1. Aquatic macrophyte diversity and water quality of 55 ponds in western Japan were related to land use and morphometric variables to identify the environmental factors that sustain biodiversity and ...the spatial extent at which these factors operate. 2. The relevant spatial extent for floating-leaved macrophyte richness (500 m from pond edge) was larger than that for submerged macrophyte occurrence (10, 75 and 100 m), whereas emergent macrophyte richness was best explained at much larger extents (1000 m). Total macrophyte richness was explained at the extent of 500, 750 and 1000 m. The extents relevant for explaining the physicochemical condition of pond water (100 and 250 m) were similar to those for submerged and floating-leaved macrophytes, suggesting that these two growth forms are more sensitive to water quality compared to emergent macrophytes. 3. Diversity of all three growth forms and that of total macrophytes collectively were inversely related to turbidity and nutrient concentration; among the three growth forms, submerged macrophytes were most affected by water quality. 4. Negative relationships were found between the proportion of urban area and the diversity of the three growth forms and that of total macrophytes and water quality. Species richness of emergent, floating-leaved and total macrophytes decreased with depth and increased with surface area up to about 5000 m², above which it declined. 5. Urbanisation and enlargement of ponds were the two main factors that decreased aquatic macrophyte diversity in irrigation ponds. To alleviate the adverse effects of urban areas on aquatic macrophyte diversity, our results suggest that management efforts should focus on the creation of buffer zones within the relevant spatial extent from the pond edge.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Species-level identification of aquatic plants, such as duckweeds (Lemnaceae), can be challenging due to reduced morphological features and high phenotypic plasticity. A taxonomic study of sect. ...Uninerves of the genus Lemna in Japan based on morphological observations and DNA analyses is reported. Two non- indigenous species, L. minuta and L. valdiviana, were confirmed to occur in Japan. Excessively small, enigmatic plants of Lemna apparently specialized to grow in spring-fed waterbodies was determined to be a form of L. minuta. It could not be concluded whether the miniature Lemna represents an ecotype adapted to cool water or an example of phenotypic variation under low temperature conditions.
The parentage of the Potamogeton hybrids P. ×nomotoensis Kadono & T. Noguchi and P. ×yamaga- taensis Kadono & Wiegleb (Potamogetonaceae) was studied by analyzing the plastid-encoded rbcL gene and ...nuclear-encoded internal transcribed spacer (ITS) from the hybrids and putative parents. The results showed P. ×nomotoensis to be a hybrid between P. natans and P. maackianus and P. ×yamagataensis a hybrid between P. natans and P. oxyphyllus. The latter is the first documentation of a hybrid between diploid and tetraploid species in Japan.
The reproductive interference between an invasive alien species, Veronica anagallis-aquatica L., and a native congener, V. undulata Wallich (Plantaginaceae) at the initial stage of invasion by V. ...anagallisaquatica, is reported. Insect pollinators, interspecific pollen transfer, and seed set rate of the two species were investigated at a site where V. undulata was still dominant. Four and two Dipteran species were observed to visit the flowers of V. undulata and V. anagallis-aquatica, respectively. Two species of Syrphidae (hover flies) were shared by them as pollinators. Pollen transfer from V. undulata to V. anagallisaquatica was observed, but transfer in the reverse direction was not detected. The lower rate of seed set in V. anagallis-aquatica is suggested to have been due to reproductive interference from V. undulata and represents a case of frequency-dependent reproductive interference of two congeneric species at the initial stage of invasion of an alien species into the population of a dominant native species.
•Farm ponds are among the most biodiverse anthropogenic freshwater habitats.•Land use and fish abundance were among the significant factors affecting the trophic states of ponds.•Multi-taxonomic ...richness patterns changed along the gradient of trophic states.•A clear-water state was associated with diverse aquatic plants, macroinvertebrates, and adult Odonata.•A turbid state was associated with diverse phytoplankton and fish.
Farm ponds are among the most biodiverse anthropogenic freshwater habitats because of their small size, shallow water depth, and aquatic vegetation. Land-use changes, such as converting riparian vegetation to human use or changing the management practices of farm ponds, are assumed to be major factors that change such ecosystems from a clear-water state to a turbid state, leading to deterioration of water quality and biodiversity in such ponds. Using the database of a large-scale pond survey, we evaluated the effects of surrounding land use (landscape factors and modern pond management practices), fish abundance, and other environmental variables on total phosphorus concentration and taxonomic richness patterns of six biological indicators associated with changes in the trophic state. Local- and landscape-level vegetation structure associated with land use and total fish abundance were among the factors influencing the total phosphorus concentration of farm ponds, a main driver of trophic state changes. In addition, a transition from a clear-water state to a turbid state was associated with lower taxonomic richness of aquatic plants, macroinvertebrates, and adult Odonata, and a higher taxonomic richness of phytoplankton and fish. Based on these results, we discuss potential land-use and pond management strategies for conserving and/or restoring the water quality and biodiversity of farm ponds through maintenance of a clear-water state.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Spring-fed waters have special environmental conditions and sets of unique fauna and flora. Thus, preservation of spring-fed wetlands is important to the conservation of biodiversity in Japan. ...Recently, invasions of alien aquatic plants have been reported in some such waters. Aquatic vascular plants were surveyed at 201 sites in spring-fed rivers, streams, and ponds in 26 prefectures of Honshu, Shikoku, Kyushu, and the Ryukyu Islands. As a result, 69 species were identified, including submerged or floating-leaved forms of terrestrial plants, from 165 sites. Among these, 20 alien species were recorded from 114 sites, and extensive invasion of alien species into spring-fed waters in Japan was documented. The most frequently recorded alien species were Nasturtium officinale R. Br. (including N. × sterile (Airy Shaw) Oefel.), Veronica anagallis-aquatica L., and Elodea nuttallii (Planch.) St. John, followed by Callitriche stagnalis Scop., Egeria densa Planch., and Iris pseudacorus L. The ecological risks posed by these alien aquatic macrophytes are discussed with special reference to environmental conditions specific to spring-fed waters. Some future subjects are proposed to promote surveys of the present status of alien aquatic plants and native flora, including mosses, in spring-fed waters throughout Japan.
DNA analysis and morphological observation were conducted for a putative Potamogeton hybrid endemic to the Fuji Five Lakes and Lake Ashi and Potamogeton × leptocephalus from Lake Biwa, Japan. Both ...proved to be hybrids between P. maackianus and P. perfoliatus. However, the hybrid from the Fuji Five Lakes and Lake Ashi was distinct from P. × leptocephalus in certain morphological characteristics. It is described as a new variety P. × leptocephalus var. fujiensis.
• Background and Aims For heterophyllous amphibious plants that experience fluctuating water levels, it is critical to control leaf development precisely in response to environmental cues that can ...serve as a quantitative index of water depth. Light quality can serve as such a cue because the ratio of red light relative to far-red light (R/FR) increases and blue-light intensity decreases with increasing water depth. Growth experiments were conducted to examine how R/FR and blue-light intensity alter leaf morphology of a heterophyllous amphibious plant, Rotala hippuris. • Methods Using combinations of far red (730 nm), red (660 nm) and blue (470 nm) light-emitting diodes (LEDs), growth experiments were used to quantitatively evaluate the effects of the R/FR ratio and blue-light intensity on leaf morphology. • Key Results Under the natural light regime in an outside growth garden, R. hippuris produced distinct leaves under submerged and aerial conditions. R/FR and blue-light intensity were found to markedly affect heterophyllous leaf formation. Higher and lower R/FR caused leaf characters more typical of submerged and aerial leaves, respectively, in both aerial and submerged conditions, in accordance with natural distribution of leaf types and light under water. High blue light caused a shift of trait values toward those of typical aerial leaves, and the response was most prominent under conditions of R/FR that were expected near the water surface. • Conclusions R/FR and blue-light intensity provides quantitative cues for R. hippuris to detect water depth and determine the developmental fates of leaves, especially near the water surface. The utilization of these quantitative cues is expected to be important in habitats where plants experience water-level fluctuation.
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BFBNIB, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Background: Heterophyllous aquatic plants show marked phenotypic plasticity. They adapt to environmental changes by producing different leaf types: submerged, floating and terrestrial leaves. By ...contrast, homophyllous plants produce only submerged leaves and grow entirely underwater. Heterophylly and submerged homophylly evolved under selective pressure modifying the species-specific optima for photosynthesis, but little is known about the evolutionary outcome of habit. Recent evolutionary analyses suggested that rbcL, a chloroplast gene that encodes a catalytic subunit of RuBisCO, evolves under positive selection in most land plant lineages. To examine the adaptive evolutionary process linked to heterophylly or homophylly, we analyzed positive selection in the rbcL sequences of ecologically diverse aquatic plants, Japanese Potamogeton. Principal Findings: Phylogenetic and maximum likelihood analyses of codon substitution models indicated that Potamogeton rbcL has evolved under positive Darwinian selection. The positive selection has operated specifically in heterophyllous lineages but not in homophyllous ones in the branch-site models. This suggests that the selective pressure on this chloroplast gene was higher for heterophyllous lineages than for homophyllous lineages. The replacement of 12 amino acids occurred at structurally important sites in the quaternary structure of RbcL, two of which (residue 225 and 281) were identified as potentially under positive selection. Conclusions/Significance: Our analysis did not show an exact relationship between the amino acid replacements and heterophylly or homophylly but revealed that lineage-specific positive selection acted on the Potamogeton rbcL. The contrasting ecological conditions between heterophyllous and homophyllous plants have imposed different selective pressures on the photosynthetic system. The increased amino acid replacement in RbcL may reflect the continuous fine-tuning of RuBisCO under varying ecological conditions.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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