Future climate change predictions indicate that there will be an increase in ambient air temperature. Increases in ambient air temperature will result in a corresponding increase in soil temperature. The consequences of further increases in soil temperature will potentially be detrimental for the soil seed bank of plants in terms of length of dormancy and viability of seeds. This experiment investigated the effect of different exposure temperatures and duration of exposure on the germination of semi-aquatic plant species. Seeds of four species (Alternanthera denticulata, Juncus usitatus, Persicaria lapathifolia and Persicaria prostrata) were exposed to temperatures ranging from 25 to 100°C for durations between 1 and 14 days, before being germinated in an incubator for 6 weeks. Germination occurred in all four species after exposure to temperatures ranging from 25 to 60°C. These temperatures appeared to promote germination as the temperature and duration of exposure increased. However, in P. lapathifolia and P. prostrata, the number of seeds germinating declined when exposed to 70°C and there was no germination for temperatures exceeding this. In contrast, A. denticulata and J. usitatus only began to decline when exposed to 80°C, with no germination at higher temperatures. These results suggest that soil temperatures exceeding potential threshold temperatures of 70 and 80°C will result in a decline in the number of seeds germinating and may potentially see a change in species distributions. As such soil temperatures are already being experienced throughout Australia, some species may already be close to their thermal threshold.

The effects of mineral element uptake on the growth and development of the aquatic plant hydrilla [Hydrilla verticillata (L.f.) Royle.] were studied in a short-term experiment under laboratory conditions. On a dry-weight basis, maximum growth of hydrilla plants was obtained at a 0.016 ppm P and 5 ppm Ca in the growing media. Hydrilla responded favorably to high concentrations of K (40 ppm in the growing media). The presence of 2,4-dinitrophenol (2,4-DNP) reduced uptake of K, Cu, Fe, Mn and did not significantly affect the uptake of Ca or P. Thus the uptake of K, Cu, Fe, and Mn by hydrilla appears to be dependent on metabolic energy.

Infection of Hydrilla verticillata by Macrophomina phaseolina was investigated using scanning and transmission electron microscopy. Sprigs of plants in petri plates were inoculated with suspensions of fungal hyphae. Samples of inoculated and noninoculated plants were taken over time. Fungal cells attached to lower epidermal cell walls but not the upper epidermal cell walls of leaves. In less than 40 h, penetration through the cell wall was completed and colonization of host cells was observed. Penetration of upper epidermis was limited to the cell wall adjacent to a lower epidermal cell. No penetration was observed through the outer cell wall of upper epidermis. Inhibition of penetration through the outer cell wall of the upper epidermis may be attributable to an osmiophilic layer below the cell wall. Disruption of the host cell walls and subsequent host cell death was preceded by massive colonization of the host by this pathogen.

Exotic aquatic plant management is a major concern for public reservoir management in many regions of the United States. A study was conducted to measure the effects of alternative aquatic plant management strategies on recreational expenditures and regional economic activity. The study area was Lake Guntersville, Alabama, and the local economy surrounding the lake. Lake Guntersville is one of the largest reservoirs in the Tennessee Valley Authority system. Results suggested that relatively moderate levels of aquatic plant control are associated with the highest levels of recreation-related economic effects on the economy surrounding Lake Guntersville.

We present a bioeconomic model of three invasive aquatic plants (hydrilla, water hyacinth, and water lettuce) in 13 large Florida lakes, and simulate one-year and steady-state impacts of three control scenarios. We estimate that the steady-state annual net benefit of invasive plant control is $59.95 million. A one-year increase in control yields steady-state gains of $6.55 million per year, and a one-year lapse causes steady-state annual losses of $18.71 million. This model shows that increased control of hydrilla, water hyacinth, and water lettuce is optimal.

Species richness of macrophytes of artificial and natural water bodies covering rivers, streams, canals and habitats with standing water was studied in two Central European biogeographical regions, Pannonian and Carpathian, represented by two model areas (the Borská nížina Lowland and the Turčianska Kotlina Basin). We found that: (i) the total number of macrophytes was higher in artificial water bodies compared to natural aquatic habitats in both regions and differences were statistically significant (P<0.05); and (ii) species richness of macrophytes is relatively low in both regions; slightly higher mean number was found in the Pannonian region (3.53) compared with the Carpathian region (3.06). Effects of environmental characteristics on species richness studied by generalized linear model (GLM) showed that explained variances of GLM were similar in both regions. The main drivers of the diversity pattern were those connected with the hydrology of water bodies, such as substrate characteristics and turbidity, less frequent were chemical characteristics, such as water conductivity and N-contents, whereas landscape characteristics manifested the smallest impact.

The anatomical characters of the scape of Echinodorus glandulosus, E. lanceolatus, E. palaefolius, E. paniculatus, E. pubescens and E. subalatus subsp. subalatus (Alismataceae) were examined. These six sympatric species occur in northeastern Brazil and demonstrate great morphological similarity. The aim of the present study was to identify anatomical characters of taxonomic importance. Scapes possess a uniseriate epidermis composed of thin-walled tabular cells. The scapes of most species have differentiated epidermis, cortex, and vascular cylinders. There are several layers of regular chlorenchyma cells immediately below the epidermis, intercalated with collateral vascular bundles, in all species. There are also laticiferous ducts throughout the scape, and aerenchyma in both the cortex and pith. The shape and outline of scapes, the presence and position of winged extensions, the absence of differentiated vascular cylinders or cortex, and the number of vascular bundles are important characters for differentiating species in Echinodorus. An identification key employing the features analysed is provided.

There are four known species of Isoetes (Family Isoetaceae) from China: I. hypsophila, I. sinensis and I. yunguiensis on the mainland, and I. taiwanensis on Taiwan. In a 4-year study we documented the distribution and habitat characteristics of all four species and evaluated their conservation status using IUCN criteria. All four species are facing a high risk of extinction and should be categorized as Critically Endangered on the IUCN Red List. Habitat degradation and loss, water pollution and eutrophication, competitive exclusion, and human disturbance are the main factors causing the decline and extirpation of Isoetes. Only I. taiwanensis is protected in situ in Yangmingshan National Park on Taiwan. None of the species or habitats of Isoetes on mainland China are presently protected, although all species have been designated by the government as State Key Protected Wild Plants. Our results suggest that conservation strategies should be implemented urgently, particularly on the mainland.