BARD NO. US-324-1 TITLE: Effects of Root Zone Temperature, Oxygen Concentration, and Moisture Content on Actual Vs. Potential Growth of Greenhouse Crops Investigators and Affiliated Institutions: Principal Investigator (PI): J. Heinrich Lieth, Professor and Department Chair Environmental Horticulture, University of California, Davis CA USA Co-Principal Investigator (Co-PI): Michael Raviv, Head Newe Ya'ar Research Center, ARO, Ramat Yishay, Israel David W. Burger, Professor Environmental Horticulture, University of California, Davis CA USA Signatures: Principal Investigator Name: Lieth, J. Heinrich Signature: Research Officer,Affiliated Institution The Regents of the University of California Signature: Page 1 of 11
Effects of Root Zone Temperature, Oxygen Concentration, and Moisture Content on Actual versus Potential Growth of Greenhouse Crops Heiner Lieth, Michael Raviv, Robert Flannery, Hamam Ziadna, Shlomit Medina and David Burger The second year of the project saw significant advancements in a number of areas, although, in general, we feel we are significantly behind schedule in our efforts. Due to the set-back that is described in the previous report, our inability to hire key personnel (US) and a major spider mite (Israel) and mealybug (US) attack, we are now a few months behind schedule. We anticipate that some portions of the project will complete on time while others will require a no-cost extension after the third year. In this report we describe the second part of the rose-temperature experiment (Israel), the lettuce-temperature experiment (Israel) and the oxygen/temperature experiment on rose (US). Materials and Methods: Israel Rose-temperature experiment This is a continuation of the experiment that was reported last year and therefore exactly the same methods were used. Last year we reported results for the period: Sept., 17 Nov. 28.22. In the current report, the results of the period through the end of the experiment (February 9, 23) are reported. Since 3 of the units suffered occasional failures we present here the results of only 6 units. Lettuce-temperature experiment The same setup, temperatures and procedures were used to grow the lettuce plants. The cultivar used was Green Rex (Butter head type) and the growing period was from 23.2.23 till 2.3.23. The ph was kept in the range 6.-6. and the EC in the range 1.8-2.2 ds m -1. Rose-DO experiment The rose cultivar in this experiment was Respect, grafted on Rosa indica. The plants, purchased from a commercial nursery, were planted in the hydroponic systems on 12.8.23. The temperature was set at 2/C for all units. This experiment was initiated, after an adaptation period, on 19.1.23 and it is still running. A dissolved oxygen sensing and controlling unit was installed. It is based on 8 multi-log-s 8/8 DO sensors, hooked to a computer through a data logger (Multi-log Oxy Guard. Both sensors and data loggers were manufactured by Oxy Guard, Denmark. Data are recorded every minutes, reflecting the average value for this period. Oxygen is added using the Rainforest spinners (General Hydroponics, USA). Once roots were active enough to consume a significant amount of oxygen, the systems were set to maintain a wide range of DO Page 2 of 11
concentrations. All other procedures are identical to those described in the previous report. As the experiment is in its early stage no results will be presented in the current report. However, and in order to demonstrate our ability to control the DO very close to the desired levels, Typical one-day results are shown in Figure 1. The results of the rose growing experiments could not be subjected to a statistical analysis, as only it was impractical to distinguish among plant material of different plant. Therefore one unit (replicate) served for each temperature of DO level. On the other hand, each lettuce plant (total of 14 per unit) served as a replicate and therefore we could calculate standard deviations and regression analyses. Calorespirometric measurements We could not find previous work where calorespirometric response of excised root tips was measured. A methodological work had therefore to be conducted, which yielded the following procedure: The amount of plant material per ampoule required for satisfactory calorimetric readings are about 6-9 root sections, having a length of 8-9 mm from the apex upwards, fresh weight of ~ 7 mg and dry weight of ~3. mg. This amount of fresh plant material requires higher water amount in the ampoule, to sustain optimal physiological condition, than is normally used. The amount we determined as optimal is 1 :L. We found that it is important to keep the root submersed in water from the sampling moment, until the start of the measurement. The order of measurements activities are as follows: first the roots alone, than with a CO 2 trap, filled with.4 N NaOH solution and then again the roots alone. The average of the readings taken when the roots are alone in the ampoule served as the q value. The measurements were performed under isothermal mode, at the same temperature in which each sample was grown. Page 3 of 11
United States So as to be able to conduce parallel experiments with the Isreali part of the project, we began building a set-up that would allow us to implement specific root zone temperature conditions and control oxygen, while taking advantage of the things that were learned earlier. We decided to use normal household refrigeration equipment (a chest freezer) as chilling unit with greater capacity than we would obtain with custombuilt scientific equipment at a significantly lower cost. Our design includes a normal household freezer, in which we installed a large water tank (Fig 2). The temperature in the freezer is controlled by a Johnson Controls secondary thermostat designed to operate freezers or refrigerators at temperatures higher than normally possible with the built-in thermostat. Furthermore it allowed us to specifically control the temperature of the water in the tank, rather than the air in the cabinet. Our current design has the water temperature set at 1C. Another part of the system has copper tubing wrapped around a hydroponic bucket set into a larger bucket (Fig 3). The space Fig 2. Freezer used as chilling unit to create cold liquid for cooling the root zone of the hydroponic units. between the two buckets is filled with water. Chilled water is pumped with small submersible pumps from the tank in the freezer, through the tubing, and back into the tank in the freezer. Initially our plan was to circulate chilled ethylene glycol as this would allow colder temperatures, but our initial tests showed that we could accomplish our objectives with plain water. As we add more hydroponics units to the experiment we may need to use colder liquid and more extensive insulation; in that case we will add ethylene glycol and run the chiller at colder temperatures. Thermocouples are used to sense the temperature in the hydroponic buckets. In this study the buckets are aerohydroponics units that contain no substrate. This unit is typically half full with water. Fig 3 Three hydroponic units, each with temperature control and instrumentation for data collection. A Campbell Scientific CR21X data logger is used to measure all the temperatures in all the hydroponics units and control the valves and pumps to maintain the desired Page 4 of 11
temperatures in the hydroponics units. In cases where temperatures greater than air temperature are needed, aquarium heaters in the hydroponics units are used to implement the desired set-point. The dissolved oxygen concentration in the hydroponics units is measured using Ocean Optics FOXY instrumentation. Figure 4 shows the probes and the analyzer. The tip of the oxygen probe contains a chemical that fluoresces in proportion to the amount of oxygen that is present. Through proper calibration and temperature compensation, this device allow measurement of oxygen at the tip of the probe. It can measure it in either liquid or in gas. Temperature sensor Oxygen probe Dissolved Oxygen Analyzer Fig 4. Oxygen analyzer - blue lines are fiberoptic cables to the oxygen probe; while lines lead to temperature sensors. Both sensors consist of stainless steel probes that are inserted in the root zone. Experimental Protocol: One or two rose plants were placed in one of three hydroponic units (see photo in Fig 3). Each unit was sealed with duct tape to prevent oxygen entry. In each, oxygen saturation was initially imposed by bubbling air in the nutrient solution. Each of three temperature treatments were imposed in subsequent 24 hour periods: 12C, 24C or 33C. Additional temperature treatments are currently being added. Once the temperature in the hydroponics solution was stable, the air bubbling stopped and oxygen depletion was monitored using the oxygen analyzer as the roots consumed the available oxygen. The same plants were used for each of the treatments so the root biomass was constant during this experiment. Mathematical Modeling research We are currently recruiting a scientists to handle the modeling work. A scientist has been identified and is being flown in for an interview next week. We had hoped to have someone on board to begin the modeling work 6 months earlier, but last year s delays forced the delay of this as well. Modeling work on nutrient uptake in the root zone has begun in a related project at UCDavis and we expect that this will be integrated into BARD project as well. Page of 11
Research Results Israel Rose-temperature experiment The cumulative results of the main measured growth parameters of the rose plants, grown in different root-zone temperatures are shown in Figure. The temperatures that appear in the abscissas are those of the actual average values for the treatments rather than the selected set-point. Root-zone temperature had a clear effect on the biomass produced and the optimum is in the range of 23-26/C. Flower production had a similar effect, although, perhaps somewhat more biomass was directed to flower stems at somewhat lower temperatures, as can be seen in Figure B. The effect of the root-zone temperature on water consumed by the plants is shown in Figure C. Except for a difficult-to-explain high water uptake in the 18/C unit, Dry weight (gr) Flowers per unit Water consumption (L/unit) 21 2 2 19 19 18 18 17 17 13 12 12 11 11 1 1 9 9 8 8 7 6 4 3 2 1 12. 1.2 17.8 22. 2.6 28. 12. 1.2 17.8 22. 2.6 28. water consumption was clearly affected by root temperature. Contrary to expectation, higher water consumption by the high-temperature unit did not result in yield increase. The relation between water consumed and biomass produced (water use efficiency, WUE) dropped from 4.3 gr/l (12 C) to 2.9 gr/l (28 C). These values are relatively high for closed systems (Raviv and Blom, 21). These high WUE values can be ascribed to the very high efficiency of the type of closed hydroponic system that was used and to the favorable environmental conditions. These results are different from what was reported in the previous year. It is assumed that the results presented in the first report were not representative as they were taken before plants were able to produce enough harvestable material. Sporadic measurements of net photosynthesis, stomatal conductivity and momentary transpiration showed no consistent trend that can be related to the root temperature (data not shown). 12. 1.2 17.8 22. 2.6 28. Fig. Biomass accumulation, flower productivity and water consumption in the six temperature treatments Page 6 of 11
- Calorespirometric response of rose roots, exposed to various temperatures before excision is shown in Figure 6. The very low (and descending with root zone temperature) values obtained are not in accordance with any of the above-ground measured parameters. However, in relative terms, more biomass was allocated to the roots at low temperatures, as can be seen in Figure 7. This temp.-dependent preferential allocation may be the reason for Microjoule mg -1 sec -1 4. 2.. -2. -4. -6. -8. -1. -12. -14. 1 1 2 2 3 Fig 6. RSG of rose roots as a function of root-zone temperature the observed trend of RSG. We assume that the growing organs in the upper parts of the plant (leaflets and buds) should respond differently to root-zone temperature but had no time to measure it in the first trial. We plan to test this hypothesis during the third year. Root DM as % of total DM 19. 18. 18. 17. 17. 16. 16. 1. 1. 12. 14. 16. 18. 2. 22. 24. 26. 28. Fig 7. Dry matter allocation to the roots as a function of root-zone temperature Lettuce-temperature experiment The cumulative results of the main measured growth parameters of the lettuce plants, grown in different root-zone temperatures are shown in Figures 8-11. The temperatures that appear in the abscissas are those of the actual readings (average value for the whole period) rather than the Dry weight (gr) 9. 8. 8. 7. 7. 6. 6... y = -.6x 3 +.86x 2 +.168x - 2.39 R 2 =.6636 4. p<.1 4. 12. 14. 16. 18. 2. 22. 24. 26. 28. Fig 8. Total dry matter allocation of lettuce Page 7 of 11
predetermined set-point. The effect of root-zone temperature on final biomass is shown in Figure 8. The general trend is similar to what have been found for roses, with a slight downwards shift in the optimal temperatures (22-24 C). Water (L) consumed per plant 3. 2. 2. 1. y = -.8x 3 +.39x 2 -.349x + 1.243 R 2 =.9883 p<.1 1... 12.. 14. 16. 18. 2. 22. 24. 26. 28. Water consumption as a function of root-zone temperature is shown in Figure 8. Unlike the case of roses, water consumption was closely related to biomass production, as can be seen by the similarity between Figures 8 and 9. WUE, in this case, dropped from approximately gr/l (at 12 C) to ~2 gr/l (at 26 C), as can be seen in Figure 9. WUE g/kg 4. 4. 3. 3. 2. 2. 12. 14. 16. 18. 2. 22. 24. 26. 28. Fig 9. Water consumption and water use efficiency as function of root zone temperature RSG of lettuce roots, as a function of root zone temperature is shown in Figure 1. As for roses (Figure 6) we measured very low (and descending with root zone temperature) RSG values, which are not in accordance with the above-ground measured parameters. However, in relative terms, more biomass was allocated to the roots at low temperatures, as can be seen in lower fram of Figure 1. This temp.-dependent preferential allocation may be the reason for the observed trend of RSG. In conclusion, optimal root zone temperature was ~26 C and 22-24 C for rose and lettuce, respectively, however rose flower production was more efficient Microjoule mg -1 sec -1 Root DM as % of total DM 3 2 1-1 -2-3 -4 - -6-7 -8 13. 12. 11. 1. 9. 8. 7. 6.. 12. 14. 16. 18. 2. 22. 24. 26. 28. Fig 1. RSG value and root biomass percentage as a function of root zone temperature. Page 8 of 11
around 22 C. Water consumption of roses was mostly affected by the temperature of the nutrient solution, while that of lettuce was affected primarily by biomass production. WUE was high, and dropped with temperature in both cases. RSG did not reflect any of the canopy relevant tested parameters, perhaps reflecting a temperature-dependent preferential allocation of assimilates. This aspect will be tested in another experiment, planned for the third year. Initial results of the DO experiment (data not shown) suggest that RSG values of roots do respond to DO levels in the nutrient solutions. They appear to be stable and low up to ~7% and rise sharply above this level. In this case calorespirometric responses of leaflets and buds are already under study, in addition to those of roots. United States Rose root zone O 2 depletion vs root zone temperature Dissolved oxygen (DO) always depleted over time, rapidly at first, declining over time. This indicated high rates of consumption at high dissolved oxygen concentrations and lower consumption rates at low concentrations. At each temperature, as the oxygen is depleted, the final DO concentration does not reach zero but rather approaches a low asymptotic level. While it is possible that this is due to Oxygen leaking back into the system, we feel that this is unlikely since we took precautions to seal the hydroponics units as much as possible. It is more likely that the respiration is essentially shut down due to the very low gradient of oxygen concentration between the inside and the outside the root. When we started to look at the effect of dissolved oxygen (DO) in the rhizosphere of hydroponically grown roses we noticed that the concentration of oxygen changes very rapidly. In fact, the dynamics Dissolved Oxygen (ppm) 1 9 8 7 6 4 3 2 1 4:48 9:36 14:24 19:12 : 4:48 9:36 3 1 9 8 7 6 4 3 2 1 14:24 16:48 19:12 21:36 : 2:24 4:48 7:12 9:36 12: 3 1 9 8 7 6 4 3 2 1 12C 14:24 16:48 19:12 21:36 : 2:24 4:48 7:12 9:36 12: Page 9 of 11 24C 33C Dissolved Oxygen Temperature Time Fig 11. Draw-down of oxygen concentration by the rose plants in the three temperature treatments 3 3 2 2 1 1 3 2 2 1 1 3 2 2 1 1
are much faster than was previously known. We attributed the results from our earlier findings to inadequate instrumentation, since conventional methods for measuring dissolved oxygen in the root zone are (1) very slow, (2) require that the liquid be in motion, and (3) consume oxygen in the measurement-process. This meant that measurement in hydroponic rose systems could not be conducted in the substrate. It could only be carried out during the recirculation process. Since this process introduces oxygen into the solution, the results were always skewed. By using our spectrophotometric analyzer we can get instantaneous DO measurements that are not affected by the measurement process. When the DO concentration levels dip into the hypoxic range, oxygen becomes a limiting factor to the root respiration. When the roots are subjected to hypoxia, the rate of respiration and oxygen absorption decreases. Observed dissolved oxygen rates reached between 1 and 2 ppm, but generally not lower. This suggests that no further oxygen is consumed, indicating that respiratoryprocesses in the roots are shut down. Thus, while there is still some small amount of oxygen present in solution, the roots are not able to use it. The data suggest a general pattern for oxygen depletion but are not adequate as yet to completely formulate or calibrate a model. We anticipate a model that declines exponentially with oxygen concentration and perhaps linearly with temperature (Fig 8). Description of the cooperation The cooperation consists of a 3-way cooperation between Dr Micheal Raviv (ARO), Dr Dave Burger (UCDavis) and myself (also UCDavis). During the first year, Dr Oxygen Depletion Rate (ppm/min).122.84.4.7 1. 6.67 3.33 Oxygen Concentration (ppm) 3 2 1. Fig 12. Proposed model for oxygen depletion in relation to root zone temperature and oxygen concentration. Burger was working on this project while on leave at UC Riverside. Drs Raviv and Burger are doing the calorimetric work while Dr Lieth is doing the modeling work and setting up the experiments requiring environmental controls (temperature, oxygen, moisture tension). We also have various students, employees, visiting scientists, and post doctoral researchers working on this project. Changes in direction from that in the original proposal, if any. No new changes. Page 1 of 11
List of publications Raviv, M. and T. J. Blom (21). The effect of water availability and quality on photosynthesis and productivity of soilless-grown cut roses - A Review. Scientia Horticulturae 88: 27-276. Report on any patents No patents have been applied for; at this point no patenting activity is planned. Page 11 of 11