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.

小叶榕气生根气体交换特征及影响因子研究

用LI-6400XT便携式光合仪测定了小叶榕(Ficus microcarpa L. f.)气生根的气体交换特征。结果表明气生根具有呼吸、蒸腾作用和空气吸湿作用。影响气生根呼吸作用的因素为年龄>空气温度>光强>相对湿度;影响蒸腾作用的因素为年龄>相对湿度>空气温度>光照。年龄小的气生根的呼吸和蒸腾作用较强,年龄大的尤其是木质化程度较高的气生根的呼吸作用较小,水分的释放(蒸腾作用)转变为水分的吸收(吸湿作用)。年龄小的气生根的CO2交换率与温度呈线性关系,温度越高,CO2交换率越大,呼吸越强;H2O交换率与相对湿度呈线性关系,相对湿度越大,H2O交换率越小,蒸腾越弱;年龄大的成熟气生根的H2O交换率与空气相对湿度呈线性关系,相对湿度越大,H2O交换率越小,蒸腾越小。     

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.     

The impact of salt stress on the water status of barley plants is partially mitigated by elevated CO2

With the changing climate, plants will be facing increasingly harsh environmental conditions marked by elevated salinity in the soils and elevated concentrations of CO₂ in the atmosphere. These two factors have opposite effects on water status in plants. Therefore, our objective was to determine the interaction between these two factors and to determine whether elevated [CO₂] might alleviate the adverse effects of salt stress on water status in two barley cultivars, Alpha and Iranis, by studying their relative water content and their water potential and its components, transpiration rate, hydraulic conductance, and water use efficiency. Both cultivars maintained their water status under salt stress, increasing water use efficiency and conserving a high relative water content by (1) reducing water potential via passive dehydration and active osmotic adjustment and (2) decreasing transpiration through stomatal closure and reducing hydraulic conductance. Iranis showed a greater capacity to achieve osmotic adjustment than Alpha. Under the combined conditions of salt-stress and elevated [CO₂], both cultivars (1) achieved osmotic adjustment to a greater extent than at ambient [CO₂], likely due to elevated rates of photosynthesis, and (2) decreased passive dehydration by stomatal closure, thereby maintaining a greater turgor potential, relative water content, and water use efficiency. Therefore, we found an interaction between salt stress and elevated [CO₂] with regard to water status in plants and found that elevated [CO₂] is associated with improved water status of salt-stressed barley plants.     

Demonstration of the root surface electrogenic ion pump activity revealed from the seasonal inversion in the phase relation between electro-radicogram and the diurnal oscillation of air temperature in a field tree (Diospyros kaki)

Re-examination of the electro-radicogram (ERG) obtained during past 10 years research (Masaki and Okamoto in Trees (Berl) 21:433–442, 2007) enabled us to discriminate the excess activity of the electrogenic ion pump in the root surface cell membrane over that of the xylem pump during most of the foliate phase. The trans-root electric potential (TRP) is defined as the difference between V _ps (electric potential difference between symplast and bulk water phase surrounding the root) and V _px (electric potential difference between symplast and xylem apoplast). The diurnal oscillation of TRP followed that of the air temperature and/or light intensity with a delay of several hours during defoliate phase. This means the superiority of the electrogenic activity of the xylem pump over that of the root surface pump. However, after leaf expansion, TRP began to oscillate inversely with the temperature change with a short delay, indicating the superiority of the electrogenic activity of the surface ion pump over that of the xylem pump. An experimental lumbering of the surroundings of the kaki tree in foliate phase prominently increased the ERG amplitude, keeping the inverted phase relation, with the increase in transpiration caused by the increased illumination. An incidental sudden fall of the temperature and illumination caused an inverse reaction.     

遮光处理对西葫芦幼苗形态特征及光合生理特性的影响

研究了不同遮光处理对西葫芦幼苗形态及光合生理特性的影响.结果表明,在60%透光率条件下,西葫芦幼苗具有较高的相对生长率、净光合速率、气孔导度、蒸腾速率、单叶水分利用效率、饱和蒸汽压、表观量子效率和叶绿素含量,而胞间CO₂浓度较低;西葫芦幼苗具有较高的光饱和点(1 125 μmol·m^-2·s^-1)、较低的光补偿点(15.2 μmol·m^-2·s^-1).弱光下西葫芦幼苗较耐低浓度CO₂,而强光下的幼苗较耐高浓度CO₂.60%透光率下西葫芦幼苗叶片丙二醛和脯氨酸含量最低,而过氧化物酶和过氧化氢酶活性则最高.     

拟单性木兰不同季节断根和剪枝后蒸腾和光合特性的变化

在2005年春季、夏季和秋季,对10a生拟单性木兰(Parakmeriaomeiensis)进行断根和剪枝处理,模拟移栽,用LICOR-6400测定了植株叶片的蒸腾速率、光合速率等生理指标,探讨这些生理指标对不同季节移栽成活率的影响。结果表明,春季处理后叶片能迅速关闭部分气孔,蒸腾速率和光合速率都减小,两者最低时约为对照的60%,生理机能的减弱有利于维持地上、地下部分的平衡,因而最有利于植株成活。夏季处理后叶片气孔导度显著增加,光合速率和蒸腾速率也随之增大,最高时约为对照的2倍左右,此时,若主要依靠剪枝来降低水分消耗,很难保证水分代谢平衡,移栽成活率低。秋季处理后植株叶片气孔导度高于对照,光合速率和蒸腾速率也增加,但增加幅度相对夏季较小,前期最高约增加40%,此时移栽可以通过适当的剪枝和增加土壤水分含量等措施提高成活率。可见,与水分相关的生理机能的调节机制,决定了移栽后的成活水平,即处理后能迅速调节自身生理机能、减少水分消耗的植株,成活率就高,反之就低。     

Analysis of Growth and Water Relations of Tomato Fruits in Relation to Air Vapor Pressure Deficit and Plant Fruit Load

The influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions. The contributions of phloem, xylem and transpiration fluxes to the fruit volume increase were estimated at an hourly scale from the growth curves of intact, heat-girdled and detached fruits, measured using displacement transducers. High VPD conditions reduced the xylem influx and increased the fruit transpiration, but hardly affected the phloem influx. Net water accumulation and growth rate were reduced, and a xylem efflux even occurred during the warmest and driest hours of the day. Changes in xylem flux could be explained by variations in the gradient of water potential between stem and fruit, due to changes in stem water potential. Misting reduced air VPD and alleviated the reduction in fruit volume increase through an increase in xylem influx and a decrease in fruit transpiration. Under low fruit load, the competition for assimilates being likely reduced, the phloem flux to fruits increased, similarly to the xylem and transpiration fluxes, without any changes in the fruit water potential. However, different diurnal dynamics among treatments assume variable contributions of turgor and osmotic pressure in F3 and F6 fruits, and hypothetical short-term variations in the water potential gradient between stem and fruit, preventing xylem efflux in F3 fruits.     

Genotypic difference in salinity tolerance in quinoa is determined by differential control of xylem Na loading and stomatal density

Quinoa is regarded as a highly salt tolerant halophyte crop, of great potential for cultivation on saline areas around the world. Fourteen quinoa genotypes of different geographical origin, differing in salinity tolerance, were grown under greenhouse conditions. Salinity treatment started on 10 day old seedlings. Six weeks after the treatment commenced, leaf sap Na and K content and osmolality, stomatal density, chlorophyll fluorescence characteristics, and xylem sap Na and K composition were measured. Responses to salinity differed greatly among the varieties. All cultivars had substantially increased K⁺ concentrations in the leaf sap, but the most tolerant cultivars had lower xylem Na⁺ content at the time of sampling. Most tolerant cultivars had lowest leaf sap osmolality. All varieties reduced stomata density when grown under saline conditions. All varieties clustered into two groups (includers and excluders) depending on their strategy of handling Na⁺ under saline conditions. Under control (non-saline) conditions, a strong positive correlation was observed between salinity tolerance and plants ability to accumulate Na⁺ in the shoot. Increased leaf sap K⁺, controlled Na⁺ loading to the xylem, and reduced stomata density are important physiological traits contributing to genotypic differences in salinity tolerance in quinoa, a halophyte species from Chenopodium family.