AGRON 183: Photosynthesis

Transcription

1 AGRON 183: Photoynthei Dr. Brian Hornbuckle December 1, 2016 Introduction I think I can afely ay that every agronomit i aware of the proce of photoynthei, a decribed by the following chemical equation. CO 2 + H 2 O + light carbohydrate + O 2 (1) Photoynthei i what make plant o pecial. A Dr. Lamkey, the chair of our department, like to ay, I got hungry and went outide and tood in the un for a while, but didn t get full. So I went and found ome plant to eat! Plant are pecial becaue they can make their own food from unlight! Thi i really an amazing feat, and when you think about it, it i perhap the primary reaon why life exit on our planet. Agronomit have the important tak of managing thee amazing plant that ue unlight, carbon dioxide, and water to provide u with food, feed for livetock, fiber for clothing and building material, and fuel for vehicle and other machinery. While the proce of photoynthei i likely familiar to everyone, there are ome detail and technical term that are often miundertood. Here are three of them. aimilation The uptake of CO 2 by a plant in order to perform photoynthei according to (1). Carbon dioxide enter into a leaf via mall hole called tomata. We will ue the variable A to quantify aimilation with the unit of mol CO 2 m 2. photoynthetically active radiation (PAR) Not all light from the Sun i ued in photoynthei. In (1), light i actually jut the photoynthetically active radiation, or PAR for hort. Note that green light i not photoynthetically active, which i why plant that are conducting photoynthei catter thi wavelength of light and look green to u. tranpiration The lo of H 2 O from a plant. Water taken by the plant from the oil via the root make it way to the leave via the plant vacular ytem. Some of thi water i ued in photoynthei according to (1). However, when the tomata open to take in carbon dioxide, ome of the left over water evaporate and leak out. Notice that thi evaporated water doe not appear in (1)! However, it i alway happening when photoynthei occur, becaue if the tomata are open to take in CO 2, H 2 O will alway be lot! We will ue the variable T to quantify tranpiration with the unit mol H 2O m 2. In thi data collection activity we will make meaurement relevant to photoynthei, both at the cale of an individual leaf, and for an entire plant canopy (collection of many plant). 1

2 Figure 1: The LI-6400XT i able to meaure tranpiration, T, and aimilation, A, by keeping track of what goe into the control volume, and what goe out of the control volume. Objective There are two objective for thi laboratory. 1. Meaure A and T while varying the following: (a) ambient carbon dioxide (CO 2 ) concentration; (b) ambient water vapor (H 2 O) concentration (humidity); (c) incident photoynthetically active radiation (PAR); and (d) temperature. 2. Meaure the area of leave of variou ize and hape. We will ue a pecial intrument called the LI-6400XT Portable Photoynthei Sytem to meaure A and T, and ue three different method to meaure leaf area. Thi equipment belong to the crop production and plant phyiology group in our department, and i ued by many to collect data for reearch project. We will be joined today by to member of that group, Dr. Emily Heaton, a faculty member in our department, and Dr. Nic Boerma, a reearch cientit working with Dr. Heaton. The data we collect will enable you to anwer quetion like the following. How doe carbon aimilation change a the amount of incident light i increaed? How doe tranpiration change a the amount of incident light i increaed? What i the optimum level of ambient CO 2 concentration? Do two method of leaf area meaurement give the ame anwer? Can meaurement of leaf length and width be ued to etimate leaf area? 2

3 Some Background How can an intrument like the LI-6400XT meaure A and T? Conider Figure 1. Think of the box labeled control volume a an imaginary boundary urrounding a leaf. It i called a control volume becaue we will keep track of what goe into the box, what goe out of the box, and ue the principle of the conervation of ma (ma i neither created nor detroyed) to determine A, T, and alo O, the releae of O 2 created through photoynthei from the tomata a hown in (1). The unit of O are mol O 2 m 2. Firt, think about all of the air going in and out of the control volume. The air contain many type of gae. We are primarily concerned with three of them: H 2 O, CO 2, and O 2. If f i i the flow rate of air into the control volume with unit, and f o i the flow rate of air out of the control volume alo with unit, then: f o = f i + T (2) where i the area of the leaf that i tranpiring. Auming the unit of are m 2, then the quantity T ha unit of mol H 2O. What (2) ay i that the rate at which mole of air (particularly H 2 O, CO 2, and O 2 ) are coming into the control volume mut equal the rate at which mole of air are going out. Note that H 2 O come into the control volume in two way. The firt i with the flow of air aociated with f i (auming the air i not perfectly dry). The econd i through the tem of the leaf. Thi water entering through the tem i releaed into the control volume via T and add to the mole of ga inide the control volume. Why don t we conider A and O from Figure 1 in (2)? It becaue the ame amount of ga taken up by the leaf (mole of CO 2 ) i releaed by the leaf (mole of O 2 ): for every molecule of CO 2 aimilated, a molecule of O 2 i produced according to (1). So the net effect of photoynthei, in term of ga molecule, i only to add water vapor to the control volume. Next, think about the mole of H 2 O going into and out of the control volume in Figure 1. If w i i the mole fraction of water vapor coming in with unit mol H 2O, and w o i the mole fraction of water vapor going out alo with unit mol H 2O, then we can write the following. f o w o = f i w i + T (3) Each term in (3) ha the unit mol H 2O = mol H 2O. Finally, conider the mole of CO 2 coming in and out of the control volume in Figure 1. If c i i the mole fraction of carbon dioxide coming in with unit mol CO 2, and c o i the mole fraction of carbon dioxide going out alo with unit mol CO 2, then we can write the following. f o c o = f i c i A (4) mol CO 2 = mol CO 2 Each term in (4) ha the unit. Alo notice the minu ign in (4): in thi cae the leaf i removing CO 2 from the air inide the control volume. Combining (2) with (3) yield the following expreion for tranpiration from the leaf inide the control volume. T = f i (w o w i ) (5) (1 w o ) And combining (2) with (4) yield the following expreion for aimilation inide the control volume. A = f i (c i c o ) T c o (6) 3

4 Figure 2: To get tranpiration or aimilation for an entire plant canopy (collection of plant), you need to know how many leave are conducting photoynthei, and their area. So what the LI-6400XT doe i form a control volume around a leaf, which define, and then meaure f i, w o, w i, c i, and c o. Then (5) and (6) can be ued to find T and A, repectively. The LI-6400XT can meaure A and T for individual leave. But how much CO 2 i being taken up and how much H 2 O i being releaed by a canopy of many plant? Look at Figure 2. To cale up A and T from a ingle leaf to a canopy, you mut determine the total area of leave conducting photoynthei. Therefore it i important to meaure leaf area. We will be uing three method to determine leaf area. A laboratory method for which leave mut be detached from a plant (detructive leaf area). A field method that can be done while a leaf i till attached to a plant (nondetructive leaf area). A manual meaurement in which grid paper will be ued to find the area of individual leave. General Intruction Each team will rotate through four data collection center. See Figure 3. One team will move from each center to the next center every 10 minute. There are four individual tation in the aimilation and tranpiration center, o during each 10 minute period there will be four team, one at each tation, at the aimilation and tranpiration center. It i at thi tation team will be uing LI-6400XT intrument to meaure A and T. Intruction and data heet for each tation can be found on Blackboard. The team that leave the fourth tation at the aimilation and tranpiration center will next go to the detructive leaf area center. Only one team at a time work in thi center, and only 10 minute i needed to complete the activity. The intrument at thi tation i the LI-3100C Area Meter. The manual can be found on Blackboard. From the detructive leaf area center team will go to the manual leaf area center and remain there for approximately 80 minute. At thi center team will do the following. 1. Cut out your paper leave. 4

5 Figure 3: Rotation among data collection center. 2. Label each leaf uing the naming convention on Blackboard. 3. Ue the graph paper to find the area of at leat three leave. Pick at leat one mall leaf, at leat one medium ized leaf, and at leat one large leaf. Note that each grid quare i 1 mm Meaure the length and width of each leaf. It may take your team longer than other to complete the tak at thi center. In any cae, one team mut leave thi center every 10 minute. If you do not finih your tak, then complete them when your team rotate back through. From the manual leaf area center, team will go to the nondetructive leaf area center. Here you will ue one of two LI-3000C intrument. See the manual on Blackboard. Meaure a many leave a you can: ome will be too mall. Again, one team mut leave thi center every 10 minute. If you do not finih your meaurement with the LI-3000C, you may have an opportunity to do o if you rotate back through. Equipment Your team will check out the following equipment. 5

6 1. A et of artificial leave for each team member. 2. Three heet of graph paper for each team member. 3. A tablet computer to record data, if o deired. At each center there will be one or more intrument that you will ue. For carbon aimilation and tranpiration, your team will ue a LI-6400XT Portable Photoynthei Sytem. For detructive leaf area meaurement, your team will ue a LI-3100C Area Meter. For nondetructive leaf area meaurement, your team will ue a LI-3000C Portable Area Meter. For manual leaf area meaurement, your team will ue our 1.5-m meauring pole and graph paper. Minimum Set of Meaurement Meaure all of each team member leave with the LI-3100C at the detructive leaf area center. Meaure a many of each team member leave with the LI-3000C at the nondetructive leaf area center. Follow the intruction and record the data a directed at the aimilation and tranpiration center. Meaure the length and width of all of each team member leave and have each team member find the area at leat three leave uing the graph paper at the manual leaf area center. Location We will meet in our normal claroom at the Hanen Agriculture Student Learning Center and then conduct ome of our work in the atrium of Hanen. Tentative Timeline 9-9:15 Determine group role. Manager check out tablet computer from Kelie, if you would like, and your group leave. Brief overview of data collection activitie. Review intruction and ak quetion through your Communicator. 9:15-11:45 Meaurement period. Four team (Rouh, Catillo, Carmenate, Knapp) will begin at the carbon aimilation and tranpiration center (one at each tation), one team (Hugen) at detructive leaf area, eight team (Schnicker, Magallane, Reick, Schumer, Weather, Bloome, Korhonen, Geiinger) at manual leaf area, and two team (Conner, Fevold) at nondetructive leaf area. See Figure 3 for the rotation among center. 11:45-11:50 Recorder upload data to CyBox. Manager return tablet computer to Kelie. 6