Stomatal sensitivity to air humidity

Stomatal sensitivity to air humidity: a hypothesis for its control through peristomatal evaporation

El-Sharkawy M. A., Cock J. H. (1984)

Mabrouk A. El-Sharkawy, James H. Cock,

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Contribution from the Cassava Physiology Program of the Centro Internacional de Agricultura Tropical (CIAT, AA 6713, Cali, Colombia, South America) –

https://www.researchgate.net/publication/280113387_Stomatal_Sensitivity_to_air_humidity_A_hypothesis_for_its_control_through_peristomatal_evaporation_1 –

Abstract.

Analysis of previously published data shows an extremely close correlation (r2 = 0.83) exists between stomatal sensitivity to changes in leaf to air vapour pressure deficit and the maximum leaf conductance at low VPD in a wide range of plant species. The hypothesis is presented that stomatal sensitivity to changes in VPD is related to evaporative are of the stomatal apparatus coupled with a large hydraulic resistance between the epidermal cells and the bulk of the leaf.

Photosynthetic research for increasing agricultural productivity

Fig. 1. Camera lucida drawings of transverse sections of leaves. (A) Palmer weed (Amaranthus palmeri); (B) Bermuda grass (Cynodon dactylon); (C) grain sorghum (Sorghum bicolor); (D) maize (Zea mays). Notice the arrangement of vascular bundles and the large compact and thick-walled cells of the bundle sheath. The black dots in the bundle sheath and the mesophyll cells represent chloroplasts. Most of the chloroplasts in bundle sheath cells are centripetally located (i.e., located at the inner side of the cells). Source: El-Sharkawy (1965) (see also El-Sharkawy 2009a,b).

Prospects of photosynthetic research for increasing agricultural productivity, with emphasis on the tropical C4 Amaranthus and the cassava C3-C4 crops

El-Sharkawy M. A. (2016)

Mabrouk A. El-Sharkawy, Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia

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in PHOTOSYNTHETICA 54 (2): 161-184 – DOI: 10.1007/s11099-016-0204-z

Author’s submission

Fig. 8. Photomicrograph of cross section of amphistomatous field-grown cassava leaf (cv. M Col 90. CIAT cassava germplasm bank). Note: the long palisade layer (PL) and the conspicuous chlorophyllous vascular bundle sheath cells (VBS) situated beneath the palisade layer; the narrow spongy tissue (ST); the short distance between vascular tissue minor veins (< 50 μm); the wide airspace between upper and lower epidermis. These anatomical features were observed in many cultivated cassava varieties, improved CIAT breeding lines, and land races. Compare Fig. 8 with Fig. 1. Source: (M. A. El-Sharkawy unpublished, El-Sharkawy and Cock 1987a,1990, Riaño 1987, Aguilar 1995).

 

Abstract

Productivity of most improved major food crops showed stagnation in the past decades. As human population is projected to reach 9-10 billion by the end of the 21st century, agricultural productivity must be increased to ensure their demands. Photosynthetic capacity is the basic process underlying primary biological productivity in green plants and enhancing it might lead to increasing potential of the crop yields.

Several approaches may improve the photosynthetic capacity, including integrated systems management, in order to close wide gaps between actual farmer’s and the optimum obtainable yield. Conventional and molecular genetic improvement to increase leaf net photosynthesis (PN) are viable approaches, which have been recently shown in few crops.

Bioengineering the more efficient C4 into C3 system is another ambitious approach that is currently being applied to the C3 rice crop. Two under-researched, yet old important crops native to the tropic Americas (i.e., the C4 amaranths and the C3-C4 intermediate cassava), have shown high potential PN, high productivity, high water use efficiency, and tolerance to heat and drought stresses.

These physiological traits make them suitable for future agricultural systems, particularly in a globally warming climate. Work on crop canopy photosynthesis included that on flowering genes, which control formation and decline of the canopy photosynthetic activity, have contributed to the climate change research effort. The plant breeders need to select for higher PN to enhance the yield and crop tolerance to environmental stresses. The plant science instructors, and researchers, for various reasons, need to focus more on tropical species and to use the research, highlighted here, as an example of how to increase their yields.

 

Fig. 9. Photomicrographs of leaf cross sections of field-grown wild Manihot spp. (CIAT germplasm bank). (A) M. carthaginensis, (B) M. crassisepala, (C) M. grahami, (D) M. rubricaulis. Note: the amphistomatous trait; the chlorophyllous vascular bundle sheaths situated beneath the upper long palisade layer; the short lower palisade layer in M. graham and M. rubricaulis; the very short distance between vascular tissue minor veins. These anatomical characteristics were observed in several wild Manihot spp. (El-Sharkawy unpublished, El-Sharkawy 2003, 2004). In normal air containing 345 μmol(CO2) mol1, and under intense light and leaf temperature of 35oC, PN in M. rubricaulis was around 50 μmol(CO2) m2 s1, and responded to CO2 up to Ci of 400500 μmol(CO2) mol1; both wild Manihot and cultivated cassava possess high PEPC activities (1030% of activities in C4 maize and sorghum). Source: El-Sharkawy unpublished, El-Sharkawy and Cock 1990, El-Sharkawy and de Tafur 2007, El-Sharkawy 2004, 2006, 2014, El-Sharkawy et al. 2008, 2012a,b. Compare Fig. 9. with Fig.1 showing typical C4 leaf Kranz anatomy in amaranth, Bermuda grass, sorghum, and maize.

Stomatal response to air humidity and its relation to stomatal density

 

 

Stomatal response to air humidity and its relation to stomatal density in a wide range of warm climate species

by El-Sharkawy M. A. (1985)

Mabrouk A. El-Sharkawy,

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in Photosynthesis Research 7: 137-149 –

Author’s submission

Abstract:

The gas exchange of 19 widely different warm climate species was observed at different leaf to air vapour pressure déficits (VPD). In all species stomata tended to close as VPD increased resulting in a decrease in net photosynthesis. The absoulte reduction in leaf conductance per unit increase in VPD was greater in those species which had a large leaf conductance at low VPDs. This would be expected even if stomata of all species were equally sensitive.

However the percentage reduction in net photosynthesis (used as a measure of the relative sensitivity of stomata of the different species) was also closely related to the maximal conductance at low VPD. Similarly the relative sensitivity of stomata to changes in VPD was closely related to the weighted stomatal density or “crowding index”.

The hypothesis is presented that stomatal closure at different VPDs is related to peristomatal evaporation coupled with a high resistance between the epidermis and the mesophyll and low resistance between the stomatal apparatus and the epidermal cells. This hypothesis is consistent with the greater relative sensitivity of stomata on leaves with a high crowding index.

The results and the hypothesis are discussed in the light of selection, for optimal productivity under different conditions of relative humidity and soil wáter availability, by observation of stomatal density and distribution on the the two sides of the leaf.

Stomatal responses to changes in air humidity

 

 

The humidity factor in stomatal control and its effect on crop productivity

by El-Sharkawy M. A. (1988)

Mabrouk A. El-Sharkawy,

in Biological Control of Photosynthesis : Marcelle R., Clijsters H., Van Poucke M. (eds.) 187-198 – Martinus Nijhoff Publishers, Dordrecht, The Netherlands –

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Author’s submission

Abstract:

Stomata of various woody and herbaceous plant species respond directly to changes in leaf-to-air vapor pressure difference (VPD). Closure of stomata upon exposure to dry air occurs in many species without changes in bulk leaf wáter status, suggesting an underlying mechanism different from the well-known closure through reduction in bulk leaf wáter potential.

Recent studies in our laboratory on the response of cassava to wáter stress demonstrated that plants grown in pots or in the field, with and without soil wáter stress, were very sensitive to changes in atmospheric humidity. Both CO2 uptake rate and H2O loss decreased greatly as VPD increased.This decrease in gas exchange rate was associated with a reduction in leaf conductance in the absence of changes in leaf wáter potential.

The strong stomatal response to changes in VPD may be of particular importance to perennial crops, such as cassava , that may have to endure a long period of drought. Under these conditions, and in the absence of stomatal response to humidity, both photosynthesis and transpiration will continue at relatively high rates until available soil wáter is depleted and leaf wáter potential drops to the level required to induce stomatal closure, at which time both photosynthesis and transpiration will approach zero.

In such case, most of the transpirational loss will occur during periods of high VPD and low photosynthesis/transpiration ratio, resulting in a low dry matter accumulation per unit wáter transpired.

On the other hand, with a direct stomatal response to changes in air humidity, available soil wáter will be depleted slowly, as most of the transpirational loss will occur during periods of the day when VPD is low and wáter use efficiency is highest. With a prolonged period of limited soil wáter, the greater wáter use efficiency will lead to a greater total accumulation of photosynthate over the stress period. Thus, the direct stomatal mechanism is beneficial for those crops that experience long period of drought. However, with non-limiting soil wáter conditions or only short periods of soil wáter stress, optimizing wáter use efficiency would not be as important as maximizing photosynthesis and consequently crop productivity.

Under these conditions non-sensitive stomata would be advantageous. An hypothesis is presented which relates stomatal sensitivity to stomatal density and is discussed in the light of selection methods for varieties with optimum productivity under different conditions of air humidity and soil wáter availability.

Effects of air humidity and water stress on stomatal conductance

Photo credit : Google

Manihot esculenta – cassava

 

Water use efficiency of cassava. I. Effects of air humidity and water stress on stomatal conductance and gas exchange

by El-Sharkawy M. A. (1984)

Mabrouk A. El-Sharkawy,

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in Crop Science 24: 497-502 –

Author’s submission

Photo credit Google – Manihot esculenta – http://3.bp.blogspot.com/-303MR63EFHw/VQHsGP8L1PI/AAAAAAAAAO8/_zKFkBciPvA/s1600/mandioca1.jpg

Abstract:

Measurements of CO2 and H2O exchange of attached cassava (Manihot esculenta Crantz) leaves in wáter stressed and control plants of cultivars M Col 90 and M Col 88 were made at various leaf-air vapor pressure differences (VPD)(0.8 to 4.5 kPa).

Apparent photosynthesis and transpiration were sharply reduced by increase in VPD above 1.8 to 2.0 kPa in both stressed and non-stressed plants. This trend coincided with changes in leaf conductance over similar ranges of VPD.

The rapid closure of stomata in dry air was independent of bulk leaf wáter potential. Furthermore, the response was completely reversible in humid air after short exposure to dry air, suggesting a direct response to changes in air humidity.

Water use efficiency decreased as VPD increased over the range of 1 to 4 kPa. The significance of the stomatal response to humidity is discussed in relation to WUE in long dry periods.

Differing sensitivity of stomata to air humidity

Photo credit: Google

Macroptilium atropurpureum – purple bush-bean or siratro

 

Water use efficiency of cassava. II. Differing sensitivity of stomata to air humidity in cassava and other warm-climate species

by El-Sharkawy M. A. (1984)

Mabrouk A. El-Sharkawy,

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in Crop Science 24:503-507 –

Author’s submission

Photo credit Google – Amaranthus retroflexus –redroot pigweed – http://luirig.altervista.org/cpm/albums/bot-010/amaranthus-retroflexus19805.jpg

Abstract:

Measurements of CO2 and H2O exchange and the calculated leaf conductance of attached leaves in well-watered plants were conducted over a range of leaf-air vapor pressure differences (VPD) (1.0 to 4.0 kPa) to compare the response of cassava with that of other warm-climate species.

Species tested were cassava (Manihot esculenta Crantz), andropogon (Andropogon gayanus Kunth), beans (Phaseolus vulgaris L.), siratro (Macroptilium atropurpureum (DC) urb), rice (Oryza sativa L.), eucaliptus (Eucalyptus deglupta Blume), amaranth weed (Amaranthus retroflexus L.) and grain sorghum (Sorghum bicolor (L.) Moench).

Plants were grown in pots outdoors at the CIAT headquarters, Palmira, Colombia, South America. All except andropogon showed a decrease in leaf conductance with increase in VPD. The degree of stomatal sensitivity decreased as follows: cassava > siratro, amaranthus, eucaliptus,bean > sorghum,rice >andropogon.

The greater sensitivity in cassava was associated with reduction in transpiration and stable leaf wáter potential at large VPD. In other less sensitive species , transpiration increased and bulk leaf wáter potential decreased at large VPD.

The response of cassava to changes in VPD resulted in higher wáter use efficiency (WUE= umol CO2 uptake per mmol H2O loss) compared with other C3 species. This may contribute to the comparative advantage of cassava when grown under conditions of limited availability of wáter.

The WUE of the C4 species (sorghum,andropogon, amaranthus) were higher than those of the C3 species. This greater WUE of C4 species was attributed mainly to the higher photosynthetic rates of the C4 species rather than to a lower transpiration rate.

Stomata in cassava cultivars (Manihot esculenta – Euphorbiaceae)

Photo credit: Google – Manihot esculenta – Cassava

Cultivated plants
Photograph by: Slav4
Creative Commons Attribution-Share Alike 4.0

Stomatal characteristics among cassava cultivars and their relation to gas exchange

by El-Sharkawy M. A. (1984)

Mabrouk A. El-Sharkawy,

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in Experimental Agriculture 20: 67-76 –

Author’s submission

Photo credit Google – Manihot esculenta – http://tropical.theferns.info/plantimages/sized/4/1/415b7560b6c2fa902a172498f6356e35fdbf62ae_960px.jpg

Abstract:

Cassava (Manihot esculenta Crantz) has generally been reported to possess hypostomatal leaves. Several cultivars have now been found to possess clusters of functional stomata around the veins on the upper leaf surface and two cultivars (M Col 88 and M Col 90) have significant numbers of stomata (83-140 square mm) dispersed over the entire upper leaf surface.

Stomatal density on the lower leaf surface ranged from 322-553 per square mm among cultivars, with a relative stomatal área of 3.4-6.1%.

The CO2 uptake by the upper leaf surface (27% of total) and the transpiration loss (32% of total) corresponded closely to the ratio of relative stomatal áreas on the upper and lower leaf surface of cv. M Col 88.

 

Response of stomata to air humidity in a parasitic mistletoe and its host

Photo credit: Google

Phthirusa pyrifolia (Loranthaceae)

 

Differential response of stomata to air humidity in the parasitic mstletoe (Phthirusa pyrifolia) and its host, mandarine orange (Citrus reticulata)

by El-Sharkawy M. A. (1986)

Mabrouk A. El-Sharkawy

in Photosynthesis Research 9: 333-343 –

Author’s submission

Photo credit Google – Citrus reticulata mandarin tree – http://www.exotic-plants.de/auktionsbilder/Citrus_reticulata1.jpg

Abstract:

Measurements of CO2 and H2O exchange rate and the calculated leaf conductance of attached leaves were conducted over a range of leaf-to-air vapour pressure difference (VPD) /1.5 to 5.5 kPa) to compare the response of the parasitic mstletoe, Phthirusa pyrifolia, with that of its host, the mandarin orange, Citrus reticulata.

Seedlings of the host infected with the parasite were grown in well-watered and adequately fertilized large pots outdoors at the CIAT headquarters, Palmira, Colombia, South America.

Observation of leaf anatomy of the parasite and nutrient analysis of young tissues of both the parasite and host were made. The photosynthetic rate of the host decreased linearly with increased VPD, whereas the parasite showed a constant rate. This trend coincided with similar responses in leaf conductance.

Due to the insensitivity of the parasite stomata, the transpiration rate increased linearly with VPD as compared with an initial increase and then a decrease in the host transpiration rate. The higher photosynthetic rate and the closure of stomata of the host resulted in high wáter use efficiency as compared with that of the parasite.

The parasite accumulated in its leaves more N, P, K and less Ca and Mg than the host. The significance of the host-parasite differential response to air humidity is discussed in relation to mechanism underlying stomatal sensitivity and in the context of host-parasite association.

Effect of humidity and wind on stomata of cassava (Manihot esculenta – Euphorbiaceae)

Photo credit: Google

Next Generation Cassava Breeding

 

Effect of humidity and wind on leaf conductance of field grown cassava

by El-Sharkawy M. A. (1990)

Mabrouk A. El-Sharkawy

in Rev. Bras. Fisiol.Vegetal 2(2): 17-22 –

Author’s submission

Photo credit Google – Fighting Famine in Kenya One (Cassava) Crop at a Time – https://www.impatientoptimists.org/~/media/Blog/Other/F/FA-FE/fc255582_jpg_autocropped.jpg

Abstract:

Stomata of cassava (Manihot esculenta Crantz) were previously reported to close in large leaf-air vapor pressure difference (VPD) under laboratory controlled studies. Field measurements made with young cassava plants grown in wet soil in the north-east of Colombia demonstrated that leaf conductance decreased rapidly (from 6.7 mm per second at 1.4 kPa in late morning to 1.8 mm per second at 2.5 kPa at midday) with increasing VPD.

Photo credit Google – Planting Cassava : How To Make More Yield In Your Cassava Farm – http://www.letstalkagric.com/wp-content/uploads/2017/02/Cassava-Farming-in-Ghana.jpg

Transpiration was also found to decrease over the same range of VPD without change in bulk leaf wáter potential. Leaves exposed to blowing wind closed their stomata at midday (leaf conductance was 0.64 mm per second for upwind leaves as compared with 3.34 mm per second for downwind leaves).

These responses were discussed in light of possible mechanisms of direct stomatal reaction to changes in atmospheric humidity and its implications for cassava productivity in the tropics.