ALA-dehydratase activity inZea mays L.

Summary The presence and activity of -aminolevulinic acid dehydratase (ALA-D, E.C.4.2.1.24) inZea mays L. was studied. Seedlings of several inbred lines and their hybrids were employed as enzyme source, and enzyme activity and the kinetic parameters (V_max and K_M) determined. The wide variations of the enzyme activity and kinetic parameters found in the tested lines support the hypothesis that ALA-D varies in concentration and isoenzyme distribution. Enzyme activity was greater in some hybrids than in their parent lines. As the same hybrids correspond to varieties appreciated for their high productivity and good morphological characteristics it is suggested that ALA-D activity levels could be adopted as an auxiliary parameter for establishing heterosis.     

On the dependence of salt tolerance of beans (Phaseolus vulgaris L.) on soil water matric potentials

Summary Bean plants (Kora cv) were grown in potted soil artificially salinized by adding NaCl and CaCl₂ to the irrigation water to obtain an electrical conductivity of the soil saturation extract (EC_e) thirty days after emergence of 0.1, 0.3, 0.5 and 0.7 S/m at 25°C and a sodium adsorption ratio (SAR) of 4 (mmol/l)². Thereafter, plants were irrigated when soil water matric potential (_M) was in the range of –20 to –30 kPa (wet treatment) and when _M was in the range of –40 to –60 kPa (dry treatment).Transpiration rates (Tr) and leaf extension rates (LER) per plant or per unit of leaf area were decreased by increasing soil salinity and by decreasing soil moisture. However, a given decrement of _M produced a considerable larger decrement in Tr of LER than an equivalent decrement of soil water osmotic potential (₀). Absolute yields of green pods under wet treatments were from twice to one and a half time as large under the wet than under the dry treatment at equivalent values of ₀. Relative yields were reduced by 25% when EC_e were about 0.5 S/m and 0.7 S/m in the dry and wet treatment respectively. Salt tolerance data of crops may not have a quantitative interest when soil irrigation regimes under which they were obtained are not specified.     

Drought susceptibility of two tomato (Lycopersicum esculentum) varieties

The effects of three levels of moisture under greenhouse conditions and also identical moisture levels under field conditions, on the growth yield and water relations of two tomato cultivars, Fireball and Ife I, were investigated. The objective was to ascertain the drought susceptibility of these two tomato cultivars. The cultivar, Ife I, was more drought susceptible than Fireball and the drought susceptibility increased with the level of soil water stress. The drought tolerance, of Fireball is attributed to a lower leaf area, better root system development in terms of average root length and rooting depth, and a higher leaf water potential. The higher leaf stomatal resistances of Fireball variety suggest an inbuilt mechanism to regulate water vapour flow in times of stress.     

木本植物气孔对不同污染类型的反应

植物气孔扩散阻力与环境中颗粒物的污染有密切关系,由此得出的生理指标可用以指示大气中飘尘污染的程度,并筛选对污染物抗性大和消耗水分少的植物种。测定结果表明：不同污染类型区的植物气孔扩散阻力的大小顺序因地区而不同,在天津为冶炼厂(重工业污染区)>水上公园(游览区)>劝业场(商业集中区)>化工厂外(化工污染区) >盘山(清洁区);而在北京是卧佛寺一樱桃沟(游览区)>东单(交通频繁区)>首钢(重工业污染区)。之所以产生上述差异的原因除了京津两市的工业污染外,还与某些人为活动有关,如重工业污染区飘尘污染严重,植物气孔扩散阻力增大,但首钢经常用水冲洗叶子,其阻力值反小;公园和商业交通区是游人熙攘地点,极易引起地面扬尘,其气孔阻力反映了相似的结果。 研究结果还阐明：随着飘尘的增加,植物气孔扩散阻力增大,蒸腾率速相应的变小。     

大田玉米、高粱、芝麻、豇豆叶片水势、蒸腾速率、气孔阻力对环境因素的反应

本文研究了田间生长的玉米、高梁、芝麻、豇豆在不同土壤供水条件下,叶水势、气孔阻力、蒸腾速率日变化及其与环境因素的关系。结果表明,四种作物气孔开闭与光强密切相关:夜间气孔关闭,rs高;白天气孔开放,rs低。ψ_(WL)、TR与环境因素(气温、RH、ψ_(WV)、光强等)密切相关,它们之间的相关系数(在0.05和0.01水平)显著。四种作物ψ_(WL)日节奏为“正弦曲线”状,13:00—15:00小时ψ_(WL)最低,黎明前最高。中午ψ_(WV)和土壤含水量愈低。ψ_(ML)愈低。四种作物TR在早晨逐斩增高,13:00—15:00小时最强;傍晚前又降低;夜间TR最低。干旱植株ψ_(WL)、TR低于灌水植株,而rs高于灌水植株。     

油蒿(Artemisia ordosica)的蒸腾作用及其群落的水分状况

 本文对比研究了处于不同生境的油蒿群落中油蒿的水分生理生态特性。结果表明：(1)半固定沙丘的油蒿比固定沙丘油蒿长势好,前者的生物量约为后者的4—5倍;(2)半固定沙丘土壤导水率是固定沙丘的10倍左右;(3)叶温与气温之差和水势能较好地反映油蒿的生长状况,而蒸腾速率与扩散阻力反映不十分敏感。     

Two ecologically distinct subspecies ofHypochaeris radicata L.

Summary Two subspecies ofHypochaeris radicata were compared with respect to differences in drought tolerance. The soil water content of the sites ofH. radicata ssp. ericetorum Van Soest was always lower than that ofH. radicata L. ssp.radicata throughout a great part of the growing season. Two water culture experiments were conducted at different light intensities. Water stress was induced by addition of NaCl to the culture solution. Both subspecies accumulated free proline andmyo-inositol during water stress. The results are compared with those of field observations. In all experiments with stress application ssp.radicata showed heavier wilting symptoms than ssp.ericetorum, concomittantly with a lower osmotic potential of the cell sap, a higher percentage of dry-weight and irreversible desiccation of older leaves in some experiments after stress application. The observed effects are attributed to the higher transpiration rate maintained by ssp.radicata during stress. Free proline accumulation depended on the severity of the internal stress rather than on the applied level of external stress. At low light intensity the stress resulted in a significantly higher proline accumulation in ssp.ericetorum than in ssp.radicata whereas at high light intensity this was the reverse. No differences inmyo-inositol accumulation were observed in the water culture experiments. Since ssp.ericetorum occurs in a nitrogen poor environment, the effect of nitrogen deprivation on accumulation of free proline andmyo-inositol was investigated. Both subspecies tended to accumulate less proline under such conditions especially ssp.radicata. Accumulation ofmyo-inositol was not favoured by nitrogen deprivation in the water culture experiments. Neither of the subspecies accumulated proline during the sampling period in the field presumably as a result of the wet summer. Leaves of whole plants collected in the field and subsequently subjected to water deprivation showed a high capacity to accumulate free proline. The level ofmyo-inositol in the field was higher in ssp.ericetorum than in either ssp.radicata or control plants in the water culture experiments. When the cytoplasmic volume is estimated as 10% of the total cell volume, free proline andmyo-inositol account for 44–69% of the osmotic potential. It is concluded that ssp.ericetorum is better adapted to the drier environment by its higher capacity to accumulate proline and reduce transpiration during stress. Grassland species research group, publication no41.     

Hydraulic properties and photosynthetic rates in co-occurring lianas and trees in a seasonal tropical rainforest in southwestern China

In this study, we examined wood anatomy, hydraulic properties, photosynthetic rate, and water status and osmotic regulation in three liana species and three tree species co-occurring in a seasonal tropical rain forest. Our results showed that the three liana species had larger vessel diameter, lower sapwood density, and consequently higher branch sapwood specific hydraulic conductivity (K _S) than the three tree species. Across species, K _S was positively correlated with leaf nitrogen concentration and maximum net CO₂ assimilation rate. However, it was also positively correlated with xylem water potential at 50% loss of hydraulic conductivity, indicating a trade-off between hydraulic efficiency and safety. Compared to the tree species, the liana species had higher predawn leaf water potential and lower osmotic adjustment in the dry season. The combination of more efficient water transport, higher photosynthetic rates, and their ability to access to more reliable water source at deeper soil layers in the dry season in the lianas should contribute to their fast growth.     

Effect of ABA on the water relations of winter-wheat cultivars varying in drought resistance

Water and osmotic potentials were measured in leaves of a drought-sensitive ('Ponca') and a drought-resistant ('KanKing') cultivar of winter wheat ( Triticum aestivum L . em. Thell.) to determine if the potentials of the drought-sensitive cultivar could be made similar to those of the drought-resistant cultivar through application of abscisic acid (ABA). Stomatal resistance was also measured. Plants were sprayed with ABA and grown in soil, which was watered or allowed to dry. In well-watered plants, ABA closed the stomata of both cultivars. Stomatal resistance of plants grown without added water and with ABA was less than that of plants grown without added water and without ABA. Under ample water supply, ABA decreased water and osmotic potentials of the drought-sensitive cultivar (Ponca), but had no effect on these potentials in the drought-resistant cultivar (KanKing). Under water-deprived conditions, ABA increased water and osmotic potentials of Ponca, but did not change these potentials in KanKing. The overall effect of ABA was to decrease the differences in the water and osmotic potentials between the two cultivars.     

Effects of soil and air drought on growth,plant water status and leaf gas exchange in three Mediterranean cedar species: <Emphasis Type="Italic">Cedrus atlantica</Emphasis>, <Emphasis Type="Italic">C. brevifolia</Emphasis> and <Emphasis Type="Italic">C. libani</Emphasis>

Three- and four-year-old potted, greenhouse-grown cedar seedlings were subjected to two different watering regimes: half received full water supply and the other half was submitted to moderate drought (50% of the full water supply). Height growth was the greatest for C. atlantica and the most-limited for C. brevifolia in the well-watered set. However, in the dry set, height growth was less affected by drought conditions for C. brevifolia than for C. atlantica. Cedrus libani gave intermediate results for both watering regimes. Moderate drought provoked a decrease in osmotic potential at full leaf turgor and a long-lasting osmotic adjustment. When irrigation was withheld completely to induce severe soil drying, gas exchange decreased and then stopped at predawn water potentials of −3.0 MPa for C. brevifolia, between −2.6 and −2.8 MPa for C. libani, and at −2.4 MPa for C. atlantica, irrespective of watering regime. For all species, the dry set showed lower net photosynthesis (A) and stomatal conductance (g _s) than the plants in the well-watered set. A and g _s responded to variations in atmospheric water-vapour pressure deficit (VPD). As VPD increased, A and g _s decreased, and this trend was proportionate to initial values at low VPD, but remained independent of previous watering treatments, plant water status or species. To conclude, C. brevifolia appears to be a species with limited growth potential but strong soil drought tolerance whereas C. atlantica has strong growth potential when an adequate water supply is available but is more sensitive to soil drought. C. libani shows an intermediate behaviour for growth and drought tolerance.     

Leaf vasculature in Zea mays L.

The vascular system of the Zea mays L. leaf consists of longitudinal strands interconnected by transverse bundles. In any given transverse section the longitudinal strands may be divided into three types of bundle according to size and structure: small, intermediate, large. Virtually all of the longitudinal strands intergrade structurally however, from one bundle type to another as they descend the leaf. For example, all of the strands having large-bundle anatomy appear distally as small bundles, which intergrade into intermediates and then large bundles as they descend the leaf. Only the large bundles and the intermediates that arise midway between them extend basipetally into the sheath and stem. Most of the remaining longitudinal strands of the blade do not enter the sheath but fuse with other strands above and in the region of the blade joint. Despite the marked decrease in number of longitudinal bundles at the base of the blade, both the total and mean cross-sectional areas of sieve tubes and tracheary elements increase as the bundles continuing into the sheath increase in size. Linear relationships exist between leaf width and total bundle number, and between cross-sectional area of vascular bundles and both total and mean cross-sectional areas of sieve tubes and tracheary elements.     

应用PV技术对7种针阔叶幼树抗旱性的研究

为进一步探讨PV(Pressure-Volume)技术在树木抗旱性研究中的应用前景,比较成、幼龄树木的抗旱性差别,在对樟子松等7种成龄树木抗旱性生理指标研究的基础上,对其幼树的抗旱性进行了研究。结果表明,对成、幼龄树木一年生小枝用PV曲线所测得的诸水分状况参数随年生长发育进程的的变化规律是一致的;用嫩枝生长初期和枝条完全木质化时期两个阶段的水分参数比较树木的抗旱性、具有较大的可靠性和实用性;幼树在嫩枝生长初期的抗旱性较成树弱,当新枝完全木质化之后,二者的抗旱性基本相近。     

Effects of light availability versus hydraulic constraints on stomatal responses within a crown of silver birch

Responses of leaf conductance (g_L) to variation in photosynthetic photon flux density (Q_P), leaf-to-air vapour pressure difference (VPD), bulk leaf water potential (_x), and total hydraulic conductance (G_T) were examined in silver birch (Betula pendula Roth) with respect to leaf position in the crown. To reduce limitations caused by insufficient water supply or low light availability, experiments were also performed with branchlets cut from two different canopy layers. The intact upper-canopy leaves demonstrated 1.8–2.0 times higher (P<0.001) daily maxima of g_L compared with the lower-canopy leaves growing in the shadow of upper branches. In the morning, g_L in the shade foliage was primarily constrained by low light availability, in the afternoon, by limited water supply. Leaf conductance decreased when _x fell below certain values around midday, while the sun foliage experienced greater negative water potentials than the shade foliage. Midday stomatal openness was controlled by leaf water status and temperature, rather than by transpiration rate (E) via the feedforward mechanism. Mean G_T was 1.7 times higher (P<0.001) for the upper-canopy foliage compared to that of the lower canopy. At least 34–39% of the total resistance to the water flow from soil up to the shade foliage, and 54% up to the sun foliage, resided in 30-cm distal parts of the branches. Artificial reduction of hydraulic constraints raised _x and made g_L less sensitive to changes in both atmospheric and plant factors. Improved water supply increased g_L and E in the lower-canopy foliage, but not in the upper-canopy foliage. The results support the idea that leaves in the lower canopy are hydraulically more constrained than in the upper canopy.     

Varietal influence of intercropped cowpea on the growth,yield and water relations of maize

The effects of three cowpea varieties namely, NewEra (a spreading type), Adzuki (an erect type) and Ife Brown (semi-erect) intercropped with maize on growth, yield and water relations of maize were investigated in the greenhouse and in the field. Cowpea varietal effects were significant on soil water extraction but insignificant on the performance of maize.     

Effects of Flooding on Susceptibility of Taxodium distichum L. Seedlings to Drought

Responses of baldcypress (Taxodium distichum) seedlings to soil moisture were studied to test the hypothesis that flooding may lead to seedling's higher susceptibility to drought. Treatments included a well-watered but drained control (C), continuously flooded (CF), control followed by drought (CD), and flooded followed by drought (FD). Gas exchange values revealed no significant effects on net photosynthetic rate (P_N) in response to flooding. In contrast, after the onset of drought, P_N was significantly reduced in CD and FD plants. Significant growth reductions under mild drought conditions indicated that baldcypress seedlings were drought sensitive. However, comparison of gas exchange rates and growth responses between CD and FD plants indicated that prior flooding had no detectable effect on subsequent sensitivity of baldcypress to drought. These findings explain baldcypress persistence in wetland habitats characterized by periodic flooding and mild drought.