Plant community controls small-scale variation in nutrient stoichiometry in a Patagonian peatland

Elemental stoichiometry of plant litter is typically interpreted to reflect nutrient availability and limitation, e.g. the N:P ratio indicates whether plant growth is N- or P-limited and might point towards the presence of N-fixation. However, in the case of plant litter and peat organic matter, resorption of nutrients during senescence, and preferential loss of nutrients during decomposition have to be taken into account. Here we study how small scale variability in species composition within peatlands affects the stoichiometry and long term apparent uptake rates of nutrients (C, N, P, K, S, Ca, Mg) in an ombrotrophic peatland in southern Patagonia. Assuming that nutrient availability is similar within one site, observed variation should be driven by vegetation and decomposition processes linked to microtopography. We studied a transect spanning 800 m. where the vegetation changed from cushion plant (Astelia pumila) dominated, to graminoid dominated, ending in Sphagnum magellanicum dominated. From six peat cores along this transect we analysed nutrient concentrations by X-ray fluorescence. The peat decomposition state, expressed as FTIR-humification index, was the best predictor of stoichiometric variation (particularly ratios C:N, C:S, and N:P), followed by current plant species composition. Comparison of average peat core stoichiometry across the transect showed that C:N and C:S ratios were larger in Sphagnum cores than cushion plant and graminoid cores (C:N 56±14 vs. 38±6; C:S 312±61 vs. 268±57; respectively), controlled by lower decomposition state in Sphagnum cores and larger C:N ratios in living biomass of Sphagnum vs. A. pumila. Larger N:P ratios in cushion plant and graminoid vs. Sphagnum cores (N:P 50±12 vs. 38±11; respectively) could furthermore indicate the presence of N-fixation in the former. Comparison with two additional Patagonian bogs showed similar distinction in C:N and C:S ratios (both: Sphagnum > cushion plant), but variation between cores within sites was more pronounced than between different peatlands. Taking the variable peat accumulation rate (0.09 ? 0.52 mm yr-1) into account, there was notable variation in apparent long term nutrient uptake rates along the transect. N and S uptake rates were larger in cushion plant and graminoid versus Sphagnum cores, while Mg uptake rates were largest in Sphagnum cores. Overall, the stoichiometry of these Patagonian peatlands suggests lower availability of N, P, and Ca compared to peatlands in Ontario, Canada, resulting in lower apparent N, P, and Ca uptake rates. In contrast, apparent Mg uptake rates were larger in Patagonia than Ontario. These results indicate that small scale variability in long term accumulation of nutrients in these ecosystems might be more pronounced than variability in long term C accumulation, and highlights the variability in nutrient availability between peatlands of different regions.Fil: Mathijssen, Paul. University of Münster; AlemaniaFil: Münchberger, Wiebke. University of Münster; AlemaniaFil: Borken, Werner. University of Bayreuth; AlemaniaFil: Pancotto, Veronica Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Kleinebecker, Till. Justus Liebig Universitat Giessen; AlemaniaFil: Knorr, Klaus Holger. University of Bayreuth; Alemania21th European Geosciences Union General AssemblyVienaAustriaAsamblea General de European Geosciences Unio

Decomposition disentangled: A test of the multiple mechanisms by which nitrogen enrichment alters litter decomposition

1. Nitrogen (N) enrichment has direct effects on ecosystem functioning by altering soil abiotic conditions and indirect effects by reducing plant diversity and shifting plant functional composition from dominance by slow to fast growing species. Litter decomposition is a key ecosystem function and is affected by N enrichment either by a change in litter quality (the recalcitrance of the plant material) or through a change in soil quality (the abiotic and biotic components of the soil that affect decomposition). How the direct and indirect effects of N alter soil and litter quality remains poorly known. 2. We designed a large grassland field experiment manipulating N enrichment, plant species richness and functional composition in a full factorial design. We used three complementary litterbag experiments, combined in a structural equation model (SEM), to quantify the effects of the treatments and various measures of functional composition and diversity on litter and soil quality and overall decomposition. 3. Our results revealed multiple drivers of litter quality and showed that nutrient concentrations (N and calcium) were about twice as important as structural components (leaf dry matter content, fibres) in determining litter quality. Overall the experimental results suggest that N enrichment increases litter decomposition mostly indirectly through a shift in functional composition toward faster growing plant species, producing higher quality litter. N enrichment also altered soil quality and thereby litter decomposition, through its effects on vegetation cover. 4. Our approach provides a mechanistic tool to test the drivers of litter decomposition across different ecosystems. Our results show that litter quality is determined by several nutrient and structure traits and highlight the importance of considering shifts in plant species composition when assessing the effects of N enrichment on decomposition.This study was supported by funding of the Swiss National Science Foundation. S.S. was supported by the Spanish Government under a Ramón y Cajal contract (RYC-2016-20604)

Zero to moderate methane emissions in a densely rooted, pristine Patagonian bog – biogeochemical controls as revealed from isotopic evidence

Peatlands are significant global methane (CH4) sources, but processes governing CH4 dynamics have been predominantly studied in the Northern Hemisphere. Southern hemispheric and tropical bogs can be dominated by cushion-forming vascular plants (e.g. Astelia pumila, Donatia fascicularis). These cushion bogs are found in many (mostly southern) parts of the world but could also serve as extreme examples for densely rooted northern hemispheric bogs dominated by rushes and sedges. We report highly variable summer CH4 emissions from different microforms in a Patagonian cushion bog as determined by chamber measurements. Driving biogeochemical processes were identified from pore water profiles and carbon isotopic signatures. Intensive root activity throughout a rhizosphere stretching over 2&thinsp;m in depth accompanied by molecular oxygen release created aerobic microsites in water-saturated peat, leading to a thorough CH4 oxidation (&lt;&thinsp;0.003&thinsp;mmol&thinsp;L−1 pore water CH4, enriched in δ13C-CH4 by up to 10&thinsp;‰) and negligible emissions (0.09±0.16&thinsp;mmol&thinsp;CH4&thinsp;m−2&thinsp;d−1) from Astelia lawns. In sparsely or even non-rooted peat below adjacent pools pore water profile patterns similar to those obtained under Astelia lawns, which emitted very small amounts of CH4 (0.23±0.25&thinsp;mmol&thinsp;m−2&thinsp;d−1), were found. Below the A. pumila rhizosphere pore water concentrations increased sharply to 0.40±0.25&thinsp;mmol&thinsp;CH4&thinsp;L−1 and CH4 was predominantly produced by hydrogenotrophic methanogenesis. A few Sphagnum lawns and – surprisingly – one lawn dominated by cushion-forming D. fascicularis were found to be local CH4 emission hotspots with up to 1.52±1.10&thinsp;mmol&thinsp;CH4&thinsp;m−2&thinsp;d−1 presumably as root density and molecular oxygen release dropped below a certain threshold. The spatial distribution of root characteristics supposedly causing such a pronounced CH4 emission pattern was evaluated on a conceptual level aiming to exemplify scenarios in densely rooted bogs. We conclude that presence of cushion vegetation as a proxy for negligible CH4 emissions from cushion bogs needs to be interpreted with caution. Nevertheless, overall ecosystem CH4 emissions at our study site were probably minute compared to bog ecosystems worldwide and widely decoupled from environmental controls due to intensive root activity of A. pumila, for example.</p

High-resolution classification of south patagonian peat bog microforms reveals potential gaps in up-scaled CH4 fluxes by use of Unmanned Aerial System (UAS) and CIR imagery

South Patagonian peat bogs are little studied sources of methane (CH4). Since CH4 fluxes can vary greatly on a small scale of meters, high-quality maps are needed to accurately quantify CH4 fluxes from bogs. We used high-resolution color infrared (CIR) images captured by an Unmanned Aerial System (UAS) to investigate potential uncertainties in total ecosystem CH4 fluxes introduced by the classification of the surface area. An object-based approach was used to classify vegetation both on species and microform level. We achieved an overall Kappa Index of Agreement (KIA) of 0.90 for the species- and 0.83 for the microform-level classification, respectively. CH4 fluxes were determined by closed chamber measurements on four predominant microforms of the studied bog. Both classification approaches were employed to up-scale CH4 closed chamber measurements in a total area of around 1.8 hectares. Including proportions of the surface area where no chamber measurements were conducted, we estimated a potential uncertainty in ecosystem CH4 fluxes introduced by the classification of the surface area. This potential uncertainty ranged from 14.2 mg·m-2· day-1 to 26.8 mg·m-2· day-1. Our results show that a simple classification with only few classes potentially leads to pronounced bias in total ecosystem CH4 fluxes when plot-scale fluxes are up-scaled.Fil: Lehmann, Jan R. K.. Westfalische Wilhelms Universitat; AlemaniaFil: Münchberger, Wiebke. Westfalische Wilhelms Universitat; AlemaniaFil: Knoth, Christian. Westfalische Wilhelms Universitat; AlemaniaFil: Blodau, Christian. Westfalische Wilhelms Universitat; AlemaniaFil: Nieberding, Felix. Westfalische Wilhelms Universitat; AlemaniaFil: Prinz, Torsten. Westfalische Wilhelms Universitat; AlemaniaFil: Pancotto, Veronica Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Kleinebecker, Till. Westfalische Wilhelms Universitat; Alemani

Organic vs. Conventional Grassland Management: Do 15N and 13C Isotopic Signatures of Hay and Soil Samples Differ?

Distinguishing organic and conventional products is a major issue of food security and authenticity. Previous studies successfully used stable isotopes to separate organic and conventional products, but up to now, this approach was not tested for organic grassland hay and soil. Moreover, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in organic and conventional management systems. Here, we studied the δ15N and δ13C isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used Δδ15N (δ15N plant - δ15N soil) to characterize nitrogen dynamics. In order to detect temporal trends, isotopic abundances in organic grasslands were related to the time since certification. Furthermore, discriminant analysis was used to test whether the respective management type can be deduced from observed isotopic abundances. Isotopic analyses revealed no significant differences in δ13C in hay and δ15N in both soil and hay between management types, but showed that δ13C abundances were significantly lower in soil of organic compared to conventional grasslands. Δδ15N values implied that management types did not substantially differ in nitrogen cycling. Only δ13C in soil and hay showed significant negative relationships with the time since certification. Thus, our result suggest that organic grasslands suffered less from drought stress compared to conventional grasslands most likely due to a benefit of higher plant species richness, as previously shown by manipulative biodiversity experiments. Finally, it was possible to correctly classify about two third of the samples according to their management using isotopic abundances in soil and hay. However, as more than half of the organic samples were incorrectly classified, we infer that more research is needed to improve this approach before it can be efficiently used in practice

Der Einfluss von konkurrenzstarken Pflanzenarten auf die kinetischen Eigenschaften von extrazellulären hydrolytischen Enzymen in Rhizosphärenproben unterschiedlicher Landnutzungsintensität

In dieser Studie wurden die katalytischen Eigenschaften von extrazellulären hydrolytischen Enzymen (EHE) in der Rhizosphäre von drei Gewinnerarten zunehmender Landnutzungsintensität (Dactylis glomerata, Taraxacum sect. ruderalia, Trifolium repens) und zwei Verliererarten (Agrimonia eupatoria, Lotus corniculatus) im Grünland (Hainich, Mitteldeutschland) untersucht. Ein besseres Verständnis der Beziehungen zwischen Erfolg der Pflanzenarten und den katalytischen Eigenschaften von EHE mikrobiellen und pflanzlichen Ursprungs ist wichtig um die Erfolgsmechanismen aufzudecken und ein besseres Verständnis für die Wirkungen der Zunahme von Landnutzungsintensitäten auf Bodenfunktionen zu erhalten. Das von der Substratkonzentration abhängige katalytische Verhalten der EHE wurde durch den Einsatz von 4-Methylumbelliferon-markierten Substraten erfasst und mittels der Michaelis-Menten-Gleichung angenähert (Vmax=limitierende Umsatzrate, Km=apparente Substrataffinität). Die Kinetiken von b-Glukosidasen (BG), Cellobiohydrolasen (CBH), Xylanasen (XYL), N-Acetylglukosaminidasen (NAG) und von Phosphatasen (PH) wurden analysiert. Das Vorkommen der Gewinner ist verbunden mit erhöhten Vmax-Werten von XYL, geringeren Substrataffinitäten von CBH und mit deutlich erhöhten Substrataffinitäten von PH. Neben diesen Effekten werden die Enzymeigenschaften von den Corg%, dem C:N Verhältnis und dem pH Wert sowie von Eigenschaften der Pflanzenbestände in der unmittelbaren Umgebung der Rhizosphäre (Shannon-Index, Deckungsgrad) beeinflusst. In aller Regel sind steigende Vmax-Werte mit einer Erhöhung der Corg% und einer Abnahme des C:N verbunden. Eine Ausnahme bildet NAG, die die höchsten Vmax-Werte unter geringster Landnutzungsintensität und weitestem C:N aufweist. Die Km-Werte zeigen häufig Beziehungen zum Rhizosphären pH. Die Ergebnisse legen nahe, dass in den Rhizosphären der Gewinner bei der Akquise von Phosphor Enzyme hoher Affinität vorkommen. Zum einen kann dies bedeuten, dass die Produzenten der Enzyme sehr effektiv niedrige Konzentrationen der entsprechenden organischen P-Substrate umsetzen können oder die Substrate aufgrund der hohen Aufnahme an P limitierend sind. Darüber hinaus zeigen die Ergebnisse die Effekte bodenchemischer Gradienten, tlw. bedingt durch die Landnutzungshistorie, auf die katalytischen Eigenschaften der EHE und so dem Umsatz der organischen Substanz

Temporal and small-scale spatial variation in grassland productivity, biomass quality, and nutrient limitation

Characterization of spatial and temporal variation in grassland productivity and nutrition is crucial for a comprehensive understanding of ecosystem function. Although within-site heterogeneity in soil and plant properties has been shown to be relevant for plant community stability, spatiotemporal variability in these factors is still understudied in temperate grasslands. Our study aimed to detect if soil characteristics and plant diversity could explain observed small-scale spatial and temporal variability in grassland productivity, biomass nutrient concentrations, and nutrient limitation. Therefore, we sampled 360 plots of 20 cm × 20 cm each at six consecutive dates in an unfertilized grassland in Southern Germany. Nutrient limitation was estimated using nutrient ratios in plant biomass. Absolute values of, and spatial variability in, productivity, biomass nutrient concentrations, and nutrient limitation were strongly associated with sampling date. In April, spatial heterogeneity was high and most plots showed phosphorous deficiency, while later in the season nitrogen was the major limiting nutrient. Additionally, a small significant positive association between plant diversity and biomass phosphorus concentrations was observed, but should be tested in more detail. We discuss how low biological activity e.g., of soil microbial organisms might have influenced observed heterogeneity of plant nutrition in early spring in combination with reduced active acquisition of soil resources by plants. These early-season conditions are particularly relevant for future studies as they differ substantially from more thoroughly studied later season conditions. Our study underlines the importance of considering small spatial scales and temporal variability to better elucidate mechanisms of ecosystem functioning and plant community assembly

Long-term success of floodplain meadow restoration on species-poor grassland

Restoration of floodplain meadows remains a challenge, as many degraded sites suffer from seed limitation. The transfer of seed-containing plant material from species-rich donor sites is a widely used method to restore semi-natural grasslands. However, most studies on the success of such restoration projects comprise limited time frames. As factors determining restoration success may only become evident after many years, long-term observations are crucial. We re-investigated 20 restored grassland sites in the floodplain of the Northern Upper Rhine 13–16 years after plant material transfer with different soil preparation treatments. To this end, we carried out vegetation surveys on 254 permanent plots and studied the potential influence of soil preparation, soil nutrients, and hydrology on plant species composition, diversity, and transfer of target species. Since sustainable agricultural use is important to ensure the long-term stability of restored semi-natural grasslands, we further investigated biomass productivity and feeding value. While most target species increased in frequency or remained stable over time, we found no positive long-term effect of soil preparation on vegetation development and target species establishment. Instead, increased biomass yield and flooding frequency led to reduced restoration success, while higher soil C/N ratios had a positive effect. Overall, restoration measures did not affect the agricultural value of the restored grasslands, which had higher dry matter biomass yields compared with the donor sites. Our results indicate that the positive effect of soil preparation on the number and cover of target species, which is regularly reported in short-term studies, diminishes over time, and other factors such as site conditions become increasingly important. Furthermore, additional plant material transfer or manual seeding may be necessary to support target species establishment. Concerning agricultural usability, the integration of restored floodplain meadows in farming systems is possible and can ensure long-term management and thus stability of these ecosystems. Our study shows that long-term monitoring of restoration projects is necessary, as factors determining restoration success may only become evident in the long-term

Testate amoebae as a proxy for reconstructing Holocene water table dynamics in southern Patagonian peat bogs

Funded by Natural Environment Research Council. Grant Numbers: NE/I022809/1, NE/I022981/1, NE/I022833/1, NE/I023104/1 Ricardo Muza and the Wildlife Conservation Society Karukinka Park Acknowledgements This work was supported by the Natural Environment Research Council (grant numbers NE/I022809/1, NE/I022981/1, NE/I022833/1 and NE/I023104/1). We thank Ricardo Muza and the Wildlife Conservation Society (WCS) Karukinka Park rangers for facilitating access to Karukinka Park. We also thank François De Vleeschouwer, Gaël Le Roux, Heleen Vanneste, Sébastien Bertrand, Zakaria Ghazoui and Jean-Yves De Vleeschouwer for fieldwork assistance. Nelson Bahamonde (INIA, Punta Arenas, Chile) and Ernesto Teneb (UMag, Punta Arenas, Chile) provided logistical support for the fieldwork in Chile. Dr Andrea Coronato (CADIC, Ushuaia) kindly provided logistical support for the research in Argentina. Thanks to Jenny Johnston for cartography, David Jolley for assistance in microscopic photography and Audrey Innes for laboratory assistance. We highly appreciate reviews by Matt Amesbury and an anonymous reviewer. R.P. is supported by an Impact Fellowship from the University of Stirling.Peer reviewedPublisher PD

Initialer Streuabbau und Enzymkinetik in Abhängigkeit von Streuqualität und Landnutzungsintensität

Extrazelluläre hydrolytische Enzyme (EHEs), die überwiegend von Bodenmikroorganismen produziert werden, übernehmen eine wichtige Rolle beim Umsatz der organischen Substanz im Boden. Die Auswirkungen von unterschiedlicher Landnutzungsintensität (Düngung, Beweidung, Mahd) in Grünlandflächen auf Enzymkinetiken und die von Ihnen gesteuerten Abbauraten organischer Substanz sind allerdings kaum untersucht (Tischer et al. 2015). Als Kenngrößen des katalytischen Verhaltens von EHEs können die limitierende Umsatzrate (Vmax) sowie die apparente Substrataffinität (Km) mittels der Michaelis-Menten Gleichung angenähert werden. Um den Einfluss unterschiedlicher Streuqualität auf Interaktionen zwischen verschiedenen Enzymen zu testen wurden Teebeutel mit grünem Tee (C/N Verhältnis 12) und Teebeutel mit Rooibos-Tee (C/N Verhältnis 43) in Anlehnung an Keuskamp et al. (2013) für drei Monate auf je 25 unterschiedlich intensiv bewirtschafteten Grünland-Flächen der DFG-Biodiversitätsexploratorien (Hainich, Schorfheide) eingebracht. In den ausgebrachten, 3-monatig-exponierten, Teeproben und in angrenzenden Bodenproben wurden die katalytischen Eigenschaftenvon drei EHEs die am Abbau von Zellulose beteiligt sind, von Hydrolasen aus dem N- und P-Kreislauf sowie die Enzymaktivitäten von Phenol- und Peroxidasen erfasst (Tischer et al. 2015). Die bisherigen Ergebnisse der Studie zeigen deutlich enge Beziehungen zwischen den Kinetiken der Hydrolasen und ökosystemrelevanten Funktionen wie dem Streuabbau und weisen zudem auf die kinetischen Zusammenhänge und Limitierungen unterschiedlicher Enzymsysteme im Abbau von Streu hin. Die Landnutzungsintensität scheint in ersten Auswertungen neben der Streuart ein weiterer Hauptfaktor für die Abbaudynamik und die Beziehungen zu den Enzymkinetiken zu sein