Aquatic Isoetes Research Articles

Isoetes candelariensis, a new species of Isoetaceae (Lycopodiidae) from Argentina.

Isoetes candelariensis is a new species of Isoetaceae from Misiones, Argentina. This species is ephemeral, and grows on basaltic bedrock outcrop pools, in Urutau Reserve from Candelaria Department. This taxon differs from other aquatic Isoetes in this region by the unique combination of characters of its leaves, ligule, labium and megaspore ornamentation.

Outcrossing Rates and Gene Flow in Natural Population of the Endangered Endemic Aquatic Lycophyte Isoetes yunguiensis as Revealed by ISSR Markers

In this study, mating system, genetic diversity, and genetic structure of the endangered endemic aquatic Isoetes yunguiensis in China was investigated using ISSR markers. The results of ISSR analyses showed that the estimate of multilocus outcrossing rate (tm) was high at species level (tm = 0.955), indicating that diploid I. yunguiensis is a predominant outcrossing species. Nine selected ISSR primers used in the study amplified 66 reproducible bands, 41 of which were polymorphic among 37 individuals. High level of genetic diversity was detected at the species level (PPB = 62.12%), whereas, relatively low genetic diversity existed within populations (PPB = 39.39%). Analysis of molecular variance (AMOVA) revealed that 31.99% of the genetic variation was attributable to differences between populations and the rest (68.01%) to variability within populationsof I. yunguiensis. Value of Fst (0.320) indicated that genetic differentiation between populations also was significant. These results showed that I. yunguiensis predominantly favors crossing, and has a high level of genetic diversity and highly significant genetic variation between and within populations. Gene flow (Nm) among populations is equal to 1.177. High outcrossing rates may be responsible for the high levels of genetic diversity observed in the I. yunguiensis population. To maintain the current level of genetic diversity for this species, we recommend increasing in situ conservation sites.

Aquatic CAM photosynthesis: A brief history of its discovery

Aquatic CAM (Crassulacean Acid Metabolism) photosynthesis was discovered while investigating an unrelated biochemical pathway concerned with anaerobic metabolism. George Bowes was a significant contributor to this project early in its infancy. Not only did he provide me with some valuable perspectives on peer review rejections, but by working with his gas exchange system I was able to take our initial observations of diel fluctuations in malic acid to the next level, showing this aquatic plant exhibited dark CO2 uptake. CAM is universal in all aquatic species of the worldwide Lycophyta genus Isoetes and non-existent in terrestrial Isoetes. Outside of this genus aquatic CAM has a limited occurrence in three other families, including the Crassulaceae. This discovery led to fascinating adventures in the highlands of the Peruvian Andes in search of Stylites, a terrestrial relative of Isoetes. Stylites is a plant that is hermetically sealed from the atmosphere and obtains all of its carbon from terrestrial sources and recycles carbon through CAM. Considering the Mesozoic origin of Isoetes in shallow pools, coupled with the fact that aquatic Isoetes universally possess CAM, suggests the earliest evolution of CAM photosynthesis was most likely not in terrestrial plants.

Ecological changes in the highest temporary pond of western Crete (Greece): past, present and future

This study explores the past, present and future ecological changes in the highest Mediterranean temporary pond (Omalos pond) in western Crete, Greece. Data from downcore pollen analysis (including pollen and spores from both aquatic vegetation, and terrestrial herbaceous, arboreal and shrub vegetation), modern vegetation monitoring and existing climate scenarios have been combined to provide a picture of the ecological changes in the pond over the last 13,600 years. Downcore pollen analysis throughout the last 13,600 years indicated the presence of species typical of Mediterranean Temporary Pond (MTP) habitats and suggested relatively drier conditions towards the present. The low number of non-native, cultivated species (such as herbaceous Trifolium and Plantago species) observed over this period suggested relatively low impact from crop agriculture, despite the increasing grazing pressure in the area. In the absence of independent proxies, we cannot reliably distinguish between natural and human-induced changes. The presence of aquatic Isoetes in the palaeo-record indicates the existence of an ephemeral pond in the area as early as the beginning of the Holocene suggesting resilience of the ecosystem over time. However, the degraded state of pollen in depths over 55 cm (i.e. 3600 year BP) increases the uncertainty of the interpretation. Currently, the pond holds 76 plant species belonging to 25 families. Therophytes and chamaephytes were the most frequent, suggesting a typical ephemeral habitat life form spectrum. Species richness was found to increase during spring surveys whereas the highest turnover was observed between summer surveys of consecutive years. Cluster analysis demonstrated a distinct zonation in four vegetation belts from the periphery to the centre of the pond which is typical of these environments. Modelling, based on two IPPC scenarios (A2 and B2), predicted relatively low climate change impacts on the pond’s hydroperiod for the next 100 years (i.e. a decrease of 16 and 24 days, respectively). This reduction in the hydroperiod of the pond will have an effect on the physiognomy and spatial extent of vegetation, particularly for the transitional belts between the core and its outer area, while it will exert more pressure on the pond as a water resource for sheep in the region. However, cumulative effects and complex interactions of climate-driven environmental changes and other anthropogenic disturbances might act synergistically to accelerate impacts in the future.

Character and Variation of Chemical Properties of the Water in the Natural Habitats of Three Species of Isoetes in China

Habitat preference has played an important role in the evolution of the genus Isoetes. Aquatic Isoetes species are generally distributed in oligotrophic softwater. However, it is still uncertain if chemical properties of the water have an impact on the pattern of distribution of Isoetes species. Investigation of habitat preference with regard to water chemistry in natural habitats of species would contribute significance to our understanding of evolution in the genus. Four species of Isoetes are known to occur in China: Isoetes taiwanensis in Taiwan island and /. hyp-sophila, I. yunguiensis and I. sinensis in the mainland, and their distribution regions do not overlap. All four species are endangered aquatic plants throughout their distribution range in the country. In this paper, 20 parameters of water chemistry in the natural habitats, of three species of Isoetes in mainland China were measured, using HANNA Pocket-sized pH Meter HI98107 (resolution = 0.1 pH, accuracy = ±0. 1 pH), HANNA Conductivity Meter Dist4/HI983004 (resolution = 0. 1 m S · cm-1, accuracy = ±0.1 m S·cm-1) and HANNA C200 Multiparameter Ion Specific Photometer (resolution of NO3-N, NO3- , P, Mn and Mo =0.1mg·L-1, accuracy = ±0.1 mg·L-1; resolution of other factors = 0.01 mg·L-1, accuracy = ±0.01 mg· L-1 ). The character and variation of the chemical properties of the water were analyzed using mean, coefficient variability and difference significance tests (ANOVA and Kruskal-Wallis). Results showed a common character in that there were bigger variations in average and coefficient variability of the 20 parameters. Average Ni was overwhelmingly greater than the other factors, and lower conductivity indicated there was litter pollution in the water. However, of the 20 factors assessed, except for pH (p 0.05), P (p 0.05), NO3-N (p 0.05) , NO3- (p 0.05) and Al (p 0.01) , the rest displayed no significant difference among habitats of the three species. This indicated that most of the factors (75% ) were relatively stable. pH had an identically positive correlation with NO3-N and NO3- (p 0.05) ; on the contrary, P had an identically negative correlation with NO3-N and NO3- (p 0.05). pH and P were also negatively correlated (p 0.05). Only Al had a positive correlation with P (p 0.05). An analysis, according to data from other research and this study, suggested the significant difference of chemical nature of the water among the three Isoetes species could be due to differences in physiological characters among them, and has no impact on their distribution.

Germinating Spores and Growing Sporelings of Aquatic Isoetes

Several techniques have been described recently for germinating spores of aquatic species of Isoetes which grow in lakes, ponds, and streams in eastern North America. Boom (1980) used glass vials containing sterile sand and pond water in which he successfully raised sporelings of I. engelmannii, I. flaccida, I. macrospora, and I. riparia. Kott and Britton (1982) germinated spores of I. acadiensis, I. echinospora, I. macrospora, I. riparia, and I. tuckermanii in small vials half filled with distilled water. However, many of their vials became contaminated with fungi that destroyed the viability of the megaspores. Sam (1982) germinated megaspores of I. engelmannii in an inorganic nutrient medium supplemented with Nystatin to inhibit fungi. Webster (1979) described a technique for germinating spores of Selaginella that is similar to the following procedure we use for Isoetes. We have been culturing plants from spores of Isoetes acadiensis, I. echinospora, I. engelmannii, I. hieroglyphica, I. macrospora, I. riparia, and I. tuckermanii for use in germination and hybridization experiments for several years. The aquatic species of Isoetes are ideal pteridophytes for germination and hybridization experiments. Their sporangia are large and contain many spores. Megaspores and microspores are borne in different sporangia on separate leaves. If necessary, unopened sporangia can be excised from sporophylls intact and surface cleansed to eliminate extraneous spore contamination. Thus, megaspores and microspores can be completely isolated for controlled breeding experiments. Also, their spores readily germinate in demineralized water and gametophytes and sporophytes develop normally for several months without supplemental nutrients. Spores are obtained from plants collected in September and October, since plants harvested earlier in the year may not have mature, viable spores. Isoetes hieroglyphica and I. macrospora retain their spores through the winter, so mature spores of these species can also be gathered in the spring. Megaspores are cleansed of microspores in a sieving apparatus made of plastic tubing approximately 10 cm long and 2.5 cm in diameter. An 8 cm square of 0.27 mm sifter mesh (available from Carolina Biological Supply Company) is fitted to one end of the tubing with a rubber band. The sieving apparatus, containing megaspores, is attached to a water faucet using plastic strapping tape. Spores are washed with a steady flow of cold water for 30 minutes, followed by a one minute rinse with sterile, demineralized water. Although megaspore surfaces appear clean after the above treatment, unopened sporangia are preferred for crossing experiments because there is less chance of contamination from microspores. Intact sporangia can be excised from

Short note Report of diurnal acid metabolism in two aquatic Australian species of Isoetes

AbstractPrevious studies have demonstrated the presence of crassulacean acid metabolism in the North American submerged aquatic Isoetes howellii (Isoetaceae). Diurnal changes in titratable acidity and malic acid levels indicate the presence of this pathway in two Australian species of Isoetes.

Crassulacean acid metabolism in the seasonally submerged aquatic Isoetes howellii.

Evidence to date is consistent with the hypothesis that the submerged aquatic Isoetes howellii Engelmann possesses crassulacean acid metabolism. Quantitative 14C uptake studies indicate that CO2 assimilation in both the light and dark are functions of pH and total inorganic carbon level. In both the light and dark, maximum uptake rates in 0.6 mM NaHCO3 were double the rates in 0.3 mM NaHCO3. At both carbon levels there was a large drop in carbon assimilation rate between pH 6 and 8. In nature water pH and inorganic carbon level fluctuated diurnally thus complicating the determination of the contribution of light vs dark CO2 uptake to the total carbon gain. On a sunny day between 0600 and 1200 h water chemistry changed markedly with ∼40% reduction in total carbon, ∼2 pH unit rise resulting from ∼100% depletion of free CO2. Under such conditions daytime deacidification in Isoetes leaves was 88% complete by noon. In contrast, on an overcast day, reduction of carbon in the water was much slower, deacidification was only 46% complete by noon and substantial malic acid levels remained in the leaves at the end of the day. Upon emergence crassulacean acid metabolism was largely lost in Isoetes leaves. Preliminary estimates suggest that under natural submerged conditions, early morning photosynthetic rates may be substantially higher than dark CO2 uptake rates, though uptake rates throughout much of the day could be substantially lower than nightime CO2 assimilation.

DISTRIBUTION OF DIURNAL ACID METABOLISM IN THE GENUS ISOETES

Previous studies have revealed a crassulacean acid metabolism‐like pathway in the submerged aquatic Isoetes howellii (Isoetaceae). A survey of 11 other species in this largely aquatic genus showed all had diurnal fluctuations in titratable acidity and malic acid concentration. The magnitude of the diurnal fluctuation in titratable acidity varied from 119 (μeq g–1 fresh weight) for I. bolanderi to 44 for I. engelmanni. Although these species were grown under similar conditions in a greenhouse, it is questionable whether or not any significance can be attached to observed species specific differences in magnitude of diurnal acid fluctuation. This is suggested by a single species comparison of plants in the field with greenhouse grown plants which indicated nearly as much variation in magnitude of acid fluctuations as observed across all species in the greenhouse. Much of this variation may be due to seasonal differences. Substrate appears to have very little effect on magnitude of acid fluctuations. Since this survey covered most of the range of the latitudinal, elevational, habitat, and morphological variation in the genus, it is likely that diurnal acid metabolism will prove to be common in the genus Isoetes.

Dark CO2-fixation and diurnal malic acid fluctuations in the submerged-aquatic Isoetes storkii.

In the leaves (but not corms) of the submerged aquatic Isoetes storkii malic acid concentration fluctuated from 22 μeg g FW-1 in the evening to 171 μeg g FW-1 in the morning. Associated with this was a change in titratable acidity of 152 μeg g FW-1 between morning and evening. 14C carbon was fixed in both the light and the dark, though the amount of carbon fixed in the light was more than that fixed in the dark. Autoradiographs show 88% of 14CO2 fixed in the dark is recovered after 1 h, in malic acid and the remainder in one other unidentified product, whereas these two products contain less than 15% of the 14C fixed after 1 h exposure to 14CO2 in the light. It is suggested that CAM metabolism in this aquatic species may be related to the low availability of CO2 for photosynthesis during the day in its aquatic environment and that this metabolic pathway may prove common in the genus Isoetes.