Jørgen Lissner

Taxonomy, chromosome numbers, clonal diversity and population dynamics of Phragmites australis

Phragmites australis (Cav.) Trin. ex Steud. (common reed) is one of the most widespread plant species in the world. The species has a high phenotypic variation in morphology and life- history traits. This high phenotypic variation can be related to variance in chromosome numbers, clonal diversity, plasticity of clones or a combination of these. An overview of our present, still limited, knowledge concerning the amounts, causes and maintenance of genetic diversity in P. australis is given. In P. australis a large range in euploid number has been found (between 3x-12x, except for 5x and 9x, with x=12). In Europe tetraploids are dominant, whereas octoploids predominate in Asia. Aneuploids also occur regularly in P. australis, and differences in chromosome numbers have been observed even within clones. Clonal diversity in P. australis has been studied using allozyme polymorphisms and molecular markers. Both mono- and polyclonal stands are known to exist. A surprisingly high number of clones has been found in European stands. Environmental and genetic factors, which may account for this high clonal diversity, are discussed. In most studies on the occurrence of ecotypes in P. australis no distinction has been made between plastic and genetic variation. But evidence exists that responses to climate, hydrology and salt have a genetic basis. Until now no attempts have been made to determine which genes or gene complexes are responsible for these different responses. [KEYWORDS: ploidy levels; ecotypes; somatic mutations; environmental gradients; life-history; die-back Trin ex steudel; genetic diversity; genotypic diversity; molecular markers; plant-populations; seed dispersal; gramineae; dieback; growth; stands]

Effects of salinity on the growth of Phragmites australis

Abstract The field salinity tolerance of Phragmites australis was evaluated by investigating 27 natural reed habitats along the eastern and western coasts of Jutland, Denmark. Die-back took place in the lower fringe of stands, before the onset of flowering, at sites where soil water salinities were higher than 15‰ within the rooting depth. In greenhouse experiments, juvenile plants produced from seeds and rhizome-grown plants, grown over a range of salinity levels, displayed different levels of salt tolerance. Both types of plants showed low mortality at salinity levels of 15‰ and lower. A total of 75% of the rhizome-grown plants survived 22.5‰ salinity in the rooting medium, whereas only 12% of the juvenile plants survived this salinity level. All plants grown at salinity levels of 35‰ and 50‰ died. Relative growth rates of juvenile plants were negatively correlated with salinity levels. Relative growth rates of rhizome-grown plants on a wet weight basis showed an optimum at 5‰ salinity. However, rates based on leaf number and shoot height were unaffected by salinities from 0–5‰, but decreased at higher salinities. Phragmites australis adapted to saline conditions by adjusting the level of osmotically active solutes in its leaves. In the salinity range allowing survival (0–22.5‰) osmolality in leaves of rhizome-grown plants was approximately 200 mmol kg −1 higher than medium osmolality. In leaves of juvenile plants, osmotic pressure and chlorinity increased exponentially at salinity levels above 10‰ in the rooting medium, indicating a lower capability of osmoregulation. However, water stress could also be responsible for the lower resistance to salinity of these juvenile plants, as was suggested by a wilted appearance of leaves exposed to high salinities. Leaf longevity was not affected by different salinity treatments. Phragmites australis did not use leaf abscission to excrete toxic salts during the growth season.

A phylogeographic study of the cosmopolitan genus Phragmites (Poaceae) based on AFLPs

Within the genus Phragmites (Poaceae), the species P. australis (the common reed) is virtually cosmopolitan, and shows considerable variation in ploidy level and morphology. Genetic variation in Phragmites was studied using AFLPs, and analysed with parsimony and distance methods. Groups of P. australis strongly supported in the analyses include one that comprises all South American clones, a distinct group from the US Gulf Coast, and a group of E. Asian and Australian octoploids. Among the other species, the paleotropical P. vallatoria is supported as monophyletic and most closely related to the paraphyletic P. mauritianus and to the Gulf Coast and S. American groups. The E. Asian species P. japonicus is closely related to a group of P. australis clones mostly from central North America. Tetraploidy predominates in the genus, and optimisation of chromosome numbers onto the phylogeny shows that higher ploidy levels have evolved many times.

EFFECT OF CLIMATE ON THE SALT TOLERANCE OF TWO PHRAGMITES AUSTRALIS POPULATIONS. II. DIURNAL CO2 EXCHANGE AND TRANSPIRATION

This study examined the effects of salinity and climate on instantaneous CO2 exchange rates and daily carbon balance for two populations of Phragmites australis. Plants propagated from seeds collected in Denmark (=Danish population) and Spain (=Spanish population) were grown at salinities of 0, 5 and 10% at outdoor experimental plots situated at a nemoral growth site (Denmark, 56N) and at a mediterranean growth site (Spain, 41N). In situ measurements of shoot CO2 exchange were made under different meteorological conditions. Maximum CO2 uptake rates were 24 and 19mmol m 2 s 1 in Spain and Denmark, respectively, and were only reached under conditions of full sunlight. On sunny days, CO2 uptake was reduced less by salinity at the Spanish site than at the Danish site. Photosynthetic photon flux densities saturating shoot photosynthesis were much lower in Spain (ca. 600mmol m 2 s 1 ) as compared to those in Denmark (ca. 1300mmol m 2 s 1 ). This affected the period of maximum CO2 uptake rates which was 2‐3 h longer at the Spanish growth site, despite shorter day length at this site (15 h) than at the Danish site (17 h). Dark respiration rates of shoots were higher at the Spanish growth site (2‐8mmol CO2 m 2 s 1 ) as compared to the Danish site (less than 2 mmol CO2 m 2 s 1 ). Salinity was observed to accelerate rates of dark respiration only at the Spanish site. Integrals of shoot CO2 exchange rates over a 24 h period indicated lower total daily carbon gain at the Danish site, which under clear sky conditions was 65‐80% of that at the Spanish site. Cloud cover was found to reduce net photosynthetic CO2 uptake considerably and could even cause a net loss of carbon during periods, which in absence of clouds could confer maximum uptake rates. The salt tolerance and productivity of P. australis is therefore strongly related to the ratio of realised to potential sun hours. This ratio may override the importance of other environmental factors such as temperature. This study also evaluated the effects of moderate salinity stress (0‐15% salinity) on in situ P. australis transpiration. Daily transpiration rates were 30‐75% higher at the Spanish site (0.38‐0.56 g H2 Oc m 2 day 1 ) as compared to the Danish site

Nutrient and growth responses of cattail (Typha domingensis) to redox intensity and phosphate availability

BACKGROUND AND AIMS In the Florida Everglades, the expansion of cattail (Typha domingensis) into areas once dominated by sawgrass (Cladium jamaicense) has been attributed to altered hydrology and phosphorus (P) enrichment. The objective of this study was to quantify the interactive effects of P availability and soil redox potential (Eh) on the growth and nutrient responses of Typha, which may help to explain its expansion. METHODS The study examined the growth and nutrient responses of Typha to the interactive effects of P availability (10, 80 and 500 microg P L(-1)) and Eh level (-150, +150 and +600 mV). Plants were grown hydroponically in a factorial experiment using titanium (Ti(3+)) citrate as a redox buffer. KEY RESULTS Relative growth rate, elongation, root-supported tissue/root ratio, leaf length, lateral root length and biomass, as well as tissue nutrient concentrations, were all adversely affected by low Eh conditions. P availability compensated for the negative effect of low Eh for all these variables except that low P stimulated root length and nutrient use efficiency. The most growth-promoting treatment combination was 500 microg P L(-1)/ + 600 mV. CONCLUSIONS These results, plus previous data on Cladium responses to P/Eh combinations, document that high P availability and low Eh should benefit Typha more than Cladium as the growth and tissue nutrients of the former species responded more to excess P, even under highly reduced conditions. Therefore, the interactive effects of P enrichment and Eh appear to be linked to the expansion of Typha in the Everglades Water Conservation Area 2A, where both low Eh and enhanced phosphate availability have co-occurred during recent decades.

Interactive effects of redox intensity and phosphate availability on growth and nutrient relations of Cladium jamaicense (Cyperaceae)

Expansion of Typha domingensis into areas previously dominated by Cladium jamaicense in the Florida Everglades has been linked to anthropogenic phosphorus (P) enrichment and increased hydroperiod. The principal stress factor for plants in flooded soils is biochemical reduction, the intensity of which is measured as redox potential (Eh). The objective of this study was to assess the growth response of C. jamaicense to Eh (-150, +150, and +600 mV) and P availability (10, 80, and 500 μg P/L). Plants were grown hydroponically in a factorial experiment using titanium (Ti(3+)) citrate as an Eh buffer. Treatment effects on growth, biomass partitioning, and tissue nutrients were recorded. Growth approximately doubled in response to a 50-fold increase in P availability. Low redox significantly reduced growth and tissue P concentration. While plant P concentrations increased 20-fold between the 10 and 500 μg P/L treatments, P concentrations were 50-100% higher at +600 mV than at -150 mV within each phosphate level. At high Eh, C. jamaicense appears well adapted to low nutrient environments because of its low P requirement and high retention of acquired P. However, at low Eh the ability to acquire or conserve acquired P decreases and as a consequence, higher phosphate levels are required to sustain growth. Findings of this study indicate that young C. jamaicense exhibits low tolerance to strongly reducing conditions when phosphate is scarce.

Erratum to “ Taxonomy, chromosome numbers, clonal diversity and population dynamics of Phragmites australis” ☆: [Aquat. Bot. 64 (1999) 185–208

Phragmites australis (Cav.) Trin. ex Steud. (common reed) is one of the most widespread plant species in the world. The species has a high phenotypic variation in morphology and life-history traits. This high phenotypic variation can be related to variance in chromosome numbers, clonal diversity, plasticity of clones or a combination of these. An overview of our present, still limited, knowledge concerning the amounts, causes and maintenance of genetic diversity in P. australis is given. In P. australis a large range in euploid number has been found (between 3x-12x, except for 5x and 9x, with x=12). In Europe tetraploids are dominant, whereas octoploids predominate in Asia. Aneuploids also occur regularly in P. australis, and differences in chromosome numbers have been observed even within clones. Clonal diversity in P. australis has been studied using allozyme polymorphisms and molecular markers. Both mono- and polyclonal stands are known to exist. A surprisingly high number of [KEYWORDS: ploidy levels, ecotypes, somatic mutations, environmental gradients, life-history, die-back]

ErratumErratum to “ Taxonomy, chromosome numbers, clonal diversity and population dynamics of Phragmites australis”: [Aquat. Bot. 64 (1999) 185–208☆

Phragmites australis (Cav.) Trin. ex Steud. (common reed) is one of the most widespread plant species in the world. The species has a high phenotypic variation in morphology and life-history traits. This high phenotypic variation can be related to variance in chromosome numbers, clonal diversity, plasticity of clones or a combination of these. An overview of our present, still limited, knowledge concerning the amounts, causes and maintenance of genetic diversity in P. australis is given. In P. australis a large range in euploid number has been found (between 3x-12x, except for 5x and 9x, with x=12). In Europe tetraploids are dominant, whereas octoploids predominate in Asia. Aneuploids also occur regularly in P. australis, and differences in chromosome numbers have been observed even within clones. Clonal diversity in P. australis has been studied using allozyme polymorphisms and molecular markers. Both mono- and polyclonal stands are known to exist. A surprisingly high number of [KEYWORDS: ploidy levels, ecotypes, somatic mutations, environmental gradients, life-history, die-back]

Erratum to “ Taxonomy, chromosome numbers, clonal diversity and population dynamics of Phragmites australis”

Phragmites australis (Cav.) Trin. ex Steud. (common reed) is one of the most widespread plant species in the world. The species has a high phenotypic variation in morphology and life-history traits. This high phenotypic variation can be related to variance in chromosome numbers, clonal diversity, plasticity of clones or a combination of these. An overview of our present, still limited, knowledge concerning the amounts, causes and maintenance of genetic diversity in P. australis is given. In P. australis a large range in euploid number has been found (between 3x-12x, except for 5x and 9x, with x=12). In Europe tetraploids are dominant, whereas octoploids predominate in Asia. Aneuploids also occur regularly in P. australis, and differences in chromosome numbers have been observed even within clones. Clonal diversity in P. australis has been studied using allozyme polymorphisms and molecular markers. Both mono- and polyclonal stands are known to exist. A surprisingly high number of [KEYWORDS: ploidy levels, ecotypes, somatic mutations, environmental gradients, life-history, die-back]