贵州葡萄属野生种光合特性的研究

为掌握野生葡萄种间和种内不同单株间的光合特性差异,利用Li-6400便携式光合测定系统测定了7种野生葡萄25个单株的光合参数.结果表明:野生葡萄种间光合特性差异明显,美丽葡萄净光合速率最高,其次是刺葡萄,腺枝葡萄的净光合速率最低.野生葡萄种内不同单株间的光合指标多样性丰富,单株间光合特性差异最大的是葛藟葡萄;种内不同单株间原产地气候条件相似,其光合特性差异较小,而原产地气候差异大的单株光合特性差异也大;野生葡萄的光合速率调控机制多样,非气孔因素调控在野生葡萄种群内非常普遍.     

Do low standing biomass and leaf area index of sub-tropical coastal dunes ensure that plants have an adequate supply of water?

Water status in relation to standing biomass and leaf area indices (LAI) of the subtropical foredune species Arctotheca populifolia, Ipomoea pes-caprae and Scaevola plumieri were studied in the Eastern Cape, South Africa. The plants showed little evidence of water stress, never developing leaf water potentials more negative than –1.55 MPa, a value which is typical of mesophytes rather than xerophytes. The plants showed no seasonal changes in osmotic potential, an indication that they did not need to osmoregulate, nor were there significant alterations in tissue elasticity. Turgor potential for the most part remained positive throughout the day or recovered positive values at night, a condition suitable for the maintenance of growth that may be essential to cope with sand accretion. All three species show relatively high transpiration rates and only I. pes-caprae showed any evidence of strong limitations of transpiration rate through reductions in midday stomatal conductance. All three species had relatively high instantaneous water use efficiencies as a result of high assimilation rates rather than low transpiration rates. Simple water budgets, accounting for losses by transpiration and inputs from rainfall, suggest that the water stored in the dune sands is sufficient to meet the requirements of the plants, although water budgets calculated for I. pes-caprae suggest that this species may on occasion be water limited. The results suggest that it is the low biomass and LAI that lead to these favourable water relations.     

Physiological responses to salt stress in young umbu plants

Soil salinity affects plant growth and development due to harmful ion effects and water stress caused by reduced osmotic potential in the soil solution. In order to evaluate the effects of salt stress in young umbu plants, research was performed in green house conditions at the Laboratory of Plant Physiology at Federal Rural University of Pernambuco, Brazil. Growth, stomatal behaviour, water relations, and both inorganic and organic solutes were studied aiming for a better understanding of the responses of umbu plants to increasing salinity. Plants were grown in washed sand with Hoagland and Arnon nutrient solution with 0, 25, 50, 75, and 100 mM NaCl. Growth, leaf water potential, transpiration, and diffusive resistance were evaluated. Na⁺, K⁺, Cl⁻, soluble carbohydrates, and free amino acid contents were measured in several plant organs. Most variables were affected with salinity above 50 mM NaCl showing decreases in: number of leaves, plant height, stems diameter, and dry masses, and increases in root-to-shoot ratio. Reductions in ψ_pd were observed in plants grown under 75 and 100 mM NaCl. All salt levels above zero increased Na⁺ and Cl⁻ contents in leaves. However, K⁺ content was not affected. Na⁺ and Cl⁻ in stems and roots reached saturation in treatments above 50 mM NaCl. Organic solute accumulation in response to salt stress was not observed in umbu plants. These results suggest that umbu plants tolerate salt levels up to 50 mM NaCl without showing significant physio-morphological alterations.     

Na+ accumulation in root symplast of sunflower plants exposed to moderate salinity is transpiration-dependent

Twenty-day-old sunflower plants (Helianthus annuus L. cv Sun-Gro 380) grown hydroponically under controlled conditions were used to study the effect of transpiration on Na(+) compartmentalization in roots. The plants were exposed to low Na(+) concentrations (25mM NaCl) and different environmental humidity conditions over a short time period (8.5h). Under these conditions, Na(+) was accumulated primarily in the root, but only the Na(+) accumulated in the root symplast was dependent on transpiration, while the Na(+) accumulated in both the shoot and the root apoplast exhibited a low transpiration dependence. Moreover, Na(+) content in the root apoplast was reached quickly (0.25h) and increased little with time. These results suggest that, in sunflower plants under moderate salinity conditions, Na(+) uptake in the root symplast is mediated by a transport system whose activity is enhanced by transpiration.     

Spatial variations in xylem sap flux density in evergreen oak trees with radial-porous wood: comparisons with anatomical observations

To estimate whole-tree water use when employing sap flow measurements, integration of the sap flux density (F _d) over the sapwood area is needed. Accordingly, it is necessary to obtain information on the characteristics of stem water transportation such as spatial variations in F _d and the active xylem area in the stem cross-section. Although evergreen oak trees with radial-porous wood represent a major component of secondary forests in western Japan, detailed information on their stem water transportation characteristics remains unclear. In the present study, we used the heat dissipation method (Granier method) to conduct measurements of azimuthal and radial variations in the F _d of Quercus glauca Thunb. ex Murray, a representative evergreen broad-leaved tree in western Japan. Further, by analyzing the anatomy of the xylem structure, we examined why F _d varies spatially in the stem cross-section. By using a dye solution injected into a radial hole bored into the tree trunk, we confirmed that the entire stem is hydroactive. We also compared the spatial variations in F _d and water conductivity per xylem area (K _s) which were estimated by using the observed vessel diameters and their density over the stem cross-section and Hagen–Poiseuille’s law. Azimuthal and radial variations in F _d reached about 60 and 50% of the maximum values, respectively, and could be explained by spatial variation in K _s. As a result, we obtained statistical parameters describing the spatial variation in F _d in Q. glauca and determined that whole-tree water use estimated from measurements in one direction had at most ±20% potential errors for studied trees.     

Antitranspirant functions of stem periderms and their influence on corticular photosynthesis under drought stress

Transpiration and photosynthesis of current-year stems and adult leaves of different deciduous tree species were investigated to estimate their probable influence on carbon balance. Peridermal transpiration of young stems was found to be rather small as compared to the transpiration of leaves (stem/leaf like 1/5–1/20). A characteristic that was mainly attributable to the lower peridermal conductance to water and CO₂, which made up only 8–28% of stomatal conductance. Water vapour conductance was significantly lower in stems, but also non-responsive to PAR, which led to a comparatively higher water use efficiency (WUE, ratio assimilation/transpiration). Thus, although corticular photosynthesis reached only 11–37% of leaf photosynthesis, it may be a means of improving the carbon balance of stems under limited water availability. The influence of drought stress on primary photosynthetic reactions was also studied. Under simulated drought conditions the drying time needed to provoke a 50% reduction (t ₅₀) in dark- and light-adapted PSII efficiency (Fv/Fm, ΔF/Fm′) was up to ten times higher in stems than in leaves. Nevertheless, up to a relative water deficit (RWD) of around 40–50% dark-adapted PSII efficiency of leaves and stems was rather insensitive to dehydration, showing that the efficiency of open PS II reaction centres is not impaired. Thus, it may be concluded that in stems as well as in leaves the primary site of drought damage is at the level of dark enzyme reactions and not within PSII. However, enduring severe drought caused photoinhibitory damage to the photosynthetic apparatus of leaves and stems; thereby RWD₅₀ values (= RWD needed to provoke a 50% reduction in Fv/Fm ad ΔF/Fm′) were comparably lower in stems as compared to leaves, indicating a possibly higher drought sensitivity of the cortex chlorenchyma.     

引种台湾桤木的水分生理特性

台湾桤木(Alnusformosana)原产台湾,是台湾地区重要的先锋造林树种和林地培肥树种。水分是限制植物地理分布和决定植物引种能否成功的重要因子之一。采用Li-6400光合测定系统对引种两年生台湾桤木苗木的水分生理特性进行了研究,结果表明:(1)在整个生长期,叶片蒸腾速率日变化均表现为宽大的单峰型曲线,以13∶00～15∶00时左右蒸腾速率最高,不同部位叶片在不同生长期的峰值有所不同,属非蒸腾午休型植物。气孔导度日变化有单峰型和双峰型2种变化曲线;(2)蒸腾速率季节变化表现为单峰曲线,以7月为最高,整个生长期叶片日均蒸腾速率为3.25mmol·m-2·s-1,表现出高光合、强蒸腾的生理特点;(3)水分利用效率日变化与光合速率日变化相似,有单峰曲线和双峰曲线2种类型,与气孔导度的日变化有显著相关性。在整个生长期,以6月、7月叶片水分利用效率为最低,8月为最高;(4)在影响水分利用效率季节变化的生理生态因子中,以温度、光合有效辐射、气孔导度和相对湿度4个因子的直接作用为最大。     

Effects of flooding and drought on stomatal activity, transpiration, photosynthesis, water potential and water channel activity in strawberry stolons and leaves

Transpiration, xylem water potential and water channel activity were studied in developing stolons and leaves of strawberry (Fragaria × ananassa Duch.) subjected to drought or flooding, together with morphological studies of their stomata and other surface structures. Stolons had 0.12 stomata mm^–2 and a transpiration rate of 0.6 mmol H₂O m^–2 s^–1, while the leaves had 300 stomata mm^–2 and a transpiration rate of 5.6 mmol H₂O m^–2 s^–1. Midday water potentials of stolons were always less negative than in leaves enabling nutrient ion and water transport via or to the strawberry stolons. Drought stress, but not flooding, decreased stolon and leaf water potential from –0.7 to –1 MPa and from –1 to –2 MPa, respectively, with a concomitant reduction in stomatal conductance from 75 to 30 mmol H₂O m^–2 s^–1. However, leaf water potentials remained unchanged after flooding. Similarly, membrane vesicles derived from stolons of flooded strawberry plants showed no change in water channel activity. In these stolons, turgor may be preserved by maintaining root pressure, an electrochemical and ion gradient and xylem differentiation, assuming water channels remain open. By contrast, water channel activity was reduced in stolons of drought stressed strawberry plants. In every case, the effect of flooding on water relations of strawberry stolons and leaves was less pronounced than that of drought which cannot be explained by increased ABA. Stomatal closure under drought could be attributed to increased delivery of ABA from roots to the leaves. However, stomata closed more rapidly in leaves of flooded strawberry despite ABA delivery from the roots in the xylem to the leaves being strongly depressed. This stomatal closure under flooding may be due to release of stress ethylene. In the relative absence of stomata from the stolons, cellular (apoplastic) water transport in strawberry stolons was primarily driven by water channel activity with a gradient from the tip of the stolon to the base, concomitant with xylem differentiation and decreased water transport potential from the stolon tip to its base. Reduced water potential in the stolons under drought are discussed with respect to reduced putative water channel activity.     

Stomatal conductance and transpiration of the two faces of Acacia phyllodes

Summary The daily course of stomatal conductance and transpiration was monitored on each separate face of vertical phyllodes of various acacias. The selected phyllodes had a north-south orientation so that one side faced eastwards and the other westwards. The principal measurements were made on Acacia longifolia and A. melanoxylon in Portugal in late summer and autumn, and additional measurements were made on A. ligulata and A. melanoxylon in Australia. In Portugal, irrespective of soil moisture status, conductance showed on early morning maximum with a subsequent gradual decline and sometimes a subsidiary peak in the late afternoon. Maximum conductances appeared to be a function of soil moisture status, whereas the decline in conductance in the late morning and afternoon was correlated with changes in phyllode-to-air vapour pressure deficits rather than changes in phyllode water status. The relationship of transpiration to phyllode water potential did not appear to be influenced by soil moisture status, although transpiration was less in drier soils and in the afternoons, this latter factor contributing to a marked hysteresis in the relationship. The opposing faces of the phyllodes exhibited a high degree of synchrony, showing parallel stomatal opening and closing, despite their large differences in irradiance. Stomatal conductance tended to be higher on the eastern faces in the morning and lower in the afternoon. In A. longifolia the daily average of relative conductance was much the same for both faces, but in A. melanoxylon that of the eastern face was higher and was retained even when the normal orientation of the phyllodes was reversed by turning them through 180°. Synchrony must be achieved by the stomata of both sides responding to common environmental or endogenous signals which are perceived by both surfaces with equal sensitivity.     

Variability in rate of human perspiration in european populations

1. 1. In the consideration of ergonomic tasks the attempt is often made to combine the results of physiological research on human perspiration with technical factors such as the transfer of moisture through specific materials.

2. 2. The result of such attempts is often unsatisfactory due to the fact that the percentiles and frequency distribution of perspiration rates are often unknown or not taken into consideration.

3. 3. Further, the interaction between the human user and a particular environmental situation remains unaccounted for.

4. 4. This interaction can produce totally different reactions in both the user and the materials depending upon the specifics of the situation.

5. 5. In response to this deficit we tested 738 persons from various areas in Europe under laboratory conditions to determine perspiration rates and their statistical distribution.

6. 6. Despite the climatic differences existing within Europe, a uniform picture characterized by an extremely skewed distribution resulted.

7. 7. However, it was also shown that these values, including their statistical distribution and percentile ranks, can be strongly influenced by specific external conditions.

8. 8. In the design of human working and living environments it is necessary to examine the situation with research subjects whose perspiration rates are known in order to gain insight into the interactions existing between the human user and the material or technical aspects of the particular environment in question.