Kathrin Kiehl

Nutrient limitation and plant species composition in temperate salt marshes

Abstract Addition of inorganic nitrogen, phosphorus and potassium in a factorial design in two ungrazed Wadden-Sea salt marshes at low and high elevations showed that nitrogen was the limiting nutrient. No effects of nutrient addition were detected in the 1st year, probably due to a considerable rainfall deficit during the growing season. In the 2nd year, which was more humid, only nitrogen addition caused significant effects in both the low salt marsh dominated by Puccinellia maritima and the high marsh dominated by Festuca rubra. No two-way or three-way interactions with phosphorus or potassium were found. In the low marsh, nitrogen addition had a negative effect on the biomass of Puccinellia, but a positive effect on the biomass of Suaeda maritima and on the total above-ground biomass. Puccinellia was replaced by Suaeda after nitrogen addition, due to shading. In the high salt marsh, no significant effects of fertilizer application on total above-ground biomass were found, due to the weak response of the dominant species Festuca rubra, which accounted for 95% of total biomass. The biomass of Spergularia maritima increased, however, as a response to nitrogen addition.The shoot length of Festuca was positively affected by nitrogen fertilization. It is suggested that stands of Festuca reached maximal biomass at the study site without fertilization and that its growth was probably limited by self-shading.

Advances in the conservation of dry grasslands: Introduction to contributions from the seventh European Dry Grassland Meeting

Abstract Dry grasslands in Europe are mostly of zoo-anthropogenic origin, but nevertheless they are among the most diverse plant communities of the world at small spatial scales, and they support a significant proportion of the biodiversity of the continent. Both agricultural intensification and abandonment of former dry grasslands caused dramatic losses in area and quality of this habitat type during recent decades. Here we report from the 7th European Dry Grassland Meeting, organised by the European Dry Grassland Group (EDGG) in Smolenice, Slovakia, in 2010. Under the motto “Succession, restoration and management of dry grasslands” one hundred researchers from throughout Europe discussed conservation issues of this threatened habitat type. We give a brief introduction to those nine articles that are included in this Special Feature. With contributions from many different countries and various dry grassland types, they address issues of conservation value, succession, management as well as regeneration and restoration. We conclude that the diversity of dry grasslands and their conservation problems require further research to develop adequate management techniques under changing frame conditions. However, also the frame conditions, such as the incentives for certain land use practices provided by the Common Agricultural Policy of the European Union need to be addressed if long-term success in conservation of dry grasslands is intended.

Potential of temperate agricultural soils for carbon sequestration: A meta-analysis of land-use effects

Restoring depleted soil organic carbon (SOC) stocks of arable land to remove carbon from the atmosphere and offset fossil fuel emissions is a promising strategy for the mitigation of climate change. In agroecosystems conservational tillage practices and the abandonment of formerly plowed fields (ex-arable land) are shown to have the highest potential to sequester SOC. Nevertheless reported sequestration rates vary and the effects of environmental site conditions remain poorly understood. Our results are based on a meta-analysis of 273 paired SOC estimates from 65 publications which included only mineral soils from the temperate zone. SOC stocks of ex-arable grasslands with an average of 14years since abandonment were 18% larger compared to the SOC of arable land. Likewise, SOC stocks of never-plowed grassland plots were 11% larger than the SOC stocks of abandoned fields. The average sequestration rate was 0.72t Cha(-1)yr(-1). Semi-arid and sub-humid climate as well as low initial SOC stocks positively affected proportional SOC gains suggesting that the recovery of carbon stocks is not limited by low primary production. Therefore, the northward shift of cultivation areas in the temperate zone will lead to the abandonment of soils with high SOC recovery potential. However, if native soils are opened up elsewhere to compensate for yield losses due to abandonment the surplus of SOC in ex-arable land can easily be overcompensated by cultivation losses.

Sedimentation in salt marshes affected by grazing regime, topographical patterns and regional differences

The future perspective of salt marshes strongly depends on a positive balance between sedimentation and an increased sea-level rise. Sedimentation itself is influenced indirectly by grazing as well as the position of the location in relation to the nearest sediment source and by amount and quality of the available sediment.Two salt marshes were studied (Sönke-Nissen-Koog marsh, Friedrichskoog marsh) at the mainland coast of Schleswig-Holstein (FRG). In both marshes experimental plots had been established which were grazed by sheep at high and intermediate intensity or remained ungrazed. To figure out the effect of topography on net-sedimentation rate, we included sites close to and far from the locations „dike“ and „creek“ in all management variants. In general, a reversible soil shrinkage in summer due to desiccation could be detected.Sedimentation rates differed significantly between grazed and ungrazed salt marshes. The ungrazedPuccinellia-dominated marsh as well as in theFestuca-dominated marsh demonstrated highest annual net-sedimentation rates of 1.8–2.1 cm and 1.2–1.7 cm, respectively, and can thus counterbalance the average sea level rise unless they show a decreasing trend in future.

Soil carbon sequestration due to post‐Soviet cropland abandonment: estimates from a large‐scale soil organic carbon field inventory

Abstract The break‐up of the Soviet Union in 1991 triggered cropland abandonment on a continental scale, which in turn led to carbon accumulation on abandoned land across Eurasia. Previous studies have estimated carbon accumulation rates across Russia based on large‐scale modelling. Studies that assess carbon sequestration on abandoned land based on robust field sampling are rare. We investigated soil organic carbon (SOC) stocks using a randomized sampling design along a climatic gradient from forest steppe to Sub‐Taiga in Western Siberia (Tyumen Province). In total, SOC contents were sampled on 470 plots across different soil and land‐use types. The effect of land use on changes in SOC stock was evaluated, and carbon sequestration rates were calculated for different age stages of abandoned cropland. While land‐use type had an effect on carbon accumulation in the topsoil (0–5 cm), no independent land‐use effects were found for deeper SOC stocks. Topsoil carbon stocks of grasslands and forests were significantly higher than those of soils managed for crops and under abandoned cropland. SOC increased significantly with time since abandonment. The average carbon sequestration rate for soils of abandoned cropland was 0.66 Mg C ha−1 yr−1 (1–20 years old, 0–5 cm soil depth), which is at the lower end of published estimates for Russia and Siberia. There was a tendency towards SOC saturation on abandoned land as sequestration rates were much higher for recently abandoned (1–10 years old, 1.04 Mg C ha−1 yr−1) compared to earlier abandoned crop fields (11–20 years old, 0.26 Mg C ha−1 yr−1). Our study confirms the global significance of abandoned cropland in Russia for carbon sequestration. Our findings also suggest that robust regional surveys based on a large number of samples advance model‐based continent‐wide SOC prediction.

The impact of goose grazing on saltmarsh vegetation at the Hamburger Hallig

Saltmarshes of the Hamburger Hallig (Nordfriesland, Germany) are an important foraging area for barnacle geese and wigeon. They were intensively grazed by sheep until 1991 when a grazing trial was started to study the impact of sheep grazing on salt marsh vegetation and fauna. In 1993 first investigations were carried out in the Puccinellia marŸ dominated low salt marsh to study the impact of goose grazing on species composition and productivity of saltmarsh vegetation not grazed by sheep. The study was continued in February 1995, when six areas of 10-15 m 2 were fenced up in the ungrazed parts of the Hamburger Hallig area in order to exclude the geese (BREDEMEIER 1997). The influence ofgoose grazing (February-April 1995:0.53-2.05 goose hours/m 2) on above-ground biomass of different plant species was detected at permanent plots inside and outside the exclosures. The question, if plant growth is stimulated by herbivory (McNAUGHTON 1983; CARGILL & JEFFERIES 1984; HIK & JEFFERIES 1990), should be answered by the study ofaboveground biomass and vegetation height during and after the foraging period of the geese. In both study years the total above-ground biomass in April, at the end of the goose foraging period, was significantly higher inside the exclosures than outside at most of the sites (Fig. lA; LIEBMiNN 1995). At this time of the year total aboveground biomass consisted mainly of Puccinellia maritima (90-100%). Only seedlings of Suaeda maritima with al low biomass were present in April, especially inside the exclosures (Fig. 2A). Although no geese were present from April until August the differences in above-ground biomass between plots inside and outside the exclosures increased. In August, three months after the geese had left the Hamburger Hallig area in spring, total above-ground biomass inside the exclosures was still significantly higher than outside in both years (Fig. 1B). This means that the growth ofPuccinellia maritima, the dominant plant species, was not stimulated by herbivory. The August biomass of Suaeda maritima, however, was positively affected by goose grazing (Fig. 2B). The biomass of Suaeda maritima, as percentage of total above-ground biomass, was significantly higher on plots which had been grazed by geese in spring than on ungrazed plots. This annual species was obviously favoured by the better light conditions in the goose grazed Puccinellia vegetation, since germination and seedling establishment depend strongly on light. These results showed that goose grazing hada lasting effect on total above-ground biomass during one vegetation period. Although posjtive effects of goose grazing were found for Suaeda maritima, primary production was not generally stimulated by herbivory. This means that the herbivore-optimiazation model (McNAUGHTON 1983; HIK &JEFFERIES 1990) cannot be generalized for the salt-marsh ecosystem.

The impact of sheep grazing on nitrogen mineralization in different salt marsh zones

Nitrogen (N) mineralization was studied during a one-year period in grazing trials with three different stocking rates (0, 3, 10 sheep/ha) in two salt marshes of the Schleswig-Holstein Wadden Sea, viz. a Puccinellia maritima dominated low sah marsh a n d a high salt marsh dominated by Festuca rubra. Mineralization rates were derived from the amounts of mineral N which accumulated in situ during six-week incubations periods in tubes with undisturbed soil cores from the upper 0-10 cm soil layer. .Seasonal dynamics o fN mineralization were similar at the grazed and ungrazed sites in the low marsh. N-mineralization rates as well as relative nitrification rates showed a peak during a three-month period from mid March to midJune and were very low during the test of the year. Correlation analyses indicated that the seasonal pattem may primarily be explained by the negative influence of soil-water logging. In the Puccinellia maritima salt marsh, grazing had neither an effect on Nmineralization rates during any of the incubation periods nor on annual mineralization rates. In the Festuca rubra salt marsh N-mineralization rates increased in spring earlier at the intensively grazed site than at the moderately grazed and the ungrazed site. N-mineralization and nitrification rates were significantly higher at the ungrazed site than at the intensively grazed site during the period of peak N accumulation. Although grazing affected the seasonality of N-mineralization in the high marsh, no significant effect on annual rates of N-mineralization could be found. The annual rates ofN-mineralization were significantly higher in the better drained high salt marsh (71-81 kg ha -1 y r 1) than in the low salt marsh (39~9 kg ha -1 yrl). This means that abiotic differences between the two salt marsh zones had a much greater effect on N-mineralization than sheep grazing.