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Plant Water Relations - Science topic

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Hello plant-water relations experts!
I've been trying to estimate minimum xylem water potentials (Pmin) in deciduous trees in Indian Savannas using a Scholander pressure chamber. I understand Pmin to be the mid-day water potential in the driest season i.e. the lowest water potential that a plant experiences. The problem is that most deciduous trees are leafless during the driest season. In our field site in the eastern ghats in India, leaf flush happens after a few showers and mature only by monsoon. Do you have any suggestions on how I could go about estimating Pmin for these deciduous species?
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thanks for the document I.V.Srinivasa Reddy
Thanks David W. Lawlor , Unfortunately frequent measurement is very difficult+expensive as our field sites are far away from where we are based.
Siddarth Machado I am seriously considering a psychrometer, but am also vary about how comparable it would be. Just trying to see if there is a way to work with pressure chambers since we already have that equipment.
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Hi, everyone. Nowadays, the lateral heterogeneity of soil water isotopic compositions and its impact on plant water sources identification has been recongnized. But I am confused about how to use this information properly to improve the accuracy of isotope-based estimations. An arithmetic mean (with spatial standard deviation), a weighted mean based on soil water content, or an interpolated value at one specific tree root zone? Which one is better and why? I am looking forward to your replies and discussions~
Best,
Qin
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Hi, Andrew, thank you for your answer. The spatially arithmetic and weighted mean of soil water isotopes are usually different owing to heterogeneity in soil water content, for example, if water content is taken as a weight. Meanwhile, the soil water content is a ratio scale variable, which is further related to the soil texture at the interest site, but water isotopes are not. Therefore, there might be some problems if soil water content is taken as a weight and the weighted mean is thus meaningless. I suppose this might be the reason why most people used arithmetic mean (±1SD) as the input of stable isotope models.
Best,
Qin
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Salicylic acid (SA) is a phenolic compound involved in many aspects of plant growth and development. Apart from its role in biotic interactions, it is also involved in the regulation of important plant physiological processes, including plant water relations under stressful conditions. However, despite the importance of SA in plant physiology, little is known about its effect on AM colonization.
So, can anyone tell me what is the relationship between mycorrhizal symbiosis and salicylic acid levels in plants?
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An interesting question . Synthesis of salicyclic acid and mycorhization has very strong inter-relationship. The process of plant defense as systemic acquired resistance operates through elevated synthesis of salicyclic acid , which is further elevated upon mycorrhization , thereby , prepares the mycorrhized plants physiologically to fight against any possible biotic stress.
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what is the relationship between Zinc fertilzer application and salinity tolerance in cereals?
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Recently, I am confused about the effect of low molecular weight organic compounds and nanoparticles on plant water uptake. I searched in Google but haven't found any useful information. Does anyone can help me? Thank you in advance.
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Thanks
Yi Wan
, very useful artcile^.^
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We are working on wastewater treatment in villages of Maharashtra, India. We are exploring if kitchen garden is safe option in the places where soak pits don't function. Waste water from kitchen and bathroom contain soap, detergent powder, shampoo, hair dyes etc. If this water is given to the kitchen garden, do roots absorb these materials? Do these harmful materials enter food chain? If no, which plants should be considered for the kitchen garden?
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If you are using water from kitchen, it would probably also has a lot of grease, in this case, it is not recommended to used it directly over plants. First you would have to install a grease filter.
You also need to investigate which species can tolerate or even storage pollutants, and be careful not to eat them because you do not know which are the pollutants the water has.
Therefore, if you are planning to recycle water for plants it would be better to build containers to avoid filtration to phreatic aquifers
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I have been working on a technique that can continuously measure stomatal conductance at 5 minute intervals. The calibrated technique shows a R2 of > 0.95 with the SF-4/5 sensor. I am currently preparing a MS, but in the meantime here is a blog article:
I am interested to hear feedback on others experiences with continuously measuring stomatal conductance. From my understanding, most gs measurements require a manual, or semi-automated, meter.
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In my opinion this sensor measures the sap flow in the petiole, which is correlated to the stomatal conductance, however, they are not the same thing.
I would compare it to measuring sap flow and transpiration, both are different but correlated...
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I am teaching a physological plant ecology course in the fall and I would like to include assignments requiring students to analyze data and write results and discussion.  I teach at a small undergraduate institution and we lack to equipment for students to conduct research projects.
Is anyone aware of a suppository of plant data that I can access?  I have some data from my research that can be used, but I do not have any data for plant water relations, canopy ecophys, or mineral nutrition.
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Dear Heather,
when I was a student during my MSc I found "Plant Physiology and Development" by Taiz and Zieger a very good book (http://www.sinauer.com/plant-physiology-and-development.html). A key point in the learning process is the availability of internet resources which are related to each chapter of the book. You may find topics, essays and study questions for almost each chapter at the following link:
I hope this helps. I'm quite confident it will help your students.
Kind regards
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I have seen several instances lately in which changes in plant water potential across environmental gradients are referred to as phenotypic plasticity. I am feeling somewhat conflicted by this, and I have been going back and forth about it in my mind, so I thought I would reach out to the community here for discussion.
Phenotypic plasticity is a change in phenotype in response to an environmental cue. Plant water potential changes in response to environmental cues, and is actively controlled by the plant by physiological processes. For example, when the soil is dry, isohydric plants respond with stomatal closure. This maintains water potential homeostasis, so the trait, i.e. water potential, is prevented from changing in response to the environmental cue.
Would you consider this phenotypic plasticity?
On the other hand, take for example anisohydric plants, which allow their plant water potential to decline appreciably before full stomatal closure. In this case the water potential changes, but not by any direct action of the plant, simply by the change in gradient in the environment.
Would you consider this phenotypic plasticity?  
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Hello Juliana,
Water potential is a state of energy and not a plant trait per se. Water potential is a measurement, like temperature, so you could also ask: Can changes in plant temperature be characterized as phenotypic plasticity? It would be difficult to argue that plant temperature is a phenotypic trait; rather a series of co-ordinated plant traits can act to regulate plant temperature. Similarly, a series of plant traits can co-ordinate to regulate plant water potential.
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Neeraj tripathi
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Polyethylene glycol molecules with a molecular weight
larger than 6,000 (PEG 6000) are inert, non-ionic and cell impermeable.
They are small enough to influence the osmotic
pressure, but large enough unabsorbed by plants. Therefore, they are frequently used
to simulate osmotic stress.
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What are some techniques for plant water potential measurements?
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Three most common methods used for measuring water status.
Leaf Water Potential
A fully expanded leaf exposed to direct sunlight is chosen for measurement. To measure mid-day leaf water potential, the targeted leaf must first be covered entirely with a small plastic bag that is wrapped tightly around the leaf and secured. Securely bagging the leaf before cutting it from the shoot avoids any further transpiration, which alters the resultant pressure reading. If this critical bagging step is omitted, the data will be inaccurate.
As quickly as possible after bagging, the petiole of the bagged leaf is cut from the shoot with a sharp razor as close to the shoot as possible. The petiole is then quickly placed through the chamber lid and secured tightly, with the cut edge of the petiole facing outside and the bagged leaf blade inside the chamber.
The chamber is sealed and then slowly pressurized with nitrogen gas. When the positive pressure exerted on the leaf in the chamber equals the negative pressure inside the leaf, liquid in the leaf blade will begin to be forced out of the cut edge of the leaf.
During pressurization, the operator carefully watches the exposed edge of the petiole for the appearance of a drop of water (sap). As soon as the drop appears, the user reads the corresponding pressure from the chamber gauge. This pressure value is the leaf water potential, read in negative (–) bars.
In comparison, mid-day stem water potential tests are done during the same time period as mid-day leaf water potential but handling of the leaf is changed. Stem water potential has been considered to be less variable than mid-day LWP, improving the ability to detect small pressure differences among treatments. But until this study was completed, a comprehensive study comparing the two had not been tested in grapes.
Stem Water Potential
The stem is thought to be less susceptible to fluctuations in environmental pressures than the leaf and, therefore, more representative of the actual level of stress in the entire vine. In the mid-day SWP test, a leaf on the shaded side of the canopy is chosen to minimize any possible heating effects.
The leaf is wrapped in a black plastic bag that is covered with aluminum foil to prevent overheating by the sun. The bag is left on the leaf 90 to 120 minutes. This effectively stops the natural transpiration from the leaf, allowing the leaf water potential to come into equilibrium with the stem water potential. After 90 to 120 minutes has elapsed, the leaf is excised and tested in the pressure chamber as stated above.
Pre-dawn Leaf Water Potential
Pre-dawn leaf water potential is determined using the same basic methodology as LWP, but the readings are taken beginning at 3:30 am and ending before sunrise, using fully expanded leaves. It has been assumed that, before sunrise, the vine is in equilibrium with the soil’s water potential, therefore making PDLWP a more sensitive indicator of soil water availability. But the obvious difficulty with the method is timing: readings must be done prior to sunrise, making its practicality questionable.
Comparison of methods
For any measure of plant water status to be a sensitive indicator of water stress, it must be responsive to differences in soil moisture status and/or the resulting growth differences due to water application. The measure should also be closely related to short- and medium-term plant stress responses and less dependent on changes in environmental conditions.
For winegrapes, it would seem that LWP, SWP, and PDLWP each meet these criteria. The best indicator of which method is the most effective and yet most practical might be as simple as the ease of operation if the data from all three plant-based measures of vine water stress can be proven to be highly correlated.
Additionally, the value of that plant-based stress data would be even greater if it could also be shown to be highly correlated with other indicators of vine water status. In the Williams and Araujo study, other indicators of vine water status used for further correlation with vine water potential are net CO2 assimilation rates (A) and stomatal conductance to water vapor (gs), both measured at solar noon, and soil water content (SWC), measured with a neutron probe.
The three indicators of vine water potential in this study were measured on both Chardonnay and Cabernet Sauvignon vines grown in Napa Valley in the 1999 growing season. Because both vineyards were part of a study on the effects of deficit irrigation, all vines had been irrigated weekly at various fractions of estimated vineyard evapotranspiration from berry set until the dates of measurements.
Vine water status and leaf gas exchange were measured on two dates in the Chardonnay vineyard and one date in the Cabernet Sauvignon vineyard.
Individual leaf replicates numbered six for each scion-rootstock combination and irrigation treatment in the Chardonnay vineyard on the first date, August 24, 1999, and five for each treatment in the Chardonnay on September 21, 1999.
Individual leaf replicates for the Cabernet Sauvignon on the only date measured (August 24, 1999) was also five. This produced 86 total data points.
Use of irrigation treatments at both locations resulted in a wide range of vine water status. The lowest values of PDLWP, LWP, and SWP recorded for an individual leaf were –0.85, –1.85, and –1.65 Mpa, (–8.5, –18.5, and –16.5 bars) respectively. The highest values of PDLWP, LWP, and SWP were –0.02, –0.75, and –0.55 Mpa, (–0.2, –7.5, and –5.5 bars) respectively. In most cases, significant differences among irrigation treatments for one measure of vine water status were also similarly different for the other two.
Test results showed that all three methods of estimating vine water status were highly correlated with one another. The best correlation was between mid-day LWP and mid-day SWP (r2 = 0.92).
All three methods were significantly (r2 = 0.69) correlated with soil water status in the Chardonnay vineyard and also significantly correlated with net CO2 assimilation (r2 = 0.67, 0.50, 0.48) and stomatal conductance at mid-day (r2 = 0.69. 0.58, 0.54) in both vineyards.
All three measures of vine leaf water potential were linearly correlated (r2 = 0.93) with berry weight and vine yield when measured the first week of October 1999. These data would indicate that either measurement of mid-day leaf water potential would give a good estimate of the water status of grapevines.
Pre-dawn leaf water potential has been used in many studies as the standard to which other measures of vine water status are compared. It is assumed that this is the period when the vine is in equilibrium with soil water potential.
However, the authors cite references showing that PDLWP of some non-grape species come into equilibrium with the wettest portion of the soil in the plant’s root zone. Therefore, the soil moisture a vine responds to at mid-day may differ from that at pre-dawn due to the flux of water that is occurring when a vine is actively transpiring. If this is correct, differences at pre-dawn may not necessarily reflect the water status of the vine later in the day, as was observed in the Williams and Araujo study.
It has also been demonstrated that season-long measurements of mid-day LWP have been shown to be highly correlated with the seasonal changes in soil water content of treatments irrigated with differing amounts of water. That data and the data from this study in Chardonnay indicated that mid-day LWP was reflective of the amount of water in the soil profile.
All three methods of estimating vine water status were similarly correlated with SWC, applied amounts of water, and with one another, and were also significantly correlated with leaf gas exchange. Therefore, under the conditions of the Williams’ and Araujo study, the criterion that measurements of plant water status should reflect: 1) the availability of soil moisture and/or, 2) applied water amounts, or 3) short- and medium-term plant-stress responses, were tested and met for all three measures of leaf water potential.
For practical use, critical values of mid-day leaf water potential, stem water potential, and pre-dawn leaf water potential could be established and utilized to make decisions such as when to begin irrigating each season and the interval between irrigation events. This would allow a grower/ manager to maintain a specific degree of vine water stress to produce winegrapes that are appropriate for the wine style.
However, from a purely practical standpoint, measurement of mid-day leaf water potential would be most convenient. The main limitation is the time frame allowable to assure consistency. In this study, that time was one half hour before and after solar noon.
The short time limits the acreage or the number of vines that can be measured in one day. The time can be lengthened, however, in a practical field situation, to one hour before and one hour after solar noon. This allows two hours for data collection and is certainly acceptable as long as the other factors affecting consistency (using the same vines each time, well-trained users, bagged samples, replicates) are carefully observed.
There is one other critical factor in using a pressure chamber to ascertain vine water status. It has been demonstrated that the individual making measurements of plant water status is a significant source of variation. It is, therefore, imperative that technicians be well-trained in use of the pressure chamber, and the choice of leaves to sample, and data discrepancy recognition. Trainees should be monitored closely for awhile to ensure they are using the equipment properly and their technique is appropriate and consistent.
Conclusions
In the above study, it was shown that mid-day leaf water potential, mid-day stem water potential, and pre-dawn leaf water potential values from two vineyards on three dates were linearly correlated with each other and with measurements of net CO2 assimilation and stomatal conductance.
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I am planning to modify the filter paper method for estimation of soil water potential. We have Whatman No 42 55 mm filter papers. But our core samples are of 60 mm and 50 mm in diameter and which core sampler is appropriate to use? Can you recommend published regression equations for Whatman No 42 55 mm filter papers?
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Thank you very much for the answer sir. We have ThetaProbe.
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Water holding ability of basil seeds has been used by the Akamba community of Kenya for removing foreign objects from eyes. The process involves introducing a small amount of dry basil seeds into the affected eye and then removing a 'ball' that forms. The ball comprises the foreign bodies and basil seeds and is formed when the seeds attract water in the eye the stream of which carries the foreign bodies.
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Dear Spencer Muthoka
The use of certain types of basils to adsorb water to form mucilages has been explored by several local communities. In India, seeds of Ocimum basilicum chemotype rich in methylcinnamate (the essential oil recovered from the herb is rich in this compound and not the seeds) are traditionally added to water and after the seeds swell, the water is consumed. This seed-water is believed to cool the body during hot summer months (when temperatures cross 40oC). I have not come across any reference where this property of basil seeds has been explored to make available the water adsorbed by them to plants. There are synthetic chemical water adsorbents that have been used as soil conditioners for supplying water to plants under water-stress conditions. CSIR-National Chemical Laboratory, Pune, India has done research on such chemical compounds. You may check with the Institute by contacting the concerned authorities.
Best wishes
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My focus is with living trees, especially with mature winged Dipterocarps (Dipterocarpus turbinatus, Hopea odorata, Shorea robusta, Anisoptera scaphula). Ecosystem: Tropical Evergreen; Altitude: <100m; Climate: Tropical-Subtropical.
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would you mind list some latest papers concering this regard?
Now I am working on subtropical forest in China, it seems to me that the difference of Carbon contents in three part of tree is not as much as N contents and other traits. I guess you are just start to make a research plan, maybe we can discuss on it.
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Relationship with hydraulic conductance during drought stress.
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I need to preserve tree stem segments, intended for sap flow probe calibration, for ~ 1 month after cutting them. I know I need to minimize dehydration but not sure if I should worry about fungal attack by leaving them wrapped in plastic for weeks until I can use them in the lab for the calibration procedure.
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Hello Michael,
I have custom made heat pulse sensors used in various species of tropical trees.
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I want to follow the flow path of fluid through branches in trees and I have been perfusing long branches (1-meter) of maple trees and it seems to be taking a much longer time than expected for the safranin dye to move through the branch system. I am using a low pressure gradient 100 mbar m-1 so that the dye does not move into the xylem parenchyma tissue. The branches that I am using have about six years of growth with all the current-year xylem excised on the downstream end, and the upstream end is attached to my dye perfusing system. The Safranin is 0.1% in 50% ethanol solution. After 30 mins, I only get dye moving about 15 -20 cm up the branch, so I was wondering if the alcohol solution was causing a problem etc. Any help from someone with experience in staining xylem through long branches would be most appreciated!
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Hi Peter, the slow rate of flow may be because the safranin is a positively charged dye and is adhering to the negatively charged xylem walls. Perhaps try a dye with a negative charge, e.g. the acid fuchsin that Josef suggested. Good luck - it's frustrating because these experiments are time-consuming.
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Water resources are getting more and more scarce. And the competition for water is increasing among different human activities. Irrigation is becoming indispensable for food production, not only in arid and semi-arid regions. Its use is also increasing in humid regions for exploring the full potentiality of crops and for reducing impacts of the climate variability and change. This is the case, for example, of large part of subtropical and tropical regions of South America, where the food production is increasing very fastly.
In most of cases, those humid regions require a supplementary irrigation, instead of the continuous systems that are used in dry regions (with exception for rice crops). In general, the main reasons are: oscillations on the rainfall regime and / or variations in plants sensibility throughout the crop cycle. This means that even a short water stress in the critical stages (maize, for example) may cause a high impact on crop yields.
In my opinion, the management of supplementary irrigation is more complex than in continuous systems. On the other hand, if well managed, the supplementary irrigation may allows to significant increases on the efficient use of water, investments, and other natural resources. However, it requires flexibility on decisions and practices, and therefore, a high level of knowledge and monitoring.
Are there new tendencies for improving the management and monitoring systems, in particular for applying on large cropping areas?
Feedbacks will be very appreciated.
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I am quite agree with you. As precipitations are getting more erratic and sparse in humid regions (due to global warming and climate change), the need for supplementary irrigation increase rapidly. But in the view of farmers in these regions (who didn't use to apply irrigation in their fields) it may seem odd that they need irrigation for their crop growth and so should pay for irrigation systems and their related equipments. These projects may face some culturally-related problems at the beginning. We have such experience in the north of Iran.