Regulation Of Stomatal Conductance Research Articles

Genotyping peculiarities of wheat photosynthesis light induction and productivity under the drought effect

Background. In agrocenoses, leaf light conditions are known to be unstable due to intermittent cloud cover and shading by other leaves or spikes. However, with a change in irradiance, photosynthesis does not reach its final value instantly, but with a certain delay. Due to this photosynthetic efficiency of leaves and crops is generally lower compared to stationary conditions. At the same time, the vast majority of works devoted to the problems of photosynthetic apparatus functioning under unstable light conditions do not take into account an adverse impact on photosynthesis of such a common stressor as drought. The aim of the present work was to study the peculiarities of flag leaves CO2 and H2O gas exchange parameters with changes in illumination under conditions of optimal and insufficient water supply in order to explore the pattern of drought effect on the photosynthetic induction processes in connection with productivity of wheat plants of different genotypes. Materials and Methods. The research was carried out on bread winter wheat varieties Yednist, Bohdana, Perlyna Podillia under conditions of pot experiment. Control plants were grown under an optimal soil moisture of 70 % field capacity (FC). In the experimental pots, soil drought was created at the level of 30 % FC for 7 days during the earing–flowering period, after that the soil moisture was restored to the optimal level. The parameters of flag leaf gas exchange were measured on the seventh day of drought. Components of plants grain productivity were determined after reaching full grain maturity. Results. It was found that according to the parameters of light induction curves of CO2 assimilation and transpiration, wheat plants of different genotypes under drought conditions are differentiated more clearly than under normal water supply. An increase in the limiting role of stomata in the induction of photosynthesis under drought conditions and changes in illumination was shown. Drought disrupts the coherence of stomatal conductance regulation in interaction with CO2 assimilation processes. This affects the light induction curves of photosynthesis and transpiration, and ultimately leads to a decrease in grain productivity. Conclusions. It was shown that in order to assess the efficiency of the photosynthetic apparatus in providing wheat plants with assimilates and maintaining their grain productivity under unfavorable conditions, the parameters of the response to the changes in illumination must be taken into account.

Preserving isohydricity: vertical environmental variability explains Amazon forest water use strategies.

Increases in hydrological extremes, including drought, are expected for Amazon forests. A fundamental challenge for predicting forest responses lies in identifying ecological strategies which underlie such responses. Characterization of species-specific hydraulic strategies for regulating water use, thought to be arrayed along an 'isohydric-anisohydric' spectrum, is a widely used approach. However, recent studies have questioned the usefulness of this classification scheme, because its metrics are strongly influenced by environments, hence can lead to divergent classifications even within the same species. Here, we propose an alternative approach positing that individual hydraulic regulation strategies emerge from the interaction of environments with traits. Specifically, we hypothesize that the vertical forest profile represents a key gradient in drought-related environments (atmospheric vapor pressure deficit, soil water availability) that drives divergent tree water use strategies for coordinated regulation of stomatal conductance (gs) and leaf water potentials (ΨL) with tree rooting depth, a proxy for water availability. Testing this hypothesis in a seasonal eastern Amazon forest in Brazil, we found that hydraulic strategies indeed depend on height-associated environments. Upper canopy trees, experiencing high VPD, but stable soil water access through deep rooting, exhibited isohydric strategies, defined by little seasonal change in the diurnal pattern of gs and steady seasonal minimum ΨL. By contrast, understory trees, exposed to less variable VPD but highly variable soil water availability, exhibited anisohydric strategies, with fluctuations in diurnal gs that increased in the dry season along with increasing variation in ΨL. Our finding that canopy height structures the coordination between drought-related environmental stressors and hydraulic traits provides a basis for preserving the applicability of the isohydric-to-anisohydric spectrum, which we show here may consistently emerge from environmental context. Our work highlights the importance of understanding how environmental heterogeneity structures forest responses to climate change, providing a mechanistic basis for improving models of tropical ecosystems.

Does drought stress eliminate the benefit of elevated CO2 on soybean yield? Using an improved model to link crop and soil water relations

Crop simulation models are indispensable tools that facilitate studies to assess climate impacts and adaptation responses, but have not been adequately tested in terms of accurately predicting crop growth and water stress responses to high carbon dioxide concentrations [CO2]. The soybean model, GLYCIM, previously modified with a coupled leaf-level gas exchange – energy balance model, was integrated with a two-dimensional convective-diffusive root growth module which linked soil and leaf water potentials with the regulation of stomatal conductance. We evaluated the accuracy of this modified GLYCIM using experimental data from a Free-Air CO2 Enrichment (FACE) site, SoyFACE, and used the calibrated model to quantify current and projected elevated CO2 effects on soybean yields in the United States (US) Midwest. The model accurately matched SoyFACE observed data including canopy temperature (RMSE, 2.26 -2.42 °C; IA, 0.89-0.90), photosynthesis rate (RMSE, 6.33 -12.88 µmol m−2 s−1; IA, 0.82-0.92), seasonal LAI (RMSE, 0.96 -1.08 cm2 cm−2; IA, 0.91-0.93), biomass (RMSE, 2.06 -2.34 Mg ha−1; IA, 0.87-0.90), soil water contents (RMSE, 5.42 -7.82 %; IA, 0.80-0.85) and root length (RMSE, 2.12 -5.64 m plant−1; IA, 0.70-0.86). GLYCIM also reproduced the observed declining response of yield to CO2 fertilization with increasing drought. Using an ensemble of five climate model projections, GLYCIM showed that the CO2 fertilization effect on yield was highest in northern counties and declined in southern and the western counties by late 21st century in response to increased drought characterized by higher daily maximum temperature and decreased rainfall. This study highlights the need to continue to test and improve crop models and use geospatially referenced adaptive strategies to capitalize the benefits from elevated [CO2] to better counteract increasing drought.

The mechanism of enhancing drought tolerance threshold of pepper plant treated with putrescine and salicylic acid

Pepper is a warm-season crop and water deficit is considered as dominant issue in pepper cultivation. Using plant growth regulators in different steps of plant growth and development could be as useful strategy to overcome adverse effects of abiotic stresses. In order to investigate the morpho-physiological responses of pepper plant to putrescine (Put) and salicylic acid (SA) foliar application and deficit irrigation (DI) strategy, the split plot experiments were laid out based on randomized complete blocks design at University of Zanjan. The highest values of leaf area and total yield were recorded in sprayed plants by Put at 1.5 mM under DI0% (5842 cm2 and 9.6 ton ha−1). SA at 1.5 mM was the best treatment to increase vitamin C content of pepper fruits. Free proline content increased by 41.34% in sprayed plants by Put at 1.5 mM (7.5 µm g−1 FW) compared to control. SA treatment increased number of pepper fruits, size of harvested fruits and total produced yield by regulation of stomatal conductance and increasing leaf chlorophyll content of pepper plants under drought stress conditions. Also, Put foliar treatment increased drought tolerance rate of pepper plant by increasing free proline content, peroxidase enzyme activity and water use efficiency and also applying this treatment could significantly reduce electrolyte leakage rate. So, SA and Put foliar application at 1.5 mM concentration could be recommended as widely used technique to overcome adverse effects of drought stress on pepper plants cultivated in arid and semi-arid regions.

Abscisic Acid and Cytokinins Are Not Involved in the Regulation of Stomatal Conductance of Scots Pine Saplings during Post-Drought Recovery

Delayed or incomplete recovery of gas exchange after water stress relief limits assimilation in the post-drought period and can thus negatively affect the processes of post-drought recovery. Abscisic acid (ABA) accumulation and antagonistic action between ABA and cytokinins (CKs) play an important role in regulation of stomatal conductance under water deficit. Specifically, in pine species, sustained ABA accumulation is thought to be the main cause of delayed post-drought gas exchange recovery, although the role of CKs is not yet known. Therefore, we aimed to study the effects of ABA and CKs on recovery of stomatal conductance in greenhouse-grown 3-year-old Scots pine saplings recovering from water stress. We analysed both changes in endogenous ABA and CK contents and the effects of treatment with exogenous CK on stomatal conductance. Drought stress suppressed stomatal conductance, and post-drought stomatal conductance remained suppressed for 2 weeks after plant rewatering. ABA accumulated during water stress, but ABA levels decreased rapidly after rewatering. Additionally, trans-zeatin/ABA and isopentenyladenine/ABA ratios, which were decreased in water-stressed plants, recovered rapidly in rewatered plants. Spraying plants with 6-benzylaminopurine (0.1-100 µM) did not influence recovery of either stomatal conductance or needle water status. It can be concluded that the delayed recovery of stomatal conductance in Scots pine needles was not due to sustained ABA accumulation or a sustained decrease in the CK/ABA ratio, and CK supplementation was unable to overcome this delayed recovery.

Stomatal conductance tracks soil-to-leaf hydraulic conductance in faba bean and maize during soil drying.

Although regulation of stomatal conductance is widely assumed to be the most important plant response to soil drying, the picture is incomplete when hydraulic conductance from soil to the leaf, upstream of the stomata, is not considered. Here, we investigated to what extent soil drying reduces the conductance between soil and leaf, whether this reduction differs between species, how it affects stomatal regulation, and where in the hydraulic pathway it occurs. To this end, we noninvasively and continuously measured the total root water uptake rate, soil water potential, leaf water potential, and stomatal conductance of 4-week-old, pot-grown maize (Zea mays) and faba bean (Vicia faba) plants during 4 days of water restriction. In both species, the soil-plant conductance, excluding stomatal conductance, declined exponentially with soil drying and was reduced to 50% above a soil water potential of -0.1 MPa, which is far from the permanent wilting point. This loss of conductance has immediate consequences for leaf water potential and the associated stomatal regulation. Both stomatal conductance and soil-plant conductance declined at a higher rate in faba bean than in maize. Estimations of the water potential at the root surface and an incomplete recovery 22 h after rewatering indicate that the loss of conductance, at least partly, occurred inside the plants, for example, through root suberization or altered aquaporin gene expression. Our findings suggest that differences in the stomatal sensitivity among plant species are partly explained by the sensitivity of root hydraulic conductance to soil drying.

Leaf nitrogen have a better relationship with photosynthesis performance across wheat species under elevated CO2 and drought

Elevated CO2 concentrations and persistent drought are predicted to inhibit the photosynthetic performance and yield of crops. Such effects vary considerably between species groups. Modern cultivated (Triticum aestivum L., AABBDD) and wild (Triticum dicoccoides Korn L., AABB and Triticum monococcum L., AA) species of wheat were subjected to elevated CO2 concentration (ambient concentration +200 μmol mol−1) and drought (well watered: 75–85% of the field water capacity; drought: 50–60% of the field water capacity) at open-top chamber experimental facilities. Elevated CO2 concentration decreased the limitation of stomatal morphology traits on stomatal conductance regulation. This could compensate the disadvantage of plants who has low stomatal density and large single stomatal area as well as low leaf water use efficiency such as modern wheat Z9023 in drought acclimation in the future CO2 rising world. Moreover, elevated CO2 concentration largely increased the dependence of light harvesting and electron transportation performance per photosynthesis system II reaction center, maximum rubisco carboxylation rate, and maximum Ribulose-1,5-bisphosphate regeneration rate on leaf nitrogen concentration across the selected wheat species and water regimes. Modern cultivated cultivars Z9023 and CH58 have higher photosynthetic performance per unit of leaf nitrogen than wild species under elevated CO2 concentrations. The increasing CO2 may present opportunities to breeders and possibly allow them to select for cultivars with better photosynthetic nitrogen use efficiency response to future CO2 rising climate.

Nighttime transpirational cooling enabled by circadian regulation of stomatal conductance is related to stomatal anatomy and leaf morphology in rice.

Rice genotypes with larger stomata maintain higher nocturnal stomatal conductance, thus having lower nocturnal leaf temperature via transpirational cooling. Incomplete night stomatal closure has been widely observed, but the mechanisms and functions of nocturnal stomatal conductance (gs,n) are not fully understood. Stomatal anatomy, leaf morphology, gs,n and nocturnal leaf temperature (Tleaf,n) were measured in 30 Oryza genotypes. Nocturnal leaf conductance (gn) showed a significant circadian rhythm; it gradually increased by 58% from 20:30 to 04:30. Contrary to cuticular conductance (gcut), gs,n was highly correlated with gn. Moreover, gs,n accounted for 76% of gn. Tleaf,n was significantly lower than the air temperature, and was negatively correlated with both gs,n and nocturnal transpiration rate (En). gs,n was positively correlated with stomatal size, intervein distance between major veins (IVDmajor), leaf thickness (LT), individual leaf area (LA), and leaf width (LW). It was also found negatively correlated with stomatal density. Reversely, Tleaf,n was negatively correlated with stomatal size, IVDmajor, intervein distance between minor veins, LA and LW. Tleaf,n presented a positive correlation with stomatal density. This study highlights the importance of stomatal anatomy and leaf morphology on regulating gs,n and Tleaf,n. The underlying mechanisms to the determinants of gs,n and the physiological and ecological functions of the Tleaf,n regulation on rice growth and production were carefully discussed.

Kaolin Reduces ABA Biosynthesis Through the Inhibition of Neoxanthin Synthesis in Grapevines Under Water Deficit.

In many viticulture regions, multiple summer stresses are occurring with increased frequency and severity because of warming trends. Kaolin-based particle film technology is a technique that can mitigate the negative effects of intense and/or prolonged drought on grapevine physiology. Although a primary mechanism of action of kaolin is the increase of radiation reflection, some indirect effects are the protection of canopy functionality and faster stress recovery by abscisic acid (ABA) regulation. The physiological mechanism underlying the kaolin regulation of canopy functionality under water deficit is still poorly understood. In a dry-down experiment carried out on grapevines, at the peak of stress and when control vines zeroed whole-canopy net CO2 exchange rates/leaf area (NCER/LA), kaolin-treated vines maintained positive NCER/LA (~2 µmol m−2 s−1) and canopy transpiration (E) (0.57 µmol m−2 s−1). Kaolin-coated leaves had a higher violaxanthin (Vx) + antheraxanthin (Ax) + zeaxanthin (Zx) pool and a significantly lower neoxanthin (Nx) content (VAZ) when water deficit became severe. At the peak of water shortage, leaf ABA suddenly increased by 4-fold in control vines, whereas in kaolin-coated leaves the variation of ABA content was limited. Overall, kaolin prevented the biosynthesis of ABA by avoiding the deviation of the VAZ epoxidation/de-epoxidation cycle into the ABA precursor (i.e., Nx) biosynthetic direction. The preservation of the active VAZ cycle and transpiration led to an improved dissipation of exceeding electrons, explaining the higher resilience of canopy functionality expressed by canopies sprayed by kaolin. These results point out the interaction of kaolin with the regulation of the VAZ cycle and the active mechanism of stomatal conductance regulation.

Impact of high atmospheric CO2 concentrations on the seasonality of water-related processes, gas exchange, and carbohydrate metabolism in coffee trees under field conditions

Increasing atmospheric CO2 concentrations ([CO2]) are unequivocal, widespread, and responsible for increased mean global temperatures and altered precipitation patterns. In this context, among the topics that need to be better understood are the changes in the water-related processes and gas exchange properties of plants grown under these conditions. Notably, the effects of climate change on coffee (Coffea spp.) production are particularly concerning given the importance of this commodity. Especially, it has been reported that coffee trees exhibit better photosynthetic efficiency when grown at higher [CO2] levels. In order to elucidate the mechanisms involved with this response, the seasonality of water-related processes, gas exchange, and carbohydrate metabolism were investigated using C. arabica var. Red Catuai grown at ambient and high [CO2] under field conditions, at a free-air CO2 enrichment (FACE) facility for coffee, in Brazil. The trees were evaluated fortnightly, from November to February (hot and rainy—summer) and from June to September (cold and dry—winter). It was found that C. arabica trees grown under high [CO2] conditions exhibited increased photosynthetic rates (averaging 121% higher in summer and 45% higher in winter) in both seasons, without displaying any significant changes in the seasonal photosynthesis pattern. Additionally, there was a tendency for the coffee trees grown at high [CO2] to exhibit increased levels of soluble carbohydrates, organic acids, and amino acids in the leaves. Our findings suggest that coffee trees adapt to increased [CO2] through increased photosynthetic rates, enhanced stomatal conductance regulation, and augmented carbohydrate and organic acid synthesis. It is plausible that these features could help mitigate the effects caused by climate change.

Differential Regulation of Stomatal Conductance as a Strategy to Cope With Ammonium Fertilizer Under Ambient Versus Elevated CO2

While nitrogen (N) derived from ammonium would be energetically less expensive than nitrate-derived N, the use of ammonium-based fertilizer is limited by the potential for toxicity symptoms. Nevertheless, previous studies have shown that exposure to elevated CO2 favors ammonium assimilation in plants. However, little is known about the impact of different forms of N fertilizer on stomatal opening and their consequent effects on CO2 and H2O diffusion in wheat plants exposed to ambient and elevated CO2. In this article, we have examined the response of the photosynthetic machinery of durum wheat (Triticum durum, var. Amilcar) grown with different types of N fertilizer (NO3−, NH4+, and NH4NO3) at 400 versus 700 ppm of CO2. Alongside gas exchange and photochemical parameters, the expression of genes involved in CO2 (PIP1.1 and PIP2.3) and H2O (TIP1) diffusion as well as key C and N primary metabolism enzymes and metabolites were studied. Our results show that at 400 ppm CO2, wheat plants fertilized with ammonium as the N source had stress symptoms and a strong reduction in stomatal conductance, which negatively affected photosynthetic rates. The higher levels of PIP1.1 and PIP2.3 expression in ammonium-fertilized plants at 400 ppm CO2 might reflect the need to overcome limitations to the CO2 supply to chloroplasts due to restrictions in stomatal conductance. This stomatal limitation might be associated with a strategy to reduce ammonium transport toward leaves. On the other hand, ammonium-fertilized plants at elevated CO2 did not show stress symptoms, and no differences were detected in stomatal opening or water use efficiency (WUE). Moreover, similar gene expression of the aquaporins TIP1, PIP1.1, and PIP2.3 in ammonium-fertilized plants grown at 700 ppm compared to nitrate and ammonium nitrate plants would suggest that an adjustment in CO2 and H2O diffusion is not required. Therefore, in the absence of a stress context triggered by elevated CO2, ammonium- and ammonium nitrate-fertilized plants were able to increase their photosynthetic rates, which were translated eventually into higher leaf protein content.

Effect of fertilization on water use and yield of hops in mature hop plantation

The effect of decreasing nutrient availability on the ecophysiology and production of hop cones was studied in a plantation of cultivar 'Premiant', in Žatec hop growing region, Czech Republic. The plantation used to be fertilized by 60 t of manure ha(-1) year(-1) until November 2011 when it was discontinued as a part of the measures towards organic farming. Measurements of total evapotranspiration from the plantation using the Bowen ratio energy balance method, transpiration of hop bines by the means of sap flow, soil water and nutrient availability were conducted from 2011 to 2014. The yield of hop cones and the content of alpha acids were monitored in this period too. The concentration of total soil nitrogen (N) dropped from 19.4 mg kg(-1) in March 2012 to 8.2 mg kg(-1) in November 2014. Similarly, the content of N in leaves declined from 4.1% of dry mass in 2012 to 2.5% in 2014. The ratio between total evapotranspiration from the plantation to the potential evapotranspiration (PET) was not affected by the soil nutrient availability and did not vary among the years of study, ranging between average to 91 and 96% of PET. In the contrast to total evapotranspiration and PET, the proportion of hop transpiration on the total evapotranspiration steadily declined from 74 to 46% in 2011 and 2014, respectively. Plant regulation of stomatal conductance changed, bringing along lower stomatal aperture, especially upon the conditions of low vapor pressure deficit. In line with decline in transpiration and stomatal conductance, yield of alpha-acids declined from 204 kg ha(-1) in 2011 to 97 kg ha(-1) in 2014. To sum up, after the stop in fertilizing, total water use of the plantation remained similar as before, but the transpiration and production of alpha acids ha(-1) significantly decreased.

A model for leaf temperature decoupling from air temperature

Leaf temperature (Tleaf) influences rates of respiration, photosynthesis, and transpiration. The local slope of the relationship between Tleaf and Tair, β, describes leaf thermal responses. A range of values have been observed, with β <1 indicating limited homeothermy where Tleaf increases at a lower rate than Tair, β = 1 indicating poikilothermy where Tleaf tracks Tair, and β >1 indicating megathermy where Tleaf increasingly exceeds Tair. However, theory for variation in β has not been developed. Here we derive an equation for β that predicts how it varies with multiple trait and microenvironment variables. The approach also predicts how maintenance of Tleaf away from lethally high values may help explain regulation of stomatal conductance (gS). The work delineates contexts in which each class of leaf thermal response is expected and develops concepts for predicting leaf responses to thermally extreme environments.

Maturation of Atriplex halimus L. leaves involves changes in the molecular regulation of stomatal conductance under high evaporative demand and high but not low soil water content.

Under high water availability, the maximum gas exchange was observed at noon in the expanding and expanded leaves. The expanded leaves showed lower gas exchange capacity due to the regulation of stomatal-movement genes. Under well-watered condition, stomatal conductance (gs) and photosynthetic rate (A) of expanding and expanded leaves of Atriplex halimus peaked at noon despite the midday decline in the leaf relative water content, suggesting deviation from typical isohydric behaviour. However, the expanding leaves had higher gs and A than the expanded ones. When light intensity was temporarily increased, A and gs were enhanced in both types of leaves though to a higher level in the expanding leaves. In well-watered expanded leaves: (1) A was mainly dependent on gs rather than photosynthetic capacity; gs was controlled by internal factors, thereby limiting water loss via transpiration (E); (2) the accumulation of total soluble sugars (TSS) along with increased Rubisco protein could be a subsidiary factor limiting A; (3) TSS and ABA seem to act in co-ordination to up-regulate ABA-dependent genes controlling gs and (4) the significant induction of DREBs suggests a role in maintaining high relative water content in these leaves compared to the expanding ones. In expanding leaves of well-watered plants, high A along with Rubisco down-regulation and elevated TSS suggests that A was regulated by signals coordinating carbon and nitrogen balance and the elevated ABA could be involved in regulating the hydraulic activity to enhance cell expansion and facilitate leaf growth. Both expanded and expanding leaves behaved in typical isohydric manner under water stress, which did not involve the accumulation of ABA suggesting that stomatal closure was primarily stimulated by hydraulic rather than chemical signals.

Effects of a Nonionic Surfactant on Growth, Photosynthesis, and Transpiration of New Guinea Impatiens in the Greenhouse1

AbstractProduction of quality greenhouse and nursery crops is dependent on high quality and quantities of water. At present, in some regions, insufficient water supply is a growing concern. This study was conducted to evaluate growth of New Guinea impatiens (Impatiens hawkerii 'Celebrate Salmon'), when watered with a polyoxyethylenesorbitan monolaurate (C58H114O26) solution commercially known as Tween 20, at differing irrigation levels compared with a conventional water regimen without the surfactant, and also to determine how Tween 20 would affect photosynthesis and transpiration. The treatment design was a 3 by 6 complete factorial design plus a control. The two factors were irrigation and Tween 20. Irrigation levels of 20%, 40%, or 60% of the full crop evapotranspiration (ET) requirements were used in combination with Tween 20 concentrations of either 0, 25, 50, 75, 100, or 125 mg·L−1 (0, 0.003338, 0.00668, 0.0100145, 0.01335, or 0.01669 oz per gallon). The control group was watered with tap water to container capacity with about 30% leachate. Evapotranspiration was determined as the difference of the applied water amount minus the leachate of the control. Plants irrigated with Tween 20 from 25 to 125 mg·L−1 (0.003338 to 0.01669 oz per gallon) at the 40% or 60% irrigation level had the same height and growth index as plants in the control after three months of growth. Plant fresh and dry weights were not different between the control and the treatments of Tween 20 from 50 to 125 mg·L−1 (0.00668 to 0.01669 oz per gallon) at the 60% irrigation level or the treatment of Tween 20 at 100 mg·L−1 (0.01335 oz per gallon) at the 40% irrigation level. Tween 20 had no effect on net photosynthetic rate. Tween 20 decreased the amount of transpired water of New Guinea impatiens 'Celebrate Salmon'. When the Tween 20 concentration increased from 0 to 100 mg·L−1 (0 to 0.01335 oz per gallon) at the 60% irrigation level, the transpiration rate and stomatal conductance decreased markedly by 43% and 47%, respectively, and water use efficiency was increased by 47%. Results from this study suggest that Tween 20 is able to increase plant water use efficiency through regulation of stomatal conductance or transpiration under deficit irrigation.Index words: irrigation management, chemigation, source-sink physiology, deficit irrigation, wetting agent, Tween 20, adjuvant.Species used in this study: New Guinea Impatiens (Impatiens hawkerii W. Bull. 'Celebrate Salmon').Chemicals used in this study: Tween 20 (polyoxyethylenesorbitan monolaurate). (aka: polysorbate 20, polyoxyethylene (20) sorbitan monolaurate)

Soil moisture control of sap-flow response to biophysical factors in a desert-shrub species, &amp;lt;i&amp;gt;Artemisia ordosica&amp;lt;/i&amp;gt;

Abstract. The current understanding of acclimation processes in desert-shrub species to drought stress in dryland ecosystems is still incomplete. In this study, we measured sap flow in Artemisia ordosica and associated environmental variables throughout the growing seasons of 2013 and 2014 (May–September period of each year) to better understand the environmental controls on the temporal dynamics of sap flow. We found that the occurrence of drought in the dry year of 2013 during the leaf-expansion and leaf-expanded periods caused sap flow per leaf area (Js) to decline significantly, resulting in transpiration being 34 % lower in 2013 than in 2014. Sap flow per leaf area correlated positively with radiation (Rs), air temperature (T), and water vapor pressure deficit (VPD) when volumetric soil water content (VWC) was greater than 0.10 m3 m−3. Diurnal Js was generally ahead of Rs by as much as 6 hours. This time lag, however, decreased with increasing VWC. The relative response of Js to the environmental variables (i.e., Rs, T, and VPD) varied with VWC, Js being more strongly controlled by plant-physiological processes during periods of dryness indicated by a low decoupling coefficient and low sensitivity to the environmental variables. According to this study, soil moisture is shown to control sap-flow (and, therefore, plant-transpiration) response in Artemisia ordosica to diurnal variations in biophysical factors. This species escaped (acclimated to) water limitations by invoking a water-conservation strategy with the regulation of stomatal conductance and advancement of Js peaking time, manifesting in a hysteresis effect. The findings of this study add to the knowledge of acclimation processes in desert-shrub species under drought-associated stress. This knowledge is essential in modeling desert-shrub-ecosystem functioning under changing climatic conditions.

Tree ring δ18O reveals no long‐term change of atmospheric water demand since 1800 in the northern Great Hinggan Mountains, China

AbstractGlobal warming will significantly increase transpirational water demand, which could dramatically affect plant physiology and carbon and water budgets. Tree ring δ18O is a potential index of the leaf‐to‐air vapor‐pressure deficit (VPD) and therefore has great potential for long‐term climatic reconstruction. Here we developed δ18O chronologies of two dominant native trees, Dahurian larch (Larix gmelinii Rupr.) and Mongolian pine (Pinus sylvestris var. mongolica), from a permafrost region in the Great Hinggan Mountains of northeastern China. We found that the July–August VPD and relative humidity were the dominant factors that controlled tree ring δ18O in the study region, indicating strong regulation of stomatal conductance. Based on the larch and pine tree ring δ18O chronologies, we developed a reliable summer (July–August) VPD reconstruction since 1800. Warming growing season temperatures increase transpiration and enrich cellulose 18O, but precipitation seemed to be the most important influence on VPD changes in this cold region. Periods with stronger transpirational demand occurred around the 1850s, from 1914 to 1925, and from 2005 to 2010. However, we found no overall long‐term increasing or decreasing trends for VPD since 1800, suggesting that despite the increasing temperatures and thawing permafrost throughout the region, forest transpirational demand has not increased significantly during the past two centuries. Under current climatic conditions, VPD did not limit growth of larch and pine, even during extremely drought years. Our findings will support more realistic evaluations and reliable predictions of the potential influences of ongoing climatic change on carbon and water cycles and on forest dynamics in permafrost regions.

Biochar soil amendment on alleviation of drought and salt stress in plants: a critical review.

Drought and salt stress negatively affect soil fertility and plant growth. Application of biochar, carbon-rich material developed from combustion of biomass under no or limited oxygen supply, ameliorates the negative effects of drought and salt stress on plants. The biochar application increased the plant growth, biomass, and yield under either drought and/or salt stress and also increased photosynthesis, nutrient uptake, and modified gas exchange characteristics in drought and salt-stressed plants. Under drought stress, biochar increased the water holding capacity of soil and improved the physical and biological properties of soils. Under salt stress, biochar decreased Na+ uptake, while increased K+ uptake by plants. Biochar-mediated increase in salt tolerance of plants is primarily associated with improvement in soil properties, thus increasing plant water status, reduction of Na+ uptake, increasing uptake of minerals, and regulation of stomatal conductance and phytohormones. This review highlights both the potential of biochar in alleviating drought and salt stress in plants and future prospect of the role of biochar under drought and salt stress in plants.

Increasing the effective use of water in processing tomatoes through alternate furrow irrigation without a yield decrease

Surface irrigation represents >85% of irrigated agriculture worldwide. Partial root zone drying (PRD) is a technique for improving crop water productivity (WP), and in practice can be applied as alternate furrow irrigation (AFI). A series of research station and on-farm trials were conducted in two consecutive years and three soil types to evaluate processing tomato crop performance under AFI vs every furrow irrigation (EFI). Crop growth and leaf gas exchange, fruit biomass and quality, soil moisture and water applied were evaluated, and changes in irrigation WP (WPi) determined in response to PRD. The AFI was consistent in maintaining fresh yields across cultivars and environmental conditions (i.e., years and soil textures) with at least 25% lower irrigation volumes than commonly applied under EFI. WPi increased by >29% and maintained fruit quality under AFI. Canopy growth was slightly lower, and a tighter plant regulation of stomatal conductance (gs) with only a small decrease in photosynthetic rates (Pn) was observed under AFI. Our results demonstrate that for California processing tomatoes AFI is effective in reducing agricultural water needs. Because of the extent of furrow irrigation worldwide, AFI can contribute to maintain highly productive agricultural land under production with lower water supply.

Role of leaf hydraulic conductance in the regulation of stomatal conductance in almond and olive in response to water stress

The decrease of stomatal conductance (gs) is one of the prime responses to water shortage and the main determinant of yield limitation in fruit trees. Understanding the mechanisms related to stomatal closure in response to imposed water stress is crucial for correct irrigation management. The loss of leaf hydraulic functioning is considered as one of the major factors triggering stomatal closure. Thus, we conducted an experiment to quantify the dehydration response of leaf hydraulic conductance (Kleaf) and its impact on gs in two Mediterranean fruit tree species, one deciduous (almond) and one evergreen (olive). Our hypothesis was that a higher Kleaf would be associated with a higher gs and that the reduction in Kleaf would predict the reduction in gs in both species. We measured Kleaf in olive and almond during a cycle of irrigation withholding. We also compared the results of two methods to measure Kleaf: dynamic rehydration kinetics and evaporative flux methods. In addition, determined gs, leaf water potential (Ψleaf), vein density, photosynthetic capacity and turgor loss point. Results showed that gs was higher in almond than in olive and so was Kleaf (Kmax = 4.70 and 3.42 mmol s(-1) MPa(-1) m(-2), in almond and olive, respectively) for Ψleaf > -1.2 MPa. At greater water stress levels than -1.2 MPa, however, Kleaf decreased exponentially, being similar for both species, while gs was still higher in almond than in olive. We conclude that although the Kleaf decrease with increasing water stress does not drive unequivocally the gs response to water stress, Kleaf is the variable most strongly related to the gs response to water stress, especially in olive. Other variables such as the increase in abscisic acid (ABA) may be playing an important role in gs regulation, although in our study the gs-ABA relationship did not show a clear pattern.