No abstract

Summary Divergence in plant traits and trait plasticity after invasion has been proposed as mechanisms favouring invasion success. Current hypotheses predict a rapid evolution in response to changes in the abiotic conditions in the area of introduction or to differences in the herbivore consumption pressure caused by a decrease in the enemies associated with the area of origin [e.g. evolution of increased competitive ability (EICA) hypothesis]. The importance of these factors in determining plant geographical divergence has not been yet simultaneously evaluated. Senecio pterophorus (Asteraceae) is a perennial shrub native to eastern South Africa and a recent invader in western South Africa (since ˜100 years ago), Australia (>70–100 years) and Europe (>30 years). These areas differ in their summer drought stress [measured as the ratio of summer precipitation to potential evapotranspiration (P/PET)] and their interactions with herbivores. We performed a common garden experiment with S. pterophorus sampled throughout its entire known distributional area to determine (i) whether native and non‐native populations diverge in their traits, as well as the plasticity of these traits in response to water availability and (ii) whether climate and herbivory play a role in the genetic differentiation across regions. Plants from the non‐native regions were smaller and had a lower reproductive output than plants from the indigenous area. No geographical differences in phenotypic plasticity were found in response to water availability. Herbivory was not related to the plant geographical divergence. In contrast, our results are consistent with the role of climate as a driver for postinvasive evolution, as suggested by adaptation of plants to a drought cline in the native range, the analogous change in plant traits in independently invaded regions and the convergence of vegetative traits between non‐native plants and native plants under similar drought conditions. Native and non‐native populations of S. pterophorus differed in plant traits, but not in trait plasticity, in response to their local climatic conditions. Our results are contrary to the role of herbivory as a selective factor after invasion and highlight the importance of climate driving rapid evolution of exotic plants.

Biochar is a high carbon material resulting from biomass pyrolysis that, when applied to croplands, can increase soil carbon and soil water retention. Both effects are of critical importance in semi-arid regions, where carbon decline and desertification are the main drivers of soil degradation. Since most environmental services provided by soil are mediated by belowground biota, effects of biochar on soil microbial and invertebrate communities must be evaluated under field conditions before its agricultural application can be recommended. We tested maize biochar for its mid-term effect on soil microbes and micro-arthropods of a Mediterranean vineyard. We applied biochar to three field plots with neutral sandy loam soils at a dose of 5 Mg ha -1 . During two years, we monitored the abundance of functional groups of soil micro-arthropods and estimated the biomass of soil microbial groups. We also analyzed the δ 13 C value of microbial PLFA biomarkers to determine biochar-C utilization by each microbial group taking advantage of the δ 13 C natural abundance differences between the applied biochar and the soil. Biochar addition significantly reduced soil microbial biomass but did not alter the functional microbial diversity nor the abundance or biodiversity of soil micro-arthropods. The contribution of biochar-C to the diet of most microbial groups was very low through the monitoring period. However, two gram-negative bacterial groups increased their biochar-derived carbon uptake under extreme soil dryness, which suggests that biochar-C might help soil microbes to overcome the food shortage caused by drought. The decrease in microbial biomass observed in our experiment and the concomitant decrease of SOM mineralization could contribute to the carbon sequestration potential of Mediterranean soils after biochar addition.