Wiktor Kotowski

Low investment in sexual reproduction threatens plants adapted to phosphorus limitation

Plant species diversity in Eurasian wetlands and grasslands depends not only on productivity but also on the relative availability of nutrients, particularly of nitrogen and phosphorus. Here we show that the impacts of nitrogen:phosphorus stoichiometry on plant species richness can be explained by selected plant life-history traits, notably by plant investments in growth versus reproduction. In 599 Eurasian sites with herbaceous vegetation we examined the relationship between the local nutrient conditions and community-mean life-history traits. We found that compared with plants in nitrogen-limited communities, plants in phosphorus-limited communities invest little in sexual reproduction (for example, less investment in seed, shorter flowering period, longer lifespan) and have conservative leaf economy traits (that is, a low specific leaf area and a high leaf dry-matter content). Endangered species were more frequent in phosphorus-limited ecosystems and they too invested little in sexual reproduction. The results provide new insight into how plant adaptations to nutrient conditions can drive the distribution of plant species in natural ecosystems and can account for the vulnerability of endangered species.

Responses of fen plant species to groundwater level and light intensity

Characteristic species of sedge-moss fen communities occur in constantly wet, nutrient-poor sites with a high penetration of light through the vegetation canopy. We studied the effects of water table depth and differences in light intensity on the performance of fen species. Three fen species (Carex curta, Viola palustris, Hydrocotyle vulgaris) and one species with a wide range of occurrence (Poa trivialis) were grown for 10 weeks in a sedge-moss peat substrate at 4 different water levels and 3 light intensities. In all species differences in light availability had a larger effect on biomass production than differences in water level. Under a light availability reduced to only 10% the root weight ratio of all the species decreased while leaf weight ratio increased. The biomass allocation ratios were hardly affected by differences in water level. For Viol a and Hydrocotyle an interaction between the two factors was observed. Poa did not show particular differences compared to the other species. We discuss the results in the context of the establishment of fen species in riparian vegetation. It is suggested that the occurrence of fen species in the landscape is directly related to the availability of light, whereas the relationship between fen species occurrence and hydrological conditions seems to be an indirect one.

Competition as a factor structuring species zonation in riparian fens - a transplantation experiment

ABSTRACT Question: What is the relative importance of competition and physical factors in restricting the occurrence of different fen species to certain zones of the riparian landscape? Location: Biebrza National Park, NE Poland. Methods: We carried out a two-season reciprocal transplantation experiment: sod-blocks were replaced between a low-productive groundwater-fed small-sedge fen and a high-productive fluviogenous tall-sedge fen. Five treatments were applied to the transplanted sods: (1) no manipulation; (2) fertilization with NPK to exclude the effect of nutrient limitation; (3) clipping vegetation around the transplant to exclude competition for light; (4) clipping + fertilizing; (5) sods were also transplanted within their own environment. Results: After two seasons, the small-sedge sods transplanted into the high-productive zone had a biomass two times lower than that of the control transplants, mainly due to a decrease in small sedges and bryophytes. Tall sedges of the high-productive zone did not respond significantly to transplantation in the low-productive zone. Removal of the surrounding vegetation largely enhanced the growth of small sedges and bryophytes and, to a lesser degree, of tall sedges. Fertilization, on the other hand, resulted in increased growth of tall sedges, grasses and non-graminoid herbs. Conclusion: Species characteristic of low-productive fen communities are competitively excluded from the high-productive zone through light competition. In contrast, the performance of tall sedges in the low-productive zone is lowered by nutrient limitation. In the long run this may lead to a complete disappearance of these species from this zone. We did not find evidence that the physical stress of flooding has a direct effect on the performance and distribution of species. Results from the experiment suggest that productivity gradients and their influence on competition intensity are of primary importance for structuring vegetation patterns in lowland riparian fens. Nomenclature: Names of vegetation types follow Palczyński (1984), species names follow Mirek et al. (1997). Abbreviations: RGR = Relative Growth Rate, SRR = Shoot : Root Ratio

Species trait shifts in vegetation and soil seed bank during fen degradation

Fens in Central Europe are characterised by waterlogged organic substrate and low productivity. Human-induced changes due to drainage and mowing lead to changes in plant species composition from natural fen communities to fen meadows and later to over-drained, degraded meadows. Moderate drainage leads to increased vegetation productivity, and severe drainage results in frequent soil disturbances and less plant growth. In the present article, we analyse changes in plant trait combinations in the vegetation and the soil seed bank as well as changes in the seed bank types along gradient of drainage intensity. We hypothesize that an increase in productivity enhances traits related to persistence and that frequent disturbance selects for regeneration traits. We use multivariate statistics to analyse data from three disturbance levels: undisturbed fen, slightly drained fen meadow and severely drained degraded meadow. We found that the abundance of plants regenerating from seeds and accumulating persistent seed banks was increasing with degradation level, while plants reproducing vegetatively were gradually eliminated along the same trajectory. Plants with strong resprouting abilities increased during degradation. We also found that shifts in trait combinations were similar in the aboveground vegetation and in soil seed banks. We found that the density of short-term persistent seeds in the soil is highest in fen meadows and the density of long-term persistent seeds is highest in degraded meadows. The increase in abundance of species with strong regeneration traits at the cost of species with persistence-related traits has negative consequences for the restoration prospects of severely degraded sites.

Understanding the Long Term Ecosystem Stability of a Fen Mire by Analyzing Subsurface Geology, Eco-Hydrology and Nutrient Stoichiometry – Case Study of the Rospuda Valley (NE Poland)

We explored the background of differences in long–term stability between two parts in an undisturbed mire system (Rospuda fen, NE Poland). We re-constructed the Holocene history of the mire and compared it with current vegetation, water level dynamics, water chemistry and nutrient availability in two basins: A, where the mire terrestrialised a deep gyttja–filled lake, and B, where peatland developed directly on fluvial sands. The current vegetation of sedge–moss fens was described in 10 relevés from each basin, groundwater was sampled from piezometers and analysed for major ions, while its relative water level was recorded during three years. N and P content was measured in above ground vascular plant samples collected within the relevés. Fens in basin A were stable in the past, whereas fens in basin B switched between open and wooded or reed–dominated phases. In basin B, where trees are more abundant, we found higher water fluctuations, occurrence of river floods and a higher N:P ratio than in basin A. Our interpretation follows that the subsurface geology of fen basin may govern mire stability by determining its hydrological–buffering capacity, which may affect N:P ratios. Our results suggest that P–limited fens are more vulnerable for changes in water level.

Tracing Si–N–P ecosystem-pathways: is relative uptake in riparian vegetation influenced by soil waterlogging, mowing management and species diversity?

Despite the growing concern about the importance of silicon (Si) in controlling ecological processes in aquatic ecosystems, little is known about its processing in riparian vegetation, especially compared to nitrogen (N) and phosphorus (P). We present experimental evidence that relative plant uptake of N and P compared to Si in riparian vegetation is dependent on mowing practices, water-logging and species composition. Results are obtained from a controlled and replicated mesocosm experiment, with a full-factorial design of soil water logging and mowing management. In our experiments, the Si excluding species Plantago lanceolata was dominant in the mown and non-waterlogged treatments, while Si accumulating meadow grasses and Phalaris arundinacea dominated the waterlogged treatments. Although species composition, management and soil moisture interacted strongly in their effect on relative Si:N and Si:P uptake ratios, the uptake of N to P remained virtually unchanged over the different treatments. Our study sheds new light on the impact of riparian wetland ecosystems on nutrient transport to rivers. It indicates that it is essential to include Si in future studies of the impact of riparian vegetation on nutrient transport, as these are often implemented as a measure to moderate excessive N and P inputs.

Large wetlands of the Biebrza Valley, Poland

The Biebrza river valley is one of the largest European high value wetlands that remain in good ecological condition. The dominating wetland type is fen with types including groundwater-fed mire. Other high value habitats include meadows and pastures on wet and mesic sites. Most of the meadows in the valley which occur within the park on wet peat soils, are inaccessible for ordinary agricultural machinery. The growing competition on the agricultural market has forced further intensification of agriculture on the land around the park, leading to the establishment of large-area farms, further specialization of production and an increase of maize cultivation and silage production. The important measures of the Rural Development Programmes from a nature conservation point of view are the Agri-Environmental schemes, support for Less Favoured Areas (LFA) and the farm advisory measures for improvement of the environmental knowledge and awareness among farmers.Keywords: agri-environmental schemes; Biebrza river valley; European high value wetlands; Less Favoured Areas (LFA); Rural Development Programmes