You're using an outdated browser. Please upgrade to a modern browser for the best experience.
Ventilation Systems in Wetland Plant Species
Edit
This entry is adapted from the peer-reviewed paper 10.3390/d14070517

Ventilation systems rely on a passive molecular diffusion process, on pressurized gas flow, or Venturi-induced convection. 

metabolic gases greenhouse gases aerenchyma

1. Introduction

The aquatic environment holds special challenges for plant survival. The diffusion of gases in water is about 104-fold slower than in air, so that aquatic plants must perform photosynthesis in water, and maintain aerobic respiration in flooded conditions [1][2]. Herbaceous wetland plants differ significantly, according to the accessibility of gases for their metabolism regarding their position in the water column. Researchers define various functional groups, namely, (1) emergent macrophytes or helophytes that are rooted in water-saturated soil, with foliage extending into the air (e.g., Typha latifolia, Phragmites australis); (2) floating-leaved macrophytes that are living in water rooted in hypoxic or anoxic sediment, with leaves floating on the water surface (e.g., Nuphar luteum, Nymphaea alba); (3) submerged macrophytes that grow completely submerged under the water, with roots or rhizoids attached to the substrate (e.g., Myriophyllum spicatum, Potamogeton crispus); and (4) free-floating macrophytes that float on or under the water surface, and are usually not rooted in the sediment (e.g., Ceratophyllum demersum) [3]. In addition, wetlands also host many different woody plants that are permanently or occasionally rooted in water-saturated sediment [4]. These species, belonging to different groups, often possess adaptations to overcome oxygen and carbon dioxide deficiencies, in order to maintain optimal conditions for photosynthesis and respiration. Emergent and floating-leaved species have an advantage over submerged species because their above-ground parts are fully or partly exposed to air. Aerial leaves have stomata in their epidermis, which can be adjusted to optimize exposure of internal tissues to the atmosphere and the exchange of gases. Thus, aerial plant parts are well supplied with oxygen, but for roots and rhizomes anchored in water-saturated soils, oxygen for respiration can be limited. Therefore, efficient ventilation systems are crucial for their survival. Ventilation systems rely on a passive molecular diffusion process, on pressurized gas flow, or Venturi-induced convection [5]; however, in submerged plant tissue, the direct exchange of gases between these tissues and water also occurs [6]. In most aquatic species, ventilation is enabled by an extended system of air canals and intercellular spaces called aerenchyma, which develop in different plant organs from roots, to stems and leaves. [7][8]. Gases in aerenchyma can originate from the atmosphere, rhizosphere, or plant metabolism [9]. Laing [10] shows a strong relationship between the leaf area and the extent of changes of oxygen and carbon dioxide concentrations in aerenchyma during periods of illumination; thus, the contribution of metabolic gases may vary significantly among species.
Aquatic plants mainly form aerenchyma constitutively in different organs, namely, roots, leaves, and stems, while some amphibious and terrestrial plants produce aerenchyma in response to an oxygen shortage [7]. The presence of aerenchyma may differ among species. Independent of habitat, aerenchyma patterns are stable at the genus level, and the consistency of pattern is stronger in the roots than in the shoots [11]. In addition to the atmosphere, gases in aerenchyma can originate from the rhizosphere or plant metabolism [9]. The formation of aerenchyma may not depend on environmental conditions, or be induced by flooding [1]. Aerenchyma cells are formed lysigenously by programmed cell death, as is the case of rice roots; schizogenously by the expansion of intercellular spaces [11]; and expansigenously (secondary aerenchyma) by cell division or enlargement, without cell separation or death [12]. These enlarged spaces may develop either in primary tissues (primary aerenchyma), or in secondary tissues (secondary aerenchyma) [13]. According to Doležal et al. [14], lysigenous aerenchyma are mostly produced by submerged plants, schizogenous aerenchyma by terrestrial and perennial wetland plants, and expansigenous honeycomb aerenchyma by aquatic floating-leaved plants. The amount of intercellular spaces varies significantly among species. In aquatic species, these intercellular spaces contribute up to 60% of the leaf volume [15], while in mesophytes, their volumes range from 2–7% [16]. Thus, in non-tolerant species, flooding may result in the demise of the plant.
Beyond ventilation, aerenchyma cells have other important ecological functions, including acting to store gases and increasing their internal conductance to roots and shoots [7]. The transfer of oxygen to underground organs, via aerenchyma during soil flooding, may prevent the suffocation of plants. Oxygen can also be transferred from roots to the rhizosphere, via aerenchyma. This critically important oxygen to oxidize and detoxify toxic chemicals formed in sediments in environments with low redox potential [17][18], noting that a lack of oxygen is associated with reduced forms of sulfur, manganese, and iron that may reach toxic levels in the soil [6].
In wetland soils, gas concentrations of several gases, such as carbon dioxide and methane, exceed atmospheric concentrations. Thus, aerenchyma can also be a path for greenhouse gas emissions from the plant, as methane and nitrous dioxide are released via plants from waterlogged sediments to the atmosphere [19][20].
Some photosynthetic O2 produced by submerged plants oxygenates the water column, while natant plants can prevent oxygen diffusion from the atmosphere to water [21][22][23][24]. Aerenchyma cells lend buoyancy and mechanical resistance to breakage, with a relatively small investment in biomass by aquatic plants [25].
The ventilation in wetland plants takes place via various plant structures, and is enabled by the presence of aerenchyma in these structures. The source of gases and influx and efflux locations may differ significantly among different species and plant groups.

2. Diversity of Ventilation Systems

Similar physical processes of ventilation occur in different taxonomical and functional plant groups that thrive in oxygen-deficient sediment; however, their morphological adaptations differ significantly (Table 1). Functional traits of these plants are not only the species’ response to specific environmental conditions, but they also depend on their phylogeny. Jung et al. [11] find specific trends of aerenchyma patterns in several taxa of higher plants, and show that these patterns partially coincide with their phylogeny. The study of Cape reeds reveals that the presence of aerenchyma correlates with the eco-hydrological niche at the population and species level, indicating that waterlogging presents an environmental filter that excludes species without aerenchyma [26]. Bedoya and Madrinán [27], studying the evolution of the aquatic habit in genus Ludwigia L., find a convergence towards the absence of secondary growth in roots, smaller proportion of lignified tissue area in underground organs, and the presence of primary aerenchyma. However, there are also studies that are not consistent with these results. For example, the study of different Carex L. species in a phylogenetic context, with an even sampling across the different clades, shows that the size of the aerenchyma has only a weak relation to soil moisture [28]. Carex species with poorly developed aerenchyma have low performance in flooded soil, while partial submergence may even affect species with a larger amount of root aerenchyma [29].
Table 1. Ventilation mechanisms in different taxonomical and functional plant groups that thrive in oxygen-deficient sediment.
Table
Plant Group Taxonomic Group Source of Gasses Ventilation Principle Special Features Reference
Submerged Isoetids Water, metabolism,
Sediment		 Diffusion,
aeration of rhizosphere via buried leaves		 Aerenchyma, CAM [30][31]
  Angiosperms Water, metabolism,
Sediment		 Diffusion Metabolic gasses trapped in aerenchyma [32][33]
Floating Nuphar spp., Nymphaea spp. Air, metabolism,
Sediment		 Pressurized ventilation, thermo-osmotic gas transport, ‘Heat pump’ drives gasses from the atmosphere via young natant leaves, petioles to roots and back, via older leaves to the atmosphere e.g., [34][35][36]
  Nelumbo nucifera Air, metabolism,
Sediment		 Pressurized ventilation,
influx via laminal stomata of natant leaves through aerenchyma to rhizomes; back from rhizomes through aerenchyma in petiole through stomata in leaf central part		 Leaf lamina with fewer and smaller stomata,
leaf central part with larger and denser stomata, which actively regulate the airflow by opening and closing		 [37][38][39]
Helophytes Equisetum spp.—4 out of 9 have through-flow
convection		 Air, possibly also metabolism, sediment Pressurized ventilation,
humidity-induced diffusion,		 Air moves through stomata through branches, via interconnecting aerenchyma channels in stem and rhizomes, with venting through the previous year’s stubble or damaged shoot. [40][41]
  Phragmites spp. Air, possibly also metabolism, sediment Pressurized ventilation,
suction via old broken stems (Venturi-effect),
air films on leaves when submerged		 Via leaves, stems to root system, partly to sediment (ROL), and back to stems, leaves, and atmosphere [42][43][44][45][46]
  Typha spp. Air, sediment, possibly metabolism,
oxygen in the rhizosphere may be obtained from the decomposition of hydrogen peroxide by catalase		 Pressurized ventilation,
leaf stomata create inner pressure,
air films on leaves when submerged		 Air enters through middle-aged leaves, and exits through the oldest ones [42][47][48][49]
  Oryza sativa Air films on leaves when submerged Flow from above-ground parts via roots by diffusion, and possibly also by mass flow Water-repellent leaf surface; air layer up to 25 µm, large air spaces inside leaves and roots, the porosity of adventitious roots, a barrier in roots to prevent radial O2 loss from roots [50][51][52]
Species of mangrove forest Acrostichum spp.     All plant parts have large air spaces [53][54]
  Nypa fruticans   Bases of abscised leaves function as air inlets, by developing a network of lenticels covering the leaf base connected to aerenchyma “snorkeling palm”
leaf bases function up to 4 years after leaf abscission		 [55]
  Mangroves   High oxygen pressure in the roots is maintained via ventilation through the lenticels on different root structures connected with aerenchyma Special structures, i.e., pneumatophores, knee roots, stilt roots, or plant roots, provide ventilation during low tides [56]
Other wetland species Alnus spp. Thermo-osmotically driven gas flow In Alnus glutinosa, the flow is from the external atmosphere through the stems to the roots Thermo-osmotic flow in alder is related to the lenticels in the bark of the stem,
stem photosynthesis		 [4][36][57][58]
  Taxodium distichum   “knees” emerging from the roots to the surface of the water, flooding increases the porosity of roots, stems, and leaves, and enhanced O2 diffusion to roots. Snorkeling [59]
  Syzygium kunstleri   Oxygen transportation occurs through aerenchyma in the root tips, periderm near the root base, and secondary aerenchyma between layers of phellem   [60]
Most species use aerenchyma as a ventilation path, and as a reservoir for gases originating from the atmosphere, soil, and metabolic processes (e.g., respiration, photorespiration, and photosynthesis). The differences among groups are related either to specific environmental conditions (e.g., emergence, submergence), to specific species anatomy, as is the case for the lotus, or to metabolic processes and properties related to their growth form (e.g., emergent, submerged, floating-leaved, rosette, woody plants).

References

  1. Jackson, M.B. Ethylene and Responses of Plants to Soil Waterlogging and Submergence. Annu. Rev. Plant Physiol. 1985, 36, 145–174.
  2. Voesenek, L.A.C.J.; Colmer, T.D.; Pierik, R.; Millenaar, F.F.; Peeters, A.J.M. How Plants Cope with Complete Submergence. New Phytol. 2006, 170, 213–226.
  3. Janauer, G.; Germ, M.; Kuhar, U.; Gaberščik, A. Ecology of Aquatic Macrophytes and Their Role in Running Waters. In Macrophytes of the River Danube Basin; Janauer, G., Gaberščik, A., Květ, J., Germ, M., Exler, N., Eds.; Academia, Živá Příroda: Prague, Czech Republic, 2018; pp. 13–33. ISBN 9788020027436.
  4. Große, W.; Schröder, P. Oxygen Supply of Roots by Gas Transport in Alder-Trees. Z. Für Nat. C 1984, 39, 1186–1188.
  5. Colmer, T.D. Long-Distance Transport of Gases in Plants: A Perspective on Internal Aeration and Radial Oxygen Loss from Roots. Plant Cell Environ. 2003, 26, 17–36.
  6. Mitsch, W.J.; Gosselink, J.G. Wetlands: Human History, Use, and Science, 4th ed.; Wiley: Hoboken, NJ, USA, 2007; ISBN 9780471699675.
  7. Jackson, M.B.; Armstrong, W. Formation of Aerenchyma and the Processes of Plant Ventilation in Relation to Soil Flooding and Submergence. Plant Biol. 1999, 1, 274–287.
  8. Justin, S.H.F.W.; Armstrong, W. The Anatomical Characteristics of Roots and Plant Response to Soil Flooding. New Phytol. 1987, 106, 465–495.
  9. Evans, D.E. Aerenchyma Formation. New Phytol. 2004, 161, 35–49.
  10. Laing, H.E. The Composition of the Internal Atmosphere of Nuphar Advenum and Other Water Plants. Am. J. Bot. 1940, 27, 861–868.
  11. Jung, J.; Lee, S.C.; Choi, H.-K. Anatomical Patterns of Aerenchyma in Aquatic and Wetland Plants. J. Plant Biol. 2008, 51, 428–439.
  12. Bailey-Serres, J.; Voesenek, L.A. Life in the Balance: A Signaling Network Controlling Survival of Flooding. Curr. Opin. Plant Biol. 2010, 13, 489–494.
  13. Takahashi, H.; Yamauchi, T.; Colmer, T.D.; Nakazono, M. Aerenchyma Formation in Plants. In Plant Cell Monographs; Springer: Berlin/Heidelberg, Germany, 2014; Volume 21, pp. 247–265.
  14. Doležal, J.; Kučerová, A.; Jandová, V.; Klimeš, A.; Říha, P.; Adamec, L.; Schweingruber, F.H. Anatomical Adaptations in Aquatic and Wetland Dicot Plants: Disentangling the Environmental, Morphological and Evolutionary Signals. Environ. Exp. Bot. 2021, 187, 104495.
  15. Laan, P.; Berrevoets, M.J.; Lythe, S.; Armstrong, W.; Blom, C.W.P.M. Root Morphology and Aerenchyma Formation as Indicators of the Flood-Tolerance of Rumex Species. J. Ecol. 1989, 77, 693–703.
  16. Larcher, W. Physiological Plant Ecology: Ecophysiology and Stress Physiology of Functional Groups, 4th ed.; Springer: Berlin, Germany, 2003.
  17. Jia, Y.; Huang, H.; Chen, Z.; Zhu, Y.-G. Arsenic Uptake by Rice Is Influenced by Microbe-Mediated Arsenic Redox Changes in the Rhizosphere. Environ. Sci. Technol. 2014, 48, 1001–1007.
  18. Smith, K.E.; Luna, T.O. Radial Oxygen Loss in Wetland Plants: Potential Impacts on Remediation of Contaminated Sediments. J. Environ. Eng. 2013, 139, 496–501.
  19. Riya, S.; Sun, H.; Furuhata, H.; Shimamura, M.; Nasu, H.; Imano, R.; Zhou, S.; Hosomi, M. Role of Leaves in Methane Emission from Sacred Lotus (Nelumbo nucifera). Aquat. Bot. 2020, 163, 103203.
  20. Villa, J.A.; Ju, Y.; Stephen, T.; Rey-Sanchez, C.; Wrighton, K.C.; Bohrer, G. Plant-mediated Methane Transport in Emergent and Floating-leaved Species of a Temperate Freshwater Mineral-soil Wetland. Limnol. Oceanogr. 2020, 65, 1635–1650.
  21. Caraco, N.F.; Cole, J.J. Contrasting Impacts of a Native and Alien Macrophyte on Dissolved Oxygen in a Large River. Ecol. Appl. 2002, 12, 1496.
  22. Carpenter, S.R.; Lodge, D.M. Effects of Submersed Macrophytes on Ecosystem Processes. Aquat. Bot. 1986, 26, 341–370.
  23. Goodwin, K.; Caraco, N.; Cole, J. Temporal Dynamics of Dissolved Oxygen in a Floatingleaved Macrophyte Bed. Freshw. Biol. 2008, 53, 1632–1641.
  24. Horvat, B.; Urbanc-Berčič, O.; Gaberščik, A. Water Quality and Macrophyte Community Changes in the Komarnik Accumulation Lake (Slovenia). In Wastewater Treatment, Plant Dynamics and Management in Constructed and Natural Wetlands; Springer: Dordrecht, The Netherlands, 2008; pp. 13–22.
  25. Raven, J.A. Into the Voids: The Distribution, Function, Development and Maintenance of Gas Spaces in Plants. Ann. Bot. Co. 1996, 78, 137–142.
  26. Huber, M.; Linder, H.P. The Evolutionary Loss of Aerenchyma Limits Both Realized and Fundamental Ecohydrological Niches in the Cape Reeds (Restionaceae). J. Ecol. 2012, 100, 1338–1348.
  27. Bedoya, A.M.; Madriñán, S. Evolution of the Aquatic Habit in Ludwigia (Onagraceae): Morpho-Anatomical Adaptive Strategies in the Neotropics. Aquat. Bot. 2015, 120, 352–362.
  28. Hoffmann, M.H. To the Roots of Carex: Unexpected Anatomical and Functional Diversity. Syst. Bot. 2019, 44, 26–31.
  29. Visser, E.J.W.; Bogemann, G.M.; van de Steeg, H.M.; Pierik, R.; Blom, C.W.P.M. Flooding Tolerance of Carex Species in Relation to Field Distribution and Aerenchyma Formation. New Phytol. 2000, 148, 93–103.
  30. Green, W.A. The Function of the Aerenchyma in Arborescent Lycopsids: Evidence of an Unfamiliar Metabolic Strategy. Proc. R. Soc. B Biol. Sci. 2010, 277, 2257–2267.
  31. Winkel, A.; Colmer, T.D.; Pedersen, O. Leaf Gas Films of Spartina Anglica Enhance Rhizome and Root Oxygen during Tidal Submergence. Plant Cell Environ. 2011, 34, 2083–2092.
  32. Winkel, A.; Borum, J. Use of Sediment CO2 by Submersed Rooted Plants. Ann. Bot. 2009, 103, 1015–1023.
  33. Borum, J.; Pedersen, O.; Greve, T.M.; Frankovich, T.A.; Zieman, J.C.; Fourqurean, J.W.; Madden, C.J. The Potential Role of Plant Oxygen and Sulphide Dynamics in Die-off Events of the Tropical Seagrass, Thalassia Testudinum. J. Ecol. 2005, 93, 148–158.
  34. Richards, J.H.; Kuhn, D.N.; Bishop, K. Interrelationships of Petiolar Air Canal Architecture, Water Depth, and Convective Air Flow in Nymphaea Odorata (Nymphaeaceae). Am. J. Bot. 2012, 99, 1903–1909.
  35. Dacey, J.W.H.; Klug, M.J. Ventilation by Floating Leaves in Nuphar. Am. J. Bot. 1982, 69, 999.
  36. Schröder, P. Characterization of a Thermo-Osmotic Gas Transport Mechanism in Alnus glutinosa (L.) Gaertn. Trees 1989, 3, 38–44.
  37. Mevi-Scutz, J.; Grosse, W. A Two-Way Gas Transport System in Nelumbo nucifera. Plant Cell Environ. 1988, 11, 27–34.
  38. Matthews, P.G.D.; Seymour, R.S. Stomata Actively Regulate Internal Aeration of the Sacred Lotus Nelumbo Nucifera. Plant Cell Environ. 2014, 37, 402–413.
  39. Vogel, S. Contributions to the Functional Anatomy and Biology of Nelumbo Nucifera (Nelumbonaceae) I. Pathways of Air Circulation. Plant Syst. Evol. 2004, 249, 9–25.
  40. Armstrong, J.; Armstrong, W. Reasons for the Presence or Absence of Convective (Pressurized) Ventilation in the Genus Equisetum. New Phytol. 2011, 190, 387–397.
  41. Armstrong, J.; Armstrong, W. Record Rates of Pressurized Gas-flow in the Great Horsetail, Equisetum Telmateia. Were Carboniferous Calamites Similarly Aerated? New Phytol. 2009, 184, 202–215.
  42. Colmer, T.D.; Pedersen, O. Underwater Photosynthesis and Respiration in Leaves of Submerged Wetland Plants: Gas Films Improve CO2 and O2 Exchange. New Phytol. 2008, 177, 918–926.
  43. Vretare Strand, V.; Weisner, S.E.B. Interactive Effects of Pressurized Ventilation, Water Depth and Substrate Conditions on Phragmites Australis. Oecologia 2002, 131, 490–497.
  44. Vretare, V.; Weisner, S.E.B. Influence of Pressurized Ventilation on Performance of an Emergent Macrophyte (Phragmites australis). J. Ecol. 2000, 88, 978–987.
  45. Armstrong, J.; Armstrong, W.; Beckett, P.M. Phragmites Australis: Venturi- and Humidity-Induced Pressure Flows Enhance Rhizome Aeration and Rhizosphere Oxidation. New Phytol. 1992, 120, 197–207.
  46. Armstrong, W.; Armstrong, J. Plant Internal Oxygen Transport (Diffusion and Convection) and Measuring and Modelling Oxygen Gradients. In Low-Oxygen Stress in Plants; Springer: Berlin, Germany, 2014; Volume 21, pp. 267–297.
  47. Tornberg, T.; Bendix, M.; Brix, H. Internal Gas Transport in Typha latifolia L. and Typha angustifolia L. 2. Convective Throughflow Pathways and Ecological Significance. Aquat. Bot. 1994, 49, 91–105.
  48. White, S.D.; Ganf, G.G. Influence of Stomatal Conductance on the Efficiency of Internal Pressurisation in Typha Domingensis. Aquat. Bot. 2000, 67, 1–11.
  49. Duarte, V.P.; Pereira, M.P.; Corrêa, F.F.; de Castro, E.M.; Pereira, F.J. Aerenchyma, Gas Diffusion, and Catalase Activity in Typha Domingensis: A Complementary Model for Radial Oxygen Loss. Protoplasma 2021, 258, 765–777.
  50. Herzog, M.; Konnerup, D.; Pedersen, O.; Winkel, A.; Colmer, T.D. Leaf Gas Films Contribute to Rice (Oryza Sativa) Submergence Tolerance during Saline Floods. Plant Cell Environ. 2018, 41, 885–897.
  51. Groot, T.T.; van Bodegom, P.M.; Meijer, H.A.J.; Harren, F.J.M. Gas Transport through the Root–Shoot Transition Zone of Rice Tillers. Plant Soil 2005, 277, 107–116.
  52. Colmer, T.D.; Cox, M.C.H.; Voesenek, L.A.C.J. Root Aeration in Rice (Oryza sativa): Evaluation of Oxygen, Carbon Dioxide, and Ethylene as Possible Regulators of Root Acclimatizations. New Phytol. 2006, 170, 767–778.
  53. Bonde, S.D.; Kumaran, K.P.N. A Permineralized Species of Mangrove Fern Acrostichum L. from Deccan Intertrappean Beds of India. Rev. Palaeobot. Palynol. 2002, 120, 285–299.
  54. Fonini, A.M.; Barufi, J.B.; Schmidt, É.C.; Rodrigues, A.C.; Randi, Á.M. Leaf Anatomy and Photosynthetic Efficiency of Acrostichum Danaeifolium after UV Radiation. Photosynthetica 2017, 55, 401–410.
  55. Chomicki, G.; Bidel, L.P.R.; Baker, W.J.; Jay-Allemand, C. Palm Snorkelling: Leaf Bases as Aeration Structures in the Mangrove Palm (Nypa fruticans). Bot. J. Linn. Soc. 2014, 174, 257–270.
  56. McKee, K.L. Soil Physicochemical Patterns and Mangrove Species Distribution-Reciprocal Effects? J. Ecol. 1993, 81, 477–487.
  57. Armstrong, W.; Armstrong, J. Stem Photosynthesis Not Pressurized Ventilation Is Responsible for Light-Enhanced Oxygen Supply to Submerged Roots of Alder (Alnus glutinosa). Ann. Bot. 2005, 96, 591–612.
  58. Schröder, P.; Grosse, W.; Woermann, D. Localization of Thermo-Osmotically Active Partitions in Young Leaves of Nuphar Lutea. J. Exp. Bot. 1986, 37, 1450–1461.
  59. Rogers, G.K. Bald Cypress Knees, Taxodium Distichum (Cupressaceae): An Anatomical Study, with Functional Implications. Flora 2021, 278, 151788.
  60. Sou, H.-D.; Masumori, M.; Kurokochi, H.; Tange, T. Histological Observation of Primary and Secondary Aerenchyma Formation in Adventitious Roots of Syzygium kunstleri (King) Bahadur and R.C.Gaur Grown in Hypoxic Medium. Forests 2019, 10, 137.
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license; additional terms may apply. By using this site, you agree to the Terms and Conditions and Privacy Policy.
Upload a video for this entry
Information
Subjects: Plant Sciences
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Lars Olof Björn
,
Beth A. Middleton
,
Mateja Germ
,
Alenka Gaberščik
View Times: 496
Revisions: 2 times (View History)
Update Date: 06 Jul 2022
Table of Contents
Academic Video Service
Feedback