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1.
P. SPIERENBURG E.C.H.E.T. LUCASSEN A.F. LOTTER J.G.M. ROELOFS 《Freshwater Biology》2009,54(9):1819-1831
1. During the past century, isoetid vegetation types in softwater lakes have often been invaded by faster‐growing elodeids. In these C‐limited systems, this may be related to rising aquatic CO2 levels. 2. In a laboratory experiment we tested the growth response of two elodeid species, Myriophyllum alterniflorum and Callitriche hamulata, at four different CO2 levels, ranging from 20 to 230 μmol L−1. In addition, we tested the effect of the nutrient status of the sediment on the growth of C. hamulata at the different CO2 levels. 3. Shoot and root growth increased with rising CO2 availability. Irrespective of sediment type, growth was minimal to negative at the lowest CO2 treatment level, while becoming positive at CO2 levels around 40–50 μmol L−1. Substantial growth was only obtained when the macrophytes were growing on mesotrophic sediments. The plants reached close to maximal growth at CO2 levels of c. 100 μmol L−1. 4. Within this experiment, the growth of C. hamulata at CO2 levels above 90 μmol L−1 may have been limited by N and P availability in both sediment types. The growth rate of M. alterniflorum did not seem to be limited by N and P availability, most likely due to its much higher relative root production. 5. The experimental results show that neither M. alterniflorum nor C. hamulata is able to invade isoetid‐dominated softwater lakes at very low aquatic CO2 concentrations. However, if the sediments contain enough nutrients, a rise in aquatic CO2 could allow the invasion of elodeid species leading to the subsequent disappearance of slow‐growing isoetids. 相似文献
2.
1. The impact of groundwater seepage on the growth of submerged macrophytes was investigated in experiments on the isoetid Littorella uniflora and the elodeid Myriophyllum alterniflorum both in the laboratory and in the field. Isoetids rely mostly on sediment‐derived CO2 and nutrients via root uptake, whereas elodeids acquire their inorganic carbon and nutrients from the water column. We thus hypothesised that L. uniflora would respond positively to seeping ground water as it should improve both CO2 and nutrient supply. 2. Laboratory experiments were conducted by percolating vegetated cores containing natural sediment or technical sand with artificial ground water of high CO2 concentrations and with either high or low levels of nutrients. Field experiments were conducted in the oligotrophic Lake Hampen, Denmark, with custom‐built seepage‐growth chambers that permitted a near‐natural flow‐through of seeping ground water. Chambers with a solid bottom, and thus no flow‐through of seeping ground water, served as controls in both laboratory and field experiments. In the field, seepage chambers were installed at a site with relatively high seepage fluxes (ground water from forest catchment), at a site with much lower seepage fluxes but with higher nutrient concentrations (ground water from agricultural catchment) and at a reference site with no net discharge or recharge of ground water. 3. Positive growth responses were observed in the field at transects with high groundwater discharge compared to the control chambers with no seepage. No growth response was observed at the reference transect with low or alternating direction of groundwater seepage. The growth rates of L. uniflora in the field were significantly higher in seepage treatments compared to control treatments, and final plant mass was up to 70% higher than that for plants where seepage was excluded. In areas with high groundwater discharge, a strong positive correlation was found between groundwater seepage fluxes, growth rates, and final plant mass for L. uniflora, while there was no such relationship at the reference transect. The growth of M. alterniflorum was also significantly affected by groundwater seepage, but to a lesser degree than L. uniflora. Laboratory experiments generally showed the same trend for both L. uniflora and M. alterniflorum, and the positive influence of seeping ground water was apparently related to increased inorganic carbon supply and, to a lesser degree, improved nutrient availability. 4. Groundwater discharge results in enhanced growth of isoetids and to some extent elodeids inhabiting a groundwater‐fed softwater lake. We propose that the shallow dense vegetation present where most of the discharge takes place acts as a biological filter that retains nutrients that otherwise would end up in the water column and could result in increased algal growth. 相似文献
3.
ESTHER C. H. E. T. LUCASSEN P. SPIERENBURG R. G. A. FRAAIJE A. J. P. SMOLDERS J. G. M. ROELOFS 《Freshwater Biology》2009,54(11):2300-2314
1. Softwater lakes are generally dominated by slow growing, small, isoetid plant species that are adapted to the carbon‐ and nutrient‐limited conditions in these lakes. We investigated the strategy of a fast growing species, Sparganium angustifolium, for occupying softwater lakes. A field survey was carried out in Norwegian carbon‐limited Isoëteto‐Lobelietum softwater lakes to compare abiotic conditions at locations with and without S. angustifolium. In addition, long term abiotic changes (1995–2008) related to the sudden establishment of the species on experimentally limed plots were studied. Based on the results, the carbon acquisition mechanism of S. angustifolium was tested in eco‐physiological laboratory experiments. 2. The redox potential was significantly lower at locations with S. angustifolium (220 ± 2.3) compared to locations without S. angustifolium (338.1 ± 13.9). The lower redox potential was accompanied by significantly higher concentrations of HCO3?, CO2 and Fe2+ in the sediment pore water, indicating in‐lake alkalinity generation due to higher iron reduction rates in the generally iron‐rich sediments. In addition, the lower redox potential was accompanied by a higher nutrient availability (NH4+ and PO43?) in the sediment pore water. Since there were no differences in water quality between the lakes, the ability of S. angustifolium to grow in softwater lakes very likely depends upon the higher dissolved inorganic carbon (DIC) and nutrient concentrations present in the sediment pore water. 3. Results from the liming experiment revealed that appearance of S. angustifolium on limed plots was related to the dissolution of Ca and Mg carbonates and development of a lower redox potential in the sediment. These processes were accompanied by a sustained increase in the availability of DIC in the sediment pore water. 4. The eco‐physiological experiments indicated that S. angustifolium can increase in biomass and produce floating leaves at a relatively high DIC availability in the root medium. In addition, it appeared that S. angustifolium can take up CO2 by the roots. As far as we know, the ability to use sediment CO2 has only been described as an adaptation typical for isoetid plant species. Use of the relatively large sediment CO2 pools present in these sediment types (>1000 μmol L?1) to enable development of long floating leaves for additional uptake of atmospheric CO2 is a very different strategy to colonise softwater lakes as compared to isoetid plant species. 相似文献
4.
1. Oligotrophic softwater lakes represent a special type of aquatic ecosystem with unique plant communities where generalisations from other aquatic plant communities to rising CO2 in the water column may not apply. 2. In the present study, we set up large in situ mesocosms and supporting laboratory experiments with isoetid vegetation (Littorella uniflora) where water column CO2 and light could be manipulated in order to test whether (i) light and CO2 availability affect nutrient concentrations in isoetid vegetation, and (ii) if changes in light and CO2 climate affect fluxes of inorganic nitrogen (N) and phosphorus (P) from sediment to water column, which potentially could result in increased growth of epiphytic algae. 3. The results showed that the standing stocks of phosphorus and nitrogen in the L. uniflora vegetation were significantly influenced by CO2 concentration and light intensity. Both standing stocks of P and N were significantly higher in the mesocosm treatments with high CO2 concentration than in those at low CO2 concentration. Similarly, standing stocks of P and N enhanced with increasing light intensity. 4. Measurements of nutrient fluxes both in the field and the laboratory did not show any significant release of nutrients to the water column from plants or sediments at any of the light or CO2 treatments. However, mats of epiphytic algae developed from the beginning of June to late September and caused a light reduction for the isoetid vegetation. 5. Increasing CO2 concentrations in the water column may over time potentially result in a change in soft water plant communities. 相似文献
5.
1. Lake eutrophication has increased phytoplankton blooms and sediment organic matter. Among higher plants, small, oligotrophic rosette species (isoetids) have disappeared, while a few tall, eutrophic species (elodeids) may have persisted. Despite recent reduction of nutrient loading in restored lakes, the vegetation has rarely regained its former composition and coverage. Patterns of recovery may depend on local alkalinity because HCO3? stimulates photosynthesis of elodeids and not of isoetids. In laboratory growth experiments with two isoetids (Lobelia dortmanna and Littorella uniflora) and two elodeids (Potamogeton crispus and P. perfoliatus), we test whether organic enrichment of lake sediments has a long‐lasting influence by: (i) reducing plant growth because of oxygen stress on plant roots and (ii) inhibiting growth more for isoetids than elodeids. We also test whether (iii) increasing alkalinity (from 0.17 to 3.20 meq. L?1) enhances growth and reduces inhibition of organic sediment enrichment for elodeids but not for isoetids. 2. In low organic sediments, higher oxygen release from roots of isoetids than elodeids generated oxic conditions to greater sediment depth for Lobelia (4.3 cm) and Littorella (3.0 cm) than for Potamogeton species (1.6–2.2 cm). Sediment oxygen penetration depth fell rapidly to 0.4–1.0 cm for all four species at even modest organic enrichment and oxygen consumption in the sediments. Roots became shorter and isoetid roots became thicker to better supply oxygen to apical meristems. 3. Growth of elodeids was strongly inhibited across all levels of organic enrichment of sediments being eight‐fold lower at the highest enrichment compared to the unenriched control. Leaf biomass of isoetids increased three‐fold by moderate organic enrichment presumably because of greater CO2 supply from sediments being their main CO2 source. At higher organic enrichment, isoetid biomass was reduced, leaf chlorophyll declined up to 10‐fold, root length declined from 7 to <2 cm and mortality rose (up to 50%) signalling high plant stress. 4. Lobelia was not affected by HCO3? addition in accordance with its use of sediment CO2. Biomass of elodeids increased severalfold by rising alkalinity from 0.17 to 3.20 meq. L?1 in accordance with their use of HCO3? for photosynthesis, while the negative impact of organically enriched sediments remained. 5. Overall, root development of all four species was so strongly restricted in sediments enriched with labile organic matter that plants if growing in situ may lose root anchorage. Other experiments demonstrate that this risk is enhanced by greater water content and reduced consolidation in organically rich sediments. Therefore, formation of more muddy and oxygen‐demanding sediments during eutrophication will impede plant recovery in restored lakes while high local alkalinity will help elodeid recovery. 相似文献
6.
OLE PEDERSEN TROELS ANDERSEN KOU IKEJIMA MD ZAKIR HOSSAIN FREDE ØSTERGAARD ANDERSEN 《Freshwater Biology》2006,51(5):865-877
1. The vulnerability of softwater, oligotrophic lakes to eutrophication has caused the disappearance of many, if not most, of the unique isoetid plant communities. We tested whether the presence or disappearance of the isoetid Littorella uniflora (L.) could be predicted from environmental parameters, soil types and land use in the catchment area, and atmospheric nitrogen deposition. 2. We found that the topographic catchment area of a lake was an irrelevant unit to study effects of soil type and land use. Instead, using a GIS‐generated buffer zone around the lakes it proved feasible to classify 472 lakes into historical (if L. uniflora had disappeared) or recent (if L. uniflora was still present) Littorella lakes, based on soil type and land use. Our analysis showed that aeolian sand deposits and heath in the buffer zone favoured the presence of L. uniflora, whereas moraine clay and agriculture were strongly linked to the disappearance of L. uniflora. 3. However, in order to understand fully the presence or disappearance of L. uniflora, environmental data were needed in addition to soil types, land use and nitrogen deposition, and the use of discriminant analysis allowed us to classify 96% of the investigated lakes correctly into recent or historical sites. Alkalinity, total phosphorus, total nitrogen, aeolian sand deposits and heath were the most important parameters explaining the presence or disappearance of L. uniflora. Our analysis also indicated that eutrophication, rather than acidification, has likely caused the disappearance of L. uniflora from 218 of the 472 lakes investigated. 4. Our findings have widespread implications for the conservation or restoration of isoetid habitats and we recommend applying a wide buffer zone around lakes, with restrictions on farming and traditional forestry activities. In addition, our buffering concept may prove a useful tool for aquatic ecologists to investigate relationships between catchment features and organisms (plants, insects and amphibians) with aquatic as well as terrestrial life forms. 相似文献
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CRISTINA PULIDO ESTHER C. H. E. T. LUCASSEN OLE PEDERSEN JAN G. M. ROELOFS 《Freshwater Biology》2011,56(5):939-951
1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects of quantity and lability of sediment organic matter on the biomass of Echinodorus repens and Littorella uniflora and on the force required to uproot plants of L. uniflora. 2. Lake sediments, rich in organic matter, were collected from four lakes, two with healthy populations of isoetids and two from which isoetids had disappeared. The four lake sediments were mixed with sand to prepare a range of experimental sediments that differed in quantity and lability of sediment organic matter. Two isoetid species, E. repens and L. uniflora, were grown in these sediments for 8 weeks. Sediment quality parameters, including elemental composition, nutrient availability and mineralisation rates, were determined on the raw sources of sediment from the lakes. Porewater and surface water were analysed for the chemical composition in all mixtures. At the end of the experiment, plants were harvested and their biomass, tissue nutrient concentration and (for L. uniflora) uprooting force were measured. 3. For both species, all plants survived and showed no signs of stress on all types of sediment. The biomass of E. repens increased as the fraction of organic matter was increased (from 6 to 39% of organic content, depending upon sediment type). However, in some of the sediment types, a higher fraction of organic matter led to a decline in biomass. The biomass of L. uniflora was less responsive to organic content and was decreased significantly only when the least labile sediment source was used to create the gradient of organic matter. The increase in shoot biomass for both species was closely related to higher CO2 concentrations in the porewater of the sediment. The force required to uproot L. uniflora plants over a range of sediment organic matter fitted a Gaussian model; it reached a maximum at around 15% organic matter and declined significantly above that. 4. Increasing organic matter content of the sediment increased the biomass of isoetid plants, as the positive effects of higher CO2 production outweighed the negative effects of low oxygen concentration in more (labile) organic sediments. However, sediment organic matter can adversely affect isoetid survival by promoting the uprooting of plants. 相似文献
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11.
K. Aulio 《Biologia Plantarum》1986,28(3):234-236
CAM-like photosynthesis was found in the isoetid aquatic plantsLittorella uniflora andIsoetes lacustris, but not in the isoetid speciesLobelia dortmanna or in the elodeidElodea canadensis. Of the taxa studied, the first three are known to utilize sediment-borne CO2, whereasElodea is dependent on bicarbonate. 相似文献
12.
1. Arbuscular mycorrhizal fungi (AMF) commonly colonise isoetid species inhabiting oxygenated sediments in oligotrophic lakes but are usually absent in other submerged plants. We hypothesised that organic enrichment of oligotrophic lake sediments reduces AMF colonisation and hyphal growth because of sediment O2 depletion and low carbon supply from stressed host plants. 2. We added organic matter to sediments inhabited by isoetids and measured pore‐water chemistry (dissolved O2, inorganic carbon, Fe2+ and ), colonisation intensity of roots and hyphal density after 135 days of exposure. 3. Addition of organic matter reduced AMF colonisation of roots of both Lobelia dortmanna and Littorella uniflora, and high additions stressed the plants. Even small additions of organic matter almost stopped AMF colonisation of initially un‐colonised L. uniflora, though without reducing plant growth. Mean hyphal density in sediments was high (6 and 15 m cm?3) and comparable with that in terrestrial soils (2–40 m cm?3). Hyphal density was low in the upper 1 cm of isoetid sediments, high in the main root zone between 1 and 8 cm and positively related to root density. Hyphal surface area exceeded root surface area by 1.7–3.2 times. 4. We conclude that AMF efficiently colonise isoetids in oligotrophic sediments and form extensive hyphal networks. Small additions of organic matter to sediments induce sediment anoxia and reduce AMF colonisation of roots but cause no apparent plant stress. High organic addition induces night‐time anoxia in both the sediment and the plant tissue. Tissue anoxia reduces root growth and AMF colonisation, probably because of restricted translocation of nutrient ions and organic solutes between roots and leaves. Isoetids should rely on AMF for P uptake on nutrient‐poor mineral sediments but are capable of growing without AMF on organic sediments. 相似文献
13.
Background and Aims
Submersed plants have different strategies to overcome inorganic carbon limitation. It is generally assumed that only small rosette species (isoetids) are able to utilize the high sediment CO2 availability. The present study examined to what extent five species of submersed freshwater plants with different morphology and growth characteristics (Lobelia dortmanna, Lilaeopsis macloviana, Ludwigia repens, Vallisneria americana and Hydrocotyle verticillata) are able to support photosynthesis supplied by uptake of CO2 from the sediment.Methods
Gross photosynthesis was measured in two-compartment split chambers with low inorganic carbon availability in leaf compartments and variable CO2 availability (0 to >8 mmol L−1) in root compartments. Photosynthetic rates based on root-supplied CO2 were compared with maximum rates obtained at saturating leaf CO2 availability, and 14C experiments were conducted for two species to localize bottlenecks for utilization of sediment CO2.Key Results
All species except Hydrocotyle were able to use sediment CO2, however, with variable efficiency, and with the isoetid, Lobelia, as clearly the most effective and the elodeid, Ludwigia, as the least efficient. At a water column CO2 concentration in equilibrium with air, Lobelia, Lilaeopsis and Vallisneria covered >75% of their CO2 requirements by sediment uptake, and sediment CO2 contributed substantially to photosynthesis at water CO2 concentrations up to 1000 µmol L−1. For all species except Ludwigia, the shoot to root ratio on an areal basis was the single factor best explaining variability in the importance of sediment CO2. For Ludwigia, diffusion barriers limited uptake or transport from roots to stems and transport from stems to leaves.Conclusions
Submersed plants other than isoetids can utilize sediment CO2, and small and medium sized elodeids with high root to shoot area in particular may benefit substantially from uptake of sediment CO2 in low alkaline lakes.Key words: Submersed rooted plants, CO2 uptake, sediment CO2, Lobelia dortmanna, Lilaeopsis macloviana, Ludwigia repens, Vallisneria americana, Hydrocotyle verticillata 相似文献14.
1. It has been hypothesised that the symbiosis with arbuscular mycorrhizal fungi (AMF) leads to a higher uptake of phosphorus (P) and nitrogen (N) in aquatic plants, but it has never been shown experimentally without the use of fungicides. In particular, the symbiosis may be important for nutrient uptake by isoetids in oligotrophic lakes, where low concentrations of inorganic N and P both in the water and in the sediment limit the growth of plants and where symbiosis facilitates the uptake of nutrients from the sediment. 2. Plants of the isoetid Littorella uniflora were propagated under the sterile conditions without an AMF infection. The plants were then grown for 60 days with and without re‐infection by AMF, and with either high (150 μm ) or low (ambient concentration approximately 15 μm ) CO2 concentration. 3. The study proved that the symbiosis between AMF and L. uniflora had a positive impact on the retention of N and P in the plants at very low nutrient concentrations in the water and on biomass development. Shoot biomass and standing stocks of both P and N were significantly higher in re‐infected plants. 4. Raised CO2 concentration resulted in a fivefold increase in hyphal infection, but had no impact on the number of arbuscules and vesicles in the cross sections. There were significantly higher biomass and lower tissue P and N concentrations in the plants from high CO2 treatments. This resulted in similar standing stocks of P and N in plants from low and high CO2 treatments. 5. The results from this study showed that the symbiosis between AMF and L. uniflora is an important adaptation enabling isoetids to grow on nutrient‐poor sediments in oligotrophic lakes. 相似文献
15.
P. Spierenburg E. C. H. E. T. Lucassen C. Pulido A. J. P. Smolders J. G. M. Roelofs 《Plant biology (Stuttgart, Germany)》2013,15(6):955-962
During spring storms massive uprooting of Littorella uniflora occurred in a shallow Dutch softwater lake. The aim of this study was to test whether changes in plant morphology and sediment characteristics could explain the observed phenomenon. Uprooting was expected to occur in plants having a high shoot biomass and low root to shoot ratio (R:S), growing on sediments with a high organic matter content. Normally, uprooting of the relative buoyant L. uniflora is prevented by an extensive root system, expressed as a high R:S. This was studied by sampling floating and still rooted L. uniflora plants, as well as sediment and sediment pore water, along a gradient of increasing sediment organic matter content. Increasing organic matter content was related to increasing L. uniflora shoot biomass and consequently decreasing R:S. Furthermore, the results indicated that uprooting indeed occurred in plants growing on very organic sediments and was related to a low R:S. The increased shoot biomass on more organic sediments could be related to increased sediment pore water total inorganic carbon (TIC; mainly CO2) availability. Additionally, increased phosphorus availability could also have played a role. The disappearance of L. uniflora might lead to higher nutrient availability in the sediments. It is suggested that this could eventually promote the expansion of faster‐growing macrophytes. 相似文献
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CO2 utilization in the production of biomass and biocompounds by three different microalgae
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Joana Assunção Ana Paula Batista João Manoel Teresa Lopes da Silva Paula Marques Alberto Reis Luísa Gouveia 《Engineering in Life Science》2017,17(10):1126-1135
The atmospheric CO2 increase is considered the main cause of global warming. Microalgae are photosynthetic microorganisms that can help in CO2 mitigation and at the same time produce value‐added compounds. In this study, Scenedesmus obliquus , Chlorella vulgaris , and Chlorella protothecoides were cultivated under 0.035 (air), 5 and 10% (v/v) of CO2 concentrations in air to evaluate the performance of the microalgae in terms of kinetic growth parameters, theoretical CO2 biofixation rate, and biomass composition. Among the microalgae studied, S. obliquus presented the highest values of specific growth rate (μ = 1.28 d?1), maximum productivities (P max = 0.28 g L?1d?1), and theoretical CO2 biofixation rates (0.56 g L?1d?1) at 10% CO2. The highest oil content was found at 5% CO2, and the fatty acid profile was not influenced by the concentration of CO2 in the inflow gas mixture and was in compliance with EN 14214, being suitable for biodiesel purposes. The impact of the CO2 on S. obliquus cells’ viability/cell membrane integrity evaluated by the in‐line flow cytometry is quite innovative and fast, and revealed that 86.4% of the cells were damaged/permeabilized in cultures without the addition of CO2. 相似文献
18.
An experiment was conducted from May to November in Lake Hampen, Denmark, to study the effect of higher CO2 concentration on the biomass of filamentous algae. Three enclosures (1.5 m diameter) were enriched with free CO2 to ∼10 times atmospheric equilibrium (∼170 μM) and three enclosures were kept at atmospheric equilibrium (∼17 μM). The isoetid Littorella uniflora dominated the vegetation in the enclosures. Low concentrations of nitrate and phosphate in the water were observed, especially in the summer months. During the summer, a high biomass of filamentous algae (dominated by Zygnema sp.) developed in both types of enclosures (18–58 g dry wt. m−2 in July and August), but the biomass of algae was significantly higher (1.9–38 times) in the CO2 enriched enclosures than in enclosures with low CO2 concentration. L. uniflora biomass, especially leaf biomass, also showed a significant positive response to increased CO2 concentration (75.0 ± 10.4 and 133.3 ± 42.5 g dry wt. m−2 at low and high CO2 concentrations, respectively) even though the massive filamentous algal growth decreased the light intensity. Both filamentous algae (in August) and L. uniflora showed lower tissue concentrations of N and P at high CO2 concentration. 相似文献
19.
Buoyancy of the gas-vacuolate alga Anabaena flosaquae Brébisson was measured under various levels of light, NH4+, and CO2. At high irradiance (50 μE · m?2·?1) the alga was non-buoyant regardless of the availability of CO2 and NH4+. At low irradiance (≤10 μE · m ?2· s?1) buoyancy was controlled by the availability of NH4+ and CO2. When NH4+ was abundant, algal buoyancy was high over a wide range of CO2 concentrations. In the absence of NH4+, algal buoyancy was reduced at high CO2 concentrations, however as the CO2 concentration declined below about 5 μmol · L?1, algal buoyancy increased. These results help explain why gas vacuolate, nitrogen-fixing blue-green algae often form surface blooms in eutrophic lakes. 相似文献
20.
Cristina Pulido Danny J. H. Keijsers Esther C. H. E. T. Lucassen Ole Pedersen Jan G. M. Roelofs 《Aquatic Ecology》2012,46(3):283-295
The increase in alkalinity and SO4 2? in softwater lakes can negatively affect pristine isoetid population because the increase in alkalinity and SO4 2? can stimulate sediment mineralization and consequently cause anoxia. The consequences of increased sediment mineralization depend on the ability of isoetids such as Lobelia dortmanna to oxidize the rhizosphere via radial O2 loss. To study how alkalinity and SO4 2? affect the isoetid L. dortmanna, and if negative effects could be alleviated by neighboring plants, three densities of L. dortmanna (“Low”?=?64 plants m?2, “Medium”?=?256 plants m?2 and “High”?=?1,024 plants m?2) were exposed to elevated alkalinity in the water column, or a combination of both elevated alkalinity and SO4 2?, and compared to a control situation. The combination of SO4 2? and alkalinity significantly increased mortality, lowered areal biomass and reduced actual photosynthetic efficiency. Plant density did not significantly alleviate the negative effects caused by SO4 2? and alkalinity. However, actual photosynthetic efficiency was significantly positively correlated to redox potential in the sediment, indicating a positive relationship between plant performance and sediment oxidation. The negative effects on L. dortmanna were probably caused by long periods of tissue anoxia by itself or in combination with H2S intrusion. Therefore, increase in both SO4 2? and alkalinity surface water can dramatically affect L. dortmanna populations, causing reduction or even disappearance of this icon species. 相似文献