Application of rapd in the determination of genetic fidelity in micropropagated Drosera plantlets

Summary Random amplified polymorphic DNA (RAPD) markers were used to verify the clonal fidelity of two micropropagated Drosera species, D. anglica and D. binata, which were regenerated by adventitious budding from leaf explants and shoot tips, respectively. Twenty arbitrary decamers were used to screen 15 randomly selected plantlets of each species. No genetic variation was detected among D. binata regenerants, whereas a 0.08% polymorphism frequency was estimated for D. anglica plantlets. These results indicate that the regeneration of plants through shoot-tip culture is a low-risk method for generating genetic variability, whereas material regenerated through leaf explants requires further verification.     

Naphthoquinone contents of in vitro cultured plants and cell suspensions of Dionaea muscipula and Drosera species

In vitro cultured carnivorous plants were grown on a hormone-free medium. They produced the following naphthoquinones: Dionaea muscipula (plumbagin: 5.3%), Drosera rotundifolia (7-methyljuglone: 0.6%), D. binata (plumbagin: 1.4%), and D. capensis (7-methyljuglone: 0.5%). A red, slow-growing suspension culture of D. muscipula was maintained in a modified McCowns Woody Plant (McC) medium and produced plumbagin (2.59%) after 30 days growth. A suspension culture of D. rotundifolia grew slowly as multicoloured small aggregates only in a modified Murashige and Skoog (MS) medium. No quantifiable amounts of naphthoquinones were produced. Several cell lines of D. capensis were developed. Green aggregates grown in a modified MS medium contained 7-methyljuglone (0.33%) and differentiated into plants when placed onto hormone-free medium. Pink cultures grown in modified McC medium contained 7-methyljuglone (1.24%), while dark red cultures produced ca. 1% in both modified McC and MS media. Though the latter medium was significantly better with regard to biomass production, cells excreted a mucin when cultured in both media (0.21 g dry mucin/g dry cells in McC) and (0.16 g dry mucin/g dry cells in MS). Effects of the presence or absence of light during the growth period of 30 days showed that there was no effect on biomass and only slight effects on mucin production and naphthoquinone contents.     

The significance of opportunistic predators for the sympatric carnivorous plant species Drosera intermedia and Drosera rotundifolia

Summary Earlier feeding experiments with Drosera in the field using adult Drosophila melanogaster as prey had shown that D. intermedia reacts three times as strong with respect to biomass production as the sympatric species D. rotundifolia. The present study shows that in D. rotundifolia only 29% of added flies remain on the leaves for more than 24 h, but 95% in D. intermedia. Opportunistic predators, mostly ants, are likely to be responsible for this difference. Ants were often observed robbing food from the leaves of D. rotundifolia, and showed a much higher activity in the microhabitat of this species. In both species of Drosera larger individuals were better than smaller ones in retaining added flies. The activity of ants significantly increased with air temperature and the duration of sunshine. The advantage of plundering seems to be more important for the ants than the danger of being caught. The prey collected from Drosera may be an important source of food for bog-dwelling ants.     

不同培养条件对勺叶茅膏菜试管苗矶松素含量的影响

为探讨培养条件对勺叶茅膏菜(Drosera spatulata)试管苗矶松素积累的影响,采用高效液相色谱(HPLC)法测定矶松素含量,对不同器官和不同培养条件下的勺叶茅膏菜试管苗矶松素含量变化进行研究。结果表明,勺叶茅膏菜试管苗根的矶松素含量显著高于叶片;光质和有机物含量对勺叶茅膏菜试管苗矶松素含量的影响不显著,但对试管苗的生长具有显著影响,最佳培养光质为白光,其次为红光和蓝光,最后为绿光;适当降低培养基中有机物含量可促进勺叶茅膏菜试管苗的生长发育;植物生长调节剂对矶松素积累的影响效应依次为6-BANAAKTGA3,而对试管苗生长的影响效应依次为6-BAGA3NAAKT。因此,勺叶茅膏菜试管苗的最佳培养条件为:以1/2MS为基本培养基,添加0~0.2 mg L–1 6-BA、0.2 mg L–1 NAA、0.5 mg L–1KT和0.1 mg L–1 GA3,于白光下培养。     

鱼藤属植物优异物种筛选及引种栽培研究

为了解粉垄“145”模式在新植蔗上的应用效果,解析其生理生态基础,该研究以桂柳05136为材料,设置常规耕作(CK)和粉垄“145”模式(FL145)2个处理,通过大田试验研究粉垄“145”模式对土壤性质以及新植蔗农艺性状、光合特性和产量品质的影响,并分析其经济效益。结果表明：(1)与CK相比,FL145的0～20 cm、20～40 cm根区,土壤容重显著降低1.25%～5.98%,土壤孔隙度显著提高1.08%～4.77%,土壤含水量显著提高1.78%～8.23%。(2)FL145促进新植蔗根系生长,出苗效果和农艺性状表现良好,株高显著增加2.20%～7.86%。(3)FL145的新植蔗单株叶面积显著增大15.88%,叶绿素含量、净光合速率、气孔导度、胞间CO₂浓度分别显著提高1.41%、6.84%、18.67%、10.06%,光合能力增强,单株干物质积累量显著增加9.26%。(4)收获时,FL145的新植蔗有效茎数、茎长、茎径显著增加,理论产量和实际产量分别显著提高5.07%和5.11%,蔗汁蔗糖分和锤度分别显著提高1.61%和1.50%,还原糖分显著下降12....     

Variation in resource abundance affects diet and feeding morphology in the pumpkinseed sunfish (Lepomis gibbosus)

Summary Growth responses and accumulation of N and P were studied in two pygmy south-west Australian species of Drosera following supplementary feeding of arthropods (collembolans, Hypogastrura vernalis and fruit flies, Drosophila melanogaster) and/or a balanced mineral nutrient supplement (N as nitrate) via the roots. One feeding experiment used glasshouse-raised germlings from vegetative propagules (gemmae) of the perennial Drosera closterostigma, the other three (two on D. closterostigma and one on the annual D. glanduligera) involved natural populations engaging in natural captures of indigenous prey. All experiments recorded highly significant increases in plant dry matter, N and P (all plant age groups) and in reproductive performance (adult plants only) from artificial feeding of arthropods, but no apparent benefits from minerals alone or additive effects of minerals above that due to insects. Unresponsiveness to mineral nutrients was suggested to relate to inability of the species to use nitrate, while up to three-fold growth and nutrient uptake response to insects indicated that growth of natural populations might be severely limited by inadequate catches of prey. It is concluded that the highly nutrient-poor conditions typical of the habitat of pygmy species of Drosera may have promoted marked specialization towards carnivory and an attendant decline in ability to utilize soil-derived sources of nutrients.     

The utilization of nitrogen from insect capture by different growth forms of Drosera from Southwest Australia

Summary Plants of Drosera species, neighbouring noncarnivorous plants, and arthropods on or near each Drosera sp. were collected at 11 contrasting habitat locations in SW Australia. At three of the sites clones of the rare glandless mutant form of D. erythrorhiza were collected alongside fully glandular counterparts. The ¹⁵N value (¹⁵N/¹⁴N natural isotope composition) of insect-free leaf and stem fractions was measured, and the data then used to estimate proportional dependence on insect N (%N_dI) for the respective species and growth forms of Drosera. The data indicated lower %N_dI values for rosette than for self-supporting erect or for climbing vine species. The latter two groups showed an average %N_dI value close to 50%. The %N_dI increased with length and biomass of climbing but not erect forms of Drosera. ¹⁵N values of stems were positively correlated with corresponding values for leaves of Drosera. Leaf material was on average significantly more ¹⁵N enriched than stems, possibly due to delayed transport of recent insect-derived N, or to discrimination against ¹⁵N in transfer from leaf to the rest of the plant. The comparison of ¹⁵N values of insects and arthropod prey, glandless and glandular plants of D. erythrorhiza indicated %N_dI values of 14.3, 12.2 and 32.2 at the respective sites, while matching comparisons based on ¹⁵N of insect, reference plants and glandular plants proved less definitive, with only one site recording a positive %N_dI (value of 10.4%) despite evidence at all sites of feeding on insects by the glandular plants. The use of the ¹⁵N technique for studying nutrition of carnivorous species and the ecological significance of insect feeding of different growth forms of Drosera growing in a large range of habitats is discussed.     

Life on a deadly trap: Buckleria paludum,a specialist herbivore of carnivorous sundew plants,licks mucilage from glands for defense

Caterpillars of Buckleria spp. (Lepidoptera: Pterophoridae) have a unique feeding habit of eating trap leaves of carnivorous sundew plants (Drosera spp.). We observed the foraging behavior of Buckleria paludum on trap leaves of Drosera spp. and discussed how the moth species avoided being caught by trap leaves. In 81.5% (66/81) of encounters with glandular hairs on adaxial surfaces of Drosera trap leaves, B. paludum larvae licked mucilage and crawled on the processed hairs. The frequency of licking mucilage was significantly higher than the frequency of other behaviors such as eating glandular hairs, chewing bases of them without eating and ignoring when encountering secreted mucilage. Licking mucilage enables the caterpillars to move safely on trap leaves and prevents bending of glandular hairs.     

Inhibition of growth,and effects on nutrient uptake of arctic graminoids by leaf extracts — allelopathy or resource competition between plants and microbes?

Previous research has shown that plant extracts, e.g. from boreal dwarf shrubs and trees, can cause reduced growth of neighbouring plants: an effect known as allelopathy. To examine whether arctic and subarctic plants could also be affected by leaching of phytochemicals, we added extracts from the commonly occurring arctic dwarf shrubs Cassiope tetragona and Empetrum hermaphroditum, and from mountain birch, Betula pubescens ssp. tortuosa to three graminoid species, Carex bigelowii, Festuca vivipara and Luzula arcuata, grown in previously sterilized or non-sterilized arctic soils. The graminoids in non-sterilized soil grew more slowly than those in sterilized soil. Excised roots of the plants in non-sterilized soil had higher uptake rate of labelled P than those in sterilized soil, demonstrating larger nutrient deficiency. The difference in growth rate was probably caused by higher nutrient availability for plants in soils in which the microbial biomass was killed after soil sterilization. The dwarf shrub extracts contained low amounts of inorganic N and P and medium high amounts of carbohydrates. Betula extracts contained somewhat higher levels of N and much higher levels of P and carbohydrates. Addition of leaf extracts to the strongly nutrient limited graminoids in non-sterilized soil tended to reduce growth, whereas in the less nutrient limited sterilized soil it caused strong growth decline. Furthermore, the N and P uptake by excised roots of plants grown in both types of soil was high if extracts from the dwarf shrubs (with low P and N concentrations) had been added, whereas the P uptake declined but the N uptake increased after addition of the P-rich Betula extract. In contrast to the adverse extract effects on plants, soil microbial respiration and soil fungal biomass (ergosterol) was generally stimulated, most strongly after addition of the Betula extract. Although we cannot exclude the possibility that the reduced plant growth and the concomitant stimulation of microbial activity were caused by phytochemicals, we believe that this was more likely due to labile carbon in the extracts which stimulated microbial biomass and activity. As a result microbial uptake increased, thereby depleting the plant available pool of N and P, or, for the P-rich Betula extract, depleting soil inorganic N alone, to the extent of reducing plant growth. This chain of events is supported by the negative correlation between plant growth and sugar content in the three added extracts, and the positive correlation between microbial activity, fungal biomass production and sugar content, and are known reactions when labile carbon is added to nutrient deficient soils.     

Breeding systems of the Japanese-endemic carnivorous sundew species Drosera makinoi and Drosera toyoakensis (Droseraceae)

In response to unfavorable environmental conditions, some Drosera species in the northern hemisphere do not open their flowers but form bud-like flowers. The bud-like flowers exhibit pseudo-cleistogamous behavior and produce similar numbers of seeds as open flowers. However, it is not clear how common this type of reproduction is in the genus Drosera. In this study, we examined the effects of flowering (opening flowers/forming bud-like flowers) and pollinator visitation on seed production in Drosera makinoi and D. toyoakensis, two endemic species in Japan. D. makinoi and D. toyoakensis plants did not open 20%–40% chasmogamous flowers to form bud-like flowers. The numbers of mature seeds produced by bud-like flowers were significantly lower than those produced by open flowers (0%–2% of open flowers). In D. makinoi, the percentage of bud-like flowers correlated negatively with the seed production per plant, suggesting that the production of bud-like flowers decreased the lifetime reproductive success. In both D. makinoi and D. toyoakensis, pollinator-excluded flowers produced similar numbers of seeds as control flowers. Our results suggest that pseudo-cleistogamy does not occur in D. makinoi and D. toyoakensis, and they produce seeds without pollinator visits once flowers open.     

Hairy root culture of <Emphasis Type="Italic">Plumbago indica</Emphasis> as a potential source for plumbagin

Hairy roots of Plumbago indica were established at high frequency (90 %) by infecting leaf explants with Agrobacterium rhizogenes strain ATCC 15834. The axenic root cultures were established under darkness in hormone-free liquid Murashige and Skoog medium containing 3 % sucrose. The highest plumbagin content was found to accumulate in roots at their exponential phase of growth. A low pH (4.6) and a low concentration of sucrose (1 %) were beneficial for root growth in darkness, while pH 5.6 and 3 % sucrose under continuous irradiance enhanced plumbagin accumulation in roots up to 7.8 mg g⁻¹(d.m.). Direct shoot regeneration from hairy root culture was also achieved under continuous irradiance, thus indicated an easy way of obtaining transformed P. indica plants.     

A sensitive flower: mechanical stimulation induces rapid flower closure in Drosera spp. (Droseraceae)

Some plants rapidly close their leaves in response to mechanical stimulation, but no case is known in which mechanical stimulation causes rapid petal closure. In this study, we found that Drosera tokaiensis closes petals within 2–10 min after experimental stimulation of the calyx, closed flowers or scapes with a pair of tweezers. Although petal closure was induced more rapidly by touching a position closer to a flower, it was not induced by stimulating stamens and pistils. The habit of petal closure varies among species of Drosera: after experimental stimulations of the calyx or scapes, D. tokaiensis and D. spatulata often closed petals but D. rotundifolia and D. toyoakensis did not close them. The petal closure may function as defense against a specialist florivore.     

Competition between siratro and kleingrass for15N labelled mineralized nitrogen

Summary Isotope dilution provides a method for measuring plant competition for mineral N and transfer of biologically fixed N from a legume to a grass. A plant growth medium was enriched with¹⁵N, and used to grow Siratro (Macropitilium atropurpureum D.C. Urb.) and Kleingrass 75 (Panicum coloratum L.) in 20 liter pots for 98 days in a glasshouse. The plants were grown in pure stand and in mixtures. When grown in 50∶50 mixture the grass obtained 59% of the labelled N and the legume obtained 41%. The grass produced nearly as much root mass as the legume even though biomass of the shoots were less than half that of the legume. Reducing the proportion of either plant species in the mixture reduced the proportion of the mineralized N absorbed by that species. The shoots of the grass were significantly more enriched (1.166 atom%¹⁵N excess) than the roots (1.036). The grass received 12% of its N as biologically fixed N from the legume.     

Agrobacterium rhizogens mediated transformation of Rauvolfia serpentina: Regeneration and alkaloid synthesis

Shoot cultures of Rauvolfia serpentina infected with Agrobacterium rhizogenes 15834 produced tumourous tissue at the site of injection, which eventually developed callus with hairy roots. Sporadic shoot formation occurred from the hairy roots. The shoots were grown to maturity in the green house. The mature transformed plants (RST) showed distinct variations in their physiological characteristics. The flowers of the transformed plants were more delicate and less pigmented when compared to the flowers of the mature normal plants. The roots of the transformed plants were hairy with a number of lateral branches, whereas the roots of the normal plant had very few lateral branches. The biomass of the transformed plant was 86.39 g/plant (fresh wt), significantly higher than the normal plant which was 77.3 g/plant (fresh wt). The total alkaloid content in the mature transformed plant (0.073 g per plant) was similar to the normal plant (0.078 g per plant), although the hairy roots contained little alkaloid.Abbreviations MS Murashige & Skoog's basal medium - MLS modified Linsmaier & Skoog's basal medium - BA benzyladenine - NAA naphthalene acetic acid - TLC thin layer chromatography - HPLC high performance liquid chromatography     

Growth and nutrient allocation in Phaseolus vulgaris L. colonized with endomycorrhizae or Rhizobium

Two cultivars of Phaseolus vulgaris L., one responsive to colonization with microsymbionts (Mexico 309) and one less-responsive (Rio Tibagi) were grown in Leonard jars containing sand/vermiculite under greenhouse conditions. Bean plants were either left non-inoculated (controls) or were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum or a strain of Rhizobium leguminosarum bv. phaseoli (UMR-1899). Plants from the Mexico 309 cultivar maintained a higher growth rate, supported proportionately more nodules and mycorrhizae, and assimilated relatively more N or P when colonized by Rhizobium or Glomus, respectively, than did plants of the Rio Tibagi cultivar. Estimated specific nodule activity for Mexico 309 beans was more than twice that of Rio Tibagi, whereas the specific phosphorus uptake rate (SPUR) was 35% greater in the non-inoculated roots of Rio Tibagi compared to Mexico 309. Colonization by G. etunicatum more than doubled the SPUR for each cultivar compared to control roots. New acid phosphatase isozymes appeared in VAM-colonized roots of both cultivars compared to controls. Acid and alkaline phosphatase activities were significantly higher in G. etunicatum-colonized Mexico 309 roots, but not in Rio Tibagi mycorrhizae, compared to uninfected roots. Polyphosphate hydrolase activity was elevated in mycorrhizae of both cultivars compared to control roots. These results indicate that the dependence of a host on a specific endophyte increases when there are limitations to the supply of a nutrient that the endophyte can provide. The greater the increase in absorption or utilization capacity following colonization by the microsymbiont, the greater the dependence by the host. More importantly, identification of enzymatic activities that influence these plant-microbe associations opens the possibility that the specific genes that code for these enzymes could be targeted for future manipulation.     

The significance of carnivory for the fitness of Drosera in its natural habitat

Summary The effects on Drosera intermedia and D. rotundifolia of supplementary feeding with Drosophila melanogaster were studied in plants growing in their natural habitat. The artificial food supply was within the natural range of prey quantity. In both species supplementary feeding led to significantly higher dry weights of summer and winter plant, more leaves, more flowers, more seeds, and a larger trapping area. The dry weight of plants increased much more than the dry weight of prey added, indicating a fertilizing effect. Thus, animal food supply is an important limiting factor in the field. The essential component of the prey is probably its mineral content. There were significant differences between the two species of sundew. In D. rotundifolia the effect of feeding on dry weight was smaller and plants nerver showed axillary budding. However the effect on the percentage of blooming plants was more than twice as strong as in D. intermedia. Considering only the prey actually absorbed per unit of plant biomass, both species show about the same fertilizing effect. The number of fruits per unit of biomass was about twice as large in D. rotundifolia as in D. intermedia. The reasons for these differences are discussed in the light of niche segregation with respect to habitat and range of prey.     

Did Drosera evolve long scapes to stop their pollinators from being eaten?

Background and Aims

Insectivorous plants frequently display their flowers on the ends of long racemes. Conventional wisdom is that long racemes in insectivorous plants have evolved to provide spatial separation between flowers and traps, which consequently prevents pollinators from being captured. However, it is also possible that long racemes evolved for better seed dispersal or to make flowers more visible to pollinators.

Methods

Two sympatric insectivorous plants with identical pollinators were studied: Drosera cistiflora, with an upright growth form but a short raceme; and Drosera pauciflora, with a basal rosette of traps and a very long raceme. If long racemes evolved to protect their pollinators then D. cistiflora should capture more pollinators than D. pauciflora. However, if long racemes evolved to attract pollinators then taller flowers should receive more pollination visits than shorter flowers.

Key Results

Examination of D. pauciflora and D. cistiflora traps revealed that no pollinators were captured by either species, suggesting that long racemes did not evolve to protect pollinators from being captured. Experimental manipulations of flower height in D. cistiflora showed that experimentally shortened plants received significantly fewer pollination visits than plants which were taller in stature.

Conclusions

Long scapes in Drosera and non-insectivorous plants probably evolved due to similar selective pressures such as pollinator attraction.     

Long-distance signals positively regulate the expression of iron uptake genes in tobacco roots

Long-distance signals generated in shoots are thought to be associated with the regulation of iron uptake from roots; however, the signaling mechanism is still unknown. To elucidate whether the signal regulates iron uptake genes in roots positively or negatively, we analyzed the expressions of two representative iron uptake genes: NtIRT1 and NtFRO1 in tobacco (Nicotiana tabacum L.) roots, after shoots were manipulated in vitro. When iron-deficient leaves were treated with Fe(II)-EDTA, the expressions of both genes were significantly reduced; nevertheless iron concentration in the roots maintained a similar level to that in roots grown under iron-deficient conditions. Next, all leaves from tobacco plants grown under the iron-deficient condition were excised. The expression of two genes were quickly reduced below half within 2 h after the leaf excision and gradually disappeared by the end of a 24-h period. The NtIRT1 expression was compared among the plants whose leaves were cut off in various patterns. The expression increased in proportion to the dry weight of iron-deficient leaves, although no relation was observed between the gene expression and the position of excised leaves. Interestingly, the NtIRT1 expression in hairy roots increased under the iron-deficient condition, suggesting that roots also have the signaling mechanism of iron status as well as shoots. Taken together, these results indicate that the long-distance signal generated in iron-deficient tissues including roots is a major factor in positive regulation of the expression of NtIRT1 and NtFRO1 in roots, and that the strength of the signal depends on the size of plants.     

Effect of nitrate supply on the in-vivo synthesis and distribution of trifollin A,a Rhizobium trifolii-binding lectin,in Trifolium repens seedlings

In-vivo synthesis of the white-clover lectin, trifoliin A, was examined by the incorporation of labeled amino acids into protein during heterotrophic growth of intact Trifolium repens L. seedlings. Lectin synthesis was quantified by measuring the level of labeled protein immunoprecipitated from root exudate, from the hapten (2-deoxyglucose) eluate of the roots, and from root and shoot homogenates. The presence of labeled trifoliin A was confirmed by non-denaturing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by fluorography and comparison with trifoliin A standards. In-vivo-labeled trifoliin A was detected in seedling root homogenate 2 h after the addition of labeled amino acids and on the root surface by 8 h. Incorporation of labeled amino acids into protein and trifoliin A was greatest with 2-d-old seedlings and was greater when the plants were grown continuously in the dark than when they were exposed to 14 h light daily. Significantly more labeled lectin accumulated on the root surface of seedlings grown with 1.5 mM KNO₃ than of seedlings grown either without N or with 15.0 mM KNO₃. The labeled lectin from the root surface in all nitrate treatments and from the rootexudate samples of seedlings grown N-free and with 1.5 mM KNO₃ was fully able to bind to Rhizobium trifolii. In contrast, only 2% of the immunoprecipitable protein found in the root exudate of seedlings grown with 15.0 mM KNO₃ was able to bind to the bacteria. Thus, excess nitrate does not repress the synthesis of trifoliin A in the root, but does affect the distribution and activity of this newly synthesized lectin in a way which reduces its ability to interact with R. trifolii. By using Western blot analysis, much more total trifoliin A is detected in the homogenates of shoots than roots. However, greater than 80% of the total labeled protein and 85–90% of the total labeled lectin were found in the root homogenates of 2-d-old dark-grown seedlings incubated for 5 h with labeled amino acids. In addition, Western blot analysis indicated that the shoot homogenate contained smaller-molecular-weight peptides which reacted with the specific anti-trifoliin A antibody. These studies indicate that stored trifoliin A in the seed is degraded in the shoots during seedling development, while newly synthesized trifoliin A in the roots is excreted to the root surface and external environment.Abbreviations IgG immunoglobulin G - LPS lipopolysaccharide - PBS 10 mM potassium-phosphate buffer, pH 7.0, containing 0.8% NaCl - PBS-T 20 mM phosphate-buffered saline, pH 7.4, containing 0.05% Tween 20 - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Factors determining the habitat of Drosera sessilifolia in the humid zone of the Brazilian Cerrado

Drosera sessilifolia, a tiny carnivorous plant whose adult size is around 3 cm, sometimes inhabits the humid zone known as the campo limpo umido in the Brazilian Cerrado region. D. sessilifolia rarely occurs in the swampy area along the stream in this region; however, its occurrence is expected to decline with agricultural development. In the present study, we examined the factors determining the habitat and growth of D. sessilifolia in the campo limpo umido as well as how these factors have been modified by agricultural developments. Our survey suggests that the growth of D. sessilifolia is greatly influenced by light in areas where sufficient soil moisture is available. The light environment at the edge of a track constructed for reasons of agricultural development is in fact more suitable for D. sessilifolia than that found in the areas formerly inhabited by it. However, soon after construction, the artificial habitat may be occupied by tall-growing plants. In the former habitat of D. sessilifolia, the amount of accumulated litter and the size of the submerged spot also influenced its growth. In order to conserve short-growing plants, like D. sessilifolia in the plant community, the accompanying tall-growing dominant grasses should be controlled by periodic human disturbance.