Wetland Grass Research Articles

Cover thresholds for impacts of an exotic grass on the structure and assembly of a wet prairie community

Potential impacts of an exotic grass, Hemarthria altissima, on restoration of wet prairie community structure (species richness and cover of indicator species) and assembly processes (temporal turnover rates of plant species) on the Kissimmee River floodplain in Central Florida, USA, were evaluated over a 12-year period before and after restoration of hydrologic regimes (2001), and implementation of herbicide treatments (2006–2007) to control its spread. Thresholds for impacts were derived from comparisons of sample sites with variable levels of H. altissima cover. Prior to herbicide treatments, cover of H. altissima exhibited a logistic increase over time, with peak colonization and expansion occurring during major flood events. Mean post-restoration cover of three native wet prairie indicator species (Polygonum punctatum, Panicum hemitomon, and Luziola fluitans) increased to 37.8 ± 3.4 % in plots in which H. altissima cover was 30 %. Prior to and after herbicide treatments, these indicator species largely accounted for observed differences in wet prairie community structure (i.e., cover of wetland forbs and grasses) between heavily infested sites and plots with low or no cover of H. altissima. The cover threshold at which H. altissima began to have these community-level effects was 40–50 %, but lower species richness was found only where H. altissima cover was >80 %. Increasing cover of H. altissima led to a significant decline in temporal turnover rates of plant species (P 75 %) cover of H. altissima. Mean temporal turnover rates of plant species increased significantly (P = 0.03) after herbicide treatments and subsequently were highest during an ensuing flood pulse. However, 2–3 years after herbicide treatments, regrowth of H. altissima reestablished high cover (mean = 59 ± 9.5 %) in over half of the treated plots. The ability of H. altissima to establish dominant cover in restored hydrologic conditions on the Kissimmee River floodplain, and documented regrowth following herbicide treatments, increase the potential for this exotic grass species to be a pervasive threat to successful reestablishment of wet prairie community structure and assembly processes.

African wetlands and their seasonal use by wild and domestic herbivores

African wetlands include dambos or headwater valley grasslands in the upper regions of catchments, circular pan grasslands in drainage sumps, linear riverine grasslands in the mid regions of catchments and broad floodplains, swamps and deltas in the lower regions of catchments. Plant zonation on flood frequency and duration gradients occurs in predictable sequences across Africa and this variation combined with increasing retention of soil moisture for plant growth over the dry season with increasing flooding provides critical resource heterogeneity for herbivores. Consequently, wetlands are essential dry-season habitats for wild and domestic herbivore populations across Africa, often providing key resources that buffer herbivore population numbers in the face of severe dry seasons and droughts. Floodplain peripheries and shallow to intermediate-depth floodplains are generally preferred over the early dry season, with deep floodplains and swamps being used by the late dry season and during droughts. Wetland grasslands are generally able to withstand extremely heavy grazing over the dry season without becoming degraded because they are inaccessible to grazers during the period of flooding over the wet season, giving plants a full growing season’s recovery period, as well as by wetland grasses storing a large proportion of their biomass in deep root systems and rhizomes. African wetlands are under siege by upstream damming and by agricultural projects and further/reinforced conservation measures are needed to protect them, such as ecologically designed water releases from dams to maintain flooding regimes and prevention of agriculture on key floodplains for grazers.

Online appendix 1:A phytosociology survey and vegetation description of inselbergs in the uKhahlamba-Drakensberg Park World Heritage Site, South Africa

No previous scientific surveys have been conducted on inselbergs in the Drakensberg. The aim of this study was to collect specimens, identify, describe and name the vegetation clusters and assess biogeographical connections with other Afromontane regions. A total of 103 relevés where sampled from six inselbergs. The plant sampling was carried out according to the Braun-Blanquet method with the plant and environmental data entered in TURBOVEG and exported as a Cornell Condensed format file (CC!) into Juice. Classification was completed using TWINSPAN (Two-way Indicator Species Analysis) (modified), resulting in 4 major communities, 11 communities, 13 sub-communities and 18 variants. Ordination (indirect) was carried out using CANOCO (version 4.5) to investigate the relationship between species. The four major communities identified are Rhodohypoxis rubella (wetland grass and forblands), Scirpus ficinioides – Crassula peploides (sheet rock grass and forblands), Pentaschistis exserta (high-altitude alpine grassland), previously undescribed, and Merxmuellera drakensbergensis – Helichrysum trilineatum (high-altitude alpine fynbos grassland), described in other vegetation and floristic studies. Four habitats were identified, namely wetlands, sheet rock shallow soil, highaltitude alpine grassland and deep soil high-altitude fynbos grasslands. Substrate and moisture availability appeared to be the defining micro-climatic conditions determining the different vegetation clusters whilst altitude is the overriding environmental factor influencing all vegetation.Conservation implications: Rising temperatures as a result of carbon dioxide increase is predicted to drastically decrease the number of endemic and near-endemic montane species, whilst altering the composition of vegetation units which comprise the alpine vegetation.

A phytosociology survey and vegetation description of inselbergs in the uKhahlamba-Drakensberg Park World Heritage Site, South Africa

No previous scientific surveys have been conducted on inselbergs in the Drakensberg. The aim of this study was to collect specimens, identify, describe and name the vegetation clusters and assess biogeographical connections with other Afromontane regions. A total of 103 relevés where sampled from six inselbergs. The plant sampling was carried out according to the Braun-Blanquet method with the plant and environmental data entered in TURBOVEG and exported as a Cornell Condensed format file (CC!) into Juice. Classification was completed using TWINSPAN (Two-way Indicator Species Analysis) (modified), resulting in 4 major communities, 11 communities, 13 sub-communities and 18 variants. Ordination (indirect) was carried out using CANOCO (version 4.5) to investigate the relationship between species. The four major communities identified are Rhodohypoxis rubella (wetland grass and forblands), Scirpus ficinioides – Crassula peploides (sheet rock grass and forblands), Pentaschistis exserta (high-altitude alpine grassland), previously undescribed, and Merxmuellera drakensbergensis – Helichrysum trilineatum (high-altitude alpine fynbos grassland), described in other vegetation and floristic studies. Four habitats were identified, namely wetlands, sheet rock shallow soil, highaltitude alpine grassland and deep soil high-altitude fynbos grasslands. Substrate and moisture availability appeared to be the defining micro-climatic conditions determining the different vegetation clusters whilst altitude is the overriding environmental factor influencing all vegetation.Conservation implications: Rising temperatures as a result of carbon dioxide increase is predicted to drastically decrease the number of endemic and near-endemic montane species, whilst altering the composition of vegetation units which comprise the alpine vegetation.

Biotic resistance, disturbance, and mode of colonization impact the invasion of a widespread, introduced wetland grass.

Disturbance and biotic resistance are important factors driving plant invasions, but how these factors interact for plants with different modes of colonization (i.e., sexual and asexual) is unclear. We evaluated factors influencing the invasion of nonnative Phragmites australis, which has been rapidly expanding in brackish tidal wetlands in Chesapeake Bay. We conducted a survey of naturally occurring small-scale disturbances (removal of vegetation and/or sediment deposition) across four plant communities; determined the effects of small-scale disturbance and biotic resistance on P. australis seedling and rhizome emergence; and tested the effects of size and frequency of small-scale disturbances on seedling emergence and survival of transplanted seedlings. The results of our study demonstrate that the invasion window for seeds is in disturbed areas in high-marsh plant communities that flood less frequently; seedling emergence in undisturbed areas was negligible. Establishment of shoots from rhizome segments was low in all plant communities. Disturbance size and frequency had no significant impact on seed germination and seedling survival. Our findings provide evidence that small-scale within-wetland disturbances are important for the invasion of the nonnative lineage of P. australis by seeds in brackish tidal wetlands in Chesapeake Bay. Efforts to reduce disturbances, large and small, in wetlands can be used to limit P. australis invasion by seed, but invasion by rhizome is still likely to occur across many plant communities irrespective of the presence of disturbance.

Plasticity of nitrogen allocation in the leaves of the invasive wetland grass, Phalaris arundinacea and co-occurring Carex species determines the photosynthetic sensitivity to nitrogen availability

Phalaris arundinacea displaces the slower-growing, native sedge, Carex stricta, where nitrogen availability is high. Our aim was to address whether morphological and physiological traits associated with carbon gain for P. arundinacea and C. stricta responded to nitrogen supply differently and if the species exhibited different degrees of plasticity in these traits. The plants were grown in gravel and provided modified Hoagland's solution containing four nitrogen concentrations from 0.15 to 15mM for 6 to 7 weeks. Supplied nitrogen affected the leaf nitrogen content to the same degree for both species. Increasing supplied nitrogen strongly increased CO2 assimilation (A), photosynthetic nitrogen use efficiency (PNUE), and respiration for P. arundinacea but had only a small effect on these parameters for C. stricta. Relative to growth at 15mM nitrogen, growth at 0.15mM for young leaves decreased carboxylation capacity and efficiency and the capacity for electron transport for P. arundinacea and a larger, stouter Carex species, Carex lacustris, by 53 to 70% but only 20 to 24% for C. stricta. Leaf nitrogen decreased approximately 50% for all species, but vacuolar nitrate did not decrease for P. arundinacea and C. stricta, suggesting that it does not serve as a nitrogen reserve for use during nitrogen deprivation in these species. After 4 months of nitrogen deprivation, P. arundinacea doubled A in 12 days after being supplied 15mM nitrogen, whereas A for C. stricta increased only 22%. We propose that one factor linking P. arundinacea abundance to nitrogen availability involves this species’ plastic response of carbon gain to nitrogen supply. C. stricta appears to be adapted to tolerate low nitrogen availability but cannot respond as rapidly and extensively as P. arundinacea when nitrogen supply is high.

Preadaptation and post-introduction evolution facilitate the invasion of Phragmites australis in North America.

Compared with non-invasive species, invasive plant species may benefit from certain advantageous traits, for example, higher photosynthesis capacity and resource/energy-use efficiency. These traits can be preadapted prior to introduction, but can also be acquired through evolution following introduction to the new range. Disentangling the origins of these advantageous traits is a fundamental and emerging question in invasion ecology. We conducted a multiple comparative experiment under identical environmental condition with the invasive haplotype M lineage of the wetland grass Phragmites australis and compared the ecophysiological traits of this invasive haplotype M in North America with those of the European ancestor and the conspecific North American native haplotype E lineage, P. australis ssp. americanus. The invasive haplotype M differed significantly from the native North American conspecific haplotype E in several ecophysiological and morphological traits, and the European haplotype M had a more efficient photosynthetic apparatus than the native North American P. australis ssp. americanus. Within the haplotype M lineage, the introduced North American P. australis exhibited different biomass allocation patterns and resource/energy-use strategies compared to its European ancestor group. A discriminant analysis of principal components separated the haplotype M and the haplotype E lineages completely along the first canonical axis, highly related to photosynthetic gas-exchange parameters, photosynthetic energy-use efficiency and payback time. The second canonical axis, highly related to photosynthetic nitrogen use efficiency and construction costs, significantly separated the introduced P. australis in North America from its European ancestor. Synthesis. We conclude that the European P. australis lineage was preadapted to be invasive prior to its introduction, and that the invasion in North America is further stimulated by rapid post-introduction evolution in several advantageous traits. The multicomparison approach used in this study could be an effective approach for distinguishing preadaptation and post-introduction evolution of invasive species. Further research is needed to link the observed changes in invasive traits to the genetic variation and the interaction with the environment.

Silica uptake by Spartina-evidence of multiple modes of accumulation from salt marshes around the world.

Silicon (Si) plays a critical role in plant functional ecology, protecting plants from multiple environmental stressors. While all terrestrial plants contain some Si, wetland grasses are frequently found to have the highest concentrations, although the mechanisms driving Si accumulation in wetland grasses remain in large part uncertain. For example, active Si accumulation is often assumed to be responsible for elevated Si concentrations found in wetland grasses. However, life stage and differences in Si availability in the surrounding environment also appear to be important variables controlling the Si concentrations of wetland grasses. Here we used original data from five North American salt marshes, as well as all known published literature values, to examine the primary drivers of Si accumulation in Spartina, a genus of prolific salt marsh grasses found worldwide. We found evidence of multiple modes of Si accumulation in Spartina, with passive accumulation observed in non-degraded marshes where Spartina was native, while rejective accumulation was found in regions where Spartina was invasive. Evidence of active accumulation was found in only one marsh where Spartina was native, but was also subjected to nutrient over-enrichment. We developed a conceptual model which hypothesizes that the mode of Si uptake by Spartina is dependent on local environmental factors and genetic origin, supporting the idea that plant species should be placed along a spectrum of Si accumulation. We hypothesize that Spartina exhibits previously unrecognized phenotypic plasticity with regard to Si accumulation, allowing these plants to respond to changes in marsh condition. These results provide new insight regarding how salt marsh ecosystems regulate Si exchange at the land-sea interface.

Plant-community responses to shrub cover in apáramograssland released from grazing and burning

Shrub encroachment can follow grazing or burning release in páramo grasslands. While encroachment decreases herbaceous species richness in some grassland systems, the effects of this process on the herbaceous community in páramo grasslands are currently unknown. We collected data on shrub cover, herbaceous-species cover and species composition in a páramo grassland 12 years after release from burning and cattle grazing near Zuleta, Ecuador. Topographic and soil measures were also included as predictor variables of differences in community composition. Contrary to studies in other systems, shrub cover did not have a significant effect on herbaceous-species richness, whereas shrub-species richness significantly increased with shrub cover. However, shrub cover was associated with significant shifts in herbaceous–community composition. Most notably, there was an increase in some shade-tolerant forbs and tall-statured wetland grasses with increasing shrub cover, and a corresponding decrease in some short-statured grasses and early successional forbs. These results could indicate that the ameliorative effects of shrubs (e.g. frost and wind protection) in harsh alpine environments may partially compensate for the expected competitive effect of shrubs due to shading.

Effects of experimental warming and nitrogen enrichment on leaf and litter chemistry of a wetland grass, Phragmites australis

As global climate is warming and the nitrogen cycle accelerates, plants are likely to respond not only by shifting community composition, but also by adjusting traits such as tissue chemistry. We subjected a widespread wetland plant, Phragmites australis, to increased nitrate supply and elevated temperature in enclosures that were established in a littoral permanently submerged freshwater marsh. The nitrogen (N) and phosphorus (P) concentrations in green leaves ranged from 11.4 to 13.8mgN and from 1.5 to 2.0mgPg−1drymass. While the N concentration changed little in brown litter, the P concentration decreased to 0.53–0.65mgPg−1litter dry mass. Neither experimental warming of the water and sediment surface, nor nitrate enrichment during the growing season affected nitrogen or phosphorus concentrations in green leaves. Concentrations of the two major structural carbon compounds in plant litter, cellulose and lignin, were also unaffected, ranging from 32.1 to 34.2% of dry mass for cellulose and from 16.3 to 17.7% of dry mass for lignin. Warming, however, significantly increased the nitrogen concentration of fully brown leaf litter. Thus, temperature appears to be more important than the supply of dissolved N in the water, especially in affecting leaf litter N concentrations in P. australis, even when only water but not air temperature is increased. This result may have implications for decomposition processes and decomposer food webs, which both depend on the quality of plant litter.

Increased invasive potential of non‐native Phragmites australis: elevated CO2 and temperature alleviate salinity effects on photosynthesis and growth

The prospective rise in atmospheric CO2 and temperature may change the distribution and invasive potential of a species; and intraspecific invasive lineages may respond differently to climate change. In this study, we simulated a future climate scenario with simultaneously elevated atmospheric CO2 and temperature, and investigated its interaction with soil salinity, to assess the effects of global change on the ecophysiology of two competing haplotypes of the wetland grass Phragmites australis, that are invasive in the coastal marshes of North America. The two haplotypes with the phenotypes ‘EU-type’ (Eurasian haplotype) and ‘Delta-type’ (Mediterranean haplotype), were grown at 0‰ and 20‰ soil salinity, and at ambient or elevated climatic conditions (700 ppm CO2, +5 °C) in a phytotron system. The aboveground growth of both phenotypes was highest at the elevated climatic conditions. Growth at 20‰ salinity resulted in declined aboveground growth, lower transpiration rates (E), stomata conductance (gs), specific leaf area, photosynthetic pigment concentrations, and a reduced photosynthetic performance. The negative effects of salinity were, however, significantly less severe at elevated CO2 and temperature than at the ambient climatic conditions. The Delta-type P. australis had higher shoot elongation rates than the EU-type P. australis, particularly at high salinity. The Delta-type also had higher maximum light-saturated rates of photosynthesis (Asat), maximum carboxylation rates of Rubisco (Vcmax), maximum electron transport rates (Jmax), triose phosphate utilization rates (Tp), stomata conductance (gs), as well as higher Rubisco carboxylation-limited, RuBP regeneration-limited and Tp-regeneration limited CO2 assimilation rates than the EU-type under all growth conditions. Our results suggest that the EU-type will not become dominant over the Delta-type, since the Delta-type has superior ecophysiological traits. However, the projected rise in atmospheric CO2 and temperature will alleviate the effects of salinity on both phenotypes and facilitate their expansion into more saline areas.

Identification of NonnativePhragmitesat Clear Creek Wildlife Management Area, Kentucky, Using Genetic Techniques

Phragmites australis (Cav.) Trin. ex Steud. (common reed), a perennial wetland grass, has been present in the United States along both Atlantic and Pacific coasts for hundreds of years (Orson 1999, Goman and Wells 2000). Phragmites was deemed rare in the 1800s (Saltonstall 2002) and according to Ward (2010), its distribution was discontinuous in portions of the Midwest, southern Canada, and California, and sporadic along the Gulf Coast from Florida to Texas throughout the 1800s. Also, during that time it was considered absent from Virginia to Georgia inclusive, and inland portions of Alabama and Mississippi (Ward 2010). The abundance and distribution of Phragmites has dramatically increased over the last century (Ward 2010) with the most significant increases along the Atlantic coast (Saltonstall 2002). The rapid expansion was primarily due to the introduction of a European strain in the late 1700s or early 1800s via one or more coastal ports along the Atlantic Coast (Saltonstall 2002). It is highly competitive, aggressive, and virtually indist inguishable morphologically from the native strains, resulting in cryptic invasions (Carlton 1996, Saltonstall 2002) going undetected for decades in various locations around the country. The European strain's spread was likely facilitated by construction of railroads, major roadways (Saltonstall 2002), and changes to hydrologie regimes and/or nutrient availability (Saltonstall 2002, King et al. 2007). Currently, it dominates and effeetively displaees native Phragmites in

First Report of Pseudomonas lurida Causing Bacterial Leaf Spot on Miscanthus sinensis

AbstractMiscanthus spp. are large perennial wetland grasses that are receiving considerable attention as bioenergy crops. In late summer 2011, leaf spot symptoms were observed in a field of Miscanthus sinensis in Jeongseon, Gangwon province, Korea. Bacterial strains that belonged to the γ‐Proteobacteria genus Pseudomonas were isolated from the affected leaves. By phylogenetic analysis and phenotypic characterization, the representative strain MDM‐03 was identified as Pseudomonas lurida. Healthy M. sinensis leaves inoculated with MDM‐03 developed leaf spots similar to those observed in field. Bacteria re‐isolated from the leaf lesions were identical to the original strain MDM‐03 based on their cultural characteristics and 16S rDNA sequencing. This is the first report of bacterial leaf spot in Miscanthus sinensis.

Invasion of Old World Phragmites australis in the New World: precipitation and temperature patterns combined with human influences redesign the invasive niche

After its introduction into North America, Euro-Asian Phragmites australis became an aggressive invasive wetland grass along the Atlantic coast of North America. Its distribution range has since expanded to the middle, south and southwest of North America, where invasive P. australis has replaced millions of hectares of native plants in inland and tidal wetlands. Another P. australis invasion from the Mediterranean region is simultaneously occurring in the Gulf region of the United States and some countries in South America. Here, we analysed the occurrence records of the two Old World invasive lineages of P. australis (Haplotype M and Med) in both their native and introduced ranges using environmental niche models (ENMs) to assess (i) whether a niche shift accompanied the invasions in the New World; (ii) the role of biologically relevant climatic variables and human influence in the process of invasion; and (iii) the current potential distribution of these two lineages. We detected local niche shifts along the East Coast of North America and the Gulf Coast of the United States for Haplotype M and around the Mississippi Delta and Florida of the United States for Med. The new niche of the introduced Haplotype M accounts for temperature fluctuations and increased precipitation. The introduced Med lineage has enlarged its original subtropical niche to the tropics-subtropics, invading regions with a high annual mean temperature (> ca. 10°C) and high precipitation in the driest period. Human influence is an important factor for both niches. We suggest that an increase in precipitation in the 20th century, global warming and human-made habitats have shaped the invasive niches of the two lineages in the New World. However, as the invasions are ongoing and human and natural disturbances occur concomitantly, the future distribution ranges of the two lineages may diverge from the potential distribution ranges detected in this study.

Can differences in salinity tolerance explain the distribution of four genetically distinct lineages of Phragmites australis in the Mississippi River Delta?

In the Mississippi River Delta, the common wetland grass, Phragmites australis, displays high genetic diversity, as several genetically distinct populations are co-occurring. Differences in salinity tolerance may be an important factor determining these populations’ distribution in the delta. Our study investigated the salt tolerance of four genotypes exposed to 0, 10, 20, 30, and 40 ppt salinity. The growth rate, biomass, and the light-saturated photosynthetic rate were stimulated at 10 ppt salinity and inhibited at salinities higher than 20 ppt, compared to controls. Increased concentrations of Cl− and Na+ were found in the roots and older leaves of plants exposed to high salinities. Salt tolerance levels differed between genotypes. High salinity tolerance was mainly achieved by reduced water uptake and vacuole compartmentalization of toxic ions. The most tolerant genotype sustained biomass and photosynthesis even at 40 ppt, whereas the most sensitive genotype did not survive salinities higher than 20 ppt. Our findings show that the observed occurrence of different genotypes in the Mississippi River Delta is correlated to genetically determined differences in salinity tolerance. Further investigations are needed to better understand the role that salinity tolerance plays in the invasion of certain introduced P. australis genotypes.

Delignification of Phragmites karka – a Wetland Grass – by Soda Pulping Process

Phragmites karka, a common wetland grass, was delignified by the soda pulping process, and all the operating parameters were optimized. The effects of both anthraquinone and surfactant on pulp yield and kappa number at optimum pulping conditions were also investigated. The pulp was beaten at different beating levels to optimize different mechanical strength properties. A detailed morphological study of soda-AQ pulp of P. karka was conducted by scanning electron microscopy.

Leaf litter variation influences invasion dynamics in the invasive wetland grass Phalaris arundinacea

High litter mass is hypothesized to produce an invader-directed invasion by changing ecosystem properties such as nutrient cycling rates and light availability. An invasive plant species that stimulates litter accumulation may induce a positive feedback when it benefits from high litter conditions. Phalaris arundinacea is an invasive wetland grass that may induce positive litter feedback, as it produces abundant litter that varies in quality due to a wide range of foliar C:N content. In this study we investigated the range of growth responses within native and invasive genotypes of Phalaris that varied in initial foliar C:N levels (high C:N content was present in the invasive genotypes) when grown under varying litter mass. Overwintering with high litter reduced establishing tiller survivorship and the presence of litter delayed tiller emergence by 2 weeks. Overall, genotypes exhibited high trait plasticity in response to litter. Our results indicate that high litter mass can stimulate Phalaris growth, specifically for the genotypes with high initial C:N foliar tissue. Additionally, genotypes with initially high C:N ratios exhibited plastic responses consistent with a Master-of-some strategy indicating that their performance under high litter may depend upon the nutrient conditions under which they are grown. This study provides evidence for conditions that may lead to a positive feedback in Phalaris’ introduced range. Future studies should investigate how changing litter quantity alters nutrient cycling and competitor growth.

Interactive effects of elevated temperature and CO2 on two phylogeographically distinct clones of common reed (Phragmites australis)

The aboveground growth, physiological and biochemical parameters of two clones of the cosmopolitan wetland grass Phragmites australis, grown at four treatment combinations of temperature and CO2, were investigated to elucidate whether their climate response differed due to inherent differences in their ecological adaptation. The two phylogeographically distinct P. australis clones (DK clone, European genetic background; ALG clone, Mediterranean genetic background) were grown for 151 days in phytotrons at 19/12 °C (day/night temperature) and 390 ppm CO2, and at elevated temperature (+5 °C) and CO2 (700 ppm) with treatment factors alone or in combination. The ALG clone had 2–4 times higher aboveground biomass, higher light-saturated rates of photosynthesis (Pmax), maximum electron transport rates (ETRmax) and Rubisco activity, and higher photosynthetic nitrogen-use efficiency than the DK clone. The DK clone, however, produced more shoots, leaves and side-shoots, and had 9–51 % higher specific leaf area and 15–39 % higher leaf nitrogen concentration than the ALG clone. Although elevated atmospheric CO2 alone barely affected the aboveground growth of the two P. australis clones, simultaneously elevated temperature and CO2 stimulated growth and aboveground biomass. Overall, elevated CO2 stimulated photosynthesis, but the clones responded differently to a concomitant increase in CO2 and temperature, depending on the phylogeographic background of the plant. The DK clone showed overall stronger responses, and can be considered the more plastic of the two clones with respect to CO2 and temperature. Thus, the DK clone may be better adapted to climate change than the ALG clone, at least in the short term.

Differences in salinity tolerance of genetically distinct Phragmites australis clones

Different clones of the wetland grass Phragmites australis differ in their morphology and physiology, and hence in their ability to cope with environmental stress. We analysed the responses of 15 P. australis clones with dis- tinct ploidy levels (PLs) (4n ,6 n ,8 n ,1 0n ,1 2n) and geographic origins (Romania, Russia, Japan, Czech Republic, Australia) to step-wise increased salinity (8, 16, 24, 32, 40, 56 and 72 ppt). Shoot elongation rate, photosynthesis and plant part- specific ion accumulation were studied in order to assess if traits associated with salinity tolerance can be related to the genetic background and the geographic origin of the clones. Salt stress affected all clones, but at different rates. The maximum height was reduced from 1860 mm in control plants to 660 mm at 40 ppt salinity. The shoot elongation rate of salt-exposed plants varied significantly between clones until 40 ppt salinity. The light-saturated photosynthesis rate (Pmax) was stimulated by a salinity of 8 ppt, but decreased significantly at higher salinities. The stomatal conduct- ance (gs) and the transpiration rate (E) decreased with increasing salinity. Only three clones survived at 72 ppt salinity, although their rates of photosynthesis were strongly inhibited. The roots and basal leaves of the salt-exposed plants accumulated high concentrations of water-extractable Na + (1646 and 1004 mmol g 21 dry mass (DM), respectively) and Cl 2 (1876 and 1400 mmol g 21 DM, respectively). The concentrations of water-extractable Mg 2+ and Ca 2+ were reduced in salt-exposed plants compared with controls. The variation of all the measured parameters was higher among clones than among PLs. We conclude that the salinity tolerance of distinct P. australis clones varies widely and can be partially attributed to their longitudinal geographic origin, but not to PL. Further investigation will help in improving the under- standing of this species' salt tolerance mechanisms and their connection to genetic factors.

Detecting ancient wild rice (Zizania spp. L.) using phytoliths: a taphonomic study of modern wild rice in Minnesota (USA) lake sediments

Wild rice (Zizania spp. L.) is a North American native grain with spiritual and dietary significance to many native people. Wild rice is also an important aquatic plant that provides critical habitat to wetland and aquatic wildlife. Past distribution of wild rice in North America is poorly understood, largely because of the limited taxonomic resolution of Poaceae pollen. A novel technique for detecting diagnostic Zizania silica phytoliths allows unambiguous identification of this taxon in lake sediments. We need to better understand modern depositional patterns of phytoliths in lake sediments, however, before attempting detailed paleoreconstructions. We analyzed distributions of diagnostic Zizania and other Poaceae phytoliths in modern sediments from three lakes with variable percent cover of wild rice and a non-wild rice control lake in central Minnesota. Absolute counts of phytoliths per gram sediment were achieved using an exotic diatom marker. Non-Zizania short-cell phytoliths, i.e. phytoliths from wetland grasses Phragmites australis and Muhlenbergia glomerata, dominate the assemblages in all lakes. Most Poaceae short-cell phytoliths appear to be derived locally, with little evidence for regional inheritance from eolian or alluvial processes. Because of anatomical differences in decay of plant debris and other taphonomic issues, Zizania inflorescence rondel phytoliths were most abundant, with morphotypes from other parts rarely encountered. Even in sediments under the densest wild rice stands, Zizania phytoliths contributed a maximum of 9 % to total Poaceae phytolith abundance. Lake morphology also affects the depositional pattern of phytoliths in modern sediments, so coring locations should be considered carefully. At least 500 phytoliths should be counted to detect a sufficient number of wild rice phytolith morphotypes. Diagnostic Zizania phytoliths are a reliable tool for wild rice detection in paleolake sediments.