Higher Leaf Water Potential Research Articles

Minimal Plant Responsiveness to Summer Water Pulses: Ecophysiological Constraints of Three Species of Semiarid Patagonia

In arid ecosystems, a few large summer rains frequently differentiate wet years from dry ones. However, use of this additional water by plants has limited experimental evidence. We applied a 16-mm summer water pulse (12% of mean annual precipitation) to two plant communities of the Patagonian steppe, and compared responses of three dominant species, which can be ordered by decreasing xerophytism and increasing rooting depth and summer activity: 1) colapiche, evergreen dwarf shrub (Nassauvia glomerulosa [Lag.] Don); 2) coirón amargo, evergreen grass (Stipa speciosa Trin. et Rupr.); and 3) neneo, drought deciduous shrub (Mulinum spinosum [Cav.] Pers.). Shallow-rooted species (S. speciosa and N. glomerulosa), which use water from dry soil layers, showed a greater leaf water potential response to watering than deep-rooted species (M. spinosum). Leaf water potential response was greater and quicker in xerophytic species than in mesophytic ones (N. glomerulosa > S. speciosa > M. spinosum). However, this response only translated into leaf conductance and transpiration responses for coirón amargo, probably because the species with winter phenological cycle (N. glomerulosa) is less able to utilize summer water inputs than species with a summer phenological cycle (S. speciosa). The lack of response of deep-rooted M. spinosum in leaf conductance, transpiration, and photosynthesis may have been due to the high leaf water potential of control plants. Instead, in S. speciosa and N. glomerulosa net photosynthesis decreased below zero following watering, suggesting the start of growth pulses. The complex chain of plant processes triggered by rainfall, and the constraints imposed to different species by rooting depth, phenology, and xerophytism, could explain the frequent low response to both large rainfall events and above-average rainfall years in this arid community. Our results suggest that, paradoxically, water may be suboptimally used at local scales in arid rangeland ecosystems. En los ecosistemas áridos, unas pocas lluvias grandes de verano frecuentemente diferencian los años húmedos de los años secos. Sin embargo, hay limitadas pruebas experimentales del uso de esta agua adicional por las plantas. Nosotros aplicamos un pulso de 16 mm de agua durante el verano (12% del promedio anual de precipitación) en dos comunidades de plantas de la estepa patagónica, y comparamos las respuestas de las tres especies dominantes, que pueden ser ordenadas por la disminución en el xerofitismo y el aumento en la profundidad de enraizamiento y la actividad estival: 1) colapiche, arbusto siempreverde enano (Nassauvia glomerulosa [Lag.] Don); 2) coirón amargo, pasto perenne (Stipa speciosa Trin. et Rupr.); y 3) neneo, arbusto cuyas hojas se secan en la época de sequía (Mulinum spinosum [Cav.] Pers.). Las especies de raíces más superficiales (S. speciosa y N. glomerulosa), que utilizan el agua de las capas de suelo seco, mostraron una mayor respuesta al riego en el potencial agua de la hoja que la especie de raíces profundas (M. spinosum). La respuesta del potencial agua de la hoja fue mayor y más rápida en las especies xerofíticas que en las especies mesofíticas (N. glomerulos > S. speciosa > M. spinosum). Sin embargo, esta respuesta sólo se tradujo en respuestas en la conductancia de la hoja y la transpiración en el coirón amargo, probablemente porque la especie con ciclo fenológico invernal (N. glomerulosa) es menos capaz de utilizar los aportes estivales de agua que las especies con ciclo fenológico estival (S. speciosa). La falta de respuesta de la especie de raíces profundas M. spinosum en la conductancia de la hoja, la transpiración y la fotosíntesis puede haberse debido al alto potencial hídrico de la hoja de las plantas control. En cambio, la fotosíntesis neta en S. speciosa y N. glomerulosa disminuyó por debajo de cero tras el riego, lo que sugiere el inicio de pulsos de crecimiento. La compleja cadena de procesos de las plantas desencadenados por las lluvias, y las limitaciones impuestas a diferentes especies por la profundidad radical, la fenología y el xerofitismo, podrían explicar la baja frecuencia de respuesta tanto a los eventos grandes de precipitación como a los años de precipitaciones por encima del promedio en esta comunidad árida. Nuestros resultados sugieren que, paradójicamente, el agua puede ser utilizada subóptimamente a escalas locales en los ecosistemas de pastizales áridos.

Water relations and organic solutes production in four umbu tree (Spondias tuberosa) genotypes under intermittent drought

In order to evaluate changes in leaf water potential (ψw) and solute accumulation induced by intermittent drought, an research was performed under greenhouse conditions using four umbu tree genotypes (GBU 44, GBU 48, GBU 50 and GBU 68) and two water treatments (control and stressed by withholding water), with four replicates. The ψw was measured in four-hour intervals during a 24-hour period at the first stomatal closure and at the end of the experimental period. Carbohydrates, amino acids, protein and proline contents were also evaluated in leaves and roots. Significant differences were found in most of the studied parameters. The lower ψw hour was between 800 h and 1200 h. GBU 50 reduced significantly ψw in stressed plants at 800 h, while control plants reduced at 1200 h . GBU 68 presented the higher ψw. The extending of the stress induced reductions to carbohydrates in the leaves of all genotypes, increases in amino acids to GBU 44 and 48, and reductions of 40% and 43% to GBU 50 and 68, respectively; results also showed alterations in proline content. In the roots, increases in carbohydrates were observed only in GBU 48. Alterations in amino acids, protein, and proline were verified. Umbu trees presented isohydric behavior maintaining high leaf water potential and a great variability in organic solutes accumulation in response to drought with marked differences among the genotypes.

Plant- and stand-level variation in biophysical and physiological traits along tree density gradients in the Cerrado

The objective of this study was to characterize and understand morphological and physiological variation in traits related to water economy, at the plant and stand level, along a gradient of tree density in a Neotropical savanna (Cerrado). Cerrado plots subjected to long-term fertilization and gallery forests were also included in the analysis to expand the axes of ecosystem variation. Consistent changes in stand level biophysical traits observed along the gradient of increasing tree density included a decrease in weighted-average wood density, and increases in leaf surface area per plant, leaf specific hydraulic conductivity, specific leaf area and stomatal conductance. A conceptual model of biophysical, morphological and physiological trait interactions was developed in an attempt to explain determinants of hydraulic architecture and variations in water economy of Cerrado trees. Consistent with the model minimum leaf water potentials were higher, during the dry season, in low wood density trees compared to high wood density trees, and higher leaf water potential was associated with higher stomatal conductance. On the other hand, variations in stand level physiological and morphological traits along the tree density gradient could not be explained by variations in single environmental factors. Some of the potential contributing factors are: higher concentration and availability of soil nutrients in the upper portion of the gradient where tree density is greatest and constrains to tree establishment and growth by waterlogging and presence of concretions in the soil profile where tree density is lowest.

Flooding tolerance of Paspalum dilatatum (Poaceae: Paniceae) from upland and lowland positions in a natural grassland

The grass Paspalum dilatatum Poir. subsp. dilatatum inhabits periodically flooded lowlands as well as non-flooded uplands of the flooding Pampa grasslands (Argentina), while P. dilatatum Poir. subsp. flavescens Roseng., B.R. Arrill. & Izag. inhabits only the upland sites. An experiment was designed to determine if there is local adaptation to flooding in physiological, anatomical and leaf morphological traits. To this end, plants of these populations were subjected to flooding (6 cm water depth) and control conditions (watered daily) for 60 days in an experimental garden. Flooded plants of the subsp. dilatatum from the lowland had 35% higher photosynthesis compared to controls without affecting their stomatal conductance, transpiration rate and leaf water potential. By contrast, both subsp. dilatatum and subsp. flavescens from the upland did not increase their photosynthesis, and had reduced their stomatal conductance and leaf transpiration rate by 35% and 45% when growing in flooded conditions. Upland populations had higher leaf water potential with respect to controls. All populations had high constitutive root aerenchyma (28–42%), and leaf sheath porosity increased by 75% in flooded conditions (from 22–28% to 35–48%). Leaf lengthening differed among populations according to their habitat: subsp. dilatatum from the lowland was the only one that had longer leaf sheaths and blade lengths when flooded. In contrast, flooded plants of subsp. dilatatum from the upland only increased leaf sheath length while subsp. flavescens neither increased leaf blade nor leaf sheath. In conclusion, both the physiological performance and the leaf length plasticity differed among populations. The results agree with those expected based on the species’ habitat, and indicate the better adaptation to the flood-prone habitat of P. dilatatum subsp. dilatatum taken from a lowland area.

QTL Mapping and Correlations between Leaf Water Potential and Drought Resistance in Rice under Upland and Lowland Environments

To reveal the role and genetic mechanism of leaf water potential (LWP) to japonica rice under various water status, 120 recombinant inbred lines (RILs) derived from a cross between IRAT109, an upland japonica rice, and Yuefu, a lowland japonica rice, were planted under both upland and lowland environments for mapping QTL associated with high LWP. LWP was measured at pre-dawn and mid-day. Drought resistance was evaluated with index of drought resistance (IDR), which was the ratio of grain yield of upland treatment to that of lowland treatment at maturity. Significant variations of LWP were observed in RILs in both upland and lowland treatments. Correlation analysis indicated that LWP at mid-day in upland (WPU) was positively correlated (r = 0.256;r = 0.259) with IDR and yield per plant (YPU), and water potential variation in upland (WDU) negatively correlated (r = 0.280;r = 0.260) with IDR and YPU. For LWP, 6 additive QTLs including 2 for LWP at pre-dawn in upland (WPIU), 1 for WPU, 2 for WDU, and 1 for LWP variation in lowland (WDL) and 5 pairs of epistatic QTLs including 1 for WPU, 1 for WPIU, 1 for LWP at pre-dawn in lowland (WPIL), and 2 for WPL were detected, respectively. Among the 6 additive QTLs, the 2 for WPIU (wpiu1 and wpiu4) and 1 for WPU (wpu6), all donated by IRAT109, can explain 5.4%, 7.9%, and 10.0% of the phenotypic variances, respectively;the 2 for WDU, wdu6 from IRAT109 and wdy12 from Yuefu, can explain 11.6% and 9.5% of phenotypic variances, respectively. For IDR, 3 additive and 2 pairs of epistatic QTLs were identified. The broad heritability of LWP was low for direct selection in the field, but may be effective via marker-assisted selection.

QTL Mapping and Correlations Between Leaf Water Potential and Drought Resistance in Rice Under Upland and Lowland Environments

The aim of this study was to show the role and genetic mechanism of leaf water potential (LWP) to japonica rice ( Oryza sativa L. subsp. japonica) under various water status parameters. To achieve the above, 120 recombinant inbred lines (RILs), derived from a cross between IRAT109 (an upland japonica cultivar) and Yuefu (a lowland japonica cultivar) were planted under both upland and lowland environments for mapping quantitative trait loci (QTLs) associated with high LWP. The LWP was measured at predawn and midday. Drought resistance was evaluated with index of drought resistance (IDR), which was the ratio of grain yield of upland treatment to that of lowland treatment at maturity. Significant variations of LWP were observed in RILs in both upland and lowland treatments. Correlation analysis indicated that LWP at midday in upland (WPU) was positively correlated with IDR ( r = 0.256, P < 0.01) and yield per plant (YPU) ( r = 0.259, P < 0.01), and water potential difference in upland (WDU) negatively correlated with IDR ( r = −0.280, P < 0.01) and YPU ( r = −0.260, P < 0.01). For LWP, 6 additive QTLs, i.e., 2 for LWP at predawn in upland (WPIU), 1 for WPU, 2 for WDU, and 1 for LWP difference in lowland (WDL) and 5 pairs of epistatic QTLs, i.e., 1 for WPU, 1 for WPIU, 1 for LWP at predawn on lowland, and 2 for LWP at midday in lowland (WPL) were detected. Among the 6 additive QTLs, the 2 for WPIU ( wpiu1 and wpiu4) and 1 for WPU ( wpu6), all donated by IRAT109, explained 5.4%, 7.9%, and 10.0% of the phenotypic variances, respectively. For IDR, 3 additive and 2 pairs of epistatic QTLs were identified. The broad heritability of LWP was low for direct selection in the field, but might be effective through marker-assisted selection.

Effects of Soil Moisture Conditions before Heading on Growth of Wheat Plants under Drought Conditions in the Ripening Stage: Insufficient Soil Moisture Conditions before Heading Render Wheat Plants More Resistant to Drought during Ripening

Plants growing on soil with insufficient moisture need deep and dense roots to avoid water stress. In crop plants, the production of dry matter during ripening of grains is critically important for grain yield. We postulated that shoot growth would be suppressed but root growth would continue under an insufficient soil moisture condition before heading, while shoot growth would be more vigorous than root growth under a sufficient soil moisture condition. We anticipated that the plants growing under an insufficient soil moisture condition before heading would produce more dry matter and grain under an insufficient soil moisture condition during ripening. In order to examine our hypotheses and to determine the fundamental conditions for improving grain yield and efficient use of irrigated water under limited irrigation, we grew wheat plants (Triticum aestivum L., cv. Ayahikari) in pots (30 cm in diameter, 150 cm in height) with insufficient soil moisture (PD-D pots) or sufficient soil moisture (PW-D pots) for six weeks before heading followed by full irrigation, and then insufficient soil moisture condition during ripening. The growth of shoots was suppressed significantly but that of roots was not before heading in PD-D plants, with a higher resultant ratio of root to shoot than in PW-D plants. The former retained a high leaf water potential and, therefore, were able to produce more dry matter and grain during soil moisture depletion during ripening as compared with the latter plants. We also obtained similar results with field-grown plants.

Influence of Irrigation Level, Growth Stages and Cultivars on Leaf Gas Exchange Characteristics in Snap Bean (Phaseolus vulgaris) under Subtropical Environment

This study was conducted to clarify the genotypic differences in diurnal variations in leaf gas exchange characteristics and the effect of irrigation levels, growth stages and cultivars on leaf water status, gas exchange characteristics and seed yields. Associations of leaf water status with photosynthetic rate in five cultivars of snap bean were also determined. Diurnally, leaf gas exchange was highest at 9:30 h, decreased but remained constant between 11:30 to 14:15 h and then decreased up to 16:15 h. Cultivars Haibushi and Ishigaki-2 displayed higher photosynthetic activity throughout the day. The cultivars having higher seed yield showed higher leaf conductance, transpiration rate and leaf vapor pressure deficit at floral bud initiation stage and higher leaf water potential and relative water content in the irrigated plot at flowering stage. The cultivars with slow development of leaf water deficit displayed higher rates of photosynthesis and vice versa. The results showed that midday hours showed large genotypic differences in leaf gas exchange characteristics with constancy of photosynthetically active radiation. Therefore, screening of snap bean cultivars can be made during midday hours for gas exchange characteristics irrespective of growth stages and irrigation levels. Cultivars maintaining higher leaf water content with increasing water deficit can be selected for higher rates of photosynthesis.

Effects of available soil volume on growth, bud fertility and water relations of young Shiraz grapevines

Effects of available soil volume (ASV) on growth, water relations and bud fertility of drip-irrigated Shiraz grapevines (Vitis vinifera) were examined during their establishment in the 2000/01 growing season under field conditions in the Goulburn Valley, Australia. Vines were planted into different size subterranean containers to create a range of confined ASV treatments (viz. 0.15, 0.4, 0.8 and 1.2 m3/vine referred to as ASV15, ASV40, ASV80 and ASV120, respectively) and compared with a deep ripped treatment where the ASV was unconfined (ASVUC). Pruning weight, trunk cross-sectional area, and daily average fractional photosynthetically active radiation interception (fdaily) increased with increasing ASV but were lowest in the ASVUC treatment. fdaily attained a maximum by mid-February 2001 in ASV15 but continued to increase in all other treatments. Water relations data showed high leaf water potential (?leaf) in ASV15 compared to the other treatments. Our results suggest that reduced growth in smaller soil volumes was not a consequence of water stress. Leaf conductance (gL) tended to be low in the ASV15 treatment in comparison with the ASVUC treatment. Increasing ASV from 0.15 to 1.2 m3/vine increased the number of bunches per vine in the following season by 32%. This increase was not due to improvement in the number of bunches per shoot, but resulted from an increased number of shoots bursting per node. By contrast, ASVUC significantly reduced bud fertility. The implications of these results for vine establishment in shallow soils are discussed.

The response of sugarcane canopy development to water stress

Water stress is a common occurrence in dryland crop production, including sugarcane production. A good understanding of how crops respond to water stress is a prerequisite for choosing the best cultivar and management practices to optimally exploit natural resources. One aspect of sugarcane growth and development that has not been investigated thoroughly is how canopy development is affected by water stress. The aim of this study was to gain a better understanding of the effect of water stress on various canopy development processes and interception of radiation. An experiment was conducted on a rainshelter facility at Mount Edgecombe, South Africa. The crop was planted and grown to four months age under optimal conditions. Subsequently, water was withheld from one half of the experiment for a period of 42 days. Soil water content for the stressed plots decreased from a field capacity of 26% at the start of drying to 15% on day 15 and a permanent wilting point of 10.5% at approximately day 40. Shoot and leaf development and interception of radiation were measured and related to soil water content, leaf water potential and stomatal conductance. Leaf senescence responded the most to drying (220% increase in leaf senescence rate as RSWC dropped from 0.7 to 0.3), followed by leaf appearance (96% decrease) and shoot senescence (113% increase for N22 and no response for NCo376). Cultivar NCo376 was able to maintain canopy development processes longer under conditions of increasing water stress than N22, at least initially. This was evidenced by lower rates of shoot senescence and leaf senescence (initially). NCo376 also maintained high stomatal conductance and leaf water potentials for longer during the drying process and at lower soil water content values than N22. The information obtained in this study should assist in simulating canopy responses in a more mechanistic way.

Marine Bioactive Substances (IPA Extract) Improve Foliar Ion Uptake and Water Stress Tolerance in Potted "Vitis vinifera" Plants.

The effect of marine bioactive substances (IPA extract) on K + and Ca 2+ fluxes and water stress tole- rance was evaluated on potted Vitis vinifera plantlets. Different foliar treatments were compared during the experiment: a control treatment (distilled water), a pure fertilizer treatment (9-5-4 at 2%), and a marine bioac - tive substances (IPA extract, supplied by BiotechMarine, Roullier Group, Pontrieux, France) treatment added to a fertilizer (0.1% solution of IPA extract with distilled water and 9-5-4 at 2%). Ion fluxes, measured by selec- tive non-invasive microelectrodes, were monitored in leaves. IPA extract significantly enhanced both potassium and calcium fluxes compared to the other treatments. Total dry weight and macro- and micro-nutrient content were subsequently measured: results showed an improved growth in IPA extract plants, together with a better capacity in accumulating macronutrients in plant organs, but not micronutrients, especially in leaves. Marine bioactive substances were finally tested for their effectiveness in promoting water stress tolerance: IP A extract was very effective in inducing waterstress tolerance, maintaining a higherleaf water potential and stomatal con- ductance during the stress period, and inducing a quick recovery in rehydrated plants.

Physiological and seed yield responses to water deficits among lentil genotypes from diverse origins

The effect of water deficits at 2 growth stages on the physiology and growth of lentil (Lens culinaris Medikus subsp. culinaris) genotypes bred/selected for 3 regions was examined in a glasshouse experiment. The water regimes imposed were: (i) a well-watered control, (ii) water withheld at flowering, from 72 to 93 days after sowing (DAS), and (iii) water withheld from podding (93 DAS) to maturity. The genotypes were a West Asian genotype released in Australia (Cassab), 2 South Asian Nepali cultivars (Khajura 2 and Simal), and 3 crossbreds between West Asian and South Asian parents (ILL 6829, ILL 7979, and ILL 7982). ILL 7979 and Simal had significantly greater total dry matter, water use, seed yield, number of pods and seeds per plant, and harvest index (HI) than the other genotypes under well-watered conditions. Water deficits reduced seed yield by up to 60% in the crossbreds and the South Asian cultivar, Simal. However, seed yield was increased by the water deficit at flowering and the water deficit at podding in the West Asian genotype, Cassab, and the South Asian genotype, Khajura 2, respectively. In the other genotypes, withholding water at flowering or podding reduced leaf area (48–55%), total dry matter (32–50%), flower production (22–55%), and number of pods and seeds (27–66%), with significantly higher flower drop and empty pods when water was withheld. The higher seed yield in Cassab and Khajura 2 when water was withheld was related to the production of more flowers and the maintenance of pod and seed set when they were re-watered after the period of water deficit. When water was withheld during flowering, the West Asian genotype Cassab and the crossbred ILL 6829 used less water and hence maintained a high leaf water potential (ψleaf), whereas ψleaf decreased earlier to lower values in the crossbred ILL 7979 and the South Asian genotypes Khajura 2 and Simal. There were no significant differences in leaf net photosynthesis (PN), or stomatal conductance (gS), among genotypes during flowering and early podding, but PN and gS were reduced by 22–38 and 19–67%, respectively, when water was withheld. The lower ψleaf in ILL 7979, Simal, and Khajura 2 induced greater osmotic adjustment (OA) during the drying cycle at flowering, whereas there was no or little OA when water was withheld at podding. Variation in physiological traits (PN, gS, OA) under both watering regimes was not directly related to seed yield, but seed number was related to seed yield under both well-watered and water-deficit conditions.

Genotypic consistency in the expression of leaf water potential in rice ( Oryza sativa L.)

Early work has shown variation in the grain yield of rice cultivars grown under water stress conditions to be associated with the plant water status, mainly with the maintenance of high leaf water potential (LWP) at flowering and grain filling stage. Considerable variation for LWP among rice varieties has been recorded. The present work was designed to investigate genotypic consistency in water potential within the plant and under canopy manipulation to vary plant water requirement. In a glasshouse experiment, with six rice genotypes, a consistent water potential gradient from stem base to leaf tip has been observed. Leaf tip water potential has been found as the minimum LWP that can be recorded at any time of stress. Genotypes with similar canopy size could maintain different levels of LWP under stress conditions. In a field experiment, with four selected lines, four canopy sizes and two canopy mixture treatments were introduced prior to the imposition of control, mild and severe water stress conditions. It was found that the line differences in LWP and relative water content (RWC) were expressed under both mild and severe stress conditions, regardless of canopy size, tiller number and whether they were mixed with another line with different capacity to maintain LWP. Although there were some differences among canopy size treatments for radiation interception in three water conditions, canopy manipulation (plant size) within a line did not affect the expression of LWP and hence genotypic variation in LWP was maintained. Under both glasshouse and field conditions, lines that maintained high LWP had larger xylem diameter and stem areas than those that had low LWP. The results indicated that the size of the vascular bundles could influence the maintenance of plant water relations under water deficit.

Ecological physiology of Pereskia guamacho, a cactus with leaves

The specialized physiology of leafless, stem-succulent cacti is relatively well understood. This is not true, however, for Pereskia (Cactaceae), the 17 species of leafy trees and shrubs that represent the earliest diverging lineages of the cacti. Here we report on the water relations and photosynthesis of Pereskia guamacho, a small tree of the semiarid scrubland of Venezuela's Caribbean coast. Sapwood-specific xylem conductivity (Ksp) is low when compared to other vessel-bearing trees of tropical dry systems, but leaf-specific xylem conductivity is relatively high due to the high Huber value afforded by P. guamacho's short shoot architecture. P. guamacho xylem is not particularly vulnerable to drought-induced cavitation, especially considering the high leaf water potentials maintained year round. This is confirmed by the lack of significant variation exhibited in Ksp between wet and dry seasons. In the rainy season, P. guamacho exhibited C3-like patterns of stomatal conductance, but during a prolonged drought we documented nocturnal stomatal opening with a concomitant accumulation of titratable acid in leaves. This suggests that P. guamacho can perform drought-induced crassulacean acid metabolism (CAM photosynthesis), although delta 13C values imply that most carbon is assimilated via the C3 pathway. P. guamacho leaves display very low stomatal densities, and maximum stomatal conductance is low whether stomata open during the day or night. We conclude that leaf performance is not limited by stem hydraulic capacity in this species, and that water use is conservative and tightly regulated at the leaf level.

Growth and physiological responses to varied environments among populations of Pinus ponderosa

We investigated population responses in physiology, morphology, and growth of mature Pinus ponderosa trees to an environmental gradient across Nebraska, USA. Ten populations from western Nebraska and eastern Wyoming were grown in three 26-year-old provenance tests from the warmest and wettest site in the east (Plattsmouth) to the intermediate site in the middle (Halsey) to the coldest and driest site in the west (Alliance). We measured leaf morphology and water potential in 1995 and 1996, carbon isotope discrimination from foliage in 1993 to 1996 and from tree-ring cellulose for 1991, 1993, 1995, and 1996, and height and diameter at breast height (dbh) in 1994. We found that populations responded significantly to the environmental gradient in all traits. Trees grew significantly larger at the eastern site than at the other locations. The trend in height and dbh growth was Plattsmouth > Halsey > Alliance. Variation among the locations in needle length and carbon isotope discrimination in both foliage and cellulose followed the same pattern as growth. However, variation in xylem water potential differed from the trend in tree growth. Trees in Halsey had higher leaf water potential than trees at other sites. Populations differed significantly in morphological characteristics (i.e. specific leaf area and leaf length, F > 3.3, P < 0.01) and growth (i.e. height and dbh, F > 3.8, P < 0.001), whereas differences in physiological traits (i.e. leaf water potential, carbon isotope composition, and foliar nitrogen, F < 1.9, P > 0.05) were lacking among populations. We conclude that physiological plasticity is the primary mechanism that allows P. ponderosa to grow in various environments. Population differentiations in growth and morphology are the results of a long-term response of these populations to natural selection in their original habitat.

Water uptake of soybean ( Glycine max L. Merr.) during exposure to O 2 deficiency and field level CO 2 concentration in the root zone

This study determined whether the field level concentration of root zone CO 2 affects transpiration rate and root water transport in soybean ( Glycine max L. Merr.). In an upland field converted from a paddy field, topsoil CO 2 during the cropping season rose to 8 kPa of partial pressure after rainfall, whereas O 2 dropped only to a minimum of 7 kPa. An elevated root zone CO 2 pressure of 6 kPa significantly reduced transpiration rate. Although the transpiration rate of soybean plants exposed to hypoxia of 1.5 kPa O 2 alone was reduced by 52% of the aerated plant, the rate was more decreased by 33 by adding CO 2 gas to low root zone O 2. Similarly, the elevated root zone CO 2 significantly reduced hydraulic conductance of roots. The low transpiration rate with a high leaf water potential and low leaf greenness in the elevated root zone CO 2 indicated that stomatal closure in high root zone CO 2 may also occur irrespective of leaf water status and be involved in depressed nitrogen supply to a shoot. The results indicate that root zone CO 2 at the field level is a growth inhibitor of waterlogged soybean through decreasing water uptake and/or stomatal aperture.

Arbuscular mycorrhizal fungi influence growth, osmotic adjustment and photosynthesis of citrus under well-watered and water stress conditions

The influence of arbuscular mycorrhizal (AM) fungus Glomus versiforme on plant growth, osmotic adjustment and photosynthesis of tangerine (Citrus tangerine) were studied in potted culture under well-watered and water stress conditions. Seven-day-old seedlings of tangerine were transferred to pots containing Glomus versiforme or non-AMF. After 97 days, half of the seedlings were subject to water stress and the rest were well-watered for 80 days. AM colonization significantly stimulated plant growth and biomass regardless of water status. The soluble sugar of leaves and roots, the soluble starch of leaves, the total non-structural carbohydrates (NSC) of leaves and roots, and the Mg(2+) of leaves were higher in AM seedlings than those in corresponding non-AM seedlings. The levels of K(+) and Ca(2+) in leaves and roots were higher in AM seedlings than those in non-AM seedlings, but differences were only significant under water stress conditions. Moreover, AM colonization increased the distributed proportions of soluble sugar and NSC to roots. However, the proline was lower in AM seedlings compared with that in non-AM seedlings. AM seedlings had higher leaf water potential (Psi), transpiration rates (E), photosynthetic rates (Pn), stomatal conductance (g(s)), relative water content (RWC), and lower leaf temperature (Lt) than corresponding non-AM seedlings. This research also suggested that AM colonization improved the osmotic adjustment originating not from proline but from NSC, K(+), Ca(2+) and Mg(2+), resulting in the enhancement of drought tolerance.

The Effects of Elevated CO2 and Its Interaction with Water Stress on a C4 Pasture Species (Blepharis linariifolia) Native to Sudan

SUMMARY A doubling of the pre-industrial atmospheric CO2 concentration (∼280 ppmv) is expected before the end of this century, if the current rate of growth in the annual emission of fossil carbon is maintained. The effects of elevated CO2 concentrations on native tropical species has received little attention to date. In this study the effects of elevated CO2, under both well-watered and water-stressed condition, on a C4 pasture species (Blepharis linariifolia (dicot) native to the western part of Sudan was investigated. Elevated CO2reduced whole plant transpiration, particularly for juvenile plants. This resulted in wetter soils and higher leaf water potentials under elevated CO2 in both well-watered and water-stressed conditions. Late in the growth cycle, elevated CO2 had less effect on whole plant transpiration as there was a significant increase of both leaf area and leaf temperature. Assimilation rates and dry weight were enhanced by CO2 enrichment under both water regimes. The results support the hypothesis that CO2-induced growth enhancements in C4 species occurs as a result of direct stimulation of photosynthesis as well as improved water relations. Carbon dioxide enrichment also hastened flowering and increased the inflorescence dry weight of B. linariifolia particularly under well-watered conditions. The results suggest a significant increase in yield and persistence of B. linariifolia in it's natural environment as atmospheric CO2 concentrations increase.

Rosa rugosa Thunb. ex Murray

Rosaceae, Rosoideae, Rosa L.; subgenus Eurosa Focke; section Cinnamomeae (DC.) Rehder. Japanese Rose. Rhizomatous multi-stemmed erect deciduous shrub, strongly suckering, mature clones forming impenetrable thickets. Rhizomes woody, with orange-brown cortex and triangulate scale leaves. Rhizome branches and suckers emerge from axillary buds subtended by scale leaves. In addition, suckers may arise from buds on the roots. Stems erect, sometimes arching, to 1.5( − 2) m, often much branched, tomentose when young, densely prickly. Cortex light yellowish brown. Prickles subulate, slender and straight, of all sizes down to acicles. Larger prickles tomentose, at least near the base, and usually glabrous in the apical part. Leaves alternate with (5–)7–9 leaflets contiguous on the rachis. Leaflets nearly equally sized, 2–5 × 1.5–3 cm, leathery and robust, widely elliptical, acute, with broadly cuneate or rounded base. Adaxial side dark green, conspicuously bullate or rugose, rather shiny. Abaxial side green-grey, tomentose to pubescent, with sessile pale glands, and with reticulate nervation. Leaf margin bluntly and simply crenate-serrate, involute, edge of teeth often deflexed. Petiole and rachis densely pubescent, and with many unequal subulate prickles. Stipules pale green, densely pubescent, 2.5 × 1–1.5 cm, divergent, the free part broadly ovate or deltoid. Flowers usually solitary or few together, 6–9 cm across, fragrant, nectarless. Sepals 2–3 cm, entire, with a broad, expanded tip, appressedly pubescent, aciculate and glandular (sometimes with stipitate glands), erect on the hip, persistent. Petals five, bright purplish-pink, sometimes white ( R. rugosa f. alba (Ware) Rehder). Stamens 200– 250 per flower, and styles often more than hundred. Styles pilose; stigmas in a large, domed head, sunk in the narrow, concave disc; disc 2.5–4 mm across; orifice large, at least half the diameter of the disc. A hypanthium (hip) encloses the achenes. It is depressed globose, 1.5–2 cm long and 2–2.5 cm wide, with a distinct neck below the sepals, dull green to orange when unripe, becoming glossy and brilliant red when ripe, most often smooth. Pedicel of the same length as the hip, tomentose, often with gland-tipped acicles, erect in flower, curved in fruit so that the hip points downwards. Achenes with a woody-bony pericarp enclosing the seed. Achenes broadly ovoid, obtusely angular, 4.0–6.0 mm long and 2.0–2.6 mm wide and 1.8–2.2 mm thick, with a distinct suture on both ventral and dorsal sides, hilum basal. Achene surface more or less lustrous, orange-brown. Mean seed (achene) mass is 6.6 mg. The albumen is oily. No subspecies of R. rugosa have been recognized in the British Isles. Despite the many cultivated varieties of the species, mainly forms close to the wild type are seen naturalized. However, naturalized clones may be confused with R. × hollandica (syn. R. × kamtchatica ). This taxon differs morphologically from R. rugosa by having soft-textured, dull leaflets, without prominent veins, less prickly stems, conspicuously glandular sepals, and smaller flowers and hips (Rutherford 1990). Taxonomic position: Rosa L., subgenus Eurosa Focke (syn. subgen. Rosa ), section Cinnamomeae (DC) Rehder (syn. sect. Rosa ; sect. Cassiorhodon Dumort.). Section Cinnamomeae is central in the subgenus Eurosa , which contains all but four of the approximately 150 Rosa species in the world. The diploid species of this section, including R. rugosa , are probably basal in the reticulate evolutionary series from diploid species to irregular polyploid species within this genus (Erlanson 1938; Grossi et al . 1998). Originally introduced as a garden and landscape ornamental, and widely used as rootstock for other cultivated roses, R. rugosa can be found in many different cultivated settings. Now a well-established naturalized alien occurring scattered throughout Britain and invasive in fixed dunes and other coastal habitats.

Correlation analysis and QTL identification for canopy temperature, leaf water potential and spikelet fertility in rice under contrasting moisture regimes

Canopy temperature (CT), leaf water potential (LWP) and spikelet fertility (SF) of a set of RILs (F9) from the cross between Zhenshan97B and IRAT109 were investigated under two soil moisture regimes in a drought screen facility. In water stress condition, CT was negatively correlated with SF (r = −0.2867) and LWP (r = −0.2740), and LWP was positively associated with SF (r = 0.1696). These results indicated that the plant with high drought tolerant ability could maintain higher LWP and lower CT, leading to higher SF. A total of 44 main effect QTLs were associated with CT, LWP and SF. The accumulated contributions of QTLs for CT, LWP and SF were 87.85%, 15.06%, 79.46% under well water condition and 72.61%, 87.68%, 33.29% under stress condition, respectively. Totally 45 pairs of digenic interactions were detected. The accumulated contribution of digenic epistasis on CT, LWP and SF were 55.69%, 47.15%, 48.15% under well water condition and 53.44%, 57.94%, 54.62% under water stress condition. Compared with other drought tolerance QTL mapping researches in rice, 19 main effect QTLs were found to be located at the same or closely conjoint regions.