Non-native trees are of major importance in forestry and urban greening but are controversially discussed with regard to their effects on native biodiversity. Existing literature reports positive as well as negative biodiversity effects of non-native trees. Geographic, climatic and phylogenetic distance between the non-native and native tree species are named as important factors shaping these biodiversity effects. However, studies with a large geographic and taxonomic coverage are missing. Here we tested the effects of geographic, climatic and phylogenetic distance on resident insect abundance and diversity for 77 native and non-native tree species in a common garden trial. We identified phylogenetic distance of tree species to be the main driver of insect abundance and diversity with a negative effect of increasing phylogenetic distance and stronger effects for phytophagous than for non-phytophagous insects. This highlights the necessity to account for phylogenetic history shared between native and non-native congeners when managing non-native trees.

Drought threatens plant growth and related ecosystem services. The emergence of plant drought stress under edaphic drought is well studied, whilst the importance of atmospheric drought only recently gained momentum. Yet, little is known about the interaction and relative contribution of edaphic and atmospheric drought on the emergence of plant drought stress. We conducted a gradient experiment, fully crossing gravimetric water content (GWC: field capacity-permanent wilting point) and vapour pressure deficit (VPD: 1-2.25kPa) using five wheat varieties from three species ( Triticum monococcum, T. durum & T. aestivum). We quantified the emergence of plant drought stress on molecular (ABA), cellular (stomatal conductance), organ (leaf water potential) and stand level (evapotranspiration). Plant drought stress increased with decreasing GWC across all organisational levels. This effect was magnified non-linearly by VPD after passing a critical threshold of soil water availability. At around 20% GWC plants lost their ability to regulate leaf water potential via stomata regulation, followed by the emergence of hydraulic dysfunction. The emergence of plant drought stress is characterized by changing relative contributions of soil vs. atmosphere and their non-linear interaction. This highly non-linear response, consequently, is likely to abruptly alter plant-related ecosystem services in a drying world.

Increasing atmospheric CO 2 and drought are major symptoms of anthropogenic climate change with profound effects on plant growth. Transgenerational memory (i.e. influence of the parental environment on offspring phenotype and performance) has been suggested as a relevant mechanism for plants to build-up adaptative capacity for rapid environmental changes. However, this mechanism of pre-adaptation remains poorly investigated so far. We investigated intra- and transgenerational effects of elevated CO 2 on drought response of wheat. We used seeds from a FACE (Free Air Carbon Dioxide Enrichment) experiment with ambient and elevated CO 2 to grow plants in climate chambers in which we varied CO 2, atmospheric water demand and soil moisture. We quantified photosynthetic efficiency, stomatal sensitivity and biomass production. We observed intragenerational upregulation of photosynthetic efficiency but transgenerational downregulation of photosynthetic efficiency, stomatal sensitivity and water use efficiency as response to maternally elevated CO 2. Plant biomass was affected by drought and experimental CO 2 but not by maternal CO 2. Our study showcases the importance of transgenerational memory effects when studying climate change response of plants and could have major implications for our understanding of global dynamics of carbon sequestration. It highlights the pressing need for multi-generational experiments accounting for transgenerational memory effects of elevated CO 2.

Lacking comparability among rainfall manipulation studies is still a major limiting factor for generalizations in ecological climate change impact research. A common framework for studying ecological drought effects is urgently needed to foster advances in ecological understanding the effects of drought. In this synthesis, we argue, that the soil-plant-atmosphere continuum, describing the flow of water from the soil through the plant to the atmosphere, can serve as a holistic concept of drought in rainfall manipulation experiments which allows for the reconciliation experimental drought ecology. Using experimental data, we show that investigations of leaf water potential in combination with edaphic and atmospheric drought -- as the three main components of the soil-plant-atmosphere-continuum -- are key to understand the effect of drought stress on plants. Based on a systematic literature survey, we show that especially plant and atmospheric based drought quantifications are strongly underrepresented and integrative assessments of all three components are almost absent in current experimental literature. Based on our observations we argue, that studying dynamics of plant water status in the framework of the soil-plant-atmosphere-continuum can foster comparability of different studies conducted in different ecosystems and with different plant species and can facilitate extrapolation to other systems, species or future climates.