Ambrosia artemisiifolia control in agricultural areas: effect of grassland seeding and herbivory by the exotic leaf beetle Ophraella communa

Interaction of traffic intensity and habitat features shape invasion dynamics of an invasive alien species (Ambrosia artemisiifolia) in a regional road network

Road corridors are important conduits for plant invasions, and an understanding of the underlying mechanisms is necessary for efficient management of invasive alien species in road networks. Previous studies identified road type with different traffic volumes as a key driver of seed dispersal and abundance of alien plants along roads. However, how the intensity of traffic interacts with the habitat features of roadsides in shaping invasion processes is not sufficiently understood. To elucidate these interactions, we analyzed the population dynamics of common ragweed (Ambrosia artemisiifolia L.), a common non-indigenous annual species in Europe and other continents, in a regional road network in Germany. Over a period of five years, we recorded plant densities at roadsides along four types of road corridors, subject to different intensities of traffic, and with a total length of about 300 km. We also classified roadsides in regard to habitat features (disturbance, shade). This allowed us to determine corridor- and habitat-specific mean population growth rates and spatial-temporal shifts in roadside plant abundances at the regional scale. Our results show that both traffic intensity and roadside habitat features significantly affect the population dynamics of ragweed. The combination of high traffic intensity and high disturbance intensity led to the highest mean population growth whereas population growth in less suitable habitats (e.g. shaded roadsides) declined with decreasing traffic intensity. We conclude that high traffic facilitates ragweed invasion along roads, likely due to continued seed dispersal, and can compensate partly for less suitable habitat features (i.e. shade) that decrease population growth along less trafficked roads. As a practical implication, management efforts to decline ragweed invasions within road networks (e.g. by repeated mowing) should be prioritized along high trafficked roads, and roadside with disturbed, open habitats should be reduced as far as possible, e.g. by establishing grassland from the regional species pool.

Seeding and Overseeding Native Hayseed Support Plant and Soil Arthropod Communities in Agriculture Areas

Using native seed mixtures to create or recover grassland habitats in rotation to crops or in strips surrounding fields is considered a cost-effective practice to enhance ecosystem resilience and agro-biodiversity. The aim of this research was to assess the effects of native hayseed mixtures on plant and microarthropod communities in an agricultural area of Northern Italy. Three different experimental treatments were set up. The first was a control (C) (i.e., non-seeded plots left to spontaneous vegetation succession after ploughing no deeper than 15 cm). The second, hayseed seeded (Hs) after ploughing no deeper than 15 cm. The third experimental treatment was hayseed overseeded (Ov) on the resident plant community after only a superficial harrowing. Ov plots exhibited the preeminent positive effects on the total productivity and quality of the grassland in terms of total vegetation cover, cover and richness of typical grassland species (i.e., Molinio-Arrhenatheretea species), and cover of legumes, grasses and perennial species. Moreover, Ov sites exhibited the highest abundance of microarthropod taxa and soil biological quality (QBS-ar) but only in spring, when the disturbance of ploughing negatively affected Hs and C plots. On the other hand, Hs sites showed a great reduction of invasive alien (i.e., Ambrosia artemisiifolia and Artemisia verlotiorum) and segetal weed species (i.e., Capsella bursa-pastoris and Spergula arvensis) in terms of cover. This study provides valuable indication on using hayseed mixtures to create grassland habitats as reservoir of native flora and soil biodiversity in agriculture areas.

Physiological Metabolic Responses of Ophraella communa to High Temperature Stress

Considering the predicted rising temperatures under current climate change and heat wave scenarios, organisms are expected to suffer more intense and frequent thermal stress. Induced heat is accumulated by organisms and can cause a variety of physiological stress responses. Ophraella communa is an effective biological control agent of common ragweed, Ambrosia artemisiifolia, but the responses of this biocontrol agent to heat stress have not been fully elucidated and, therefore, its potential responses to climate change are uncertain. We investigated the physiological metabolism of subsequent O. communa adults after: (1) different developmental stages (egg, larval, pupal, and adult) were exposed to thermal stress for 3 h each day for 3, 5, 5, and 5 days, respectively (by stage); and (2) individuals were exposed to thermal stress throughout the egg-to-adult period for 3 h each day. The high temperatures of 40, 42, and 44°C were used to induce thermal stress. A control group was reared at 28 ± 2°C. The results showed that short- or long-term exposure to daily phasic high temperatures significantly decreased water and lipid contents and significantly increased glycogen and glycerol contents in all adults (i.e., after exposure of different stages or throughout the egg-to-adult period). However, the total sugar content significantly increased in adults after the eggs and larvae were exposed to brief short-term thermal stress. Compared to the control, the total sugar content was also significantly higher in the adults and pupae exposed to 44°C. Total sugar content in females increased significantly in response to long-term phasic thermal stress at 40°C. However, sugar content of males exposed to 44°C decreased significantly. After long-term phasic thermal stress, water and glycogen contents in males were significantly higher than in females; however, females had higher total sugar and lipid contents. Therefore, our study provides a basic understanding of the metabolic responses of O. communa to thermal stress and offers insights into its potential as a natural biocontrol agent against A. artemisiifolia during the summer season and under predicted climate change scenarios.

Rapid growth and defence evolution following multiple introductions

Rapid adaptation can aid invasive populations in their competitive success. Resource allocation trade-off hypotheses predict higher resource availability or the lack of natural enemies in introduced ranges allow for increased growth and reproduction, thus contributing to invasive success. Evidence for such hypotheses is however equivocal and tests among multiple ranges over productivity gradients are required to provide a better understanding of the general applicability of these theories.Using common gardens, we investigated the adaptive divergence of various constitutive and inducible defence-related traits between the native North American and introduced European and Australian ranges, while controlling for divergence due to latitudinal trait clines, individual resource budgets, and population differentiation, using >11,000 SNPs.Rapid, repeated clinal adaptation in defence-related traits was apparent despite distinct demographic histories. We also identified divergence among ranges in some defence-related traits, although differences in energy budgets among ranges may explain some, but not all, defence-related trait divergence. We do not identify a general reduction in defence in concert with an increase in growth among the multiple introduced ranges as predicted trade-off hypotheses. Synthesis: The rapid spread of invasive species is affected by a multitude of factors, likely including adaptation to climate and escape from natural enemies. Unravelling the mechanisms underlying invasives' success enhances understanding of eco-evolutionary theory and is essential to inform management strategies in the face of ongoing climate change.

OPEN RESEARCH BADGES

This article has been awarded Open Materials, Open Data, Preregistered Research Designs Badges. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.6084/m9.figshare.8028875.v1, https://github.com/lotteanna/defence_adaptation,https://doi.org/10.1101/435271.