Effects of substrate types on nitrogen removal efficacy and growth of Canna indica L.

Constructed wetlands (CWs), a cost effective technology for wastewater treatment, consist of substrates and wetland plants, which should be selected carefully to gain highest treatment efficiency. However, studies on plant growth and responses to different types of substrates are very few. This study aims to assess the effects of substrate types on growth and root morphology of Canna indica L. and nitrogen (N) removal. Twenty-four similar sized approximately 1 month old C. indica plants were selected and grown on different substrates (gravel, pumice and biochar). All plants were supplied with a standard growth medium to which 14 mg L-1 NH4+, 14 mg L-1 NO3-, 3 mg L-1 PO43- were added and pH was adjusted to 6.5. The growth solution was renewed every week. The plants were grown under greenhouse conditions for 45 d. Results showed that growth of C. indica was not significantly different among treatments but differences on root morphology were found. Plants grown on pumice had the largest root diameters while plants grown on biochar had the longest roots. In the gravel-filled treatment, C. indica showed the lowest root diameter and root length but formed more internal air space in its roots. It indicates that types of substrate can affect O2 supply and root morphological adaptation. Moreover, the porous substrate bed systems were capable of eliminating more NH4+ than gravel bed systems, with the NH4+ removal rates of 5.6–6.3 mg L-1 d-1 compared to 4.7 mg L-1 d-1, respectively. The results show that porous substrates can act as plant supporting substrates and play important roles in N adsorption. Also, they can improve oxygen supply and stimulate root growth. Thus, application of porous substrates as filter media could help to increase pollutant removal efficacy of CWs

Soil Seed Banks of Tree Species from Natural Forests, Restoration Sites, and Abandoned Areas in Chiang Mai, Thailand

Soil seed banks have been used for investigation of natural regeneration of forests. In this study, we compared seed density and species composition of soil seed banks of trees among natural forests, restored forests of different ages, and abandoned agricultural land. The soil seed banks were collected from a natural forest (NF), 12-year-old and 17-year-old restoration sites (RF12y and RF17y), and 17-year-old abandoned site (AA) at Ban Mae Sa Mai, Chiang Mai, Thailand. A seedling emergence technique was used to assess seed density and species of emerged seedlings was identified. We found 5-8 tree species at each site. Seed densities in the study areas ranged from 43 to 298 seeds/m2. The seed density of RF12y was significantly higher than that of both NF and AA but not significantly different than RF17y (p < 0.01). Although there was no significant relationship between the restoration ages and the seed densities of the soil seed banks, the species composition of standing vegetation was related to the seed bank species. Sorensen’s similarities between the species composition of the soil seed banks and the existing trees in each area were between 0 and 13.79%, suggesting seed dispersal of both within and across study sites. Eight out of fourteen species in the soil seed banks were dispersed into restoration sites without standing vegetation of those species. Seven of those were animal-dispersed species. The selected native trees, framework species, attracted small seed dispersers into the study areas, especially at the restoration sites. This finding suggests that active forest restoration improved natural regeneration in restoration sites as well as neighboring areas via seed dispersal

Rapid analysis for the identification of the seagrass Halophila ovalis (Hydrocharitaceae)

Seagrasses are considered as one of the most important species as they play key ecological roles in various types of ecosystems and also provide a food source for endangered animal species. There are two main  characteristics of seagrasses that hinder efforts to correctly identify species based on conventional identification keys alone: i) the variability of  morphological characteristics and ii) lack of needed morphological  characters especially flowers. A taxonomically unresolved complex such as Halophila spp. is reported. Plant DNA barcoding regions (rbcL and trnH-psbA) were used to confirm species of collected seagrasses from the southern coast of Thailand. Small and big-leaved samples of Halophila spp. were analysed in this study. The big-leaved samples were identified on the field as Halophila ovalis whilst it was uncertain whether the small-leaved samples belonged to H. ovalis. DNA analysis revealed that the small-leaved samples could be H. ovalis. We also coupled PCR with high resolution melt (HRM) to more cost-effectively identify individuals of H. ovilis than using barcoding alone. Using HRM to resolve differences in the sequence of two genes showed that the two unknown seagrasses belonged to the same species as H. ovalis.  In conclusion, using HRM proved to pose great potential in seagrass identification. Key words: DNA barcoding, Halophila ovalis, rbcL, trnH-psbA, species identification

Clone-specific differences in Phragmites australis: Effects of ploidy level and geographic origin

Phragmites australis (Cav.) Trin. ex Steud. is virtually cosmopolitan and shows substantial variation in euploidy level and morphology. The aim of this study was to assess clone-specific differences in morphological, anatomical, physiological and biochemical traits of P. australis as affected by the geographic origin, the euploidy level (4x, 6x, 8x and 12x), and to assess differences between native and introduced clones in North America. Growth, morphology, photosynthetic characteristics, photosynthetic pigments and enzymes were measured on 11 geographically distinct clones propagated in a common environment in Denmark. Any differences between the measured parameters were caused by genetic differences between clones. Overall, the largest differences between clones were found in ontogeny, shoot morphology and leaf anatomy. The North Swedish clone was adapted to short growing seasons and sprouted very early in the spring but senesced early in July. In contrast, clones from southern regions were adapted to warmer and longer growing seasons and failed to complete the whole growth-cycle in Denmark. Some clones from oceanic habitats with climatic conditions that do not differ much from conditions at the Danish growth site did flower in the common environment. The octoploid genotype in general had larger dimensions of leaves, taller and thicker shoots and larger cell sizes than did the hexaploid and tetraploid clones. The dodecaploid clone was neither bigger than the octoploid, nor significantly different from tetraploid and hexaploid clones in most of the morphological characters observed. Stomatal density decreased with increasing ploidy level, while length of guard cells increased. Tetraploid clones generally had morphometric dimensions, similar to hexaploids. Hence, polyploidy did not always result in an increase in plant size, probably because the number of cell divisions during development is reduced. Four North American clones were included in the study. The clone from the Atlantic Coast and the supposed invasive European clone resembled each other. The Gulf Coast clone differed from the rest of the clones in having leaf characters resembling Phragmites mauritianus Kunth. Thus, morphological characters are not unmistakable parameters that can be used to discriminate between introduced and native clones. The physiological and biochemical processes also differed between clones, but these processes showed considerable phenotypic plasticity and were therefore very difficult to evaluate conclusively. It is concluded that P. australis is a species with very high genetic variability which is augmented by its cosmopolitan distribution, clonal growth form and the large variation in chromosome numbers. It is therefore not surprising that large genetically determined differences in ontogeny, shoot morphology and leaf anatomy occur between clones. \ua9 2006 Elsevier B.V. All rights reserved