Water and Plant Water Relations

Transcription

1 Water and Plant Water Relations Environmental Patterns Classic Water Cycle basis for other patterns 1

2 (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? 2

3 Ecologically, Plants have 2 Problems Plants live in places that has sufficient water for them ( just right ) Plants evolutionarily modify their morphology or their life history to restrict their requirements for water The Cost I. Plants can live in places that has sufficient water for them Habitats are now restricted in distribution and abundance II. Plants can evolutionarily modify their morphology or their life history to restrict their requirements for water Photosynthetic and growth rates are now restricted and plants may be competitively restricted in distribution and abundance 3

4 I. Places with enough water Definition depends on plant adaptations Reflect on patterns of solar radiation Remember water runs downhill Remember the source of water is rainfall Distribution of water in the environment is strongly influenced: Temporally (how long, how frequent is water available) By Location (how permanent features of the environment influence water flux) By Quality (availability and the presence of salts in water) 4

5 Smaller-scale: Time: annual variation 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 Location: Continental Effect Continential Continental Effect Winter Air Movements Summer Air Movements 5

6 Location: Orographic Effect Orographic Effect 135 in 80 in 100 in 3-9 in 35 in Pacific Ocean Olympic Peninsula Seattle Cascades High Desert Location: Topography South North Ravines and Ridges (riparian/nonriparian) 6

7 Continental Effect Location Mountains to the west of sites can create largescale 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) Other Location coastal fog and fog drip post-fire non-wettable soils deserts soils with impermeable caliche layers estuaries and freshwater & saltwater tidal marshes lowlands and marshes, glacial potholes, desert salt lakes 7

8 Quality Frozen Water Arctic tundra - low rainfall, permafrost, water often 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) Transpiration can be restricted to more favorable times of the day (CAM and nighttime) Plants can grow only when water is available (ephemerals) 8

9 Store Water Xerophytic Adaptations succulents (use CAM); balsa wood in tropics Deep-rooted Desert palms, desert wash vegetation - establishment? CAM & C4 PS/Other physiology water efficiency osmotic adjustment metabolic tolerance of changes in hydration in enzymes Ephemerals (annuals) initiate and complete life cycle during moist seasons survive as seeds complex germination controls Store Water - succulence Succulents also only open stomata at night modified photosynthesis that fixes CO 2 first as organic acids. 9

10 Deep rooted-desert wash Roots reach permanent water tables Ironwood Fan-palm Palo Verde Ephemerals (annuals) 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. 10

11 Xerophytic Adaptations 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 Larrea Cross-section Thick wax cover stomate Larrea-Creosote bush: small, compact leaves 11

12 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. Hiding stomata in holes 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. Cross section of Nerium leaf. Leaf cross section of pine 12

13 Deciduous and dormant- Ocotillo Leaves die back and fall-off as drought gets worse. Plants goes dormant. We ve focused on limited water as the issue What if there s too much water? 13

14 Adaptations to Excessive Water Problems Anaerobicity buildup of ethanol from anaerobic respiration Reduced Ions Ferrous Iron - toxic Sulfide - inhibits mineral uptake in roots, even waterlogged soils like after snowmelt, wetland soils Adaptations to Excessive Water Adaptations to Anaerobicity Modify physiology: nitrate as an alternative electron acceptor to O2 via nitrate reductase and amino acid synthesis Modify structure: aerenchyma Tolerance: tolerance of high ethanol (rice only) 14

15 Respiration 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. Respiration when oxygen is present or when it s absent 2. Internal toxins and Aerobic vs Anaerobic Respiration Aerobic respiration breaks glucose down to CO 2 and H 2 O. versus 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. 15

16 glucose pyruvate CO 2 H 2 O No 1 2 O2 1- if oxygen is available, then aerobic respiration produces CO 2 and H 2 O and 36 ATP O2 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. ethanol (plants) lactate (animals) 1 NAD NADH 2 NADH 2 NAD 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 O 2 is the last electron or hydrogen acceptor forming water 16

17 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 adaptations 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. Leaf x.s. of Syringa (lilac). Castalia leaf. Normal vs leaf with aerenchyma 17

18 Transverse section of stem cortex in sweetflag (Acorus). 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. 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). 18

19 Mangroves as examples of woody plants in tidal waters. 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. 19

20 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 Plants can modify their morphology or life history to tolerate either too little water or too much water 20

21 Overall All ecological choices restrict distribution or abundance 21