B-Ware (Netherlands)

Mammalian herbivores play a pivotal role in nutrient cycling and plant community composition. Their excreta and grazing activity influence plant diversity, but the relative or interactive effects of these influences are unclear. We manipulated dung quantity, quality (three herbivores with varying dung-N:P), and grazing type (bulk, selective, no) in a 3-year experiment. Neither dung quantity nor bulk grazing influenced plant diversity, despite strongly impacting plant productivity and light. Dung's impact on plant diversity varied among herbivore species but could not be ascribed to nutrients. Effects of selective grazing on plant diversity interacted with dung type (herbivore species), depending on whether it promoted dominance of the consumed plants. Our results highlight that the interactive effects between herbivore species-specific dung characteristics and grazing activities have important indirect effects on plant diversity in terrestrial ecosystems.

Due to various human activities, including intensive agriculture, traffic, and the burning of fossil fuels, in many parts of the world, current levels of reactive nitrogen emissions strongly exceed pre-industrial levels. Previous studies have shown that the atmospheric deposition of these excess nitrogen compounds onto semi-natural terrestrial environments has negative consequences for plant diversity. However, these previous studies mostly investigated biodiversity loss at local spatial scales, that is, at the scales of plots of typically a few square meters. Whether increased atmospheric nitrogen deposition also affects plant diversity at larger spatial scales remains unknown. Here, using grassland plant community data collected in 765 plots, across 153 different sites and 9 countries in northwestern Europe, we investigate whether relationships between atmospheric nitrogen deposition and plant biodiversity are scale-dependent. We found that high levels of atmospheric nitrogen deposition were associated with low levels of plant species richness at the plot scale but also at the scale of sites and regions. The presence of 39% of plant species was negatively associated with increasing levels of nitrogen deposition at large (site) scales, while only 1.5% of the species became more common with increasing nitrogen deposition, indicating that large-scale biodiversity changes were mostly driven by "loser" species, while "winner" species profiting from high N deposition were rare. Some of the "loser" species whose site presence was negatively associated with atmospheric nitrogen deposition are listed as "threatened" in at least some EU member states, suggesting that nitrogen deposition may be a key contributor to their threat status. Hence, reductions in reactive nitrogen emissions will likely benefit plant diversity not only at local but also at larger spatial scales.

Rewetting drained peatlands for paludiculture purposes is a way to reduce peat oxidation (and thus CO2 emissions) while at the same time it could generate an income for landowners, who need to convert their traditional farming into wetland farming. The side effect of rewetting drained peatlands is that it potentially induces high methane (CH4) emission. Topsoil removal could reduce this emission due to the removal of easily degradable carbon and nutrients. Another way to limit CH4 emission is the choice in paludiculture species. In this study we conducted a field experiment in the coastal area of the Netherlands, in which a former non-intensively used drained peat grassland is rewetted to complete inundation (water table ~+18 cm) after a topsoil removal of ~20 cm. Two emergent macrophytes with a high potential of internal gas transport (Typha latifolia and Typha angustifolia), and a free floating macrophyte (Azolla filiculoides) were introduced and intensive measurement campaigns were conducted to capture CO2 and CH4 fluxes, soil and surface water chemistry. Greenhouse gas fluxes were compared to a high-productive peat meadow as reference site. Topsoil removal reduced the amount of phosphorus and iron in the soil to a large extent. The total amount of soil carbon per volume stayed more or less the same. The salinity of the soil was in general high defining the system as brackish. Despite the topsoil removal and salinity, we found very high CH4 emission for T. latifolia (84.7 g CH4 m -2 yr -1 ), compared to the much lower emissions from T. angustifolia (36.9 g CH4 m -2 yr -1 ) and Azolla (22.2 g CH4 m -2 yr -1 ). The high emission can be partly explained by the large input of dissolved organic carbon into the system, but it could also be caused by plant stress factors, like salinity level and herbivory. For the total CO2 flux (including C-export), the rewetting was effective, with a minor uptake of CO2 for Azolla (-0.13 kg CO2 m -2 yr -1 ) and a larger uptake for the Typa species (-1.14 and -1.26 kg CO2 m -2 yr -1 for T. angustifolia and T. latifolia, respectively) compared to the emission of 2.06 kg CO2 m -2 yr -1 for the reference site. Azolla and T. angustifolia seem to have the highest potential in reducing greenhouse gas emissions after complete rewetting of drained peatlands. When considering the total greenhouse gas balance, other factors like biomass use, and storage of topsoil after removal should be considered. Especially the latter could cause substantial carbon losses if not kept in anoxic conditions.

Peat decomposition driven by soil metabolic processes is responsible for approximately 2 % of global annual anthropogenic greenhouse gas emissions. A peat soil's redox potential (Eh) and pH reflect its biogeochemical state and are therefore linked to the rate of peat decomposition and greenhouse gas production. In this study, we aim to establish if continuous Eh measurements are an effective tool to monitor metabolic peat decomposition processes and thus to quantify the effects of peat wetting efforts. We applied continuous in-situ Eh measurements (>150 sensors 2020–2022) as a proxy for metabolic peat decomposition processes, which we validated under field conditions with extensive sampling of porewater chemistry (pH, NO3–, SO42−, Mn(II), Fe(II), S2− and CH4, >2000 samples) for five agricultural, drained, minerotrophic peatland sites in the Netherlands. These 5 sites consisted of plots with and without subsoil irrigation (SSI), where SSI aims to raise groundwater levels and thus wet the peat soil. We found that in-situ continuous Eh measurements closely reflected spatial and temporal heterogeneity in pore water chemistry. Therefore, we concluded that Eh is a robust proxy for peat decomposition processes. Building on this result, we used continuous Eh measurements to study the prevalence of specific metabolic processes from site-to-site in relation with groundwater level changes. We found that, while groundwater levels are an important driver for (an)aerobic conditions, groundwater levels do not explain the full dynamics and extent of (an)aerobic conditions. O2 intrusion was mostly limited to approximately 0.5 m depth at deep (>0.8 m) groundwater levels, likely due to air diffusion limitation. Higher and more constant groundwater levels year-round at SSI plots decreased oxygen intrusion and tended to deplete porewater Fe(II) and SO42−, which led to more reducing Eh and higher porewater CH4 concentrations. The depletion of electron acceptors and occurrence of methanogenesis differed from site to site. In summary, high-frequent Eh monitoring is found to be an effective tool to monitor metabolic peat decomposition processes and quantify the effects of peatlands wetting efforts. Therefore, this methodology is suitable to evaluate and further optimize peatland monitoring and preservation.

Peatlands are among the world's most carbon-dense ecosystems and hotspots of carbon storage. Although peatland drainage causes strong carbon emissions, land subsidence, fires and biodiversity loss, drainage-based agriculture and forestry on peatland is still expanding on a global scale. To maintain and restore their vital carbon sequestration and storage function and to reach the goals of the Paris Agreement, rewetting and restoration of all drained and degraded peatlands is urgently required. However, socio-economic conditions and hydrological constraints hitherto prevent rewetting and restoration on largescale, which calls for rethinking landscape use. We here argue that creating integrated wetscapes (wet peatland landscapes), including nature preserve cores, buffer zones and paludiculture areas (for wet productive land use), will enable sustainable and complementary land-use functions on the landscape level. As such, transforming landscapes into wetscapes presents an inevitable, novel, ecologically and socio-economically sound alternative for drainage-based peatland use.

Abstract Peat decomposition, driven by soil metabolic processes, was responsible for 2% of the anthropogenic greenhouse gas emissions in 2019. The peat soil redox potential (Eh) and pH reflect the chemical state of the soil and the (biogeo)chemical processes that occur and are therefore linked to the rate of peat decomposition and greenhouse gas production. We related porewater chemistry (pH, NO3-, SO42-, Mn(II), Fe(II), S2- and CH4, >2000 samples) to continuous Eh measurements (2020-2022) from five agricultural drained peatland sites in the Netherlands that consist of measuring plots with and without subsoil irrigation and drainage (SSI) in order to establish Eh ranges that identify specific metabolic processes. We found that methanogenesis, reduction of SO42-, Fe(III), NO3-/ Mn(IV) and O2 occurred at Eh (at pH 5.5) of < -49 mV, -49 – 104 mV, 104- 364 mV, 364- 700 mV and >700mV respectively. Eh over depth and time closely followed temporal and spatial fluctuations in groundwater level and porewater chemistry, and revealed the extent of O2 intrusion and the occurrence of methanogenesis. Higher and more constant groundwater levels year-round tended to deplete porewater Fe(II) and SO42-, which led to more reducing Eh and higher porewater CH4 concentrations. These mechanistic insights help to optimize GHG mitigation strategies for drained peat regions.

Abstract Many degraded ecosystems need active restoration to conserve biodiversity and re‐establish ecosystem function, both highlighted targets of the UN Decade on Ecosystem Restoration and the proposed EU Nature restoration law. Soil translocation, where both plant propagules and their associated soil biota are co‐introduced, has increasingly been proposed as a powerful restoration technique for terrestrial ecosystems. However, a synthesis of the effectiveness of this method across ecosystems is lacking. To address how soil translocation affects restoration success, we performed a meta‐analysis synthesizing data from 46 field experiments and their respective reference ecosystems in 17 countries across four continents. In each experiment, vegetation composition was recorded in response to soil translocation treatments and the resultant vegetational changes (diversity and composition) were quantified. We found that soil translocation leads to plant community development further away from the control and more towards the reference plant communities compared with treatments where only plant propagules were introduced. However, the variability of effect sizes among experiments was large, suggesting strong dependence of restoration success on restoration context. We found that restoration success was more likely on loamy soils and when translocation treatments were implemented over larger spatial areas (>180 m2). Furthermore, we found that restoration success either consistently increased or decreased over time depending on the experiment. Not only is this congruent with positive feedbacks between plant and soil communities driving plant community development, but it also suggests that the composition of the translocated plant and soil communities, and initial starting conditions, are critical for long‐term restoration success. Synthesis and applications. Our analysis highlights soil translocation can be a successful restoration method across a broad range of ecosystems. However, its implementation needs to depend on a thorough evaluation of local conditions and the potential added value. Further refinement of soil translocation techniques is needed to increase success rates.

Isoetids are slow growing ecosystem-engineers that maintain an oligotrophic environment through high radial oxygen losses (ROL) from their roots. This ROL could potentially reduce methane (CH4) emission by maintaining sediment redox conditions unfavourable for methanogenesis. Isoetids have declined in many European countries as an effect of eutrophication and inorganic carbon enrichment. To assess the effect of sudden disappearance of isoetids on biogeochemical carbon and nutrient cycling in organic rich sediments, we set up a greenhouse experiment. Intact vegetated sediment patches with Lobelia dortmanna and Littorella uniflora were collected from ten boreal Norwegian softwater lakes. From half of the patches, isoetids were manually removed. We determined the effect of removal on sediment redox potential, pore water chemistry and CH4 emission. In addition, germination success of L. dortmanna seeds was tested on the sediments where isoetids were removed. The absence of ROL after isoetid removal led to a drop in sediment redox potential, resulting in anaerobic breakdown of organic matter using alternative electron acceptors, especially iron(hydr)oxides. Consequently, increased porewater concentrations of ammonium, iron, inorganic carbon and CH4 were observed in sediments where isoetids had been removed compared to the isoetid vegetated sediments. Moreover, over 20 times higher emission of CH4 was observed from the sediments where isoetids had been removed. On the highly reduced sediments, the germination of L. dortmanna was hampered. When isoetids are unable to recolonise after disturbance events, it is expected that the absence of ROL eventually results in a long-term increase in lake productivity and CH4 emission.

Dead wood is a source of life as it provides habitat and substrate for a wide range of fungal species. A growing number of studies show an important role of wood quality for fungal diversity, but in most cases for a limited number of wood traits or tree species. In this study, we evaluate how abiotic and biotic factors affect the fungal diversity and composition during dead wood decomposition. For ten common European tree species, fresh similar‐sized logs were incubated simultaneously in two Dutch forests. Annual surveys of fungal fruiting bodies were made for an 8‐year period. For each tree species, 20 fresh stem traits were measured that are important for chemical and physical defence and for nutritional quality. Throughout eight years, 4644 fruiting bodies belonging to 255 species and 90 genera were recorded on the logs of ten tree species. Fungal frequency and richness were higher for Angiosperms than for Gymnosperms, both for individual tree species and as a group, and higher for tree species with more acquisitive stem trait strategies (i.e. high nutritional value and low physical defence). Differences in fungal communities were strongly driven by phylogenetic group (Gymnosperms versus Angiosperms), stem traits, decay time and forest sites, together explaining 23% of the variation. Fungal communities in sandy site diverged early in the decay process but converged later because of substrate homogenization. Of the 128 fungal species included in the analyses, 41% showed a preference for specific tree species and 34% for a specific successional year. In conclusion, dead wood quality, determined by tree species and decay stage, is an important driver of fungal diversity. For forest management, promoting a wide array of dead tree species (especially angiosperm species), a range of stem trait values and decay stages will increase fungal and, thereby, forest biodiversity.