Reduction In Leaf Water Potential Research Articles

Climate extremes initiate ecosystem‐regulating functions while maintaining productivity

Summary 1. Studying the effects of climate or weather extremes such as drought and heat waves on biodiversity and ecosystem functions is one of the most important facets of climate change research. In particular, primary production is amounting to the common currency in field experiments world‐wide. Rarely, however, are multiple ecosystem functions measured in a single study in order to address general patterns across different categories of responses and to analyse effects of climate extremes on various ecosystem functions. 2. We set up a long‐term field experiment, where we applied recurrent severe drought events annually for five consecutive years to constructed grassland communities in central Europe. The 32 response parameters studied were closely related to ecosystem functions such as primary production, nutrient cycling, carbon fixation, water regulation and community stability. 3. Surprisingly, in the face of severe drought, above‐ and below‐ground primary production of plants remained stable across all years of the drought manipulation. 4. Yet, severe drought significantly reduced below‐ground performance of microbes in soil indicated by reduced soil respiration, microbial biomass and cellulose decomposition rates as well as mycorrhization rates. Furthermore, drought reduced leaf water potential, leaf gas exchange and leaf protein content, while increasing maximum uptake capacity, leaf carbon isotope signature and leaf carbohydrate content. With regard to community stability, drought induced complementary plant–plant interactions and shifts in flower phenology, and decreased invasibility of plant communities and primary consumer abundance. 5. Synthesis. Our results provide the first field‐based experimental evidence that climate extremes initiate plant physiological processes, which may serve to regulate ecosystem productivity. A potential reason for different dynamics in various ecosystem services facing extreme climatic events may lie in the temporal hierarchy of patterns of fast versus slow response. Such data on multiple response parameters within climate change experiments foster the understanding of mechanisms of resilience, of synergisms or decoupling of biogeochemical processes, and of fundamental response dynamics to drought at the ecosystem level including potential tipping points and thresholds of regime shift. Future work is needed to elucidate the role of biodiversity and of biotic interactions in modulating ecosystem response to climate extremes.

Comparison of Tolerant Ability of Mature Field Grown Tea (<i>Camellia sinensis</i> L.) Cultivars Exposed to a Drought Stress in Passara Area

The response of some selected physiological and biochemical parameters of tea ( Camellia sinensis L.) plants to moisture stress was evaluated using field grown, mature plants, in Field Gene Bank at Passara, Sri Lanka, to identify traits that are associated with drought tolerance which could be used for cultivar screening programs. This study was carried out from July - October 2008. Known contrasting cultivars in terms of drought tolerance were selected from the existing gene bank for the measurements. Physiological and biochemical parameters were measured to study the response of tea plants to drought stress. Identification of traits was done by using cluster analysis, cultivar × environment interaction and drought susceptibility index. Reduction of leaf water potential up to -0.75 to -1.5 MPa at the end of the dry period indicated that the plants were exposed to a sufficient level of moisture stress. The drought tolerant cultivars maintained a high water status with substantial rate of photosynthesis as a result of osmotic adjustments, elevated total soluble sugars and also according to previous research, due to deep rooting. Drought susceptible cultivars maintained a lower water status with lower osmotic adjustment. With cluster analysis using rates of photosynthesis and transpiration, relative water content, stomatal conductance and leaf total soluble sugar content, the cultivars could be clearly grouped as tolerant and susceptible cultivars, which agreed with their tolerance level. The parameters which could be successfully incorporated into a drought screening procedure were rate of photosynthesis, stomatal conductance, transpiration rate, relative water content and total soluble sugar content. Key words: Cultivar differences; Drought; Physiological and biochemical responses; Tea ( Camellia sinensis L.). DOI: 10.4038/tar.v22i1.2671 Tropical Agricultural Research Vol. 22 (1): 66-75 (2010)

IMPACT OF REGULATED DEFICIT IRRIGATION ON FRUIT QUALITY AND POSTHARVEST STORAGE PERFORMANCE OF 'CRIPPS PINK' APPLE

This study aimed to develop an irrigation strategy for apples to improve fruit skin colour without adversely affecting postharvest life and quality. Regulated deficit irrigation (RDI) at different levels [(i) 100%, commercial irrigation (CI) (70 L·h -1 ); (ii) 25% RDI (50 L·h -1 ); (iii) 50% RDI (35 L·h -1 ); and (iv) 75% RDI (20 L·h -1 )] was applied from 135 days after full bloom (DAFB) continuously for 72 days till harvest. RDI (75%) significantly reduced leaf water potential as compared to Cl. RDI (75%) improved fruit skin colour via enhanced accumulation of anthocyanins, increased soluble solids concentration (SSC), fruit firmness and slightly decreased fruit diameter. The RDI fruit (75%) stored for 135 days at 0±0.1°C, 90±2% RH remained firmer and had higher SSC compared to CI fruit. Similarly, RDI fruit (75%) stored for 155 days in controlled atmosphere (CA) comprising of 2.7% O 2 + 1.9% CO 2 at 0°C had higher SSC and fruit firmness than in CI fruit. In conclusion, RDI (75%) imposed at the late fruit development stage improved the fruit quality of 'Cripps Pink' apple at harvest without adversely affecting postharvest quality in cold and CA storage, and also saved irrigation water.

FRUIT QUALITY AND POSTHARVEST PERFORMANCE OF 'CRIPPS PINK' APPLE IN RELATION TO WITHHOLDING IRRIGATION

We investigated the effects of withholding irrigation (WHI) at various stages of apple fruit development in improving fruit quality at harvest, particularly fruit colour without adversely affecting storage life and quality. WHI treatments were applied during stage II and III of fruit development commencing from 135, 145 and 155 days after full bloom (DAFB). Treatments were (i) T1, commercial irrigation as a control, (ii) T2, WHI from 135 to 153 DAFB, (iii) T3, WHI from 145 to 175 DAFB, and (iv) T4, WHI from 155 to 200 DAFB. WHI applied in T3 significantly reduced leaf water potential, 10 days after the commencement of WHI. WHI treatments did not significantly affect the cumulative fruit drop on 195 DAFB than T1. WHI treatment (T3) enhanced red skin colour, concentration of total anthocyanins, soluble solids concentration and firmness at harvest as compared to T1. Fruit from T3 stored at 0±0.1°C, 90±2% RH for 70 and 140 days retained higher firmness (>68N) and SSC (>15°Brix) as compared to T1. However, prolonged cold storage periods decreased titratable acidity of the fruit from irrespective of WHI treatments. WHI fruit from T3 stored for 140 days showed increased levels of ascorbic acid and total antioxidants in the pulp as compared to other treatments. In conclusion, WHI applied 145 to 175 DAFB (middle of stage II) improved fruit colour and other major fruit quality parameters at harvest without adversely affecting postharvest quality and also reduced water use.

The impact of drought on leaf physiology of Quercus suber L. trees: comparison of an extreme drought event with chronic rainfall reduction

Understanding the responses of cork oak (Quercus suber L.) to actual and predicted summer conditions is essential to determine the future sustainability of cork oak woodlands in Iberia. Thermal imaging may provide a rapid method for monitoring the extent of stress. The ecophysiology of cork trees was studied over three years. Three treatments were applied by means of rainfall capture and irrigation, with plots receiving 120%, 100%, or 80% of natural precipitation. Despite stomatal closure, detected using both thermal imaging and porometry, leaf water potential fell during the summer, most drastically during the third year of accumulative stress. The quantum efficiency (ΦPSII) and the maximum efficiency Fv' /FM' of photosystem II also fell more intensely over the third summer, while non-photochemical quenching (NPQ) increased. The reduced precipitation treatment sporadically further reduced leaf water potential, stomatal conductance (gs), IG (an index of gs derived from thermal imaging), ΦPSII, and Fv' /FM', and increased leaf temperature and NPQ. It is concluded that these are very resilient trees since they were only severely affected in the third year of severe drought (the third year registering 45% less rainfall than average), and removing 20% of rainfall had a limited impact..

Effect of foliar application of antitranspirant on photosynthesis and water relations of pepper plants under different levels of CO 2 and water stress

Strategies such as foliar application of antitranspirants have the potential to regulate transpiration, but often, the limitation of CO 2 exchange as a result of reduced stomatal conductance can impair this beneficial effect. Elevated ambient [CO 2] could significantly improve CO 2 diffusion while effectively reducing transpiration. In this experiment, we examined the response of sweet pepper ( Capsicum annuum L.) to the foliar application of antitranspirant (AT) under two [CO 2] (380 and 2000 μmol mol −1) and two drought intensities (4 or 8 d without irrigation). The results showed that stomatal conductance and transpiration were reduced, while AT impaired photosynthesis at standard, but not at elevated [CO 2] of fully irrigated plants. This effect was already apparent after 4 d of drought. Drought had a minor impact on chlorophyll fluorescence ( F v/ F m). Additionally, root respiration was increased at elevated [CO 2] but, after 8 d of drought, it was higher for plants treated with AT than for non-sprayed plants. Leaf water potential was affected more by drought at ambient compared to elevated [CO 2], and, especially after 8 d of drought, AT minimized the reductions in leaf water potential. Leaf concentrations of proline and starch were affected by both [CO 2] and AT, especially after 8 d of drought. Moreover, increasing [CO 2] promoted the accumulation of starch, but led to decreases in the tissue concentrations of the soluble organic osmolytes, and hence diminished osmotic adjustment after 8 d of water withholding, relative to ambient [CO 2]. This study indicates that, in addition to the reported beneficial effect of elevated [CO 2] on drought stress, AT could significantly improve drought tolerance in sweet pepper plants.

Do photosynthetic limitations of evergreen Quercus ilex leaves change with long‐term increased drought severity?

Seasonal drought can severely impact leaf photosynthetic capacity. This is particularly important for Mediterranean forests, where precipitation is expected to decrease as a consequence of climate change. Impacts of increased drought on the photosynthetic capacity of the evergreen Quercus ilex were studied for two years in a mature forest submitted to long-term throughfall exclusion. Gas exchange and chlorophyll fluorescence were measured on two successive leaf cohorts in a control and a dry plot. Exclusion significantly reduced leaf water potential in the dry treatment. In both treatments, light-saturated net assimilation rate (A(max)), stomatal conductance (g(s)), maximum carboxylation rate (V(cmax)), maximum rate of electron transport (J(max)), mesophyll conductance to CO2 (g(m)) and nitrogen investment in photosynthesis decreased markedly with soil water limitation during summer. The relationships between leaf photosynthetic parameters and leaf water potential remained identical in the two treatments. Leaf and canopy acclimation to progressive, long-term drought occurred through changes in leaf area index, leaf mass per area and leaf chemical composition, but not through modifications of physiological parameters.

Physiological and biochemical responses of peanut genotypes to water deficit

The effects of drought on water relations, gas exchanges, solutes accumulation, and catalase (CAT), ascorbato peroxidase (APX), and guaiacol peroxidase (GPX) activities were studied in five Arachis genotypes, grown under control or withholding water conditions. Drought stress reduced plant growth of all genotypes; the genotypes A. duranensis 7988 and A. stenosperma SV2411 being characterized as the most drought-sensitive and A. ipaensis as the most drought-tolerant. Data of transpiration and stomatal conductance confirmed the findings that A. ipaensis was more tolerant to drought conditions. Water deficit increased organic solutes content and reduced leaf water potential in all genotypes. The data suggest that solutes accumulation in roots may, at least in part, explain the greater tolerance of A. ipaensis to drought stress. CAT activity showed a significant increase in stressed leaves of sensitive genotypes. APX and GPX activities either increased or were not affected by drought in leaves of all genotypes.

Growth evaluation and water relations of Erythrina velutina seedlings in response to drought stress

Erythrina velutina Willd. (common name: mulungu) is a deciduous, heliophyte found in the semi-arid region of northeastern Brazil. To evaluate the growth and water relations of mulungu seedlings in soils with different degrees of moisture content, an experiment was carried out under greenhouse conditions using four water treatments (100%, 75%, 50% and 25% of the field capacity- FC). Predawn (Ψpdw) and midday leaf water potential (Ψmdw), relative water content (RWC), plant height, number of leaves, stem diameter, leaf area (LA), specific leaf area (SLA), leaf area ratio (LAR), dry matter in different organs, biomass partitioning and root:shoot ratio were evaluated. No differences were detected between treatments for Ψpdw after 30 days; however, at midday, control plants and those under 75% FC underwent a greater reduction in Ψmdw than plants cultivated with 50% and 25% FC. After 90 days, only the plants under 50% FC exhibited a reduction in Ψmdw. RWC was reduced at midday, but there were no differences between treatments. Nearly all growth parameters were reduced due to water deficit, especially in the plants with 25% FC, as determined by the number of leaves, stem diameter, plant height, LA, SLA and dry mass in several organs. LAR and root:shoot ratio were not affected. Mulungu seedlings seem to have developed rusticity to overcome intermittent droughts with no change in the pattern of dry matter distribution. The maintenance of turgor pressure seems to be more associated to a reduction in the growth ratio than a reduction in leaf water potential.

Mucilage and polysaccharides in the halophyte plant species Kosteletzkya virginica: Localization and composition in relation to salt stress

Mucilage is thought to play a role in salinity tolerance in certain halophytic species by regulating water ascent and ion transport. The localization and composition of mucilage in the halophyte Kosteletzkya virginica was therefore investigated. Plants were grown in a hydroponic system in the presence or absence of 100 mM NaCl and regularly harvested for growth parameter assessment and mucilage analysis with the gas liquid chromatography method. NaCl treatment stimulated shoot growth and biomass accumulation, had little effect on shoot and root water content, and reduced leaf water potential ( Ψ w), osmotic potential ( Ψ s) as well as stomatal conductance ( g s). Mucilage increased in shoot, stems and roots in response to salt stress. Furthermore, changes were also observed in neutral monosaccharide components. Levels of rhamnose and uronic acid increased with salinity. Staining with a 0.5% alcian blue solution revealed the presence of mucopolyssacharides in xylem vessels and salt-induced mucilaginous precipitates on the leaf abaxial surface. Determination of ion concentrations showed that a significant increase of Na + and a decrease of K + and Ca 2+ simultaneously occurred in tissues and in mucilage under salt stress. Considering the high proportion of rhamnose and uronic acid in stem mucilage, we suggest that the pectic polysaccharide could be involved in Na + fixation, though only a minor fraction of accumulated sodium appeared to be firmly bound to mucilage.

Orange varieties as interstocks increase the salt tolerance of lemon trees

SummaryWe investigated the ability of interstocks to increase salt tolerance in lemon trees. We compared 2-year-old ‘Verna’ lemon trees [Citrus limon (L.) Burm.; VL] grafted on Sour Orange (C. aurantium L.; SO) rootstock either without an interstock (VL/SO), or interstocked with ‘Valencia’ orange (C. sinensis Osbeck; VL/V/SO), or with ‘Castellano’ orange (C. sinensis Osbeck; VL/C/SO). Trees were grown under greenhouse conditions and supplied with nutrient solutions containing 0, 30, or 60 mM NaCl. Reductions in leaf growth caused by salt treatment were greatest in non-interstocked (VL/SO) trees, followed by VL/C/SO trees, and were the least in VL/V/SO trees. Although the levels of Cl− and Na+ ions in the roots and stems were not affected by either interstock, leaf concentrations of Cl− and Na+ were higher in VL/SO trees than in VL/C/SO or VL/V/SO trees, suggesting that an interstock in Citrus trees could limit the uptake and transport of such ions to the shoots. Saline-treated VL/SO trees also tended to have the lowest shoot:root (S:R) ratios; so, overall, there was a negative relationship between S:R ratio and leaf Cl- ion concentration. Leaf transpiration (Eleaf) may also be involved in the reduction in leaf Cl− concentration, as interstocked trees had lower Eleaf values at mid-day than non-interstocked trees. Salinity increased leaf concentrations of Ca2+ in VL/C/SO trees and increased both leaf K+ and N concentrations in all trees, regardless of interstock. Salinity reduced leaf water potentials and osmotic potentials, such that leaf turgor was increased in all trees.

Coordination of leaf structure and gas exchange along a height gradient in a tall conifer

The gravitational component of water potential and frictional resistance during transpiration lead to substantial reductions in leaf water potential (Psi(l)) near the tops of tall trees, which can influence both leaf growth and physiology. We examined the relationships between morphological features and gas exchange in foliage collected near the tops of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees of different height classes ranging from 5 to 55 m. This sampling allowed us to investigate the effects of tree height on leaf structural characteristics in the absence of potentially confounding factors such as irradiance, temperature, relative humidity and branch length. The use of cut foliage for measurement of intrinsic gas-exchange characteristics allowed identification of height-related trends without the immediate influences of path length and gravity. Stomatal density, needle length, needle width and needle area declined with increasing tree height by 0.70 mm(-2) m(-1), 0.20 mm m(-1), 5.9 x 10(-3) mm m(-1) and 0.012 mm(2) m(-1), respectively. Needle thickness and mesophyll thickness increased with tree height by 4.8 x 10(-2) mm m(-1) and 0.74 microm m(-1), respectively. Mesophyll conductance (g(m)) and CO(2) assimilation in ambient [CO(2)] (A(amb)) decreased by 1.1 mmol m(-2) s(-1) per m and 0.082 micromol m(-2) s(-1) per m increase in height, respectively. Mean reductions in g(m) and A(amb) of foliage from 5 to 55 m were 47% and 42%, respectively. The observed trend in A(amb) was associated with g(m) and several leaf anatomic characteristics that are likely to be determined by the prevailing vertical tension gradient during foliar development. A linear increase in foliar delta(13)C values with height (0.042 per thousand m(-1)) implied that relative stomatal and mesophyll limitations of photosynthesis in intact shoots increased with height. These data suggest that increasing height leads to both fixed structural constraints on leaf gas exchange and dynamic constraints related to prevailing stomatal behavior.

Chlorophyll fluorescence as a tool for evaluation of drought stress in strawberry

The effect of water deficit on chlorophyll fluorescence, sugar content, and growth parameters of strawberry (Fragaria×ananassa Duch. cv. Elsanta) was studied. Drought stress caused significant reductions in leaf water potential, fresh and dry masses, leaf area, and leaf number. A gradual reduction of photochemical quenching (qP) and quantum efficiency (ΦPS2) was observed under drought stress while non-photochemical quenching (qN) increased. Maximum efficiency of photosystem 2 (Fv/Fm) was not affected by drought stress.

Caractéristiques hydriques du mil ( Pennisetum glaucum (L.) R. Br.) en présence de contraintes hydriques

The variations in the hydrous characteristics – leaf water potential ( ψ F ) and relative water content (TRE) – of plants indicate their hydrous status and also their capacity to incorporate water, particularly in situations of hydrous stress. These characteristics were used to differentiate the behaviour of six autochthonous ecotypes of pearl millet ( Pennisetum glaucum (L.) R. Br.) subjected to various hydrous modes. The results showed that the ψ F and the TRE evolve in the same direction and decrease in the presence of hydrous stress. These hydrous characteristics are also very important, since they condition the yield. The study also showed that the six pear millet ecotypes present two standard behaviours: the first type is characterized by an important fall of the ψ F and TRE, representing an osmotic adjustment of adaptive type, whereas the second group showed a weak reduction of leaf water potential while maintaining a TRE appreciably higher, which could be the result of an important reduction of the osmotic potential due to an active accumulation of solutes (constitutive osmotic adjustment). Moreover, the genetic variability of ecotypes with respect to the hydrous stress does not seem related to the geographical origin of the millet ecotypes, but rather to their phenology and their morphology. To cite this article: L. Radhouane, C. R. Biologies 331 (2008).

Seasonal change in the drought response of wood cell development in poplar

Field-grown poplar trees (Populus nigra L. x P. maximowiczii Henry, clone Kamabuchi) were exposed to severe drought twice during the growing season to evaluate the impact on wood cell development. The drought treatment caused a reduction in leaf water potential, leaf wilting and a decreased concentration of osmotically active solutes in the cambial zone. Drought-induced changes in the anatomy of developing xylem cells were examined in stem sections and macerated wood samples. In early summer, drought significantly reduced the length and cross-sectional area of newly formed fibers, whereas no such effects were observed in late summer. In well-watered trees, fiber cross-sectional area declined between early and late summer. Similarly, drought reduced the cross-sectional area of vessel elements in early summer but not in late summer, whereas in both control and drought-treated trees, the cross-sectional area of vessel elements decreased between early and late summer. The vessel area to xylem area ratio was unaffected by drought because the drought-induced decrease in vessel size was matched by an increase in the number of newly formed vessel cells. In contrast to its effect in early summer, late-summer drought had no significant effect on fiber and vessel cell development, indicating that sensitivity of wood cell development to drought varies seasonally.

Low carbon dioxide concentrations can reverse stomatal closure during water stress

Leaf water potentials below threshold values result in reduced stomatal conductance (gs). Stomatal closure at low leaf water potentials may serve to protect against cavitation of xylem. Possible control of gs by leaf water potential or hydraulic conductance was tested by drying the rooting medium in four herbaceous annual species until gs was reduced and then lowering the [CO2] to determine whether gs and transpiration rate could be increased and leaf water potential decreased and whether hydraulic conductance was reduced at the resulting lower leaf water potential. In all species, low [CO2] could reverse the stomatal closure because of drying despite further reductions in leaf water potential, and the resulting lower leaf water potentials did not result in reductions in hydraulic conductance. The relative sensitivity of gs to internal [CO2] in the leaves of dry plants of each species averaged three to four times higher than in leaves of wet plants. Two species in which gs was reputed to be insensitive to [CO2] were examined to determine whether high leaf to air water vapor pressure differences (D) resulted in increased stomatal sensitivity to [CO2]. In both species, stomatal sensitivity to [CO2] was indeed negligible at low D, but increased with D, and low [CO2] partly or fully reversed closure caused by high D. In no case did low leaf water potential or low hydraulic conductance during drying of the air or the rooting medium prevent low [CO2] from increasing gs and transpiration rate.

Stomatal regulation by microclimate and tree water relations: interpreting ecophysiological field data with a hydraulic plant model

Dynamics in microclimate and physiological plant traits were studied for Pubescent oak and Scots pine in a dry inner-alpine valley in Switzerland, at a 10 min resolution for three consecutive years (2001-2003). As expected, stomata tended to close with increasing drought in air and soil. However, stomatal aperture in oak was smaller than in pine under relatively wet conditions, but larger under dry conditions. To explore underlying mechanisms, a model was applied that (i) quantifies water relations within trees from physical principles (mechanistic part) and (ii) assumes that signals from light, stomatal aperture, crown water potential, and tree water deficit in storage pools control stomata (systemic part). The stomata of pine showed a more sensitive response to increasing drought because both factors, the slowly changing tree water deficit and the rapidly changing crown water potential, closed the stomata. By contrast, the stomata of oak became less drought-sensitive as the closing signal of crown water potential was opposed by the opening signal of tree water deficit. Moreover, parameter optimization suggests that oak withdrew more water from the storage pools and reduced leaf water potentials to lower levels, without risking serious damage by cavitation. The new model thus suggests how the hydraulic water flow and storage system determines the responses in stomatal aperture and transpiration to drought at time scales ranging from hours to multiple years, and why pine and oak might differ in such responses. These differences explain why oaks are more efficient competitors during drought periods, although this was not the case in the extremely dry year 2003, which provoked massive leaf loss and, from July onwards, physiological activity almost ceased.

Assessing Drought Tolerance of Snap Bean (Phaseolus Vulgaris) From Genotypic Differences In Leaf Water Relations,Shoot Growth and Photosynthetic Parameters

The Leaf Water Relations, Photosynthetic Parameters and Shoot Growth of Five Snap Bean Cultivars Were Assessed During The Drought Period To Determine Their Role In Alleviating Plant Water Deficit Imposed By Withholding Irrigation At Flowering. Soil Water Content of Irrigated Plants Was 18-20% While That of Unirrigated Plants Was 6-10% At 60 Days After Seeding (Das). Leaf Water Potential Was Approximately 0.15Mpa Lower and Relative Water Content Was Approximately 5% Lower In Unirrigated Plants Than In Irrigated Plants At 57 Das. Unirrigated Plants Had A Lower Stomatal Conductance (Gs) and Intercellular Co2 Concentration (Ci). Reduced Leaf Water Potential and Relative Water Content Were Associated With A Decreased Stem Elongation Rate. Plants With A Lower Stem Elongation Rate Had A Higher Specific Leaf Weight and Succulence Index (Suci). Significant Differences Among Five Cultivars of Snap Bean Were Found For All Parameters Measured. Decreased Leaf Water Potential and Stem Elongation Rate Resulting From Drought Participated In Preserving Relative Water Content and Improving Specific Leaf Weight and Suci. Maintenance of Higher Relative Water Content Increased Gs and Ci. Cultivars That Maintained A High Relative Water Content When Leaf Water Potential and Stem Elongation Rate Were Decreased Markedly, Were More Tolerant To Drought Than Those Which A Reduced Relative Water Content and The Leaf Water Potential and Stem Elongation Rate Were Only Slightly Lowered. Reduced Yield (Pods Per Plant and Seed Biomass) Resulting From Drought Was Associated With Reduced Relative Water Content.

Commercially available plant growth regulators and promoters modify bulk tissue abscisic acid concentrations in spring barley, but not root growth and yield response to drought

AbstractField and lysimeter experiments were conducted in 2002 to investigate the effects of an antigibberellin growth regulator (Moddus, active ingredient trinexapac‐ethyl, Syngenta Crop Protection UK Ltd, Whittlesford, Cambridge, UK) and an auxin‐stimulating (Route, active ingredient zinc ammonium acetate, De Sangosse Ltd, Swaffham Bulbeck, Cambridge, UK) growth promoter on root growth, soil water extraction and the drought response of spring barley. The effects on root growth and distribution were investigated in the field. The effects on the drought response were studied in 1.2‐m‐deep lysimeters packed with a loamy sand subsoil and sandy loam topsoil. Lysimeters were located under a fixed rain shelter, and drought was imposed by withholding irrigation. In both field and lysimeter experiments, growth regulator/promoters were applied to cv. Optic at early tillering according to the manufacturers’ recommendations. After withholding irrigation from lysimeters at Zadoks growth stage (GS) 21 (37 days after sowing), 50% of the profile available water had been depleted by flag leaf emergence (GS 37/39; 62 days after sowing). Drought significantly reduced stem biomass at ear emergence (GS 59; 78 days after sowing) but not leaf or ear dry weight; this was before there was any significant reduction in leaf water potential or stomatal conductance to water vapour. The reduction in stem biomass may reflect a change in partitioning between shoot and root in response to soil drying. When averaged over growth regulator/promoter treatments, drought reduced grain yield by approximately 1 t ha−1. This was associated with a reduction in both ears per m2 and grains per ear. The mean grain weight was not reduced by drought, in spite of significant reductions in stomatal conductance and canopy lifespan post‐anthesis. Route, and to a lesser extent Moddus, significantly increased abscisic acid accumulation in the stem base of droughted plants, and there was some indication of a possible delay in stomatal closure in Route‐treated plants as the soil moisture deficit developed. However, there was no significant effect on the amount of soil water extracted or grain yield under drought. Similarly, in field experiments, neither Route nor Moddus significantly altered total root length, biomass or distribution. There is little evidence from these experiments or in the literature to support the use of antigibberellin or auxin‐simulating growth regulator/promoters to modify root growth and drought avoidance of spring barley.

Physiological implications of metabolite biosynthesis for net assimilation and heat-stress tolerance of sugarcane ( Saccharum officinarum) sprouts

Global increase in ambient temperature is a critical factor for plant growth. In order to study the changes in growth over short intervals, various primary and secondary metabolites, and their relationships with thermotolerance, 1-month-old sugarcane (Saccharum officinarum) sprouts were grown under control conditions (28 degrees C) or under heat-stress conditions (40 degrees C), and measurements were made at six 12-h intervals. Heat stress greatly reduced dry matter and leaf area of sprouts initially but only nominally later on. Changes in the rates of relative growth and net assimilation were greater than relative leaf expansion, indicating an adverse effect of heat on assimilation of nutrients and CO(2) in producing dry matter. Although reduction in leaf water potential was an immediate response to heat, this effect was offset by early synthesis of free proline, glycinebetaine and soluble sugars (primary metabolites). Among secondary metabolites, anthocyanin synthesis was similar to primary metabolites; carotenoids and soluble phenolics accumulated later while chlorophyll remained unaffected. Relationships of growth attributes and metabolite levels, not seen in the controls, were evident under heat stress. In summary, observed changes in metabolite levels were spread over time and space and were crucial in improving net assimilation and heat tolerance of sugarcane.