DOCSLIB.ORG

Topic 9.1 Answers

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Topic 9.1 Answers 9.1 Transport in the Xylem of Plants Plant Structure Label the diagram of the leaf tissue of a plant 1. ……………………………………Vascular bundle 4. ……………………………………Epidermis (lower) 7. ……………………………………Stoma 2. ……………………………………Xylem 5. ……………………………………Waxy cuticle 8. ……………………………………Palisade mesophyll 3. ……………………………………Phloem 6. ……………………………………Guard cell 9. ……………………………………Spongy mesophyll Explain the location of the mesophyll (palisade and spongy) and vascular bundle within the leaf On the upper surface of the leaf, the cells are packed tight and rich in chloroplasts Palisade Mesophyll: ………………………………………………………………………………………………………………………… This increases light absorption for photosynthesis ………………………………………………………………………………………………………………………………………………….......... Spongy Mesophyll: …………………………………………………………………………………………………………………………..On the lower surface of the leaf, the cells are interspersed by space and near stomata …………………………………………………………………………………………………………………………………………………..........This increases gas exchange for photosynthesis Vascular Bundle: ……………………………Vascular bundles exist……………………………………………………………………………………………….. centrally between the two layers (allowing equal access) …………………………………………………………………………………………………………………………………………………..........Have xylem for water transport to leaf & phloem for food transport from leaf Identify the following plant tissues (monocot vs dicot ; root vs stem) Monocot root Monocot stem Dicot root Dicot stem ………………………… ………………………… ………………………… ………………………… Xylem Structure Describe the structure of the xylem ………………………………………………………………………………………………………………………………………………….......... Inner lining is composed of dead cells that have fused into a continuous tube …………………………………………………………………………………………………………………………………………………..........These cells lack a cell membrane, allowing water to enter the xylem freely ………………………………………………………………………………………………………………………………………………The cell walls have thickened cellulose and are reinforced with lignin (annular or spiral) ….......... …………………………………………………………………………………………………………………………………………………..........The outer layer is perforated (has pores), enabling water movement out of xylem Draw the structure of primary xylem vessels in stems MICROSCOPE DRAWING Xylem Phloem Xylem Phloem Meta Proto Pit Lignin Cell wall Transpiration Define transpiration Transpiration is the loss of water vapour from the leaves and stems of the plant ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Differentiate between fibrous and tap root systems Fibrous: …………………………………………………………………………………………………………………………………………..Fibrous roots are thin and very spread out Tap: ………………………………………………………………………………………………………………………………………………...Tap roots penetrate deeply (for stability) and have many connected lateral branches Explain the uptake of mineral ions into the root by direct and indirect active transport Direct Active Transport Protein pumps use ATP to translocate ions against their concentration gradient ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Indirect Active Transport …………………………………………………………………………………………………………………………………………………..........Proton pumps expel H+ ions into the soil, displacing the cationic minerals from clay ………………………………………………………………………………………………………………………………………………….Displaced minerals will passively diffuse into the root (along a concentration gradient) ......... …………………………………………………………………………………………………………………………………………………..........Anionic minerals may bind to the H+ ions and be reabsorbed with the proton Outline the role of stomata in regulating the level of evaporation from the leaf …………………………………………………………………………………The transpiration rate can be regulated by the guard cells …………………………………………………………………………………which flank the stomata …………………………………………………………………………………Guard cells occlude the opening when flaccid …………………………………………………………………………………Guard cell turgor is regulated by abscisic acid ………………………………………………………………………………… Define cohesion and adhesion Water molecules stick together (by H-bonding) Cohesion: ……………………………………………………………………………………………………………………………………….. Water molecules form polar associations with the wall of the xylem vessel Adhesion: ……………………………………………………………………………………………………………………………………….. Explain how water is transported around the plant via a transpiration stream …………………………………………………………………………………………………………………………………………………..........Some of the light energy absorbed by leaves changes into heat, converting water to vapour …………………………………………………………………………………………………………………………………………………..........The vapour diffuses out and is evaporated, creating a negative pressure gradient in leaves …………………………………………………………………………………………………………………………………………………..........New water is drawn via the xylem from roots (which enters from soil via osmotic uptake) …………………………………………………………………………………………………………………………………………………..........Water rises up (against gravity) through xylem vessels via mass flow due to cohesion and adhesion …………………………………………………………………………………………………………………………………………………..........The flow of water from the roots to the leaf (via the xylem) is called the transpiration stream ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Explain how abiotic factors affect the rate of transpiration in a typical terrestrial plant Light: ………………………………………………………………………………………………………………………………………………Increasing the light intensity to which a plant is exposed increases the rate of transpiration ………………………………………………………………………Increasing light exposure causes more stomata………………………………………………………………………….......... to open to facilitate photosynthetic gas exchange Temperature: …………………………………………………………………………………………………………………………………Increasing ambient temperature causes an increase in the rate of transpiration . …………………………………………………………………………………………………………………………………………………..........Higher temperatures lead to an increase in the rate of evaporation within the mesophyll Wind: ……………………………………………………………………………………………………………………………………………...Increasing the level of wind exposure causes an increase in the rate of transpiration …………………………………………………………Wind / air circulation removes water……………………………………………………………………………………….......... vapour from near the leaf, effectively reducing proximal humidity Humidity: ………………………………………………………………………………………………………………………………………..Increasing the humidity is predicted to cause a decrease in the rate of transpiration …………………………………………………………………………………………………………………………………………………..........Less vapour will diffuse from the leaf if there is more vapour in the air Identify four adaptations in xerophytes and halophytes that help reduce or increase transpiration Xerophyte Halophyte Arid / dry and high temperatures Saline (salty soil / water) Conditions ……………………………………………………………. ……………………………………………………………. …………………………………………………………….Increased water loss via evaporation …………………………………………………………….Reduced water uptake due to hypertonic Issue …………………………………………………………….Reduced water uptake via roots …………………………………………………………….soil conditions (+ high levels of salt uptake) 1. ………………………………………………………Reduced leaves (⬇ evaporation) 1. ………………………………………………………Cellular sequestration (salt in vacuoles) 2. ………………………………………………………Thick cuticles (prevents water loss) 2. ………………………………………………………Tissue partitioning (leaf abscission) Adaptations 3. ………………………………………………………Stomata in pits (traps water vapour) 3. ………………………………………………………Salt excretion (active salt removal) 4. ………………………………………………………CAM physiology (open stomata at night) 4. ………………………………………………………Root level exclusion (avoid salt uptake) List three ways water transport can be modelled in xylem 1. …………………………………………………………………………………………………………………………………………………...Capillary tubing 2. …………………………………………………………………………………………………………………………………………………...Porous pots 3. …………………………………………………………………………………………………………………………………………………...Filter paper Describe how potometers can be used to measure transpiration rates ………………………………………………………………………………………………………………………………………………….......... Potometers estimate transpiration rate by measuring the rate of water loss or uptake by a plant …………………………………………………………………………………………………………………………………………………..........They record the distance moved by an air bubble or meniscus to indicate the rate of water uptake .
Load more

Recommended publications
  • Transport in Flowering Plants
    Transport in flowering plants Transport systems in plants Plants may not have blood vessels and a heart, but they nevertheless have transport systems of cells which form tubular vessels to transport molecules and ions in solution from one place to another. The xylem tissue carries water and dissolved ions from the roots to the aerial parts of the plant. In the tallest trees this can be over 100 metres. Phloem carries water and dissolved food molecules from the leaves to all parts of the plant. For more about the solvent properties of water see Soil water. Turgor and plasmolysis The shape of plant cells is defined by their cell wall. This is normally slightly stretched and rigid, due to the uptake of water by osmosis. Water will move from a less concentrated solution into a more concentrated solution through a partially permeable membrane, as there will be a diffusion gradient from where there is more water to where there is less water. The ability of water to move from one place to another is called water potential. Water will move from higher to lower water potential. The water potential of a cell,, is given by: = s + p Where s is the solute potential, due to particles dissolved in the water in the cytoplasm (which lowers water potential), and p is the pressure potential due to the stretching of the cell wall (which in increases water potential). The water potential of pure water at one atmosphere pressure is zero, so adding solutes has a negative effect on water potential, tending to make water enter a system.
    [Show full text]
  • The Transpiration Stream and Upward Translocation of Mineral Ions1' 2
    No. 6 MULTIPLE TILLS NEAR SHENANDOAH 357 THE TRANSPIRATION STREAM AND UPWARD TRANSLOCATION OF MINERAL IONS1' 2 JAMES W. O'LEARY Department of Botany, University of Arizona, Tucson ABSTRACT Ca46 and P32 were supplied simultaneously to young Phaseolus vulgaris L. seedlings grown in solution. After short periods of uptake, the Ca45/P32 ratios in opposite leaves and opposite leaflets were very similar. This relationship also held when Ca45 and Cs137 were paired. Ca45/P32 ratios in lateral halves of the same leaf were in good agreement, also. However, the basal halves of leaves always had higher Ca4B/P32 ratios than terminal halves. There was a negative acropetal gradient of Ca45/P32 ratio in the stem, but the ratio in the trifoliate leaves was higher than in the primary leaves. When roots were removed prior to supplying the radioisotopes, the Ca45/P32 ratios in the foliage and stems were lower than in plants with roots intact. The data obtained support the en masse flow concept of ion movement through the stem. The usual mechanism proposed for the upward translocation of mineral ions in plants is visualized as a bulk transport of these ions in the transpiration stream. This concept has led to considerable investigation attempting to ascertain the precise dependency of salt uptake and distribution on the movement of water through the plant. Several investigators have shown that an increase in transpira- tion rate is accompanied by an increase in salt uptake and movement to the shoots (Hylmo, 1953, 1955, 1958; Brouwer, 1954, 1956; Kylin and Hylmo, 1957; Smith, 1957). However, the mechanism whereby transpiration influences the overall p No.
    [Show full text]
  • Measurement of Root Hydraulic Conductance
    Measurement of Root Hydraulic Conductance Albert H. Markhart, III Department of Horticulture Science and Landscape Architecture, University of Minnesota, St. Paul, MN 55108 Barbara Smit Center for Urban Horticulture, University of Washington, Seattle, WA 98195 Plant root systems provide water, nutrients, and growth regulators transpiration at the shoot and osmotic potential. The latter is gen- to the shoot. Growth and production of a plant are often limited by erated by the combination of active solute accumulation, passive the ability of the root to extract water and nutrients from the soil solute leakage, and rate of water movement from the soil to the and transport them to the shoot. The transport of most nutrients and xylem. This is difficult, if not impossible, to determine. Conduc- growth regulators occurs via the transpiration stream. The velocity tivity of the radial pathway is determined by structures through and quantity of water moving from the root to the shoot determines which the water flows. Water flows along the path of least resis- the quantity and concentration of substances that arrive at the shoot. tance. Resistance of the interstices in the cell wall is considered Understanding the forces and resistances that control the movement lower than across plasmalemma and cytoplasm. For these reasons, of water through the soil-plant-air continuum and the flux of po- it is thought that water moves apoplasticly across the root until a tential chemical signals is essential to understanding the impact of significant barrier is encountered, at which point the water is forced the soil environment on root function and on root integration with through the plasmalemma.
    [Show full text]
  • The Dynamics of Transpiration to Evapotranspiration Ratio Under Wet and Dry Canopy Conditions in a Humid Boreal Forest
    Article The Dynamics of Transpiration to Evapotranspiration Ratio under Wet and Dry Canopy Conditions in a Humid Boreal Forest Bram Hadiwijaya 1 , Steeve Pepin 2, Pierre-Erik Isabelle 1,3 and and Daniel F. Nadeau 1,* 1 CentrEau—Water Research Center, Department of Water and Civil Engineering, Université Laval, 1065 avenue de la Médecine, Québec, QC G1V 0A6, Canada; [email protected] (B.H.); [email protected] (P.-E.I.) 2 Centre de Recherche et d’Innovation sur les Végétaux, Department of Soil and Agri-Food Engineering, Université Laval, 2480 boulevard Hochelaga, Québec, QC G1V 0A6, Canada; [email protected] 3 Premier Tech, 1 avenue Premier, Rivière-du-Loup, QC G5R 6C1, Canada * Correspondence: [email protected] Received: 31 January 2020; Accepted: 19 February 2020; Published: 21 February 2020 Abstract: Humid boreal forests are unique environments characterized by a cold climate, abundant precipitation, and high evapotranspiration. Transpiration (ET), as a component of evapotranspiration (E), behaves differently under wet and dry canopy conditions, yet very few studies have focused on the dynamics of transpiration to evapotranspiration ratio (ET/E) under transient canopy wetness states. This study presents field measurements of ET/E at the Montmorency Forest, Québec, Canada: a balsam fir boreal forest that receives ∼ 1600 mm of precipitation annually (continental subarctic climate; Köppen classification subtype Dfc). Half-hourly observations of E and ET were obtained over two growing seasons using eddy-covariance and sap flow (Granier’s constant thermal dissipation) methods, respectively, under wet and dry canopy conditions. A series of calibration experiments were performed for sap flow, resulting in species-specific calibration coefficients that increased estimates of sap flux density by 34% ± 8%, compared to Granier’s original coefficients.
    [Show full text]
  • Grandidentata in the Field at Ambient and Twice Ambient CO2 in Open
    grandidentata in the field at ambient and twice ambient CO2 in open productivity(1-4) This observation has led to the suggestion that, by bottom root boxes filled with organic matter poor native soil. Nitrogen taking up CO2, the terrestrial biosphere might mitigate the potential was added to all root boxes at a rate equivalent to net N mineralization greenhouse warming associated with anthropogenic CO2 emissions(5). in local dry oak forests. Nitrogen added during August was enriched Whiting and Chanton(6) have found, however, that for wetlands of with N-25 to trace the flux of N within the plant-soil system. Above- and varying productivity around the world, higher net primary production is belowground growth, CO2 assimilation, and leaf N content were associated with higher emissions of methane-another important measured non- destructively over 142 d. After final destructive harvest, greenhouse gas. Here we present measurements of methane emissions roots, stems, and leaves were analyzed for total N and N-15. There was from a marsh that has been exposed to twice the present ambient no CO2 treatment effect on leaf area, root length, or net assimilation concentration of atmospheric CO2. We find that over a one-week period, prior to the completion of N addition. Following the N addition, leaf N the CO2-enriched sites had significantly higher emissions of methane content increased in both CO2 treatments, but net assimilation showed than the control sites. Our results suggest that future increases in a sustained increase only in elevated CO2 grown plants. Root relative atmospheric CO2 concentration may lead to significant increases in extension rate was greater at elevated CO2, both before and after the N methane emissions from wetlands.
    [Show full text]
  • The Role Op Transpiration in the Absorption And
    THE ROLE OP TRANSPIRATION IN THE ABSORPTION AND TRANSLOCATION OP MINERAL IONS IN PLANTS, AS MEASURED WITH RADIOACTIVE CALCIUM AND PHOSPHORUS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By RAFIQ AHMAD, B.Sc. (Alig), M.Sc. (Punjab) The Ohio State University 1959 Approved hy Adviser Department of Botany and Plant Pathology ACKNOWLEDGMENT The ■writer wishes to express his gratitude to the faculty and graduate students of the Department of Botany and Plant Patho­ logy, The Ohio State University, for their great help during his stay in the U. S. A. Special thanks are due to Dr. C. A. Swanson for his guidance and encouragement during this investigation and other graduate studies. The writer is also thankful to Dr. R. S. Platt, Jr. for his help in preparing this manuscript and a critical reading of the draft. Thanks are also extended to Dr. C. G. Weis- haupt for critical reading of the manuscript. The writer also wishes to express his appreciation to The University of Karachi, Pakistan, for the grant of study leave, and to the Institute of International Education for the award of a travel grant to pursue these studies. ii TABLE OP CONTENTS Page INTRODUCTION ......................................... 1 LITERATURE R E V I E W ................................... 4 MATERIALS AND M E T H O D S ............................... 8 EXPERIMENTS AND R E S U L T S ............................. 14 Section 1 ....................................... 14 Experiments to investigate whether a low transpiration rate can he growth-limiting Section 2 ....................... .. 2 6 Experiments to determine the rate at which metabolically-absorbed phosphorus^ and c a l c i u m ^ become available for upward trans­ location into shoot Section 3...
    [Show full text]
  • Atmospheric Continuum Model to Study Hydrodynamic Soil‐
    PUBLICATIONS Water Resources Research RESEARCH ARTICLE A vegetation-focused soil-plant-atmospheric continuum model 10.1002/2017WR020467 to study hydrodynamic soil-plant water relations Key Points: Zijuan Deng1,2,3 , Huade Guan1,2, John Hutson1, Michael A. Forster4,5, Yunquan Wang6, and A new SPAC model is developed to Craig T. Simmons1,2 simulate soil/plant water flux and water status at subdaily resolution 1School of the Environment, Flinders University, Adelaide, South Australia, Australia, 2National Centre for Groundwater The model uses a dynamic plant 3 resistance system which is described Research and Training, Bedford Park, South Australia, Australia, Now at Centre for Carbon, Water and Food, Faculty of 4 by a plant physiological vulnerability Agriculture and Environment, University of Sydney, Sydney, New South Wales, Australia, School of Agriculture and Food curve Science, University of Queensland, Brisbane, Queensland, Australia, 5Edaphic Scientific Pty Ltd., Port Macquarie, New The model can be easily South Wales, Australia, 6School of Environmental Studies, China University of Geosciences, Beijing, China parameterized under field conditions and particularly useful to assimilate leaf/stem water potential data Abstract A novel simple soil-plant-atmospheric continuum model that emphasizes the vegetation’s role in controlling water transfer (v-SPAC) has been developed in this study. The v-SPAC model aims to incorpo- Supporting Information: Supporting Information S1 rate both plant and soil hydrological measurements into plant water transfer modeling. The model is differ- ent from previous SPAC models in which v-SPAC uses (1) a dynamic plant resistance system in the form of a Correspondence to: vulnerability curve that can be easily obtained from sap flow and stem xylem water potential time series Z.
    [Show full text]
  • Water Movement in Plants
    Chapter 3 - Water movement in plants Chapter editors: Brendan Choat and Rana Munns Contributing Authors: B Choat1, R Munns2,3,4, M McCully2, JB Passioura2, SD Tyerman4,5, H Bramley6 and M Canny* 1Hawkesbury Institute of the Environment, University of Western Sydney; 2CSIRO Agriculture, Canberra; 3School of Plant Biology, University of Western Australia; 4ARC Centre of Excellence in Plant Energy Biology; 5School of Agriculture, Food and Wine, University of Adelaide; 6Facutly of Agriculture and Environment, University of Sydney; *Martin Canny passed away in 2013 Contents 3.1 - Plant water relations 3.2 - Long distance xylem transport 3.3 - Leaf vein architecture and anatomy 3.4 - Water movement from soil to roots 3.5 - Water and nutrient transport through roots 3.6 - Membrane transport of water and ions 3.7 - References Evolutionary changes were necessary for plants to inhabit land. Aquatic plants obtain all their resources from the surrounding water, whereas terrestrial plants are nourished from the soil and the atmosphere. Roots growing into soil absorb water and nutrients, while leaves, supported by a stem superstructure in the aerial environment, intercept sunlight and CO2 for photosynthesis. This division of labour results in assimilatory organs of land plants being nutritionally inter-dependent; roots depend on a supply of photoassimilates from leaves, while shoots (leaves, stems, flowers and fruits) depend on roots to supply water and mineral nutrients. Long-distance transport is therefore a special property of land plants. In extreme cases, sap must move up to 100 m vertically and overcome gravity to rise to tree tops. Karri (Eucalyptus diversicolor) forest in Pemberton, Western Australia.
    [Show full text]
  • Environmental Factors Influence Plant Vascular System and Water
    plants Review Environmental Factors Influence Plant Vascular System and Water Regulation Mirwais M. Qaderi 1,2,* , Ashley B. Martel 2 and Sage L. Dixon 1 1 Department of Biology, Mount Saint Vincent University, 166 Bedford Highway, Halifax, NS B3M 2J6, Canada; [email protected] 2 Department of Biology, Saint Mary’s University, 923 Robie Street, Halifax, NS B3H 3C3, Canada; [email protected] * Correspondence: [email protected] Received: 9 January 2019; Accepted: 11 March 2019; Published: 15 March 2019 Abstract: Developmental initiation of plant vascular tissue, including xylem and phloem, from the vascular cambium depends on environmental factors, such as temperature and precipitation. Proper formation of vascular tissue is critical for the transpiration stream, along with photosynthesis as a whole. While effects of individual environmental factors on the transpiration stream are well studied, interactive effects of multiple stress factors are underrepresented. As expected, climate change will result in plants experiencing multiple co-occurring environmental stress factors, which require further studies. Also, the effects of the main climate change components (carbon dioxide, temperature, and drought) on vascular cambium are not well understood. This review aims at synthesizing current knowledge regarding the effects of the main climate change components on the initiation and differentiation of vascular cambium, the transpiration stream, and photosynthesis. We predict that combined environmental factors will result in increased diameter and density of xylem vessels or tracheids in the absence of water stress. However, drought may decrease the density of xylem vessels or tracheids. All interactive combinations are expected to increase vascular cell wall thickness, and therefore increase carbon allocation to these tissues.
    [Show full text]
  • Root Uptake of Organic Contaminants Into Plants: Species Differences
    Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 8-2012 Root Uptake of Organic Contaminants into Plants: Species Differences Naho Orita Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Civil and Environmental Engineering Commons Recommended Citation Orita, Naho, "Root Uptake of Organic Contaminants into Plants: Species Differences" (2012). All Graduate Theses and Dissertations. 1287. https://digitalcommons.usu.edu/etd/1287 This Thesis is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. ROOT UPTAKE OF ORGANIC CONTAMINANTS INTO PLANTS: SPECIES DIFFERENCES by Naho Orita A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Civil and Environmental Engineering Approved: _____________________ _____________________ William J. Doucette Bruce Bugbee Environmental Chemist Plant Physiologist Major Professor Committee Member _____________________ _____________________ David K. Stevens Mark R. McLellan Environmental Engineer Vice President for Research and Committee Member Dean of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2012 ii Copyright © Naho Orita 2012 All Rights Reserved iii ABSTRACT Root Uptake of Organic Contaminants into Plants: Species Differences by Naho Orita, Master of Science Utah State University, 2012 Major Professor: Dr. William J. Doucette Department: Civil and Environmental Engineering Trace amounts of xenobiotic organic contaminants have been frequently identified in the environment, including surface water and wastewater streams, and some are even in drinking water.
    [Show full text]
  • Water Is a Very Important Substance Obtained and Transported Throughout Plants
    Water is a very important substance obtained and transported throughout plants Transpiration stream is the movement of water through a plant. Transpiration stream is maintained by: 1. Osmosis 2. Root pressure 3. Transpiration Osmosis is the movement of water from high water concentration to low water concentration across a semi-permeable membrane. Root pressure is the force exerted by water within the xylem tissue of the roots. Transpiration is the loss of water from the aerial parts of a plant. Water and mineral uptake: Water enters the root hairs by osmosis, moving from high water concentration to low water concentration. Minerals dissolve easily in water and move into the root by diffusion - either by passive transport or by active transport (requires ATP). Water moves across the ground tissue and into xylem tissue. Water is then transported up the plant. Cohesion-tension model of water transport John Joly and Henry Dixon were two Irish scientists who first proposed the cohesion-tension model of water transport. Water moving into the xylem tissue of the root causes a pressure build up - this is called root pressure. Root pressure contributes to the upward movement of water molecules. Water molecules have hydrogen bonds between them maintaining them in the liquid form - this is cohesion of the water molecules. Water molecules also tend to stick easily to the sides of the xylem vessels - this is called adhesion of the water molecules. Transpiration of the water molecules occurs mainly from the leaves - this pulls the column of water molecules upwards through the xylem, creating a tension in the water molecules.
    [Show full text]
  • Evaporation and Transpiration
    VOL. 17, N0. 6 REVIEWS OF GEOPHYSICS AND SPACE PHYSICS SEPTEMBER 1979 EVAPORATION AND TRANSPIRATION Robert R. Ziemer Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Berkeley, California, stationed at Arcata, California 95521 For years, the principal objective of evapo- evapotranspiration equation to include a term for transpiration research has been to calculate the canopy resistance signaled a shift in emphasis in loss of water under varying conditions of climate, evapotranspiration research from a physically soil, and vegetation. The early simple empirical controlled process to one which can be physio- methods have generally been replaced by more de- logically controlled. This change in direction tailed models which more closely represent the was acknowledged by Federer [1975] in his earlier physical and biological processes involved. review and has continued for the past four years. Monteith's modification of the original Penman The scope of this review, as were the reviews of Ekern [1971] and Federer [1975], is, for the most This paper is not subject to U.S copyright. Pub- part, limited to evaporation from terrestrial lished in 1979 by the American Geophysical Union. surfaces rather than from lake or ocean surfaces. Paper number 9R0474 1175 1176 A review of the literature since 1974 shows Stomata that substantial interest has been maintained in The role of stomata in the regulation of trans- understanding the influence of advection and piration has been widely studied. The environ- interception on evapotranspiration. As the com- mental factors that have a major influence on plexity of the models increases, the data require- stomatal resistance are irradiance [Hall et al., ments to drive the equations often make the model 1976], leaf water status [Jarvis, 1976; Shirazi useless for field applications.
    [Show full text]