Plant Science I Have Provided All Information As Requested

· Only answer these questions BELOW /PRAC manuals only for READING Read PRAC MANUAL 1 (SEE ATTACHED FILE) 1.. Calculate stomatal density of the three species in the attached sheet. Select the species which has the highest stomatal density. a- Grass b- Wheat c- Citrus d- Citrus and Wheat 2..Find the right question for this answer (use what and add the question mark at the end): Controls the exchange of gases, particularly carbon dioxide and water vapour, between the leaf and the atmosphere. 3..Why are all the safety precautions taken when using the Scholander Bomb? 4..You have measured two leaves. The reading of the first leaf was 15.6 bars, and the second was 21.3 bars. What is their respective ΨL and which plant was less water stressed?  5.Why do the measurements taken before sunrise differ between trees?  6.Why are measurements of ΨL taken before sunrise of particular importance when assessing the water status of a plant?  7.During what phase of the day does the plant rehydrate and how does gs assist this process? READ PRAC MANUAL 2 (SEE ATTACHED) What was the percentage increase in average photosynthetic rate when leaves were exposed to high CO2 relative to ambient CO2? Species A: ------------ Species B:- ------------ What was the average WUE measured at ambient [CO2]? (use Equation 5; units in mmol CO2 uptake mmol-1 H2O loss) Species A: ---------- Species B: ---------- What was the average WUE measured at elevated [CO2]? (use Equation 5; units in mmol CO2 uptake mmol-1 H2O loss) Species A: -------- Species A: -------- Which species exchanged more CO2 with the atmosphere relative to H2O? Species A: ------------ Species A: --------- · Identify the C3 and C4 species. · Species A: ---- · Species B: ------- Prac #2 results - CO2: 400 ppm CO2: 600 ppm Session Group Species Plant Photo CO2S Ci Cond Trmmol Photo CO2S Ci Cond Trmmol 1 1 A 1 19.5 373.3 290 0.578 4.7 27.5 563 431 n/a 4.47 1 1 B 2 29.1 363.1 206 0.37 3.89 34.5 555.7 283 0.298 3.14 1 2 A 1 14.6 380.8 282 0.28 5.78 21.1 572.1 434 0.285 3.82 1 2 C 2 15.3 379.3 269 0.257 3.25 21.4 571.9 407 n/a 2.77 1 3 A 1 21.1 373.3 300 0.585 5.2 25.5 566.9 446 0.41 4.45 1 3 B 2 24.8 368.4 175 0.225 2.96 27.8 565.7 277 0.168 2.26 1 4 A 2 14.1 381.3 269 0.228 3.57 30 561.2 399 0.348 4.41 1 4 B 1 21.3 372.2 204 0.188 3.05 24.2 568.9 323 0.177 2.96 2 1 B 1 19.3 376 175 0.175 2.25 22.1 570.9 271 0.133 1.51 2 1 B 2 10.1 387.1 166 0.085 1.52 11.5 586.7 319 n/a 1.38 2 2 B 1 16.5 380 226 0.193 2.8 21.1 573 346 0.162 2.5 2 2 A 2 11.7 384.5 273 0.2 3.4 21.7 572.1 435 0.295 3.76 2 3 A 1 4.2 393.9 313 0.103 1.72 6.11 591.3 449 0.0801 1.27 2 3 B 2 12.2 385.1 197 0.112 1.72 14.1 582.9 299 0.084 1.38 2 3 C 3 16.2 379.4 279 0.303 3.91 21.5 572.4 423 0.269 3.53 2 4 A 1 4.25 395.5 276 0.063 1.14 22.9 563 412 0.27 3.6 2 4 B 2 20.2 373.2 166 0.172 2.74 24.7 568.2 276 0.148 2.46 Plant Sc_BIOS3032 Page 3 of 5 By rearranging equations 1-3, we can define two variables; the concentration of CO2 inside leaf air spaces (Ci) and water use efficiency (WUE): • Ci = Ca- A/gCO2 (µl L-1) (Equation 4) • WUE = (A/1000)/E (mol CO2 uptake mol-1 H2O loss) (Equation 5) We often express Ci as a percentage of atmospheric CO2 to represent the drop in CO2 from outside the leaf to inside the leaf. This is called Ci/Ca The ratio of Ci/Ca is useful because it represents the diffusional gradient for CO2 across the leaf surface, and it can be a key diagnostic of the water status of the plant as it is functioning during gas exchange. But be careful, because the Ci/Ca can also be an indicator of photosynthetic biochemistry. WUE is a useful metric of how much CO2 a plant acquires relative to the amount of H2O it loses. Leaves can often increase their assimilation rate (A) by increasing gCO2, which allows Ci to increase and increases the catalytic rate of rubisco. However, an increase in gCO2 also increases gH2O, and this increases the transpiration rate of H2O (E). Plant Science Plant Sc_BIOS3032 Page 4 of 5 Measuring leaf gas exchange with a gas analyser This prac involves an infra-red gas analyser (IRGA) for the measurement of leaf gas exchange (Licor 6400). This machine is an expensive and state-of-the art instrument. Please handle it carefully and follow instructions from your lead Lecturer/Professor. See the video for Licor. After the instructor has warmed up the gas analyser, the screen will look something like this: CO2R and H2OR are the concentrations of CO2 and H2O in the reference gas cell; the gas in the reference cell does not interact with the leaf. CO2S and H2OS are the CO2 and H2O concentrations in the sample gas cell, which measures Ca and ea (equations 1 and 2) of the air surrounding the leaf. Leaf gas exchange influences CO2S and H2OS, but not CO2R and H2OR. The difference between the sample and reference cell gas concentrations are shown as ΔCO2 and ΔH2O, along with the flow rate and relative humidity in the sample cell. Based on the measured gas concentrations, the machine calculates the photosynthetic rate (Photo, A), stomatal conductance (symbol for this is gH2O; shorthand is Cond), Ci, and the transpiration rate (Trmmol, E). If a leaf is actively photosynthesizing, should CO2S be higher or lower than CO2R? Should H2OS be higher or lower than H2OR? (Note that for the figure above, there is no leaf in the sample chamber.) Discuss these questions in your group; you do not have to answer them in writing. Exercise: measure leaf gas exchange of two plant species with regard to their biochemical pathways For this prac, we will have two different plant species ('species A' and 'species B') with contrasting photosynthetic biochemistry. Can you identify which is which on the basis of your observations during this prac? Under the supervision of your instructor, carefully clamp the gas analyser sampling head onto a leaf. Set the lamp to deliver a high light intensity of 1800 umol m-2 s-1, set the CO2 mixer to control CO2R at 400 umol mol-1, and ensure that the flow rate is set to 500 umol s-1 (first press 2, then control these settings using the red f-keys). It will take 1-5 minutes for the leaf and gas analyser to stabilize. You can assess the stability of the data by looking at graphs (first press 4, then f4), or the total coefficient of variation (press h: totalCV will then be displayed in the main screen). The data are stable when the total CV is between 0.1 and 0.3. Now https://www.youtube.com/watch?v=4eO-5zxl8wk FreeText Plant science Plant Sc_BIOS3032 Page 5 of 5 match the reference and sample cells (press 1, then f5); this passes the gas from the sample cell into the reference cell and matches the calculated CO2 and H2O concentrations. Exit match mode, wait a minute, and then record the photosynthetic rate, CO2S, Ci, Cond, and Trmmol in the table. Note that the data will continue to update every second- just record an approximate average for each value. Then increase CO2R to 600 umol mol-1; it will take several minutes for CO2R to reach this high concentration. Wait an additional minute for CO2S to stabilize, match the gas analyzers again, record Photo, CO2S, and Ci (Cond and Trmmol should not have changed appreciably) and then return CO2R to 400 umol mol-1 and measure the next plant. Refer to your instructor if you’re not sure what to do. Record the data for both of your plants in the table below and on the board in the front of the class. As other groups record their data on the front board, copy down all the data on your own table below. Calculate the average of each variable for each species. Table 1: Summary of practical data Measured at CO2R=400 Measured at CO2R = 600 Species Plant Photo CO2S Ci Cond Trmmol Photo CO2S Ci Trmmol Averages for species A: Averages for species B: Definitions CO2R = CO2 concentration in the reference gas cell; CO2S = CO2 concentration in the sample gas cell (i.e., CO2 concentration in air or Ca); Photo = photosynthetic rate, Cond = stomatal conductance (same as gH2O described earlier); Ci = CO2 concentration inside the leaf or intercellular space; Photo = photosynthetic rate; Trmmol = transpiration rate. Photo or photosynthetic rate is sometimes denoted 'Anet' which stands for net CO2 assimilation rate. Trmmol or transpiration rate is sometimes denoted 'E' for evapotranspiration. FreeText Plant science