Institute of Food and Agricultural Sciences IFAS Biogeochemistry
Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands Science and Applications Adaptations of Plants to Anaerobiosis Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida Instructor Mark Clarkmw@ufl. edu 9/30/2020 WBL 1 1
Adaptations of Plants to Soil Anaerobiosis Topic Outline v. Role of oxygen in the plant v. Potential stresses due to lack of oxygen v. Physiological v. Gas transport processes v. Oxidation v. Flux and morphological adaptations of the rhizosphere of reduced gases 9/30/2020 WBL 2
Adaptations of Plants to Soil Anaerobiosis Learning Objectives v Understand impacts of hypoxia and anoxia on plants. v Understand physiological and morphological adaptations that wetland plants have to overcome or minimize stress. v Learn about passive gas exchange processes that occur in wetlands vegetation. v Understand what an oxidized rhizosphere is and what implications it has for the plant and soil biogeochemistry. v Realize that gas transport is a bidirectional pathway. 9/30/2020 WBL 3
OXYGEN: Sources and Sinks Water Plants and Algae Air Soil Oxygen Respiration Oxidation of Reductants Release by Plant Roots Chemical oxidation Chemolithotrophic oxidation
Do wetland plants require oxygen? Do all plant organs require oxygen?
Gas Exchange in Soil / Water / Plant System Drained Soil Flooded Soil O 2 ? CO 2 Dissloved metals sulfides, and organic acids CO 2, CH 4, and other gases
Glucose Metabolism Presence of Oxygen 32 ATP Glucose Absence of Oxygen 2 ATP Pyruvate Lactate Acetyl-Co. A TCA Cycle Acetyl-Co. A Acetaldehyde Electron transport chain Ethanol O 2 + 2 H+ H 2 O Acetate
Stresses on plant v Decrease in Cell Energy Charge v Can’t produce or maintain enzymes and cell membrane v Glycosidic acidosis due to loss of ion gradients v Hormonal imbalance v Accumulation of toxic compounds under anaerobic metabolism (acetaldehyde, ethanol) v Cyanogenesis v. Hydrolysis of cyanogenic glycosides produce Cyanide v Death by Anaerobic Starvation v Inefficient metabolism of non structural carbohydrates v Water Balance v Suberization and loss of root area for water uptake
Adaptation to soil anaerobiosis v Physiological Adaptations v. Anaerobic respiration v. Alternative metabolic byproducts v Morphological Adaptations v. External: Prop roots, Pneumatophores, Lenticels, Stem Elongation, v. Internal: Aerenchyma, Hypertrophied Stems v Oxidized Rhizosphere v. Oxidizing the root environment via radial oxygen loss v. Precipitation of dissolved metals in the root zone v. Oxidation of reduced compounds in the root zone
How Does Oxygen/Air Enter the Plant?
Stomates v v v Typically associated with leaves, can be found on herbaceous stems. Open and closed by guard cells, regulated by CO 2 and moisture. Link between atmosphere and vascular bundles. http: //www. cropsci. uiuc. edu/ocgs/cpsc 399/Plantsystems. Su 02. htm
Lenticels v v v Pores that form between the atmosphere and the cambium layer of stems and trunks 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 O 2 concentration in Red Mangrove prop roots by 90% if blocked.
Lenticels Outer Bark Xylem Phloem Cortex O 2 CH 4 O 2 O 2 Lenticels O 2
Prop Roots v. Modified root, only found in Red Mangrove Species v. Each Root originates from the trunk above the water surface v. Roots are very spongy and porous v. Lenticels on roots just above the air/water interface provide connection with atmospheric oxygen v. Oxygen concentration measured in roots as high as 15 -18%
Pneumatophores v Modified root perpendicular to main roots running horizontal just below the sediment surface v. Found only in Black Mangrove species v. Lenticels on root provide connection to atmospheric O 2 when exposed above the water surface
Mangrove CO 2 Air Pneumatophores Water Soil
Stem / Petiole Elongation v. Elongation of stem not associated with cell replication. v. Triggered by inundation and most likely linked to increases in ethylene concentration. v. Maintains connection between atmospheric oxygen and below-water organs of the plant.
What are the Internal Passageways for Gas Transfer?
Hypertrophied Stem v. Swelling along stem/trunk not associated with growth but resulting from the enlargement of cells v. Buttressing in trees v. Expanded tissue can provide passageway for gases between the atmosphere and below -water tissue
Aerenchyma v. Genetically predisposed v. Develop with growth v. Sensitive to ethylene induced cellulase v. Induced v. Response to increased concentration of ethylene
Aerenchyma Genetically Predisposed Cattail Root Typha latifolia Aerenchyma (intercellular air space)
Induced Aerenchyma Synthesis of 1 -aminocyclopropand-1 -carboxylic acid (ACC) O 2 Primary aerobic Root Ethylene ACC 10 cm 2 day anaerobic 4 day anaerobic
Porosity influenced by redox potential 40 b Root porosity (%) b 30 a 20 10 Radial O 2 loss (mmol g-1 dry root d-1) b b 5 a 0 200 -200 Eh (m. V) -300 Kludze and De. Laune, Sci. Soc. Am J. , 1938)
How do Gases Move Inside the Plant?
Oxygen movement through the plant v. Diffusion - due to partial pressure differences v. Convective / Mass flow - due to total pressure differences as a result of thermoosmotic pressure differences at the leaf surface. v Temperature induced v Humidity induced v CO 2 solubilization v. Venutri effect
1 meter
1 meter
Atmosphere New Leaf Water Rhizome Old Leaf
Leaf Section Upper Leaf Surface Stomata N 2 Porous Partition (<0. 1 mm) Lower Leaf Surface
Internal Pressurization Temperature Induced T 0 T 1 P 0 T 2 P 1 T 1 = T 2 > T 0 Porous Partition (< 0. 1 um) new leaf Energy P 2 old leaf P 1 > P 2 > P 0 T 0 = temperature outside T 1 = temperature inside new leaf T 2 = temperature inside old leaf P 0 Pressure outside P 1 Pressure inside new leaf P 2 Pressure inside old leaf Porous Partition (> 0. 1 um)
Effect of temperature and age of leaf 120 ΔT = 1 K ΔT = 5 K (m. L air h-1) 100 ΔT = 8 K 80 60 40 20 0 Young Old Leaf Age Grosse, 1989
Internal Pressurization Humidity Induced Energy [ H 2 O ]o [O 2 , CO 2 , N 2]0 P 1 Porous Partition (< 0. 1 um) new leaf [ O 2 ]2 [ H 2 O ]2 [ O 2 ]1 [ H 2 O ]1 P 2 [H 2 O]1 = [H 20]2 > [H 20]o [O 2, CO 2, N 2]1 > [O 2, CO 2, N 2]o old leaf Porous Partition (> 0. 1 um) P 1 > P 2 > P 0 [H 2 O]0 = Humidity outside [H 2 O]1 = Humidity inside new leaf [H 2 O]2 = Humidity inside old leaf [O 2]0 Concentration outside [O 2]1 Concentration inside new leaf [O 2]2 Concentration inside old leaf P 0 Pressure outside P 1 Pressure inside new leaf P 2 Pressure inside old leaf
Atmosphere Air Exhaust Air Intake Old Leaves Young Leaves Water Air Exhaust Floodwater Rhizome Soil Rhizome
Mass flow – CO 2 Solublization Plant Water Air N 2 O 2 N 2 CO 2(aq) CO 2 CO 32 - ⇆ HCO 3 CO 2(aq) CO 2 N 2 CO 2 O 2 Leaf O 2 N 2 O 2 O 2 N 2 Water (Redrawn from Taskin, I. , and Kende, H. , Science 1985)
Mass flow - Venturi Effect Wind speed Air
Gas Exchange in Soil / Water / Plant System Drained Soil Flooded Soil O 2 ? CO 2 Dissloved metals sulfides, and organic acids CO 2, CH 4, and other gases
Oxidized Rhizosphere v Most adaptations discussed relate to longitudinal transfer of oxygen to root. v Oxygen concentration inside root is high, oxygen concentration outside root low/absent v 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 7 mm back from apex W. Armstrong et al 2000, Annals of Botany 86: 687 -703
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
Conceptual model of oxidized rhizosphere with barrier to ROL near root base
Oxygen Flux Phargmites australis O 2 Flux 2. 08 g/m 2 day Net Release 0. 02 g/m 2 day Root Respiration 2. 06 g/m 2 day Brix and Schierup, 1990
Oxidation-Reduction Carbon Root O 2 CO 2 + OM Aerobic soil Anaerobic soil OM VFA Nitrogen Root O 2 NO 3 O 2 + NH 4+ Aerobic soil Anaerobic soil OM NH 4+
Oxidation-Reduction Iron Root Manganese O 2 Fe 3+ O 2 + Fe 2+ Aerobic soil Anaerobic soil Fe 3+ Fe 2+ Root O 2 Mn 4+ O 2 + Mn 2+ Aerobic soil Anaerobic soil Mn 4+ Mn 2+
Oxidizing Activity of Roots v. Toxicity of reduced compounds (e. g. , sulfides) is decreased. v. Supports nitrification and methane oxidation. v. Precipitates metals and in some cases nutrient uptake is decreased.
Does Gas Transport Only Occur in One Direction?
Methane Exchange Through Plant CO 2 CH 4 O 2 Atmosphere Water O 2 + CH 4 CO 2 Soil CH 4 + O 2 CO 2
Gas Exchange through Plants Gas flux, mg/m 2 hour 100 80 Methane 60 Oxygen 40 20 0 Sagittaria latifolia Canna flaccida Scirpus pungens Scirpus validus Typha latifolia Emergent aquatic macrophytes Pontederia cordata
Learning Objectives Summary v Loss of oxygen has significant implications for plant metabolism/survival. v Wetland adapted plants have numerous physiological and morphological adaptations to deal with these stresses. v Movement of gases within the plant is the result of a combination of diffusive and convective mechanisms. v Radial oxygen loss from roots result in an oxidized rhizosphere that significantly increases the aerobicanaerobic interface in a wetland can reduce anaerobic stress on vegetation. v Gas exchange is bidirectional: oxygen in - reduced gases out.
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