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Funding Information: This open-access publication was funded by the University of Freiburg. Funding Information: Financial support. The project is supported by the Wassernetzwerk Baden-Württemberg (Water Research Network of the State Baden-Württemberg), which is funded by the Ministerium für Wissenschaft, Forschung und Kunst Baden-Württemberg (Ministry of Science, Research and the Arts of the State Baden-Württemberg) (grant no. AZ. 7532.21/2.1.6) and Maa-ja vesitekniikan tuki ry foundation. Doris E. Wendt acknowledges her support as part of the NERC-funded Groundwater Drought Initiative (NE/R004994/1). Lucy J. Barker was supported by the Natural Environment Research Council (NE/R016429/1) as part of the UK-SCAPE programme delivering National Capability. The contributions of Mirek Trnka, Lenka Bartošová, and Jaak Jaagus have been supported by SustES – Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797). Publisher Copyright: © 2022 Veit Blauhut et al. Drought events and their impacts vary spatially and temporally due to diverse pedo-climatic and hydrologic conditions, as well as variations in exposure and vulnerability, such as demographics and response actions. While hazard severity and frequency of past drought events have been studied in detail, little is known about the effect of drought management strategies on the actual impacts and how the hazard is perceived by relevant stakeholders. In a continental study, we characterised and assessed the impacts and the perceptions of two recent drought events (2018 and 2019) in Europe and examined the relationship between management strategies and drought perception, hazard, and impact. The study was based on a pan-European survey involving national representatives from 28 countries and relevant stakeholders responding to a standard questionnaire. The survey focused on collecting information on stakeholders' perceptions of drought, impacts on water resources and beyond, water availability, and current drought management strategies on national and regional scales. The survey results were compared with the actual drought hazard information registered by the European Drought Observatory (EDO) for 2018 and 2019. The results highlighted high diversity in drought perception across different countries and in values of the implemented drought management strategies to alleviate impacts by increasing national and sub-national awareness and resilience. The study identifies an urgent need to further reduce drought impacts by constructing and implementing a European macro-level drought governance approach, such as a directive, which would strengthen national drought management and mitigate damage to human and natural assets.

Agronomic and ecological analyses of plant life history regarding longevity and resource use along an axis from annual to perennial species provides a framework to evaluate trade-offs in plant-environment-management interactions in agroecosystems necessary for a future bio-based society. This field study on a sandy loam soil in Denmark compared annual crops grown in either (1) monocultures of maize and triticale, (2) conventional rotation of barley and wheat or (3) rotation optimized for large biomass yields including maize, beet, hemp, triticale and winter rye, with perennials from Poaceae and Fabaceae families as (4) intensively fertilized festulolium, (5) low-fertilized miscanthus and (6) grass-legume mixture without nitrogen (N) fertiliser. The agro-environmental analysis comprised statistical comparison of 5-years (2013-2017) observed data on N in biomass and leached out of the root zone of the different agroecosystems.The results showed that biomass N differed highly across the agroecosystems due to an integrative effect of plant-specific characteristics and management actions. Of the seven agroecosystems and on mean annual basis, the lowest leaching of about 20 kg N ha-1 was observed for grass-clover mixture with 217 kg N ha-1 in biomass at no N-fertilizer cost, highlighting plausible option to extensity agroecosystems with perennial legumes. Leaching below the highly-fertilized festulolium was highly variable, but on average 53 kg N ha-1 and similar to 48 kg N ha-1 for the conventional rotation, yet, at significantly larger harvest of 480 versus 140 kg N ha-1. The high productivity of the perennial grass observed under intensification was ascribed to high canopy radiation interception (800-1200 MJ m-2) with large synchronized soil N uptake (150 kg N ha-1 cut-1 of biomass at three-cut frequency fertilised125-175 kg N ha-1 post-cut), though the latter appears to diminish with the age of this agroecosystem. Renewal of the festulolium showed large peak in nitrate concentrations in the end of the root zone the following year, followed by rapid stabilization thereafter, prompting for agronomic intervention such as grass re-sowing together with a fast-growing single-season cover crop and N-fertilizer adjustments. The renewal dynamics of the soil nitrate for grass-clover mixture was slightly extended, but at a much lesser intensity compared to festulolium. Leaching from the optimized crop rotation was either comparable or lower to that from the conventional systems, alongside equally or higher biomass N and associated agroecosystem diversification benefits.Altogether with positive effects of perennial crops on the soil N and carbon stocks observed by concomitant studies at the site, these results provide novel insights to advance the understanding of resource use efficiency of both perennial and annual crops in agroecosystems targeting provision of biomass for the bio-based society.

Sustainable refining of biomass requires increased biomass yield while protecting soil carbon (C) stock. Here, we compared 14 different cropping systems grown on a sandy loam soil in central Denmark, including (1) two continuous monocultures of annual crops, (2) one conventional crop rotation, (3) four optimized crop rotations, (3) five intensively fertilized perennial grasses, and (4) two grass-legume mixtures without nitrogen (N) fertilization. Our results showed that biomass yield and yield stability differed highly across the cropping systems, highlighting crop-specific characteristics. Of all the cropping systems, tall fescue significantly increased soil C and N content by 7% for both, while sustaining high biomass yield and yield stability compared to the other annual crops. Increases in soil C stock were positively and significantly correlated with biomass yield (R2 = 0.175, p = 0.007), suggesting a win-win strategy for climate mitigation and food security by promoting land conversion from annual to perennial crops. We also compared soil extracellular enzyme activity (EEA) between annual and perennial crops. These results showed significantly reduced oxidative carbon-degrading EEAs by 79% for tall fescue, concomitant with the increased soil C content for this perennial grass, compared to triticale. Moreover, tall fescue significantly increased EEAs targeting soil N and phosphorus cycling by 28-29% compared to triticale, supporting the emerging findings that perennial crops can be more resource efficient. Altogether, our results provide novel perspectives from soil EEAs to advance the understanding of climate-smart and resource-efficient perennial agroecosystems targeting refining of biomass.

Aarhus University Centre for Circular Bioeconomy (CBIO): Production and management of agricultural biomasses research infrastructure