, but the methanotrophic microbial communities, their activities, locations, and overall impact, is poorly understood. Several techniques including ¹⁴CH₄ oxidation assays, culture-based most probable number (MPN) estimates of methane-oxidizing bacteria (MOB) and protozoan abundance, MOB strain isolation and characterization, and PCR techniques were used to investigate methanotrophy at a forested swamp near Ithaca, New York. The greatest methanotrophic activity and largest numbers of MOB occurred predominantly at the low oxygen sediment/water interface in the water column. Seasonally, methanotrophic activity was very dynamic, ranging from 0.1 to 61.9 μ moles CH₄ d^?1 g^?1 dry sediment, and correlated most strongly with dissolved inorganic carbon (r = 0.896). Incorporation of methanotrophic variables (abundance and activity) into existing CH₄ flux regression models improved model fit, particularly during mid summer when CH₄ fluxes were most dynamic. Annually integrated methane flux and methanotrophic activity measurements indicate that differences in methanotrophic activity at the sediment/water interface likely accounted for differences in the annual CH₄ emission from the field site. Direct isolations of MOB resulted in the repeated isolation of organisms most closely related to Methylomonas methanica S1. A single acidophilic, type II MOB related to Methylocella palustris K was also isolated. Using a PCR-based MPN method and 16S rRNA genome copy number from isolates and control strains, type I and type II MOB were enumerated and revealed type I dominance of the sediment-associated MOB community.     

Methane dosage to soil and its effect on plant growth

Two protocols for following soil methane enrichment were used, one with methane dosed as a carbon source ([C]-soil) and one with methane plus minerals ([C+M]-soil). Methane oxidation occurred much faster in soil receiving minerals in addition to methane than in the control soil receiving only methane. In both treatments, only a small fraction of methane (2% to 14%) was converted into microbial biomass C. Nevertheless, a strong increase in soil microbial biomass (up to 1.5 to 2.0-fold) was achieved in the [C+M]-soil in a 3-week period. Due to methane application, the NO₃ ^- content of the soil was significantly decreased, by 83% to 90% in the [C]-soil and by 56% to 83% in the [C+M]-soil. Soil enzymatic activities were slightly increased in the [C+M]-soil only. The soil-methane incubation did not alter the composition of the monitored microbial populations in the soil or in rhizosphere of plants. In the [C]-soil, methane incubation resulted in reduction of the shoot dry wt of maize by 8% to 12%. In the [C+M]-soil under non-limiting mineral-nutrient status, a significant increase in shoot dry wt was observed for maize (13%), a neutral effect was registered for spinach and a negative effect was observed for wheat.     

Elevated CO<Subscript>2</Subscript> Effects on Peatland Plant Community Carbon Dynamics and DOC Production

Northern peatlands are important stores of carbon and reservoirs of biodiversity that are vulnerable to global change. However, the carbon dynamics of individual peatland plant species is poorly understood, despite the potential for rising atmospheric CO₂ to affect the vegetation’s contribution to overall ecosystem carbon function. Here, we examined the effects of 3 years exposure to elevated CO₂ (eCO₂) on (a) peatland plant community composition and biomass, and (b) plant carbon dynamics and the production of dissolved organic carbon (DOC) using a ¹³CO₂ pulse–chase approach. Results showed that under eCO₂, Sphagnum spp. cover declined by 39% (P < 0.05) and Juncus effusus L. cover increased by 40% (P < 0.001). There was a concurrent increase in above- and belowground plant biomass of 115% (P < 0.01) and 96% (P < 0.01), respectively. Vascular species assimilated and turned over more ¹³CO₂-derived carbon than Sphagnum spp. (49% greater turnover of assimilated ¹³C in J. effusus and F. ovina L. leaf tissues compared with Sphagnum, P < 0.01). Elevated CO₂ also produced a 66% rise in DOC concentrations (P < 0.001) and an order of magnitude more ‘new’ exudate ¹³DOC than control samples (24 h after ¹³CO₂ pulse-labelling 2.5 ± 0.5 and 0.2 ± 0.1% in eCO₂ and control leachate, respectively, P < 0.05). We attribute the observed increase in DOC concentrations under eCO₂ to the switch from predominantly Sphagnum spp. to vascular species (namely J. effusus), leading to enhanced exudation and decomposition (litter and peat). The potential for reduced peatland carbon accretion, increased DOC exports and positive feedback to climate change are discussed.     

Patterns in Vegetation and CO<Subscript>2</Subscript> Dynamics along a Water Level Gradient in a Lowland Blanket Bog

The surface of bogs is commonly patterned and composed of different vegetation communities, defined by water level. Carbon dioxide (CO₂) dynamics vary spatially between the vegetation communities. An understanding of the controls on the spatial variation of CO₂ dynamics is required to assess the role of bogs in the global carbon cycle. The water level gradient in a blanket bog was described and the CO₂ exchange along the gradient investigated using chamber based measurements in combination with regression modelling. The aim was to investigate the controls on gross photosynthesis (P_G), ecosystem respiration (R_E) and net ecosystem CO₂ exchange (NEE) as well as the spatial and temporal variation in these fluxes. Vegetation structure was strongly controlled by water level. The species with distinctive water level optima were separated into the opposite ends of the gradient in canonical correspondence analysis. The number of species and leaf area were highest in the intermediate water level range and these communities had the highest P_G. Photosynthesis was highest when the water level was 11 cm below the surface. Ecosystem respiration, which includes decomposition, was less dependent on vegetation structure and followed the water level gradient more directly. The annual NEE varied from −115 to 768 g CO₂ m⁻², being lowest in wet and highest in dry vegetation communities. The temporal variation was most pronounced in P_G, which decreased substantially during winter, when photosynthetic photon flux density and leaf area were lowest. Ecosystem respiration, which is dependent on temperature, was less variable and wintertime R_E fluxes constituted approximately 24% of the annual flux.     

Methane emissions from wetlands and their relationship with vascular plants: an Arctic example

This paper investigates the relationship between vascular plant production and CH₄ emissions from an arctic wet tundra ecosystem in north‐east Greenland. Light intensity was manipulated by shading during three consecutive growing seasons (1998–2000). The shading treatment resulted in lower carbon cycling in the ecosystem as mean seasonal net ecosystem exchange (NEE) decreased from ?336 to ?196 mg CO₂ m^?2 h^?1 and from ?476 to ?212 mg CO₂ m^?2 h^?1 in 1999 and 2000, respectively, and total ecosystem respiration decreased from 125 to 94 mg CO₂ m^?2 h^?1 in 1999 and from 409 to 306 mg CO₂ m^?2 h^?1 in 2000. Seasonal mean CH₄ emissions in controls and shaded plots were, respectively, 6.5 and 4.5 mg CH₄ m^?2 h^?1 in 1999 and 8.3 and 6.2 mg CH₄ m^?2 h^?1 in 2000. We found that CH₄ emission was sensitive to NEE and carbon turnover, and it is reasonable to assume that the correlation was due to a combined effect of vegetative CH₄ transport and substrate quality coupled to vascular plant production. Total above‐ground biomass was correlated to mean seasonal CH₄ emission, but separation into species showed that plant‐mediated CH₄ transport was highly species dependent. Potential CH₄ production peaked at the same depth as maximum root density (5–15 cm) and treatment differences further suggest that substrate quality was negatively affected by decreased NEE in the shaded plots. The concentration of dissolved CH₄ decreased in the control plots as the growing season progressed while it was relatively stable in the shaded plots. This suggests that a progressively better developed root system in the controls increased the capacity to transport CH₄ from the soil to the atmosphere. In conclusion, vascular plant photosynthetic rate and subsequent allocation of recently fixed carbon to below‐ground structures seemed to influence both vegetative CH₄ transport and substrate quality.     

Methane flux in relation to growth and phenology of a high yielding rice variety as affected by fertilization

Influence of urea application on growth parameters (shoot height, and weight, root volume, weight and porosity; number of tillers; grain yield) and their relationship with methane (CH₄) flux was investigated in Oryza sativa (var. Pant Dhan-4) under flooded soil condition. The study design consisted of (a) fertilized vegetated, (b) control vegetated, (c) fertilized bare, and (d) control bare plots. Crop growth and CH₄ flux measurements were conducted from 9 to 115 days of rice transplanting at regular intervals of 10 days. Results showed that there were significant differences due to days (dates of measurement) and fertilization in all growth parameters except shoot height. Day × fertilization interaction was significant for all growth parameters. CH₄ fluxes ranged from 0.4 to 20.2, 0.1 to 11.9, 0.09 to 2.2 and 0.004 to 1.5 mg m^-2 h^-1 under treatments (a), (b), (c) and (d), respectively. Maximum CH₄ flux was recorded at the flowering stage. All the growth parameters, including number of tillers, showed strong positive relationship with total methane flux. Root porosity was also strongly correlated with total CH₄ emission. It was concluded that CH₄ emission was substantially influenced by crop phenology and growth, and fertilization. The study emphasizes the substrate production and conduit effects of rice plants on CH₄ flux.     

Plant Demography and Habitat: A Comparative Approach

Abstract Progress in plant demography will depend upon being able to synthesize a large body of data and this requires a means of comparing populations between sites and species. We have employed a comparative technique using elasticity analysis of stage-projection matrices to partition the contributions of fecundity (F), survival (L) and growth (G) to the finite rate of increase λ. Ordination of populations of 77 perennial herbs and trees in G-L-F space has shown that species segregate in this triangular space according to their life history and habitat. In the present paper we use the correspondence between demographic parameters and habitat revealed by this method to predict how succession and a variety of environmental factors such as grazing and fire are likely to alter the demography of populations and ultimately to change the composition of communities.     

以龟裂地植丛发生演替为例探讨植物对环境的反应与反馈效应

准葛尔盆地荒漠龟裂地植丛发生演替的研究结果表明：在荒漠龟裂地发生演替的初始阶段,环境因子对植物发生具有极大的限制作用。但是,一旦有先锋植物侵入,植物就会通过自身的生命活动不断改善其生存环境,为新植物的进入创造条件,新植物的定居又会反作用于环境,使其生存条件进一步改善,如此往复,推动整个微生态系统由简单至繁杂呈顺序性、方向性发展。生命的存在及其活动过程对环境的反应和对于环境的反馈作用,是导致生态系统顺向发展的根本动力。该研究将为如何改善生境质量提供理论基础,对植被恢复及受损生态系统的重建,特别是对加深全球变化环境下气候与植被关系的理解,提高预测陆地生态系统对全球变化反应的能力有重要的意义。     

Climate Change,Risks and Contaminants: A Perspective from Studying the Arctic

The Arctic faces threats from climate change and contaminants. Together, these two threats are likely to present surprises centered around the zero-degree isotherm because the phase change of water has enormous potential to affect contaminant transport and transfer, and biological distribution and stress. Particularly at risk are top aquatic predators, migratory species, and species narrowly adapted to ice. These species are most exposed to contaminants, are most likely to become stressed by climate change, or contain within their life cycles efficient vectors of contaminants and diseases. In the Arctic, mercury presents a special case where risks can be altered at many places in the biogeochemical cycle. Atmospheric mercury depletion events offer one such location; however, the methylation of mercury in aquatic systems appears a far more important and presently neglected component of risk from mercury to Arctic ecosystems. Climate variables alter transport, transfer, and capture of contaminants. Therefore, monitoring for contaminants must be conducted with a systems approach that includes climate-related factors. To ensure that the perception of risk is accurate and that priority risks are addressed first, a closer dialogue between scientists, the public, and public administers is urgently required.     

A Stochastic Population Dynamics Model for Aedes Aegypti: Formulation and Application to a City with Temperate Climate

Aedes aegypti is the main vector for dengue and urban yellow fever. It is extended around the world not only in the tropical regions but also beyond them, reaching temperate climates. Because of its importance as a vector of deadly diseases, the significance of its distribution in urban areas and the possibility of breeding in laboratory facilities, Aedes aegypti is one of the best-known mosquitoes. In this work the biology of Aedes aegypti is incorporated into the framework of a stochastic population dynamics model able to handle seasonal and total extinction as well as endemic situations. The model incorporates explicitly the dependence with temperature. The ecological parameters of the model are tuned to the present populations of Aedes aegypti in Buenos Aires city, which is at the border of the present day geographical distribution in South America. Temperature thresholds for the mosquito survival are computed as a function of average yearly temperature and seasonal variation as well as breeding site availability. The stochastic analysis suggests that the southern limit of Aedes aegypti distribution in South America is close to the 15^∘C average yearly isotherm, which accounts for the historical and current distribution better than the traditional criterion of the winter (July) 10°C isotherm.     

The effect of trophic/contaminant interactions on chironomid community structure and succession (Diptera: Chironomidae)

The effects of contaminants and organic pollution on the chironomid communities of two basins in Lac St. Louis, a river-lake on the St. Lawrence River above Montreal, Quebec, were assessed and compared using lake classification theory techniques and morphological deformity indices based on the ligulae and antennae ofProcladius, the dominant surviving component of the south-shore communities. Contaminants from the industrial complex around Beauharnois, Quebec, have seriously degraded communities along the south-shore gradient while the introduction of untreated domestic wastes from Laprairie, Quebec, has seriously affected the communities of the Laprairie basin. The interaction between trophic and contaminant effects constitutes a classic example of the setback or deflection in the trajectory of ecological succession in biological communities hypothesized by ODUM (1981, 1985).     

Latitudinal differentiated water table control of carbon dioxide, methane and nitrous oxide fluxes from hydromorphic soils: feedbacks to climate change

The possibility of carbon (C) being locked away from the atmosphere for millennia is given in hydromorphic soils. However, the water-table-dependent feedback from soil organic matter (SOM) decomposition to the climate system is less clear. At least three greenhouse gases are produced: carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). These gases show emission peaks at different water table positions and have different global warming potentials (GWP), for example a factor of 23 for CH₄ and 296 for N₂O as compared with the equivalent mass of CO₂ on a 100-year time horizon. This review of available annual data on all three gases revealed that the radiative forcing effect of SOM decomposition is principally dictated by CO₂ despite its low GWP. Anaerobic SOM decomposition generally has a lower potential feedback to the climatic system than aerobic SOM decomposition. Concrete values are constrained by a lack of data from tropical and subarctic regions. Furthermore, data on N₂O and on plant effects are generally rare. However, there is a clear latitudinal differentiation for the GWP of soils under anaerobic conditions compared with aerobic conditions when looking at CO₂ and CH₄: in the tropical and temperate regions, the anaerobic GWP showed a range of 25–60% of the aerobic value, but values varied between 80% and 110% in the boreal zone. Hence, particularly in the vulnerable boreal zone, the feedback from ecosystems to climate change will highly depend on plant responses to changing water tables at elevated temperatures.     

城市水资源生态足迹核算模型及应用——以沈阳市为例

水资源生态足迹可以直接反映区域人类社会经济活动对水资源的压力.本研究在现有的生态足迹模型基础上,充分考虑城市自然生态系统对水资源的需求,建立了包括居民日常生活用水、生产运营用水、公共服务用水和生态需水4类帐户的城市水资源生态足迹核算模型,并结合沈阳市实际情况,确定了模型中的相关参数,对沈阳市水资源生态足迹和生态承载力进行分析.结果表明:2000-2009年,沈阳市人均水资源生态足迹总体呈下降态势,但各年度均为水生态赤字;2005年较2000年水资源生态足迹人均下降0.31 hm2,2006、2007年有小幅回升,2008、2009年趋于平稳,说明沈阳市水资源可持续利用状况有一定改善,但仍处于不可持续状态.     

Methane emission from natural wetlands: interplay between emergent macrophytes and soil microbial processes. A mini-review

Background

According to the Intergovernmental Panel on Climate Change (IPCC) 2007, natural wetlands contribute 20–39 % to the global emission of methane. The range in the estimated percentage of the contribution of these systems to the total release of this greenhouse gas is large due to differences in the nature of the emitting vegetation including the soil microbiota that interfere with the production and consumption of methane.

Scope

Methane is a dominant end-product of anaerobic mineralization processes. When all electron acceptors except carbon dioxide are used by the microbial community, methanogenesis is the ultimate pathway to mineralize organic carbon compounds. Emergent wetland plants play an important role in the emission of methane to the atmosphere. They produce the carbon necessary for the production of methane, but also facilitate the release of methane by the possession of a system of interconnected internal gas lacunas. Aquatic macrophytes are commonly adapted to oxygen-limited conditions as they prevail in flooded or waterlogged soils. By this system, oxygen is transported to the underground parts of the plants. Part of the oxygen transported downwards is released in the root zone, where it sustains a number of beneficial oxidation processes. Through the pores from which oxygen escapes from the plant into the root zone, methane can enter the plant aerenchyma system and subsequently be emitted into the atmosphere. Part of the oxygen released into the root zone can be used to oxidize methane before it enters the atmosphere. However, the oxygen can also be used to regenerate alternative electron acceptors. The continuous supply of alternative electron acceptors will diminish the role of methanogenesis in the anaerobic mineralization processes in the root zone and therefore repress the production and emission of methane. The role of alternative element cycles in the inhibition of methanogenesis is discussed.

Conclusions

The role of the nitrogen cycle in repression of methane production is probably low. In contrast to wetlands particularly created for the purification of nitrogen-rich waste waters, concentrations of inorganic nitrogen compounds are low in the root zones in the growing season due to the nitrogen-consuming behaviour of the plant. Therefore, nitrate hardly competes with other electron acceptors for reduced organic compounds, and repression of methane oxidation by the presence of higher levels of ammonium will not be the case. The role of the iron cycle is likely to be important with respect to the repression of methane production and oxidation. Iron-reducing and iron-oxidizing bacteria are ubiquitous in the rhizosphere of wetland plants. The cycling of iron will be largely dependent on the size of the oxygen release in the root zone, which is likely to be different between different wetland plant species. The role of the sulfur cycle in repression of methane production is important in marine, sulfate-rich ecosystems, but might also play a role in freshwater systems where sufficient sulfate is available. Sulfate-reducing bacteria are omnipresent in freshwater ecosystems, but do not always react immediately to the supply of fresh sulfate. Hence, their role in the repression of methanogenesis is still to be proven in freshwater marshes.     

Safeguarding Ecosystem Services: A Methodological Framework to Buffer the Joint Effect of Habitat Configuration and Climate Change

Ecosystem services provided by mobile agents are increasingly threatened by the loss and modification of natural habitats and by climate change, risking the maintenance of biodiversity, ecosystem functions, and human welfare. Research oriented towards a better understanding of the joint effects of land use and climate change over the provision of specific ecosystem services is therefore essential to safeguard such services. Here we propose a methodological framework, which integrates species distribution forecasts and graph theory to identify key conservation areas, which if protected or restored could improve habitat connectivity and safeguard ecosystem services. We applied the proposed framework to the provision of pollination services by a tropical stingless bee (Melipona quadrifasciata), a key pollinator of native flora from the Brazilian Atlantic Forest and important agricultural crops. Based on the current distribution of this bee and that of the plant species used to feed and nest, we projected the joint distribution of bees and plants in the future, considering a moderate climate change scenario (following IPPC). We then used this information, the bee’s flight range, and the current mapping of Atlantic Forest remnants to infer habitat suitability and quantify local and regional habitat connectivity for 2030, 2050 and 2080. Our results revealed north to south and coastal to inland shifts in the pollinator distribution during the next 70 years. Current and future connectivity maps unraveled the most important corridors, which if protected or restored, could facilitate the dispersal and establishment of bees during distribution shifts. Our results also suggest that coffee plantations from eastern São Paulo and southern Minas Gerais States could suffer a pollinator deficit in the future, whereas pollination services seem to be secured in southern Brazil. Landowners and governmental agencies could use this information to implement new land use schemes. Overall, our proposed methodological framework could help design novel conservational and agricultural practices that can be crucial to conserve ecosystem services by buffering the joint effect of habitat configuration and climate change.     

Child Centred Approach to Climate Change and Health Adaptation through Schools in Bangladesh: A Cluster Randomised Intervention Trial

Background

Bangladesh is one of the most vulnerable countries to climate change. People are getting educated at different levels on how to deal with potential impacts. One such educational mode was the preparation of a school manual, for high school students on climate change and health protection endorsed by the National Curriculum and Textbook Board, which is based on a 2008 World Health Organization manual. The objective of this study was to test the effectiveness of the manual in increasing the knowledge level of the school children about climate change and health adaptation.

Methods

This cluster randomized intervention trial involved 60 schools throughout Bangladesh, with 3293 secondary school students participating. School upazilas (sub-districts) were randomised into intervention and control groups, and two schools from each upazila were randomly selected. All year seven students from both groups of schools sat for a pre-test of 30 short questions of binary response. A total of 1515 students from 30 intervention schools received the intervention through classroom training based on the school manual and 1778 students of the 30 control schools did not get the manual but a leaflet on climate change and health issues. Six months later, a post-intervention test of the same questionnaire used in the pre-test was performed at both intervention and control schools. The pre and post test scores were analysed along with the demographic data by using random effects model.

Results

None of the various school level and student level variables were significantly different between the control and intervention group. However, the intervention group had a 17.42% (95% CI: 14.45 to 20.38, P = <0.001) higher score in the post-test after adjusting for pre-test score and other covariates in a multi-level linear regression model.

Conclusions

These results suggest that school-based intervention for climate change and health adaptation is effective for increasing the knowledge level of school children on this topic.