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Download Biogeochemistry of Wetlands Adaptations of Plants to Anaerobiosis
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Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands S i Science and dA Applications li ti Adaptations of Plants to Anaerobiosis Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida Instructor Mark Clark [email protected] 6/22/2008 6/22/2008 WBL 1 1 Adaptations of Plants to Soil Anaerobiosis Topic Outline Role of oxygen in the plant Potential stresses due to lack of oxygen Physiological Gas transport processes Oxidation Flux and morphological adaptations of the rhizosphere of reduced gases 6/22/2008 WBL 2 1 Adaptations of Plants to Soil Anaerobiosis Learning Objectives Understand impacts of hypoxia and anoxia on plants. Understand physiological and morphological adaptations that wetland plants have to overcome or minimize stress. Learn about passive gas exchange processes that occur in wetlands vegetation. Understand what an oxidized rhizosphere is and what implications it has for the plant and soil biogeochemistry. Realize that gas transport is a bidirectional pathway. 6/22/2008 WBL 3 OXYGEN: Sources and Sinks Water Plants and Al Algae Air Release by Plant Roots Soil Oxygen Respiration Oxidation of Reductants Chemical oxidation Chemolithotrophic oxidation 2 Do wetland plants require oxygen? ? Do all plant organs require oxygen? Gas Exchange in Soil / Water / Plant System Drained Soil Flooded Soil O2 O2 ? CO2 Dissloved metals sulfides, and organic acids CO2, CH4, and other gases 3 Glucose Metabolism Presence of Oxygen 32 ATP Absence of Oxygen Glucose 2 ATP Pyruvate Lactate Acetyl-CoA TCA Cycle Acetyl-CoA Acetate Acetaldehyde Electron transport chain Ethanol O2 + 2H+ H2O Stresses on plant Decrease in Cell Energy Charge Can’t produce or maintain enzymes and cell membrane Glycosidic acidosis due to loss of ion gradients Hormonal imbalance Accumulation of toxic compounds under anaerobic metabolism (acetaldehyde, ethanol) Cyanogenesis Hydrolysis of cyanogenic glycosides produce Cyanide Death by Anaerobic Starvation Inefficient metabolism of non structural carbohydrates Water Balance Suberization and loss of root area for water uptake 4 Adaptation to soil anaerobiosis Physiological Adaptations Anaerobic respiration Alternative metabolic byproducts Morphological Adaptations External: Prop roots, Pneumatophores, Lenticels, Stem Elongation, Internal: Aerenchyma, Hypertrophied Stems Oxidized Rhizosphere Oxidizing the root environment via radial oxygen loss Precipitation of dissolved metals in the root zone Oxidation of reduced compounds in the root zone How Does Oxygen/Air yg Enter the Plant? 5 Stomates Typically associated with leaves, can be found on herbaceous stems. Open and closed by guard cells, regulated by CO2 and moisture. Li k b Link between t atmosphere and vascular bundles. http://www.cropsci.uiuc.edu/ocgs/cpsc399/PlantsystemsSu02.htm Lenticels Pores that form between the atmosphere and the cambium l layer off stems t and d ttrunks k Triggered by ethylene production Only occur on woody species Increase gas transfer to the cambium Have greatest concentration near the air water interface Have been shown to influence O2 concentration in Red Mangrove prop roots by 90% if blocked. 6 Lenticels Outer Bark Xylem Phloem Cortex O2 CO2 CH4 O2 O2 O2 Lenticels O2 O2 Prop Roots Modified root, only found in Red Mangrove Species Each Root originates from the trunk above the water surface Roots are very spongy and porous Lenticels on roots just above the air/water interface provide connection with atmospheric oxygen Oxygen concentration measured in roots as high as 15-18% 7 Pneumatophores Modified root perpendicular to main roots t running i horizontal h i t l just below the sediment surface Found only in Black Mangrove species Lenticels on root provide connection to atmospheric O2 when exposed above the water surface 8 Mangrove Air CO2 Pneumatophores Water Soil Stem / Petiole Elongation Elongation of stem not associated i t d with ith cellll replication. Triggered by inundation and most likely linked to increases in ethylene concentration. Maintains connection between atmospheric oxygen and below-water organs of the plant. 9 What are the Internal Passageways for Gas Transfer? Hypertrophied Stem Swelling along stem/trunk not associated with growth but resulting from the enlargement of cells Buttressing in trees Expanded tissue can provide passageway for gases between the atmosphere and below-water tissue 10 Aerenchyma Genetically predisposed Develop with growth Sensitive to ethylene induced cellulase Induced Response to increased concentration of ethylene 11 Aerenchyma Genetically Predisposed Cattail Root T h Typha latifolia Aerenchyma (intercellular air space) Induced Aerenchyma Synthesis of 1-aminocyclopropand-1-carboxylic acid (ACC) O2 Primary aerobic Root Ethylene ACC 10 cm2 day anaerobic 4 day anaerobic 12 Porosity influenced by redox potential 40 b Root poros sity (%) b 30 a 20 10 0 10 Radial O2 lo oss (μmol g-1 dry ro oot d-1) b b 5 a 0 200 -200 Eh (mV) -300 Kludze and DeLaune, Sci. Soc. Am J., 1938) How do Gases Move Inside the Plant? 13 Oxygen movement through the plant Diffusion - due to partial pressure diff differences Convective / Mass flow - due to total pressure differences as a result of thermoosmotic pressure differences at the leaf surface. Temperature p induced Humidity induced CO2 solubilization Venutri effect 1 meter 14 1 meter Atmosphere New Leaf Old Leaf Water Rhi Rhizome 15 Leaf Section Upper Leaf Surface Stomata N2 Porous Partition (<0.1 mm) Lower Leaf Surface Internal Pressurization Temperature Induced T0 T1 P0 T2 P1 T1 = T2 > T0 Porous Partition (< 0.1 um) Energy P2 old leaf new leaf P1 > P2 > P0 T0 = temperature outside T1 = temperature inside new leaf T2 = temperature inside old leaf Porous Partition (> 0.1 um) P0 Pressure outside P1 Pressure inside new leaf P2 Pressure inside old leaf 16 Effect of temperature and age of leaf 120 ΔT = 1K ΔT = 5K (mL air h-1) 100 ΔT = 8K 80 60 40 20 0 Young Old Leaf Age Grosse, 1989 Internal Pressurization Humidity Induced Energy [ H2O ]o [O2 , CO2 , N2]0 P0 P1 Porous Partition (< 0.1 um) new leaf [ O 2 ]2 [ H2O ]2 [ O2 ]1 [ H2O ]1 P2 [H2O]1 = [H20]2 > [H20]o [O2, CO2, N2]1 > [O2, CO2, N2]o old leaf Porous Partition (> 0.1 um) P1 > P2 > P0 [H2O]0 = Humidity outside [H2O]1 = Humidity inside new leaf [H2O]2 = Humidity inside old leaf [O2]0 Concentration outside [O2]1 Concentration inside new leaf [O2]2 Concentration inside old leaf P0 Pressure outside P1 Pressure inside new leaf P2 Pressure inside old leaf 17 Atmosphere Air Exhaust Air Intake Air Intake Air Intake Water Old Leaves Young Leaves Air Exhaust Floodwater Rhizome Soil Rhizome Mass flow – CO2 Solublization Plant Water Air Air N2 O2 O2 N2 CO2 O2 CO2(aq) CO2 2 ⇆ HCO CO323 CO2(aq) CO2 O2 N2 CO2 O2 O2 O2 N2 CO2 O2 O2 O2 Leaf O2 N2 Water (Redrawn from Taskin, I., and Kende, H., Science 1985) 18 Mass flow - Venturi Effect Wind sp peed Air Air Gas Exchange in Soil / Water / Plant System Drained Soil Flooded Soil O2 O2 ? CO2 Dissloved metals sulfides, and organic acids CO2, CH4, and other gases 19 Oxidized Rhizosphere Most adaptations discussed relate to longitudinal transfer of oxygen to root. Oxygen concentration inside root is high, oxygen concentration outside root low/absent Strong concentration gradient can results in radial oxygen loss (ROL) forming an Oxidized Rhizosphere. Oxygen Levels in Root and Oxidized Rhizosphere (cross section) Phragmities australis 7mm back from apex W. Armstrong et al 2000, Annals of Botany 86:687-703 20 Oxygen Levels in Root and Oxidized Rhizosphere (cross section) Phragmities australis 100 mm back from apex W. Armstrong et al 2000, Annals of Botany 86:687-703 Oxygen Levels in Root and Oxidized Rhizosphere (longitudinal profile) T. D. Colmer, 2003, Plant, Cell and Environment 26, 17-36 21 Conceptual model of oxidized rhizosphere with barrier to ROL near root base Oxygen Flux Phargmites australis O2 Flux 2.08 gg/m2 dayy Net Release 0.02 g/m2 day Root Respiration 2.06 g/m2 day Brix and Schierup, 1990 22 Oxidation-Reduction Carbon Nitrogen O2 O2 O2 + OM CO2 Aerobic soil Anaerobic soil OM VFA NO3O2 + NH4+ Aerobic soil Anaerobic soil OM NH4+ Oxidation-Reduction Iron Manganese O2 Fe3+ O2 + Fe2+ Aerobic soil Anaerobic soil Fe3+ Fe2+ O2 Mn4+ O2 + Mn2+ Aerobic soil Anaerobic soil Mn4+ Mn2+ 23 Oxidizing Activity of Roots Toxicity of reduced compounds (e.g., sulfides) lfid ) iis d decreased. d Supports nitrification and methane oxidation. Precipitates metals and in some cases nutrient uptake is decreased. decreased Does Gas Transport p Only y Occur in One Direction? 24 Methane Exchange Through Plant CO2 CH4 O2 Atmosphere Water O2 + CH4 CO2 Soil CH4 CH4 + O2 CO2 Gas Exchange through Plants Gas flux, mg/m2 hou ur 100 80 Methane Oxygen 60 40 20 0 Sagittaria latifolia Canna flaccida Scirpus pungens Scirpus validus Typha latifolia Pontederia cordata Emergent aquatic macrophytes 25 Learning Objectives Summary Loss of oxygen has significant implications for plant metabolism/survival. W Wetland tl d adapted d t d plants l t h have numerous physiological h i l i l and d morphological adaptations to deal with these stresses. Movement of gases within the plant is the result of a combination of diffusive and convective mechanisms. Radial oxygen loss from roots result in an oxidized rhizosphere that significantly increases the aerobic aerobicanaerobic interface in a wetland and can reduce anaerobic stress on vegetation. Gas exchange is bidirectional: oxygen in - reduced gases out. 26
