Slimme maatregelen voor schoon oppervlaktewater

De Kaderrichtlijn Water (KRW) vereist dat alle Europese wateren in het jaar 2015 een goede ecologische kwaliteit hebben. Om dit te bereiken kan het nodig zijn dat belasting van het oppervlaktewater met stikstof en fosfaat wordt teruggedrongen. De overheid scherpt het mestbeleid aan. Het nog verder terugdringen van nutriëntenoverschotten is kostbaar, terwijl de effecten op de waterkwaliteit lang op zich laten wachten. In dit onderzoeksbericht een aantal veelbelovende alternatieve maatregelen op percelen, op perceelsranden en in sloten, die laten zien dat landbouw en goede waterkwaliteit elkaar niet in de weg hoeven te staan

Slimme maatregelen voor schoon oppervlaktewater

De Kaderrichtlijn Water (KRW) vereist dat alle Europese wateren in het jaar 2015 een goede ecologische kwaliteit hebben. Om dit te bereiken kan het nodig zijn dat belasting van het oppervlaktewater met stikstof en fosfaat wordt teruggedrongen. De overheid scherpt het mestbeleid aan. Het nog verder terugdringen van nutriëntenoverschotten is kostbaar, terwijl de effecten op de waterkwaliteit lang op zich laten wachten. In dit onderzoeksbericht een aantal veelbelovende alternatieve maatregelen op percelen, op perceelsranden en in sloten, die laten zien dat landbouw en goede waterkwaliteit elkaar niet in de weg hoeven te staan

Between- and within-population differences in Phragmites australis - 1. The effects of nutrients on seedling growth

Phragmites australis (common reed) is a dominant clonal species in the interface between land and water in many European wetlands. Along the land-water gradient, strong consistently different selective forces might operate to give rise to genetic substructuring. I have investigated the occurrence of genetic substructuring in European P. australis populations. The present paper examines whether seedlings, from seeds collected at both ends of the land-water gradient, showed differences in response to nutrient supply. Under controlled conditions, the relative growth rate (RGR) in the exponential growth phase, and growth characters of 10-week old seedlings were assessed. Among populations, no differences in response to nutrient supply were found. Although total dry weight was not related to the geographic origin of the populations, northem/western compared to southern/eastern European populations (1) formed more but shorter shoots, (2) formed thinner but longer rhizomes, and (3) invested more dry matter in leaves at the expense of stems. It was concluded that these trait differences are likely to originate from differences in the length of the growing season in the native habitat. Within populations, 'waterside' seedlings had a higher RGR under sub- optimal while for 'land-side' seedlings this was under optimal nutrient conditions. Ten-week-old 'water-side' seedlings had a higher total dry weight than 'land-side' ones, irrespective of nutrient loading. Differences in growth could not clearly be related to differences in single biomass allocation and morphological traits. A discriminant analysis on these traits, however, revealed that 'water-side' seedlings showed higher plasticity in discriminant scores than 'land-side' seedlings in response to nutrient supply. Discriminant scores also pointed towards a subtle trade-off between height versus expansion growth of seedlings, from the water to landward side. In the Romanian population, this could be related to morphological differences between ploidy levels. Overall, it was concluded that within populations, selection on growth form rather than on adaptations to the nutrient status of the habitat might have taken place. [KEYWORDS: wetlands; die-back; genetic diversity; environmental gradients; relative growth rate Reed decline; plants; dieback; typha; differentiation; performance; nitrogen; trin; size]

Germination and Seedling Emergence of Scirpus-Lacustris L and Scirpus-Maritimus L with Special Reference to the Restoration of Wetlands

Germination and seedling emergence of Scirpus lacustris L. ssp. lacustris (S.l. lacustris), S. lacustris L. ssp. tabernaemontani (C.C. Gmelin) Syme (S.l. tabernaemontani) and Scirpus maritimus L. were investigated in order to assess their ability to establish from seed in former tidal waters, where the original standing population has almost completely disappeared. Germination of 1-year-old seeds of all three taxa was improved by stratification (wet/cold storage) and in the case of S.l. lacustris and S. maritimus, by bleach- scarification (deeds pre-soaked in sodium hypochlorite). Germination of S.l. lacustris and S. maritimus was equally improved by both pretreatments. When light was supplied during daytime, the minimum stratification period required for maximum germination was lower for S. maritimus (4 weeks) than for both S. lacustris subspecies (more than 6 weeks). In continuous darkness, seeds of the three taxa hardly germinated after a stratification period of less than 6 weeks, but after 80 weeks of stratification, germination in light and darkness were almost equal. Fluctuating temperatures compared with constant temperatures improved germination of S.l. tabernaemontani and S. maritimus, but not that of S.l. lacustris. The amplitude between day and night temperature (from 5 to 25 degrees C) did not affect germination. Germination of S. maritimus increased with increasing day temperature. Generally, at constant temperatures the germination of 66-month-old seeds was reduced compared with that of 14-month-old seeds of all three taxa. At a fluctuating temperature of 30/5 degrees C, germination of old compared with young seeds of S.l. lacustris and S. maritimus was not reduced; it was halved, however, in S.l. tabernaemontani. Underwater the three Scirpus taxa were able to emerge from the substrate after being buried at substrate depths of 0.5 and 2 cm. At a burial depth of 5 cm only a small portion of the S. maritimus seeds and none of the two S. lacustris subspecies emerged. The failure to germinate and emerge at 5 cm burial depth could not be ascribed to diminishing fluctuation of temperatures with increasing burial depth. [KEYWORDS: Diurnally-fluctuating temperatures; recruitment; plants; typha; vegetation; responses; zonation; oxygen; growth; light]

The effects of litter on growth and plasticity of Phragmites australis clones originating from infertile, fertile or eutrophicated habitats

In many European countries a strong decline of Phragmites australis (Cav.) Trin. Ex Steudel (common reed) has been observed. In some instances this decline has been related to the accumulation of litter. A greenhouse experiment was conducted with P. australis cuttings from different stable and die-back populations in the Czech Republic and the Netherlands, which were grown in sand (oxidised substrate) and a mixture of sand and litter (reduced substrate). The stable populations were from fertile and infertile habitats, and the die-back populations from originally infertile and now eutrophicated habitats. It was hypothesised that (i) clones from stable populations in fertile habitats are better adapted to accumulated litter (reduced substrate) than those in infertile habitats, and (ii) clones from dieback populations in eutrophicated habitats are more similar to those from stable populations in infertile than fertile habitats, and (iii) the allocation and morphological traits induced in the different environments are adaptive i.e. result in a higher total dry weight (as a measure of fitness) in a particular environment. No significant population x substrate type interaction terms were present, therefore, populations did not differ in their responses to accumulated litter. Population differences in total dry weight, allocation and morphological traits could not be related to adaptations to accumulated litter. Therefore, the different hypotheses were rejected. Generally, clones from infertile habitats were more similar and less plastic than those from the fertile and eutrophicated habitats. Some of these latter clones had a significantly higher total dry weight in sand, but others in sand-litter. Although substrate-type had no overall effect on total dry weight, it affected almost all other plant traits. Clones growing in sand-litter had a higher dry matter allocation to leaves, leaf weight ratio, specific leaf weight ratio, and number of shoots than plants growing in sand, whereas the allocation of dry matter to stems and roots, shoot length and the distance between shoots was lower for clones growing in sand-litter than in sand. Between substrate- types no differences in dry matter of rhizomes were present, however, clones growing in sand-litter produced longer, but thinner rhizomes than those in sand. It was concluded that responses of P. australis to accumulated litter were directed towards a high input of oxygen into a small volume of substrate. It was concluded that a low dry matter allocation to roots, short shoots and a small distance between primary shoots seem to be stress reactions rather than adaptive responses in sand-litter. In contrast, a high number of especially primary shoots seems to be adaptive in this substrate. [KEYWORDS: die-back; reduced soil conditions; genetic diversity; clonal growth; adaptations Phenotypic plasticity; vascular systems; root death; dieback; reed; phytotoxins; populations; management; blockages; aeration]

Effects of litter accumulation and water table on morphology and productivity of Phragmites australis

Phragmites australis (Common reed) occurs in the interface between water and land. The water depth gradient from deep water to dry land is inversely related to litter accumulation. Eutrophication can result in an excessive production of litter, which may have a large impact on the occurrence of P. australis in this gradient. In an outdoor pot experiment, it was investigated how water tables in combination with substrates containing variable amounts of litter affect morphology and productivity of P. australis. Vegetatively propagated P. australis was grown in pots filled with river sand, litter, and different mixtures of sand and litter (25, 50 and 75% by volume). Four water table treatments were applied; drained (–12 cm), waterlogged (0 cm), flooded (+12 cm), and weekly fluctuating drained and flooded conditions (–12/+12 cm of water relative to substrate level). When drained, no differences between substrate treatments were present. Waterlogging, flooding fluctuating water table treatments caused growth reduction in substrate containing litter. The plants formed short shoots and thin rhizomes. With increasing water table, allocation of dry matter to stems increased at the expense of leaves and rhizomes. At intermediate levels of litter in the substrate, allocation to leaves was lowest. In both instances a lower leaf weight ratio (LWR) was (partly) compensated for by a higher specific leaf area (SLA), resulting in less pronounced differences in leaf area ratio (LAR). Aquatic roots developed when plants were waterlogged or flooded, and increased when litter was present in the substrate. Aquatic roots were formed in the top soil layer when waterlogged. The percentage of aquatic roots increased with increasing amount of litter in the substrate when plants were flooded. It was concluded that the morphological responses of P. australis to litter strongly constrain its ability to maintain itself in deep water when the substrate contains litter. This might one of the explanations for the disappearance of P. australis along the waterward side of littoral zones. [KEYWORDS: biomass allocation; die-back; emergent macrophytes; eutrophication; reduced soil conditions]

ERRATUM to: Taxonomy, chromosome numbers, clonal diversity and population dynamics of Phragmites australis (vol 64, pg 185, 1999)

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]

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]

Geographic variation in growth responses in Phragmites australis

Phragmites australis is a cosmopolitan wetlands species occurring in a wide range of climatic habitats, It can be assumed that adaptations to climate have evolved to enable the synchronization of growth with the seasonality of the environment. To study these adaptations, European P. australis was collected in different geographic regions, and grown in common environments situated in the Czech Republic, Denmark and The Netherlands. Phragmites australis originating from higher latitudes showed higher relative length growth rates (RLGR), and flowered earlier in time than that from lower latitudes. Plants from Spain even continued growth until the first autumn frosts. When grown in the different common environments, population differences were found in RLGR, but no general trend was apparent. On average, shoots started to grow 2 weeks earlier in The Netherlands than in Denmark and 6 weeks earlier than in the Czech Republic. These differences could be largely related to lower spring temperatures in the latter two countries. When shoot-growth was plotted against the temperature sum, no differences in RLGR between Denmark and The Netherlands were apparent, whereas shoot-growth was slower in the Czech Republic. Results from a greenhouse experiment showed that seedlings from southern populations formed taller but fewer shoots and thicker but shorter rhizomes than those from northern populations, irrespective of total dry weight. They also allocated more dry matter to stems at the expense of leaves, whereas no differences in allocation to below-ground plant parts were found. It was concluded that populations of P. australis showed clinal variation in (i) the length of the growing season, (ii) time of flowering, and (iii) morphology and biomass allocation. These results are discussed with respect to the possible effects of global warming on population functioning. [KEYWORDS: cline; latitudinal gradient; relative length growth rate; flowering time; morphology; biomass allocation; Phragmites australis Latitudinal variation; plant size; population; romania; trin]

Growth, Photosynthesis and Carbohydrate Utilization in Submerged Scirpus-Maritimus L During Spring Growth

The importance of underwater photosynthesis and the use of reserve-carbohydrates were assessed in submerged Scirpus maritimus L. during spring growth. Submerged plants were grown in outdoor ponds (90 cm deep) using different initial tuber sizes (mean 8.9 and 16.2 g f. wt) and different light treatments (0, 40, 50 and 100 % of full daylight). After shoot emergence the recovery from shading and darkness was studied. The period of submerged growth lasted 9 wk. During this period the mean relative growth rate (RGR) was independently affected by shading and tuber size. At the end of this period dry weight of plants grown in darkness was only 50 % of that of plants grown in full daylight or shade (70 or 40 % of full daylight), whereas that of plants from small tubers was only 67 % of that from large ones. As a result plants grown from small tubers in darkness had only 33 % of the dry weight of those grown from large tubers in full daylight or shade. Despite these large differences in total dry weight at the end of the submerged period, shoot length remained unaffected by shading and tuber size. Shoots grown in darkness were strongly etiolated, with a slower rate of leaf appearance, but with longer leaves, than those grown in full daylight or shade. Only after emergence was shoot length as well as dry matter production greater in plants grown previously in full daylight or shade than in darkness, and greater in plants grown from large than from small tubers. During the submerged period, the relative depletion rate of reserve-carbohydrates increased with time, but remained unaffected by shading and tuber size. The reserve-carbohydrates were replenished after plants emerged. It was concluded that both underwater photosynthesis and tuber size had a large impact on total dry matter production in S. maritimus. They did not, however, affect the ability of S. maritimus to emerge from 90 cm deep water. [KEYWORDS: Emergent macrophytes; maximum water depth; submerged growth; reserve carbohydrates; photosynthesis Trin ex steudel; phragmites-australis; typha-angustifolia; aquatic plants; macrophytes; latifolia; carbon; anaerobiosis; metabolism; resistance]