Photosynthetic Metabolism and Activity of Carboxylating Enzymes in Emergent,Floating, and Submersed Leaves of Hydrophytes

Radioisotope techniques were used to compare photosynthetic CO₂ fixation, activities of carboxylating enzymes, and the composition of photosynthates in 42 species of aquatic plants (emergent, floating, and submersed hydrophytes) collected from rivers Sysert' and Iset' in Sverdlovsk oblast (Russia). The submersed leaves, in comparison with the emergent and floating leaves, featured lower rates of potential photosynthesis (by 2.2 mg CO²/(dm² h) on average), low content of the fraction I protein, and low activity of Rubisco and phosphoenolpyruvate carboxylase (PEPC). The averaged activities of Rubisco and PEPC were diminished in submersed leaves by 10 and 1 mg/(dm² h), respectively. Different hydrophyte groups showed similar composition of assimilates accumulated after 5-min photosynthesis and did not differ in this respect from terrestrial plants. However, the incorporation of ¹⁴C into sucrose and starch in submersed leaves (30 and 9% of total labeling, respectively) was lower than in emergent and floating leaves (45 and 15%, respectively). At the same time, the incorporation of ¹⁴C into C₄ acids (malate and aspartate) was 1.5 times higher in submersed leaves than in other leaf types. Analysis of leaf differentiation, the Rubisco/PEPC activity ratio, the PEPC activity, and the composition of primary photosynthates in the pulse–chase experiments revealed no evidence of the C₄ effect in the submersed hydrophytes examined. The adaptation of hydatophytes to specific conditions of an aquatic environment was structurally manifested in the reduction (by a factor of 3–5) in the number of chloroplasts per 1 cm² leaf area. This small number of chloroplasts was responsible for low photosynthetic rates in submersed leaves, although metabolic activities of individual chloroplasts were similar for all three hydrophyte groups.     

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 2. Quantitative Characterization of Leaf Mesophyll and the Functional Activity of Leaves with Different Degrees of Submersion

The structure of leaf photosynthetic elements was investigated on 42 boreal plant species characterized by different degrees of submergence (helophytes, neustophytes, and hydatophytes). Six main types of mesophyll structures were identified. Quantitative characteristics for the mesostructure of the photosynthetic apparatus in these groups were determined, such as the size and abundance of cells and chloroplasts in the mesophyll and epidermis, the number of plastids per cell in each tissue, the total surface area of the mesophyll cells, epidermal cells, and chloroplasts per unit leaf area. Analysis showed that quantitative characteristics of the photosynthetic apparatus in hydrophytes are determined by two factors: (a) the degree of leaf submergence and (b) the type of mesophyll structure. With an increasing degree of immersion in water, the mesophyll types change in a sequence isopalisade dorsoventral homogeneous. The leaves become thinner, their weight per unit area diminishes, cells and chloroplasts become less numerous (on a per unit leaf area basis), but their dimensions become larger. Adaptation to aquatic medium is also manifested in the increasing contribution of the epidermal tissue to the overall photosynthesis: in submerged leaves, the epidermis accounts for more than 50% of the photosynthetic activity. The occurrence of six structural types of leaves contrasting in their characteristics was confirmed by discriminatory analysis according to the qualitative parameters of mesophyll.     

Mycorrhizal associations in the Patagonian steppe,Argentina

The mycorrhizal status of plant species in north-west Patagonia was examined. Communities representative of Patagonian steppe and marshes were compared with respect to the mycorrhizal status of their species.Most of both native and exotic plant species sampled were arbuscular mycorrhizal (AM). The percentage of species with mycorrhizal association was higher for perennial herbs and shrubs than for annual herbs. The higher ratio of mycorrhizal/nonmycorrhizal (NM) species found for dicotyledons than for monocotyledons, could reflect the presence of a considerable number of NM monocotyledons in the marsh. The mycorrhizal status of plants differed slightly between the steppe and the marsh. In the steppe, native AM species were more frequent than in the marsh. In contrast, in the marsh, the NM species were proportionally more represented than in the steppe. The Juncaceae and Cyperaceae, which include hydrohytic NM plants, accounted for many of these differences. Moreover, the dominant species in the marshes, Juncus arcticus, is a NM species.In the present study, most of species belonging to the same taxonomic family tended to have the same mycorrhizal associations, in agreement with studies on plants from other regions. Exceptions to this general behaviour were observed in the families Cyperaceae, Scrophulariaceae, Berberidaceae and Amaryllidaceae. The most represented families in which mycorrhizal behaviour differed between species of the same family were Asteraceae, Fabaceae and Poaceae. Senecio neaei (Asteraceae) and Boopis australis (Calyceraceae) showed facultative mycorrhizal behaviour.     

Changes in chemical composition of hydrophyte leaves during adaptation to aquatic environment

Leaf chemical composition of 19 hydrophytes was studied. The content of carbon, nitrogen, nonstructural carbohydrates, organic acids, minerals, and water was determined. Hydrophytes were shown to contain less carbon (below 410 mg/g dry wt in 60% species) than terrestrial plants. Hydrophytes and terrestrial plants did not differ in the nitrogen concentration in the leaves (33 and 29 mg/g dry wt, respectively). Hydrophytes were characterized by a low content of organic acids (40–90 mg/g dry wt in 60% species) and high content of mineral compounds (90–170 mg/g dry wt in 50% species). Total amount of nonstructural carbohydrates was similar in the leaves of hydrophytes and terrestrial plants (from 120 to 190 mg/g dry wt), but the proportions of various carbohydrate fractions differed substantially. In the hydrophyte leaves, the content of soluble carbohydrates was 2.4-fold lower, whereas the content of nonstructural polysaccharides 1.2-fold higher than in terrestrial plant leaves. Two groups of correlations between parameters of leaf chemical composition were distinguished: the contents of carbon, nitrogen, and soluble sugars were positively correlated, and the negative correlation was observed between these parameters and the amounts of mineral compounds, organic acids, water, and nonstructural polysaccharides. We concluded that hydrophyte leaf chemical composition reflects a specificity of plant adaptation to aquatic environment.     

Energy content of water- and bog-plant associations in the region of Valdivia (Chile)

Summary Mapping the vegetation of the littoral zone of different types of aquatic habitats in the region of Valdivia (Chile) submerged Egerietum densum, the emergent Sagittario-Alismetum and the Scirpetum californiae were found. In the littoral zone of the banados (i.e. lakes) formed by inundation after subsidence the submerged Egerietum densum, the floating-leaved Polygono-Jussiaetum and the emergent Juncetum procerii; the analyzed pond of Mehuin contained the Callitrichetum stagnalis chilensis and the artificial ponds close to La Union the Lemno-Azolletum. The caloric values of 18 hydrophytes showed a decline from the large emergent hydrophytes (3 818 cal/g) to the submerged (2 907 cal/g) and there was also a decrease from the free-floating (3 652 cal/g) to the floating-leaved (3 364 cal/g) and to the submerged plants. In the most eases high caloric values correspond to a high content of lignin (large emergent hydrophytes) or lipids (floating-leaved plants).We thank Mrs. Bölke and Mr. Delgado for technical help and the Universidad Austral de Chile, Valdivia for fluancial support.     

Occurrence of Arbuscular Mycorrhizas and Dark Septate Endophytes in Hydrophytes from Lakes and Streams in Southwest China

In this study, the colonization of arbuscular mycorrhizas (AM) and dark septate endophytes (DSE) in 140 specimens of 32 hydrophytes collected from four lakes and four streams in southwest China were investigated. The arbuscular mycorrhizal fungi (AMF) and DSE colonization in these hydrophytes were rare. Typical AM structures were observed in one of the 25 hydrophytic species collected in lakes and six of the 17 species collected in streams. Spores of 10 identified AMF species and an unidentified Acaulospora sp. were isolated from the sediments. The identified AMF came from the four genera, Acaulospora, Gigaspora, Glomus and Scutellospora . Glomus and G. mosseae were the dominant genus and species respectively in these aquatic environments. The presence of DSE in hydrophytes was recorded for the first time. DSE occurred in one of the 25 hydrophyte species collected in lakes and three of the 17 species collected in streams. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

两种水生植物对抗生素污染水体的修复作用

采用水培方法,通过检测水样中氨苄青霉素（Ampicillin）、盐酸四环素（Tetracycline）、盐酸土霉素（Oxytetracycline）和盐酸金霉素（Chlortetracycline）含量的动态变化,确定水生植物大漂（Pistia stratiotes）和凤眼莲（Eichhornia crassipes）对水体中抗生素的清除作用。结果显示：①在系列高浓度（10～50 μg/mL）抗生素的条件下,凤眼莲去除水中盐酸金霉素与盐酸土霉素的效果优于大漂;②对于采集的污水（抗生素浓度＜2.5 μg/mL）,培养72 h后,大漂和凤眼莲对盐酸四环素的去除率分别达80%和90%以上,对氨苄青霉素的去除率分别达80%和70%以上。大漂和凤眼莲对4种抗生素污染的水体均表现出不同程度的修复功能,特别是凤眼莲效果更佳,可作为去除水体抗生素污染的首选材料。     

利用水生植物净化河涌污水能力的比较研究

以8种水生植物为材料,在单一、复合种植的组合条件下,对污染物的去除效率及各植物的生长发育状况进行研究.结果表明：总磷、总氮、氨氮、浊度等水质指标的去除速率随着处理时间延长而逐渐升高,而CODMn的去除效果为开始较高,然后有所降低,后期又提高的波动现象.整体上除个别植物种类外,所有组合单元的处理效果均优于对照.经过植物净化处理,原污水的TP含量约为重污染水Ⅴ类水的4倍、TN含量为Ⅴ类水的5~6倍、水中上述污染物有30％~33．3％的种植组合达到Ⅲ类水的水平,其中20％~25％的组合达到了Ⅱ类水的水平.其他20％~30％的种植组合能使TP、TN污染物含量减少2~3倍,污染水水质相当或接近于Ⅴ类水的水平.原污水氨氮含量为Ⅴ类水的6~7倍,经过植物各组合的处理,58．3％组合的水平在Ⅲ类水以上,其中50％的组合达到Ⅱ类水的水平.其他约35％的组合使氨氮含量减少4~5倍,接近Ⅴ类水的水平.在植物形态学指标方面,除个别大薸单元出现负增长及植株坏死外,其余植物根、茎、叶有一定增长,表明植物能适应这样的污水而生长;植物复合种植比单一种植单元的处理表现出更高的净化水平及稳定性,应得到重视;挺水植物比漂浮植物和沉水植物的净化能力强,在水处理实践中可优先考虑.