Differential salt tolerance and similar responses to nitrogen availability in plants grown from dimorphic seeds of Suaeda salsa

Suaeda salsa is an annual halophyte which produces two morphologically distinct types of seeds on the same plant. The main purpose of this study was to investigate growth responses of S. salsa plants to different levels of NaCl and nitrate nitrogen, and its significance from the viewpoint of photosynthetic physiology. In a pot experiment, we sowed seeds belonging to the two morphs into a substrate with three salinity and three nutrient levels. Plants derived from brown seeds grew well at moderate salinity (300 mmol L⁻¹ NaCl). Shoot weight of plants from black seeds gradually decreased with the increase of salinity. Plants derived from both seed morphs had the same growth rates under similar nitrogen levels. Plant growth status was generally related to chlorophyll content and photosynthetic rates. Our study shows that plants grown from the two different seed morphs of S. salsa exhibit different salt tolerance, but have similar responses to nitrate nitrogen. This is the first report on different responses to salinity and nitrogen availability in plants with heteromorphic seeds.     

典范分析法在黄河三角洲莱州湾滨海区盐生植物群落研究中的应用

典范变量分析能同时处理两种类型的变量集并给出它们之间的相关系数。本文采用该方法对黄河三角洲地区的10个植物群丛及其土壤的有关性质进行了分析。典范相关系数是0.9和1。文中同时求出了所有典范变量,保留了原数据的全部信息。结果表明该地区植被的动态变化与土壤水盐及有机质含量的动态变化显著相关。土壤的水盐动态是这一地区植被演替的制约因素。二维典范变量图较直观地表示出了群丛间的演替关系。初步判断出芦苇和白茅群丛是这一地区植被演替过程中相对稳定的阶段。该方法对研究植物群落的分布及植被演替等内容是很有帮助的。     

Diversity patterns of wet meadows along geochemical gradients in central Spain

Four measures of biodiversity (species number per site, total species number, mean similarity and mosaic diversity) and their relationships with soil chemical composition were studied in vascular plant communities in groundwater discharge ecosystems of central Spain. Species richness decreased with increasing salinity, alkalinity and halite concentration. Species richness was apparently controlled more by soil toxicity than by soil nutrient levels, although a positive correlation of Ca²⁺ with species richness was found after accounting for the effects of toxic compounds. All relationships were strictly monotonic. Six community types were identified based on their soil chemical characteristics: glycophyte, subglycophyte, tolerant, subalkalinophyte, alkalinophyte, and halocalcicole communities. Within community types, species richness showed very few significant relationships with soil characteristics. Mean species richness was lowest in the environmentally stressful communities. Total species richness was greatest in the ecotonal community type. Mean similarity, a measure of among-community diversity, and mosaic diversity, a measure of landscape complexity, differed among community types. Mean similarity was smaller (higher diversity) in species-poor community types, while mosaic diversity was greatest (greater complexity) in species-rich community types. The halocalcicole community type was richest in rare species.     

Nitrogen nutrition in the estuarine zone: the case of Suaeda maritima var. macrocarpa

Suaeda maritima L. var. macrocarpa is a halophytic species distributed in the lower parts of salt marshes of the French coasts. The influence of salinity on nitrogen nutrition and on levels of the key enzymes involved in nitrogen assimilation is analyzed by growing Suaeda under experimental conditions. Use of ¹⁵N-labelled NO₃ ^- and NH₄ ⁺ shows that both ions are effective sources of inorganic nitrogen for Suaeda. The plant is found to use NH₄ ⁺ ions with a good yield, chiefly at high salinities (up to 130 mM). Nitrate reduction and ammonium assimilation by the glutamine synthetase/glutamate synthase pathway occurs mainly in leaves when Suaeda is grown at optimal saline conditions (130 mM NaCl). Absence of NaCl creates less favourable conditions and lowers the activity of nitrate reductase and glutamine synthetase but leads to an important activity of glutamate dehydrogenase in roots. This enzyme could play a major role under suboptimal environmental conditions (i.e., absence of NaCl for Suaeda maritima).Part of this paper is taken from a thesis that was submitted by J. P. Billard in fulfillment of the Doctorat d'Etat degree at the University of Caen, France.     

中国的盐生植物

本文主要讨论了有关中国盐生植物的五个方面的问题：（１）中国盐生植物的种类；（２）中国盐生植物的类型；（３）中国盐生植物的植被类型；（４）世界盐生植物名录中漏录的中国盐生植物；（５）中国盐生植物的经济潜势。最后还讨论了我国今后盐生植物研究方向和重点。     

Hydrogen isotope fractionation during water uptake by woody xerophytes

Stable isotope measurements are employed extensively in plant–water relations research to investigate physiological and hydrological processes from whole plant to ecosystem scales. Stable isotopes of hydrogen and oxygen are routinely measured to identify plant source water. This application relies on the assumption that no fractionation of oxygen and hydrogen isotopes in water occurs during uptake by roots. However, a large fraction of the water taken up through roots in halophytic and xerophytic plants transverses cell membranes in the endodermis before entering the root xylem. Passage of water through this symplastic pathway has been hypothesized to cause fractionation leading to a decrease in ²H of root xylem water relative to that in the surrounding soil medium. We examined 16 woody halophytic and xerophytic plant species in controlled conditions for evidence of hydrogen isotope fractionation during uptake at the root–soil interface. Isotopic separation (Δ²H = δ²H_{soil water} − δ²H_{xylem water}) ranging from 3‰ to 9‰ was observed in 12 species. A significant positive correlation between salinity tolerance and the magnitude of Δ²H was observed. Water in whole stem segments, sapwood, and roots had significantly lower δ²H values relative to soil water in Prosopis velutina Woot., the species expressing the greatest Δ²H values among the 16 species examined. Pressurized water flow through intact root systems of Artemisia tridentata Nutt. and Atriplex canescens (Pursh) Nutt. caused the δ²H values to decrease as flow rate increased. This relationship was not observed in P. velutina. Destroying the plasma membranes of root cells by excessive heat from boiling did not significantly alter the relationship between δ²H of expressed water and flow rate. In light of these results, care should be taken when using the stable isotope method to examine source-water use in halophytic and xerophytic species.     

Ultrastructure of the salt glands of the mangrove,Avicennia marina (Forssk.) Vierh., as indicated by the use of selective membrane staining

Each salt-excreting gland of the mangrove Avicennia marina (Forsskål) Vierh. consists of two to four collecting cells, one stalk cell, and eight to twelve excretory cells. Differential membrane staining by zinc iodide-osmium tetroxide (as a post-fixative) or phosphotungstic acid (as a section-stain) was used to characterise the ultrastructure of the glands. A large amount of tubular endoplasmic reticulum was found in the stalk and excretory cells of the gland, but not in the collecting cells. The ultrastructural arrangement of the endoplasmic reticulum indicates that salt is loaded from the apoplasm into the endoplasmic reticulum of the symplasm at the base of the stalk cell, traverses both cell types in the endoplasmic reticulum, and is excreted at the outer edge of the gland by an eccrine-type mechanism. Increasing development of the tubular endoplasmic reticulum accompanied differentiation of the gland cells.Abbreviations ER endoplasmic reticulum - PTA phosphotungstic acid - ZIO zinc iodide-osmium tetroxide     

Salinity, growth and root respiration in the grey mangrove, Avicennia marina

Relationships between growth parameters and root respiration under various conditions of salinity were investigated in seedlings of the grey mangrove Avicennia marina (Forsk.) Vierh. Growth, root/shoot ratios, leaf succulence and osmotic potential of leaves were measured for seedlings grown for 6–8 weeks in 100, 50, 25 and 0% seawater. Oxygen uptake of root segments, from distal to proximal ends of roots, was measured for all treatments. Total growth was maximal in 25% seawater, highest leaf succulence was obtained in 50% seawater, and highest leaf osmotic potential in 100% seawater. Oxygen uptake in distal root segments, as measured both by Clark oxygen electrode and Warburg manometry, showed a stimulation in the presence of salt that closely paralleled growth stimulation. The rates of respiration were highest in 25% seawater. The oxygen uptake was not stimulated by salt per se, since concentrations higher than 25% were associated with a decline in rate of oxygen uptake from the maximum. Values for the respiratory quotient approximated to one in all treatments. Avicennia marina has been reported to exclude from its roots about 90% of the salt in the surrounding medium. It might have been expected that increased concentrations of salt in the growth medium would be associated with a standard salt respiration response in the roots; however, this was not obtained.     

Photoperiod buffers responses to salt and temperature during germination of two coastal salt marsh colonizers Juncus acutus and Juncus maritimus

Juncus acutus and J. maritimus are two colonizers of coastal marsh rangeland with worldwide distribution. We tested the effect of salt, temperature, and photoperiod on the germination capacity of seeds of the two Juncus from the Rhône delta (south of France). We measured the first day of germination, the mean time, speed, and rate of germination on seeds subjected to five salinity levels, three Dark–Light temperatures and two D-L photoperiods (12–12 and 10–14). The 10–14 D-L photoperiod, although it corresponds to one of the two main germination periods of J. acutus and J. maritimus in the northern Mediterranean, has never been previously used to study their germination capacity. Analyses showed significant effects of salinity and temperature on the germination parameters tested, and for these two factors we found results comparable to those of previous studies. Salinity slowed down and reduced the germination process while spring temperatures had a positive effect. A surprising result was obtained by changing the D-L photoperiod from 12–12 to 10–14 which then largely buffered the negative effect of salt and high temperatures on germination. This capacity of J. acutus and J. maritimus to withstand salty conditions during the germination phase due to the spring photoperiod could be decisive in the ability of both species to colonize saline environments.     

Comparative Ni tolerance and accumulation potentials between Mesembryanthemum crystallinum (halophyte) and Brassica juncea: Metal accumulation,nutrient status and photosynthetic activity

Saline soils often constitute sites of accumulation of industrial and urban wastes contaminated by heavy metals. Halophytes, i.e. native salt-tolerant species, could be more suitable for heavy metal phytoextraction from saline areas than glycophytes, most frequently used so far. In the framework of this approach, we assess here the Ni phytoextraction potential in the halophyte Mesembryanthemum crystallinum compared with the model species Brassica juncea. Plants were hydroponically maintained for 21 days at 0, 25, 50, and 100 μM NiCl₂. Nickel addition significantly restricted the growth activity of both species, and to a higher extent in M. crystallinum, which did not, however, show Ni-related toxicity symptoms on leaves. Interestingly, photosynthesis activity, chlorophyll content and photosystem II integrity assessed by chlorophyll fluorescence were less impacted in Ni-treated M. crystallinum as compared to B. juncea. The plant mineral nutrition was differently affected by NiCl₂ exposure depending on the element, the species investigated and even the organ. In both species, roots were the preferential sites of Ni²⁺ accumulation, but the fraction translocated to shoots was higher in B. juncea than in M. crystallinum. The relatively good tolerance of M. crystallinum to Ni suggests that this halophyte species could be used in the phytoextraction of moderately polluted saline soils.