Effects of soil salt levels on the growth and water use efficiency of Atriplex canescens (Chenopodiaceae) varieties in drying soil

The effect of salt stress on the growth and water use efficiency of the xerohalophyte Atriplex canescens (Pursh.) Nutt. in drying soil was determined by growing plants to the wilting point in soils receiving a one-time irrigation of nutrient solution containing low, medium, and high levels of NaCl. The experiment compared three varieties of A. canescens that differed in salt tolerance and capacity for Na and K uptake in previous research. Contrary to expectations, we did not find that water and salt stress were strictly additive in reducing plant performance. Soil salts enhanced the growth performance of the plants in drying soil by increasing their days to wilting, ability to extract water from the soil, organic matter production, and water use efficiency. The variety with the highest salt tolerance also had the highest growth rates and water use efficiency on drying soils. We conclude that tolerances to water and salt stress are linked through a common mechanism of Na uptake for osmotic adjustment in this species.     

ARE TRIOECY AND SEXUAL LABILITY IN ATRIPLEX CANESCENS GENETICALLY BASED?: EVIDENCE FROM CLONAL STUDIES

Prior studies have alternatively considered floral phenotypes in Atriplex canescens as trioecious (having three sexual genders) and/or dioecious and having a “leaky genetical switch.” Clones transplanted from three populations and grown in common gardens reveal the existence of two distinctly different genetic controls regulating gender expression. In some clones gender is fixed as male (staminate) or female (pistillate), while in other clones gender varies, ranging from a mixture of male and female ramets to simultaneous hermaphrodites with various proportions of male and female flowers. For clones which vary their sex expression, variation occurs within irrigation treatments, between treatments and over time, as a consequence of the combined effects of genotype plus environment. The magnitude of sex change is also a product of the interaction of genetics and environment. Some clones have been repeatedly examined for 20 years.     

中亚滨藜甜菜碱醛脱氢酶基因的表达特性

根据已发表的几种植物的甜菜碱醛脱氢酶（BADH）基因的同源保守区设计了一对兼并引物,通过RT-PCR方法从中亚滨藜中扩增出BADH基因的近5′端序列,共395bp,与菠菜、山菠菜、甜菜、千穗谷、大麦的BADHcDNA相应片段的同源性较高。以此片段为探针,对中亚滨藜的基因组进行Southern杂交分析,证明该基因可能是单拷贝的。Northern印迹杂交结果表明NaCl250mmol/L处理的植株的BADHmRNA水平比对照植株约高2倍,说明中亚滨藜中BADH基因的表达受盐诱导。     

采用RT-PCR扩增方法从犁苞滨藜中扩增NHX基因

采用RT-PCR扩增的方法,从新疆野生植物犁苞滨藜中克隆获得1.7 kb的cDNA片段,测序和序列分析表明该基因片段包含NHX基因完整的读码框架.序列同源性分析结果显示犁苞滨藜NHX基因与滨藜NHX基因同源性高达95%,与碱蓬同源性达到86%,与柑桔同源性为88%,与拟南芥同源性为84%,表明它是植物中高度保守的一种基因,同时说明野生植物犁苞滨藜中也存在与拟南芥相似的植物耐盐相关基因.     

An inland and a coastal population of the Mediterranean xero-halophyte species Atriplex halimus L. differ in their ability to accumulate proline and glycinebetaine in response to salinity and water stress

Soil salinity and drought compromise water uptake and lead toosmotic adjustment in xero-halophyte plant species. These importantenvironmental constraints may also have specific effects onplant physiology. Stress-induced accumulation of osmocompatiblesolutes was analysed in two Tunisian populations of the Mediteraneanshrub Atriplex halimus L.—plants originating from a salt-affectedcoastal site (Monastir) or from a non-saline semi-arid area(Sbikha)—were exposed to nutrient solution containingeither low (40 mM) or high (160 mM) doses of NaCl or 15% polyethyleneglycol. The low NaCl dose stimulated plant growth in both populations.Plants from Monastir were more resistant to high salinity andexhibited a greater ability to produce glycinebetaine in responseto salt stress. Conversely, plants from Sbikha were more resistantto water stress and displayed a higher rate of proline accumulation.Proline accumulated as early as 24 h after stress impositionand such accumulation was reversible. By contrast, glycinebetaineconcentration culminated after 10 d of stress and did not decreaseafter the stress relief. The highest salt resistance of Monastirplants was not due to a lower rate of Na⁺ absorption; plantsfrom this population exhibited a higher stomatal conductanceand a prodigal water-use strategy leading to lower water-useefficiency than plants from Sbikha. Exogenous application ofproline (1 mM) improved the level of drought resistance in Monastirplants through a decrease in oxidative stress quantified bythe malondialdehyde concentration, while the exogenous applicationof glycinebetaine improved the salinity resistance of Sbikhaplants through a positive effect on photosystem II efficiency. Key words: Atriplex halimus, glycinebetaine, halophyte, NaCl, osmotic adjustment, proline, salinity, water stress     

Shade facilitates an invasive stem succulent in a chenopod shrubland in South Australia

Abstract The invasive stem succulent Orbea variegata (L) Haw. (Asclepiadaceae) tends to be more abundant underneath shrubs than in open areas in chenopod shrublands near Whyalla, South Australia. To assess the role of facilitation in the life cycle of O. variegata, we investigated the effect of chenopod shrubs on different life stages of the species by experimentally manipulating temperature, light, soil moisture and nutrient levels. Experimental results suggest that the reduction in light and temperature under shrubs, but not increased nutrient levels, are the main facilitative mechanisms for O. variegata. Temperatures above 30°C, which are more likely to occur on the soil surface of open areas than under shrubs, inhibited seed germination. Seedling survival at low watering frequency and the growth of established ramets were increased by 75–80% shade cloth. Ramets growing in full light contained a high concentration of anthocyanin pigments. One of the functions of these pigments is to absorb excess radiation, suggesting that O. variegata experiences radiation stress in full light. In the field O. variegata performed considerably better under Atriplex vesicaria Heward ex Benth. (Chenopodiaceae) or under 75–80% shade cloth than in full light. Monthly irrigation of 20 mm did not reduce this positive effect of the A. vesicaria canopy on O. variegata, suggesting that O. variegata is inhibited by high light intensities or temperatures, independent of water availability. In conclusion, whereas shrub canopies do not seem to be required for the establishment or survival of O. variegata, shrubs improve adult growth and can improve establishment. The possibility of exotic plants being facilitated by other plants has to be taken into account when assessing the probability and rate of invasion.     

Enhanced tolerance of photosynthesis against high temperature damage in salt-adapted halophyte Atriplex centralasiatica plants

Thermotolerance of photosynthesis in salt‐adapted Atriplex centralasiatica plants (100–400 mm NaCl) was evaluated in this study after detached leaves and whole plants were exposed to high temperature stress (30–48 °C) either in the dark or under high light (1200 mol m^?2 s^?1). In parallel with the decrease in stomatal conductance, intercellular CO₂ concentration and CO₂ assimilation rate decreased significantly with increasing salt concentration. There was no change in the maximal efficiency of PSII photochemistry (F_v/F_m) with increasing salt concentration, suggesting that there was no damage to PSII in salt‐adapted plants. On the other hand, there was a striking difference in the response of PSII and CO₂ assimilation capacity to heat stress in non‐salt‐adapted and salt‐adapted leaves. Leaves from salt‐adapted plants maintained significantly higher F_v/F_m values than those from non‐salt‐adapted leaves at temperatures higher than 42 °C. The F_v/F_m differences between non‐salt‐adapted and salt‐adapted plants persisted for at least 24 h following heat stress. Leaves from salt‐adapted plants also maintained a higher net CO₂ assimilation rate than those in non‐salt‐adapted plants at temperatures higher than 42 °C. This increased thermotolerance was independent of the degree of salinity since no significant changes in F_v/F_m and net CO₂ assimilation rate were observed among the plants treated with different concentrations of NaCl. The increased thermotolerance of PSII induced by salinity was still evident when heat treatments were carried out under high light. Given that photosynthesis is considered to be the physiological process most sensitive to high temperature damage, increased thermotolerance of photosynthesis may be of significance since A. centralasiatica, a typical halophyte, grows in the high salinity regions in the north of China, where the temperature in the summer is often as high as 45 °C.     

野榆钱菠菜（Atriplex aucheri）的种子多型性及生态型

对野榆钱菠菜的花、果实及种子进行了观察,表明野榆钱菠菜具有1种雄花、2种雌花,却产生3种果实和种子。这3种种子在形状、大小、颜色、着生方式及包被其苞片的大小上均有差异。且该种植物种内的生态型在生长习性、结实率和种子类型上都存在很大的差异。     

四翅滨藜生理生化特征对盐胁迫的响应

采用温室盆栽试验研究四翅滨藜(Atriplex canescens)幼苗株高、地径、生物量、净光合速率、蒸腾速率、气孔导度、叶绿素含量、抗氧化酶活性及丙二醛含量对不同浓度NaCl和Na_2SO_4(0、100、200、300和400mmol·L~(-1))胁迫的响应,以探讨四翅滨藜对不同种类及不同浓度盐渍环境的适应机制及其耐盐机理。结果显示:(1)随着盐分浓度的升高,四翅滨藜幼苗的株高、地径及生物量增量呈现出先升高后降低的趋势,低盐浓度下2种盐均促进幼苗生长,盐浓度超过400mmol·L~(-1)时,NaCl对幼苗生长具有明显抑制作用。(2)2种盐处理下,四翅滨藜幼苗净光合速率(Pn)和叶绿素含量(Chl)随盐浓度增大而升高,即2种盐均对幼苗Pn和Chl含量具有促进作用,且Na_2SO_4的促进效果大于NaCl;而幼苗蒸腾速率(Tr)和气孔导度(Gs)随盐浓度升高呈先增大后减小的趋势,且Na_2SO_4的促进作用强于NaCl。(3)与对照相比,四翅滨藜幼苗的丙二醛、SOD、POD酶活性在NaCl和Na_2SO_42种盐处理下,随着盐浓度的升高均呈现出不同程度的增大,且增大幅度总体表现为NaClNa_2SO_4。研究表明,四翅滨藜在NaCl和Na_2SO_4胁迫下,叶绿素的分解速率以及发挥作用的渗透调节物质均有差异,使得幼苗叶片健康程度不同,导致叶片光合能力大小的差异,最终表现为植株的生长差异;四翅滨藜具有较强的耐盐能力,而且对Na_2SO_4的适应能力强于NaCl。     

Growth response of Atriplex nummularia to inoculation with arbuscular mycorrhizal fungi at different salinity levels

Chenopods are generally regarded as non-host plants for mycorrhizal fungi and are believed not to benefit from colonization by mycorrhizal fungi. Perennial Atriplex nummularia Lindl., growing under field conditions, showed a relatively high level of colonization by mycorrhizal fungi (10–30% of root length colonized) in spring and summer. Accordingly, two glasshouse experiments were designed to assess the effects of inoculation with mycorrhizal fungi (with a single species or a mixture of different species) on growth, nutrient uptake, and rhizosphere bacterial community composition of A. nummularia at high and low salinity levels (2.2 and 12 dSm^–1). Only low and patchy colonization by mycorrhizal fungi (1–2 of root length colonized) was detected in inoculated plants under glasshouse conditions which was unaffected by salinity. Despite the low colonization, inoculation increased plant growth and affected nutrient uptake at both salinity levels. The effects were higher at an early stage of plant development (6weeks) than at a later stage (9–10 weeks). Salinity affected the bacterial community composition in the rhizosphere as examined by ribosomal intergenic spacer amplification (RISA) of 16S rDNA, digitization of the band patterns and multivariate analysis. The effects of inoculation with mycorrhizal fungi on growth of A. nummularia may be attributed to (i) direct effects of mycorrhizal fungi on plant nutrient uptake and/or (ii) indirect effects via mycorrhizal-induced changes in the bacterial community composition.