Water and Plant Water Rela,ons

Transcription

1 Classic Water Cycle as basis for other patterns Water and Plant Water Rela,ons Environmental Pa3erns (1) Plants lose water during photosynthesis. Water travels through xylem (mostly dead cells) to replace water lost and maintain turgor in the leaves. Anatomical structure and a water potential gradient moves water through the plant. 1

2 Bark Phloem Vascular cambium Xylem vessels (1) Plants lose water during photosynthesis. Water travels through xylem (mostly dead cells) to replace water lost and maintain turgor in the leaves. (2) How to plants regulate their environmental water balance? Ecologically, Plants have 2 Problems Plants live in places that have sufficient water for them ( just right ) Plants evolu,onarily modify their morphology, physiology, or their life history to track their requirements for water in the environment they are within The Cost I. Places with enough water Defini,on depends on plant adapta,ons Reflect on pa3erns of solar radia,on Remember water runs downhill Remember the source of water is rainfall 2

3 Distribu,on of water in the environment is strongly influenced: Temporally (how long, how frequent is water available) By Loca,on (how permanent features of the environment influence water flux) By Quality (availability and the presence of salts in water) Time: Smaller- scale: Within- year and annual varia,on Calif: 2 droughts or 2 rainy years/decade El Niño every 5 years Large- Scale: Mediterranean climates winter rainfall Monsoon climates summer rainfall Deciduous tropical forests Loca,on: Con,nental Effect Continental Effect Loca,on: Orographic Effect Winter Air Movements Summer Air Movements Loca,on: Topography South North Ravines and Ridges (riparian/nonriparian) Loca,on Con,nental Effect Mountains to the west of sites can create large- scale rainshadows Orographic Effect Local rainshadow effects Topography Moisture differs by slopes (South slopes drier in northern hemisphere) Moisture runs downhill (ravines moister than ridges; usually more moisture downhill) 3

4 Loca,on Other coastal fog and fog drip post- fire non- we3able soils deserts soils with impermeable caliche layers estuaries and freshwater & saltwater,dal marshes lowlands and marshes, glacial potholes, desert salt lakes Quality Frozen Water Arc,c tundra - low rainfall, permafrost, water oben unavailable Freshwater vs Salinity e.g., Atriplex radiated in arid/saline areas N- America ~ 59 species 78% endemism S- America 73 species 86% endemism Mediterranean 42 species 7% endemism N. Asia 38 species 26% endemism Australia 59 species 68% endemism II. Plants modify morphology or life history Morphology can restrict water loss from leaves (restricts photosynthesis) Transpira,on can be restricted to more favorable,mes of the day (CAM and nighkme) Plants can grow only when water is available (ephemerals) Xerophy,c Adapta,ons Store Water succulents (use CAM); balsa wood in tropics Deep- rooted Desert palms, desert wash vegeta,on - establishment? CAM & C4 PS/Other physiology water efficiency osmo,c adjustment metabolic tolerance of changes in hydra,on in enzymes Ephemerals (annuals) ini,ate and complete life cycle during moist seasons survive as seeds complex germina,on controls Store Water - succulence Succulents also only open stomata at night modified photosynthesis that fixes CO 2 first as organic acids. Fan-palm Deep rooted- desert wash Roots reach permanent water tables Ironwood Palo Verde 4

5 Ephemerals (annuals) Xerophytic Adaptations Ephemerals usually germinate in the spring following winter rains. They grow quickly, flower and produce seeds before dying and scattering their progeny to the desert floor. Modified leaf structure Thicker leaves Thicker wax layers covering leaf More compact internal structure Smaller Other traits that might limit water loss when stomata are open like: hairy surface, stomata sunken into leaf OR drop leaves when it s really dry (deciduous) Compact inside of leaf Small leaves Encelia or brittlebush: hairy leaves For this small shrub of the desert, the green leaf can absorb 85% of solar radiation, i.e., reflect only 15%, whereas the silvery one may absorb less than 40% of solar radiation, i.e., reflect more than 60%, including the infrared radiation that causes heating of leaf tissues. Larrea Cross-section Thick wax cover stomate Larrea-Creosote bush: small, compact leaves Hiding stomata in holes or sunken areas of leaves (crypts) Some evergreen leaves have areas called stomatal crypts. These are caves or deep grooves in leaves, allowing water vapor to accumulate, slowing down the loss of water by transpiration. Deciduous and dormant- Oco,llo Leaves die back and fall-off as drought gets worse. Plants goes dormant. Cross section of Nerium leaf. Leaf cross section of pine 5

6 We ve focused on limited water as the issue What if there s too much water? Adapta,ons to Excessive Water Problems Anaerobicity buildup of ethanol from anaerobic respira,on Reduced Ions Ferrous Iron - toxic Sulfide - inhibits mineral uptake in roots, even waterlogged soils like aber snowmelt, wetland soils Adapta,ons to Excessive Water Adapta,ons to Anaerobicity Modify physiology: nitrate as an alterna,ve electron acceptor to O2 via nitrate reductase and amino acid synthesis Modify structure: aerenchyma Tolerance: tolerance of high ethanol (rice only) Respira,on when oxygen is present or when it s absent There are two basic types of cellular respiration: aerobic (oxygen present) and anaerobic (oxygen absent). 1. Energy and Aerobic vs Anaerobic Respiration Aerobic respiration is the more efficient of the two because more energy is gained. Plant and animal cells yield 36 ATPs per molecule of glucose because of their aerobic process. versus Organisms that must depend on anaerobic respiration gain only 2 ATPs per molecule of glucose. Respira,on when oxygen is present or when it s absent 2. Internal toxins and Aerobic vs Anaerobic Respiration glucose pyruvate CO 2 H 2 O No 1 Aerobic respiration breaks glucose down to CO 2 and H 2 O. 2 O2 1- if oxygen is available, versus then aerobic respiration produces CO 2 and H 2 O and 36 ATP Anaerobic respiration can not break glucose down very far because the processes depend on O 2. Instead, intermediate compounds are formed. The problem is, as the intermediates accumulate, they can become toxic to the cells forming them. 2 if oxygen is unavailable, then alternative compounds are made. Ethanol is the most common in plants, while lactate is the most common in animals. Only 2 ATP are the additional net products. O2 ethanol (plants) lactate (animals) 6

7 1 NAD NADH 2 NADH 2 glucose pyruvate CO 2 H 2 O The biochemical issue is to extract the stored energy in glucose. This is accomplished by removing the Hydrogens, releasing energy. The energy release is captured in both ATP (not shown) and NADH 2. The energy from NADH 2 is released by completing the oxidation of glucose to CO 2, and reducing O 2 to H 2 O. (after pyruvate, this happens in the mitochondria of the cell) O 2 NAD O 2 is the last electron or hydrogen acceptor forming water 1 glucose Ethanol or lactate are used as electron or hydrogen acceptors to keep respiration working. NAD NADH 2 NADH 2 2 NAD pyruvate No O2 ethanol (plants) lactate (animals) 3 NADH 2 NAD nitrate (NO 3 ) amino acids (NH 4 ) nitrate reductase Plant structural adapta,ons aerenchyma A spongy tissue with large air spaces found between the cells of the stems and leaves of aquatic plants, providing buoyancy and allowing the circulation of gases. Transverse section of stem cortex in sweetflag (Acorus). Leaf x.s. of Syringa (lilac). Castalia leaf. Normal vs leaf with aerenchyma Acorus (sweet flag) leaf, cross section Oxidized Rhizosphere Aerenchyma permits plants to bring oxygen from the atmosphere down leaves and stems to the root system in the anaerobic soils. Mangroves as examples of woody plants in tidal waters. Oxygen leaks from the plant roots, oxidizing the wetlands soils near the roots. Iron in the soils often is oxidized near roots, creating a rusty color, that is literally iron oxide (rust). 7

8 Pneumatophore is the name given to these erect roots that promote gas exchange. Internal structure is analogous to aerenchyma in that it is loose and contains air passages. Bald Cypress (Taxodium) Bald Cypress (Taxodium) also use woody growths from roots called cypress knees for aeration. Overall Plants can live where the amount of moisture is just right Overall All ecological choices restrict distribu,on or abundance Plants can modify their morphology or life history to tolerate either too li3le water or too much water 8