Tag Archives: drought

Climate Change-Induced Water Stress: How Leaf Position Affects Water Use Efficiency in the Grape Vine

Posted on February 25, 2013 by Becca| Leave a comment

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According to scientists, climate change will affect various parts of the world differently than one another. Specifically, in regards to the Mediterranean region (as well as many others), a decrease in annual precipitation is currently predicted, based on past data and future forecast models. As a result of this predicted change, there has been substantial interest in research related to water use efficiency in both viticulture and agriculture in general, as precipitation changes will likely bring changes to the sustainability and quality of crops, so determining how to adapt to these changes is absolutely necessary for the future of viticulture and agriculture as a whole.

This type of research is not exactly new, and has been going on for many years. Current strategies for combating decreased water availability due to climate change include (but are not limited to) controlled irrigation and partial root zone drying. The problem with using irrigation in a climate that has significantly

By Photo by Lynn Betts, USDA Natural Resources Conservation Service. (USDA NRCS Photo Gallery: NRCSCA00061.tif) [Public domain], via Wikimedia Commons

reduced precipitation is the issue of where the water used for irrigation would come from. To work around this issue, scientists are currently looking at plant water use efficiency, and how pruning or other viticulture strategies can optimize plant water use in such a way that the need for supplemental irrigation is reduced. Of course, there are some “issues” with looking only at water use efficiency, as higher water use efficiency has been linked to lower fruit yield in grapevines. Therefore, optimization, and not necessarily maximization of water use efficiency is key.

The goal of the study presented today was to examine variations in leaf water use efficiency in the grapevine (Tempranillo, to be specific) under water-stressed conditions as well as under different light conditions, as well as throughout different parts of the canopy.

Methods

This study took place at a commercial vineyard in Mallorca, Spain during 1997, 1998, and 2000. 20 year old Vitis vinifera grapevines of the Tempranillo variety were utilized for the study. The study consisted of two plots (located adjacent to one another) containing 350 plants each and underwent one of the two following treatments: 1) Irrigation: irrigation was applied via a drip system twice per week, and was set to drip enough to account for 30% of evapotranspiration; 2) No irrigation: soil progressively became more and more water stressed throughout the treatment period.

Climate conditions were determined by a local weather experimental station nearby. Pre-dawn and mid-day leaf water potential, as well as leaf gas exchange was measured in June, July, and early August. There were a total of 6 replicates per treatment.

Net photosynthesis, stomatal conductance, and transpiration were all measured 6 times a day for every 3 hours between the hours of 6am and 8pm.

All measurements were done on leafs located in 8 different locations within the plant canopy. For each measurement day, 6 replicates per leaf location were measured.

Daily-integrated intrinsic water use efficiency and instantaneous water use efficiency were both calculated.

After harvest, leaves from each canopy location were harvested from six plants per treatment. Fresh weight, leaf area, specific leaf weight, and total leaf area of each canopy location were measured or calculated.

Results

• Irrigation resulted in stable plant water status throughout the growing season.
• Pre-dawn water potential decreased throughout the growing season for those plants in the non-irrigation treatment.
• The ratio of photosynthesis to stomatal conductance was significantly higher in water-stressed plants compared with irrigated plants.
• Photosynthetic active radiation (PAR) interception varied depending upon where in the canopy the leaf was located, with a decrease in PAR noted from the upper part of the canopy to the lower part of the canopy.
o Those leaves in the innermost part of the canopy showed the lowest PAR values, which makes sense due to the fact that the leaves are in the shade do not experience as much radiation from the sun as leaves in full sunlight.
• Water stress did not affect PAR values for any leaf position.
• Midday leaf temperature and leaf-to-air vapor pressure deficit did not differ between any of the leaf positions.
• Water stress resulted in an increase in midday leaf temperatures.
• Water use efficiency was extremely variable between the different leaf positions in the canopy.
o The lowest water use efficiency was in shaded leaves, whereas the highest water use efficiency was in the leaves at the top of the canopy.
o Leaves in sunnier positions had 3x greater water use efficiency than leaves in the shade.
• Water use efficiency was increased in water-stressed plants.
o Those leaves near the top (but not all the way on the top) of the canopy (i.e. those leaves with 67.5% light interception compared with the top leaves) were found to have the highest water used efficiency.
• There was a significant relationship between water use efficiency and the daily intercepted PAR of the leaf.
• South-facing leaves at the top of the canopy had the highest water consumption levels per leaf area than all other leaves.
• Shaded leaves showed the lowest rates of transpiration, however, since there were so many of them (making up 37% of the total number of leaves on the plant), the water use efficiency actually decreased compared to leaves at the top of the canopy.
• Total water consumption decreased in water-stressed plants.
o Moderately-stressed plants showed a 47% decrease in water consumption compared to irrigated plants.
o Severely-stressed plants showed a 70% decrease in water consumption compared to irrigated plants.

Conclusions

The results of this study indicate that there were significant differences between the locations of the leaves in the canopy in regards to water use efficiency. The authors speculated that these differences could be due to the differences found in PAR and light exposure. In regards to the entire plant, it was found that water use efficiency increased when the plants were under water stress. This makes sense, as when the plant has less water to work with it needs to make sure it’s spending the appropriate amount of resources on water consumption while at the same time reducing the resources needed for evapotranspiration. In other words, it is in the plants’ best interest to become more efficient at using water when water is scarce, so it doesn’t prematurely shrivel and die due to poorly managed resources (though at some point, this will happen anyway if no water is ever seen again).

The results also indicated that the shadiest of areas on the plant had cumulatively the lowest water use efficiency (or highest daily water loss)

By Agne27 at en.wikipedia [Public domain], from Wikimedia Commons

compared to all other locations. The authors suggested that by using selective thinning or pruning in this area could decrease the total water loss and increase the water use efficiency of the grape vine. Of course, one must be careful when undertaking a new pruning management plan, as water use efficiency will not be the only thing changed after the pruning occurs.

It is important to note that pruning has influence on many other factors, including the maturation of the grape and the overall quality of the fruit, so it is important to find some sort of middle ground if selective pruning is of interest to you. Selective pruning may be a good approach to adjusting to climate change-induced water stress, however, it is important to take all factors into consideration before just tearing apart your entire vineyard canopy. It is advised to experiment with a small number of vine first prior to partaking in a vineyard-wide pruning management regime.

One other side note to mention is that this study examined just one grape variety (Tempranillo). It’s possible other grape varieties may behave slightly differently in regards to their water use efficiency and their ability to adapt to changes in water availability, so certainly further studies using more grape varieties is warranted.

What do you all think of these results? What other vineyard management programs do you think could be applied after seeing the results of this study? Those of you with experience in vineyards under high water stress, or those that may be experiencing change in water availability at your vineyard: what sorts of vineyard management practices are you doing to adapt to the conditions? Please feel free to comment!

Source: Medrano, H., Pou, A., Tomás, M., Martorell, S., Gulias, J., Flexas, J., and Escalona, J.M. 2012. Average daily light interception determines leaf water use efficiency among different canopy locations in grapevine. Agricultural Water Management 114: 4-10.

Posted in Viticulture

Tagged climate change, drought, grape vines, irrigation, vineyard management, water stress, water use efficiency

The Effect of Irrigation on the Chemical Composition of Grapes

Posted on July 31, 2012 by Becca| 4 Comments

Every chemical compound in grapes and in wine play some role in the life of the grape/wine, be it during physiological processes during the growth stage, or in the finished wine itself, where it may contribute to the taste and flavor of the wine or the stability of the beverage over time. For example, anthocyanins are responsible for the color of the grape berries, and ultimately for the finished wine. Also, flavonols, while they are colorless in the skins of grapes, they are thought to act as a sort of shield against UV radiation. The exact composition of these compounds in grapes and wine depend on a variety of factors, including grape variety/genetics, environmental factors, and viticulture and winemaking practices. Studies have also suggested that anthocyanin and flavonol composition is a function of grape growth and skin characteristics.

http://www.environment.gov.au/water/
topics/images/drip-irrigation.jpg

Most research to date has focused on the phenolic composition of grapes and wine, with very little focus on the many remaining chemical compounds in the fruit and finished beverage. Phenolics should not be the only thing considered during these research studies, as there is likely a synergistic effect between multiple compounds in the system. Understanding of the full chemical composition of grapes and wines are important not only from a purely scientific standpoint, but also for the grape grower and winemaker due to the direct effects on fruit and wine quality.

The goals of the study presented today were to determine the effect of irrigation management (a viticultural factor that may possibly alter the chemical composition of grapes/wine) on plant yield and physiology, as well as grape berry morphological characteristics, polyphenol and metal composition. The study also sought to determine the absence of irrigation all together could have an effect on grape quality.

Methods

The experiment was performed in 2008 in a 5 year old vineyard in Montegiordano Marina, Southern Italy. The climatic conditions there are considered “very hot” (climatic region 5).

The experimental vineyard plot was 0.3ha, with 10 rows of spur-pruned vines trained to a permanent horizontal unilateral cordon. Distance between vines was 2.5m with 1m between rows. Final plant density was 4000 vines per hectare. Rows were planted in a north-south orientation.

Half of the plants were subject to irrigation from the early stages of fruit set to veraison using water amounts equal to 100% of cultural evapotranspiration. Specifically, this equaled 24L per plant per each irrigation event (10 total) at 5 day intervals. The other half of the plants were not subject to irrigation.

Meteorological variables that were measured or calculated were: temperature, rainfall, and photosynthetic photon flux density. Physiological characteristics measured or calculated were leaf-to-air vapor pressure deficit, stem water potential (in order to determine plant water status), leaf gas exchange, chlorophyll florescence, basal florescence yield in dark-adapted leaves, maximal florescence yield in dark and light conditions, maximum quantum yield of PSII photochemistry in dark-adapted leaves, and finally the effective quantum yield of PSII in light-adapted leaves.

At harvest, 30 plants per treatment were randomly selected and the following were measured/calculated: number of clusters and yield per plant, cluster weight, number of berries per cluster, total berry weight per cluster, and the number of leaves per shoot. For each plant, 3 clusters were randomly selected.

Berries from each cluster were separated into different weight categories: 1) less than 0.60g; 2) between 0.60 and 0.90g; 3) between 0.90 and 1.25g; and 4) greater than 1.25g. For each plant, 20 grapes per weight class were randomly selected to measure/calculate berry fresh weight, berry diameter at the “equator”, and berry diameter at the “poles”. The following characteristics were calculated for the berries: surface, volume, surface/volume ratio, the ratio of berry surface/berry weight, and the ratio of skin weight/berry weight. Skin thickness and soluble solid content of berries was also measured.

For anthocyanin and flavonol extraction and analysis, three clusters per plant were randomly selected and berries separated into the aforementioned weight categories. Anthocyanins and flavonols were measured, as well as levels of iron, copper, zinc, and calcium.

Results

(Note: I’m leaving out many exact details about values due to space limitations, but if you need to know exact numbers/values of any item presented in the results, just ask and I’ll see if those details are available and will let you know).

The growing season was marked with high temperatures and low rainfall.

o Max temperatures ranged between 15.3 and 38.5^oC.

o Min temperatures ranged from 12.3 and 29.1^oC.

o Rainfall during the experimental growing season was a very low 21.9mm.

There were no significant differences between irrigated and not irrigated plants in regards to net photosynthesis.
There were no significant differences in transpiration values between either of the treatments.
There were no significant differences in stomatal conductance between either of the treatments.
Maximum quantum yield of photosystem II and actual quantum yield of PSII reaction centers in leaves were not affected by irrigation treatment.
Mean numbers of clusters per plant were not different between treatment groups.
Yield per plant, cluster weight, and total berry weight were significantly different between treatment groups, with higher values occurring in the irrigation group.

o Irrigation significantly increased the frequency of grapes with greater than 1.25g mass and reduced the frequency of grapes with less than 0.6g mass.

Irrigation treatment significantly affected berry fresh weight and skin fresh weight.

o Irrigation significantly affected berry surface/volume ratios, and were significantly higher in irrigated plants.

o Skin fresh weights were higher in non-irrigated plants, which resulted in a decrease in skin specific surface and increased in skin specific weight.

o For the two intermediate weight categories, there were significant differences between the two treatment groups were noted for seed weight per berry as a result in the differences between seed number per berry.

§ There were more seeds in non-irrigated plants than in the irrigated treatment group.

Soluble solid content was significantly higher in the non-irrigated group than the irrigated group.
Total anthocyanins were significantly higher in the non-irrigation group than the irrigation group.

o This result was positively correlated with berry weight.

Significant differences were found in the concentrations of petunidin-3-O-acetylglucoside, peonidin-3-O-acteylglucoside, and petunidin-(6-O-caffeoyl)glucoside.

o Levels were higher in non-irrigated plants (9x, 18x, and 10x, respectively).

Levels of single anthocyanins increased with decreasing berry weight.
Berries from irrigated plants had significantly lower ratios of acetylated anthocyanins/coumaroylated anthocyanins.
Total flavonols were not significantly different between the two treatment groups.

o Levels of single flavonols were significantly higher in heavier berries.

Iron, copper, and zinc levels were significantly higher in berries from irrigated plants than from non-irrigated plants.
Calcium levels were not significantly different between the two treatment groups.
Metal levels significantly decreased in increasing berry weight.
There were no differences in berry skin thickness between either treatment group.
No significant differences were found in the number of skin layers and thickness of the berries between either treatment group.

Conclusions

One undesired outcome of this experiment was the near drought-like conditions of the weather during the experiment. This resulted in plants being subject to moderate-severe water stress, which caused some leaf necrosis and can influence the micro-climate at the cluster. Specifically, it has been shown that this type of stress may affect berry size and chemical composition, thereby potentially changing the outcomes of some of the tests, and making it generally more difficult to tease out cause and effect.

The results of this study also showed that total anthocyanins were higher in grapes from non-irrigated plants than in irrigated plants. This results in a positive influence on the long-term color stability of wines, as these compounds working in concert with tannins and flavonols to strengthen color stability in the aging beverage. Additionally, increases in these compounds and well as the observed increases in petunidin-3-O-acetylglucoside and peonidin-3-O-acteylglucoside, can have positive sensory benefits to the finished wine as well.

Another interesting result from this study is that metal levels significantly decreased with increasing berry weight. Excess metal concentrations in wine are known to cause negative sensory characteristics, delay the fermentation process, and increase instability. Fe, Cu, and Zn were all found to be significantly lower in grapes from non-irrigated plants than in irrigated plants.

Overall, the results of this study suggest that less irrigation increased the quality of the finished wine. Specifically, little to no irrigation results in lower berry yield and a reduction in berry size without negatively affecting grape quality in terms of the chemical composition of the grapes. This study confirms what many in the wine industry in that grapes grown under water stress conditions can result in higher quality wine (provided there are no set-backs during the winemaking process). Even though many already knew less water is better, this study paints a good picture of exactly how the chemical composition of the grapes changes when subject to these drier conditions.

There are many more results to this study that I did not cover due to time and space considerations, but I’d love to hear your thoughts or questions on them, even if I didn’t specifically cover it. What do you all think of the study? What would you like to have seen done differently (if anything). I, for one, would have liked to see them create experimental wines from these two treatment groups and measure the same compounds to see how irrigation actually alters the chemical composition of the finished wine and not just the starting point grapes. Do these differences carry through the winemaking process? Are different winemaking techniques better suited to maintaining the original/similar chemical composition of the grapes?

I’d love to hear what you think! Please feel free to comment below!

Source: Sofo, A., Nuzzo, V., Tataranni, G., Manfra, M., De Nisco, M., and Scopa, A. 2012. Berry morphology and composition in irrigated and non-irrigated grapevine (Vitis vinifera L.). Journal of Plant Physiology 169: 1023-1031.

DOI: 10.1016/j.plph.2012.03.007
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!

Posted in Chemistry

Tagged agriculture, chemistry, drought, grape vines, grapes, irrigation, viticulture

The Effect of Water Deficits on Anthocyanin and Tannin Concentrations of Merlot Grapes

Posted on May 29, 2012 by Becca| 2 Comments

http://blog.selenewines.com/wp-content/
uploads/2009/09/Bare-Merlot-vine.jpg

Flavonoids in grapes, particularly anthocyanins and tannins, have great impact on the quality of wines, specifically in the areas of color and astringency. The composition of these compounds in grapes depends on many factors, including grape variety, water status, and other environmental/climatic variability. This variability in grapes leads to a large variability in flavonoid concentration in finished wine as well, which can further be manipulated by different wine making procedures and techniques. In regards to water status during the growing season, it is known that changes in water availability alters the concentrations of these major flavonoids, however, it is unclear precisely how and to what extent these changes are reflected in the grape.

Berry ripening may be either accelerated or decelerated depending upon the timing and duration/severity of the drought. Skin growth itself could be inhibited during droughts, which could alter the proportion of skins and seeds to total berry weight, which is an important indicator of grape quality. In terms of flavonoid synthesis, tannins are synthesized earlier in the season, while anthocyanins are synthesized later. Therefore, the timing of the water deficit could be critical in the development of one or both of these important quality components of grapes and wine. Specifically, it is thought that since flavonoids are primarily located in the skins of grapes, when berry growth is inhibited by some mechanism, the resulting concentrations of flavonoids in the grape will be increased due to an increased surface:volume ratio.

The goal of the current study, therefore, was to examine the influence of water status on grape berry growth, skin tannins, and anthocyanins in Merlot grapes in order to determine the extent that which water deficits induce changes in grape berry composition. To date, results of similar studies have been inconsistent. By understanding how water deficits alter flavonoid composition (specifically tannins and anthocyanins), one may be able to develop specific vineyard management strategies in order to maximize the quality of the grapes, and ultimately quality of the wine produced from those grapes.

Methods

Experiments were performed in 2004, 2005, 2007, and 2008 in a vineyard of Merlot (Vitis vinifera) which was planted in 1993. The vineyard was located at an experimental farm at the University of Udine in northeast Italy on soil (49% sand, 31.5% silt, and 19.5% clay) with 12% gravel, 0% slope, 29.3% field capacity, and a permanent wilting point of 19.3%. Orientations of the rows were north-south, with spacing at 1m between plants, and 2.5m between rows, and about 4000 vines per hectare. Vines were trained on a spur cordon system.

Water control to the vines was achieved by sheltering the rows under a tunnel covered by a polyethylene film. The tunnel was placed over the whole experimental block that included four rows of 60m in length (240 vines). Experimental rows were the two center rows of the four, since rain water could possibly seep into the edges of the tunnel and uncontrollably change the water status of the two rows closest to the edge. The first and last 8 plants of each experimental row were also excluded due to the same reasons as mentioned just previously. Water was supplied to the vines by a sub-surface drip irrigation system with emitters at 2.5L per square meter per hectare. Each emitter was 0.6m apart and there was 2.5m between each irrigation line.

Plant water status was measured by midday measurements of stem water potential. To measure this, two leaves per plot (on each side of the row) were covered with aluminum foil coated plastic bags for one hour, in order for the stem and leaf water potential to equilibrate. After one hour, the leaves were removed and stem water potential was measured by a pressure chamber.

Two water/irrigation treatments were established: a control were vines were irrigated once a week in order to keep the stem water potential between -0.2 and -0.6MPa, and a water deficit (WD) treatment were vines were irrigated to maintain a stem water potential of -0.8 and -1.4MPa during the ripening period. To maintain this level, irrigation was cut off on the WD vines 43, 34, 45, and 47 days after anthesis in 2004, 2005, 2007, and 2008, respectively. With the exception of 2007, one more irrigation was applied to WD vines between veraison and harvest.

Each irrigation treatment was replicated on four plots of 12 vines each. Both control and water deficit treatments were performed under the polyethylene tunnels, to account for any microclimatic variation caused by being under the tunnel.

Grape berries were sampled every 7-14 days, from 21-40 days after anthesis to harvest. For each sampling day, two sets of 30 berry samples were collected from each plot. One set was collected to measure juice soluble solids (^oBrix) and titratable acidity, while the other set was collected for anthocyanin and tannin analysis.

Results

Midday stem water potentials were significantly lower in water deficit treatments than in control treatments from 55 days after anthesis until harvest.
Stem water potential decreased progressively in water deficit treatment vines throughout the ripening period, while stem water potential for the control vines remained consistently higher than -0.65MPa.
There were differences in the severity and the timing when the deficit became very severe.
Across all four seasons, water deficit significantly reduced the final berry weight and pH, and had no effect on soluble solids, titratable acidity, skin weight, or skin/berry weight.

o There was a significant effect of season on all size and chemistry parameters, as well as a significant season x irrigation treatment interaction for berry weight, soluble solids, and titratable acidity (parameters were significantly different in some years but not others).

Anthocyanin concentrations significantly increased in the water deficit treatment but had no effect on skin tannin concentrations.

o There were significant season effects on anthocyanin and tannin concentrations, and significant season x irrigation treatment interactions for tannin concentrations (significant changes in some years but not others).

o Tannin concentrations were not affected by irrigation treatment.

Water deficit inhibited berry growth, though it did not alter the berry growth pattern during the season.
Maximum berry weight was reached at the same time for both treatments.
At harvest, water deficit berries were 7.6% to 20.1% smaller than control berries.
Skin tissue was 7-15% of berry weight, though skin and berry growth was relatively inconsistent from season to season.
Berry soluble solids were not consistently affected by irrigation treatment.
Titratable acidity was not affected by irrigation treatment.
Anthocyanin concentrations increased faster in water deficit berries than control berries, and were significantly higher in water deficit berries after 30 days into the treatment.

o Water deficit increased the overall mean anthocyanin concentration at harvest by 50% compared to controls.

Overall mean tannin concentrations at harvest were not significantly different between treatments.

o There was a significant treatment x year interaction (the treatment was significant in some years, but not others), and water deficit significantly increased tannins in 3 out of the 4 years.

Conclusions

The results of this study showed that anthocyanin concentrations in Merlot grapes significantly increased with the water deficit treatment; whereas only in certain years did this deficit alter skin tannin concentrations. These results indicate that the relationship between fruit ripening and water status is complex. Other studies have shown that tannin synthesis occurs earlier on in the ripening period, whereas anthocyanin synthesis occurs later on in the season. Therefore if most or all of the tannins are synthesized before the water deficit occurs, it is likely that the drought will not significantly affect the concentrations of the compound. However, if the water deficit occurs before synthesis is complete, as it happened with the anthocyanin concentrations in this experiment, final concentrations will likely be much more variable and affected by the drought.

The authors continued to elaborate on this relationship between flavonoid concentrations and water deficits in that the increase is due to an upregulation of anthocyanin biosynthesis but no corresponding increase in tannin biosynthesis. Based on the results from other studies, the authors could not rule out a possible inhibition of anthocyanin degradation instead of the upregulation theory described earlier. More research that focused on this type of physiology would need to be performed in order to get a more accurate understanding of the mechanisms involved with the increase in anthocyanin concentration when under a water deficit.

Generally speaking, the results of this study give some insight into how water deficits may alter the quality of grapes which would ultimately lead to changes in the quality of the wine produced from those grapes. More work needs to be done to further understand the mechanisms behind the changes observed in the study, and should include many more parameters, as chemical composition of grapes can be very complex with each part playing a different role in different environmental and climatic situations.

I’d also be curious to see a study that combined not only the types of experiments performed in this study, but to also take it one step further and create wines from the grapes under the different irrigation treatment, in order to determine how water deficits actually affect overall wine quality, instead of simply making assumptions. Also, a study incorporating several different varieties of grapes may be important as well, as studies have shown that different grape varieties are affected by environmental or climatic conditions differently.

I’d love to hear what you all think of this study. Can you think of ways to improve upon this study?

Source: Bucchetti, B., Matthews, M.A., Falginella, L., Peterlunger, E., and Castellarin, S. 2011. Effect of water deficit on Merlot grape tannins and anthocyanins across four seasons. Scientia Horticulturae 128: 297-305.

DOI: 10.1016/j.scienta.2011.02.003
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!

Posted in Environmental Science

Tagged climate change, drought, global warming, grape vines, merlot, red wine