Global climate change and in particular changes in the hydroclimate towards dryer and warmer summers will impact the structure and composition of central European and other forests on the planet. The extremely hot and dry summers that Europe has experienced in 2003 and in 2018 have already demonstrated the severe impacts that a changing climate will have on tree and forest function and composition for these ecosystems. Critical mechanisms that determine how drought will impact the functioning of trees and forests are, however, poorly understood. This makes it difficult to anticipate the consequences of a future and dryer climate for key ecosystem functions and prevents the development of silvicultural management plants for more resistant and resilient forest ecosystems. Here we propose to close this gap and to address the effects of drought on mature trees from ten different temperate European species in a large-scale ecosystem manipulation experiment. From our work, we expect the following outcome: we will provide thefirst comprehensive empirical characterization of the drought response strategies of key temperate European tree species, we will identify the trait syndromes that govern the different drought response strategies in these species and will identify important tradeoffs between traits and function, we will provide one of the first large scale across-species assessments of the acclimation potential of mature temperate European tree species to reduced water availability and we will identify the key traits that are responsible for these acclimations.

Rising global temperatures, fewer number of precipitation days and an increased intensity of drought events are projected to shape the future climate of central Europe. Changes in water availability and more intense drought events will have significant impacts on the central European vegetation and on temperate European forests in particular. Importantly, critical mechanisms that determine how changes in water availability and drought will impact the functioning of temperate European forests are poorly understood and not well represented in earth system models. Anticipating the consequences of a future climate for the functioning of temperate European forests is therefore difficult and hinders the design of mitigation options and future forest management plans. Most experiments that attempt to improve the mechanistic understanding of drought responses of terrestrial ecosystem have to date focused either on the experimental manipulation of grasslands or on investigations with tree seedlings or saplings. Although forests play an essential role for the delivery of ecosystem goods and services, very few experiments exist in established temperate European forests that mechanistically investigate the responses of mature trees and forest to changes in water availability or drought. To close this critical research gap, it is the goal of this proposal to establish an experimental research platform in a species rich and mature temperate forest in Switzerland. This experimental platform will provide the opportunity over the next two decades to host research projects addressing some of the most important unresolved questions with respect to tree and forests responses to changes in the precipitation regime and drought. Specifically, these projects will address the long-term acclimation potential of individual species or entire forests to precipitation changes, physiological and biogeochemical thresholds and tipping points during drought, and recovery processes during and after extended drought events. The experimental research platform that we seek to establish will combine a unique infrastructure that we request with this proposal. This infrastructure will include (i) a canopy crane that will allow scientific investigations in the canopy of more than 250 mature trees, (ii) six mobile roofs that will be installed 2.5 m above the ground and will cover a total area of 3398 m2 for the manipulation of precipitation inputs into the forest, and (iii) state of the art scientific instrumentation.

In the years to come, sustainable land use is one of the big challenges for plant science. One promising low-input strategy is to make use of the potential of intercropping. In dryland agriculture, deep-rooting plants, intercropped within shallow-rooting ones, may act as "bioirrigators" that can transfer water from deep soil layers to the topsoil for the benefit of the system. Our recent experiments have shown that bioirrigation is facilitated by the presence of arbuscular mycorrhizal fungi (AMF), which connect the intercropped plants by a common mycorrhizal network (CMN). The ambition of the research that we propose in this project is to identify the morphological, physiological and competitive traits that make plants ideal bioirrigators in CMN facilitated intercropping systems. With this research we seek to establish the basic knowledge that will allow establish effective CMN facilitated bioirrigation in intercropping systems as a measure to stabilize and increase the yield of small holder or subsistence farmers in dryland agriculture.

Im Rahmen des Projektes sollen die individuellen und kombinierten Auswirkungen von unterschiedlichen Szenarien von Klimaerwärmung, erhöhten atmosphärischen CO2-Konzentrationen und Dürre auf die Ökohydrologie von bewirtschaftetem Grünland untersucht werden, insbesondere, wie sich wiederkehrende Dürreereignisse unter aktuellen und künftigen Klimabedingungen auf die dem Wasserhaushalt zugrundeliegenden Prozesse auswirken.

Yields of dryland agriculture in developing countries suffer from nutrient mining and in particular water limitation, due to increasing drought events as a consequence of climatic change (IAASDT 2008). 50% of the crop production in these regions is achieved by small holder or subsistence farmers (World Bank, 2007). These farmers have little access to capital intensive technical equipment such as irrigation and mineral fertilizers to stabilize and increase their crop yields. As a consequence, smart and sustainable low input solutions are needed to stabilize and increase yields in dryland farming and to improve the livelihoods of small holder and subsistence farmers. Improving and stabilizing yields in dryland agriculture could come from designing sustainable agroecosystems that are built on in-depth ecological knowledge and that capitalize on beneficial plant-plant and plant-microbe interactions (Tscharntke et al., 2012; Brooker et al. 2014). One such sustainable low-input solution could be bioirrigation through intercropping (Liste and White, 2008; Burgess, 2011, Prieto et al., 2012). Bioirrigation is the result of an ecological interaction between two neighboring plants, where a deep-rooted plant supports the water supply and nutrient uptake of a neighbouring shallow-rooted plant. The concept of bioirrigation is linked to the ecohydrologically important process of hydraulic lift, where water from deep and wet soil layers is transported via the roots of plants to shallow and dry soil layers as a consequence of a soil water potential gradient (Dawson, 1993; Caldwell et al. 1998). Over the past three decades, hydraulic lift has been described to be performed by hundreds of plant species from different taxonomic groups and in various habitats. In contrast, very few studies were able to show that hydraulically lifted water from one species can effectively be utilized by another neighboring species. Bioirrigation has thus not yet been established as an ecological intercropping system that allows to stabilize and increase yields in marginal dryland farming (Burgess, 2011). Objective: The main objective of this project is to develop the ecological know-how that will allow to establish intercropping systems for dryland agriculture, where deep rooted legume species can effectively bioirrigate shallow rooted millets and increase as such the water relations, nutrient uptake and yields of these staple food crops of southern India and sub-Saharan Africa.

HYDROCARB is motivated by the enormous potential that stable hydrogen isotope ratios (δ2H values) in plant compounds have as hydrological proxy, but in particular as new proxy for the carbon metabolism in plants. Current conceptual models suggest that δ2H values in plant organic compounds are composed of (i) hydrological and (ii) metabolic signals. The hydrological information that is contained in δ2H values of plant material is now well understood and is often applied in (paleo-) hydrological research. In contrast, the metabolic information that is contained in plant δ2H values is mostly unknown. Intriguing recent research suggests, however, that metabolic signals in the δ2H values of plant organic compounds reflect the balance of autotrophic and heterotrophic processes in plants. This suggests that exciting and previously unknown opportunities exist to exploit δ2H values in plant compounds for information on the carbohydrate metabolism of plants, which would be relevant for a broad range of biological and biogeochemical disciplines. The goal of HYDROCARB is to perform the experimental work that is now needed to identify the key biochemical and physiological processes that determine the metabolic information that is recorded in the δ2H values of plant organic compounds such as leaf wax lipids, lignin and cellulose. With this HYDROCARB will provide the basis for semi-mechanistic models that will allow (i) disentangling hydrological from metabolic signals in plant δ2H values and (ii) identifying the precise physiological processes with respect to a plants carbohydrate metabolism that can be deducted from the δ2H values of different plant compounds. If successful, HYDROCARB will establish with this research δ2H values in plant organic compounds as a powerful new proxy that will allow ground-breaking and innovative research on plant and ecosystem carbon cycling, which has implications for plant biology, biogeochemistry and the earth system sciences.

In this project we will build on the experience of partners of the previous ISCB biofertilizer network and that of new Indian and Swiss partners to use arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) as "biofertilizers". Central to our approach is a mixed cropping system of finger millet and pigeon pea, which will make optimal use of the biofertilizers by the allocation and re-distribution of water through hydraulic lift ("bioirrigation"). Our principal output will be a "package" consisting of seeds for mixed-culture and compatible strains of biofertilizers of Indian origin, to be used by small-holder farms, especially in rainfed and saline fields in South India, where most of the current finger millet production takes place. In more detail, our "package" will be composed of polybags containing seeds of a pigeon pea cultivar suitable for transplantation, specifically selected to suit our proposed "bioirrigation" scheme, with an appropriate inoculum of biofertilizers, i.e., selected strains of AMF and PGPR; and seeds of a finger millet cultivar optimally suited for biofertilizer- and bioirrigation-enhanced performance in mixed culture with pigeon pea. Our biotechnological "package" will be a ground- breaking tool for rainfed fields not only in India, but on a global scale.

Nebst Veränderungen in der Landnutzung und durch den Klimawandel werden heute erhöhte bzw. aktuelle Raten an atmosphärischen Stickstoffeinträgen und die Überschreitungen (Exceedance) der kritischen Grenzwerte als die wichtigsten Ursachen von Veränderungen im Artenspektrum von Pflanzengemeinschaften und von Verlusten an Arten in (semi-) natürlichen Ökosystemen (inkl. Grasländern) angesehen. Allerdings bestehen nach wie vor grosse Wissenslücken zur Wirkung von relativ tiefen Stickstoffdepositionsraten auf naturnahe, siedlungsferne Lebensräume. Das Projekt will durch die empirische Überprüfung der "critical N loads" beitragen, den Wissensstand über wirkungsbasierte Effekte von erhöhten Stickstoffeinträgen auf alpine Grasländer zu verbessern. Nach bisherigem Wissen dürfte die atmosphärische Stickstoffdeposition in den Hochalpen neben der Veränderung der Schneelage das grösste "global change Risiko" für die Biodiversität darstellen.

Der Klimawandel stellt die Waldfachleute vor neue Herausforderungen und verlangt nach guten Grundlagen für die künftige Waldbewirtschaftung. Solche Grundlagen wissenschaftlich abgestützt bereitzustellen ist von öffentlichem Interesse. Das Departement für Umweltwissenschaften - Botanik, startet einen Langzeitversuch im Freiland zu den Auswirkungen des Klimawandels auf einen artenreichen Mischwald. Die Ergebnisse des Versuchs lassen detaillierte Ergebnisse zur Trockenheitsempfindlichkeit verschiedener Baumarten unter Freilandbedingungen erwarten. Solche Ergebnisse können nur in Langzeitversuchen erlangt werden, in denen auch alle anderen beeinflussenden Grössen gemessen werden. Das Projekt an der Universität Basel dient dem Schliessen von Kenntnislücken, insbesondere hinsichtlich des Verhaltens von Laubmischwäldern in der kollinen Stufe. Diese wird klimatisch voraussichtlich sehr grossen Veränderungen ausgesetzt sein, deren Auswirkungen auf die Wälder nicht gut zu berechnen sind.

Dynamic isotope model to trace the geographical origin of agricultural products.