Salisbury, A. | bioRxiv Science

bioRxiv2023

Top dressed biochar increases tree seedling growth and decreases sodium leaching

De-icing salts on roadways are nearly ubiquitous in northern cities during winter months, leading to contamination of soils adjacent to roadways. Sodium chloride salts often have detrimental impacts on water and trees, though some species are more sensitive than others. Biochar has the potential to mitigate sodiums harmful effects due to its large surface area:volume ratio and subsequent ability to sorb ions from solution. We conducted a four-month greenhouse experiment to test if biochar applied as either a top dressing or incorporated into the growing medium reduced sodium leaching and buffered tree responses to sodium stress. We also evaluated the effects of salt addition and biochar on four tree species that vary in salt tolerance: Catalpa speciosa (tolerant), Gleditsia triacanthos (tolerant), Acer saccharum (intolerant), and Quercus rubra (intolerant). We found no interactive effects of sodium addition and biochar on sodium leaching or tree growth and physiology. However, we did find that top dressed biochar broadly decreased sodium leaching, likely via positive effects of top dressed biochar on tree seedling growth, Catalpa speciosa in particular. Incorporated biochar, on the other hand, had positive or neutral effects on sodium leaching and negative effects on the production of new shoots and fine roots. Given that biochar is a relatively expensive amendment, it should be used sparingly to improve urban tree growth and health. Overall, this study shows that biochar application decisions have implications for tree growth and soil management.

plant biology↗

bioRxiv2023

Urbanisation generates multiple trait syndromes for terrestrial taxa worldwide

Cities can host significant biological diversity. Yet, urbanisation leads to the loss of habitats and, potentially, to local extinctions. Understanding how multiple taxa respond to urbanisation globally is essential to promote and conserve biodiversity in cities and surrounding landscapes. Using a dataset with site-level occurrence and trait data of 5302 species from six terrestrial fauna taxonomic groups across 379 cities on 6 continents, we show that urbanisation produces taxon-specific changes in trait composition, with traits related to reproductive strategy consistently showing the strongest response. The effect of urbanisation on community trait composition is strongest at the largest spatial scale considered, and more closely linked to landscape composition (% urban) than arrangement (aggregation), although latitude and climatic variables remain a stronger influence. This study did not find evidence in support of a global urban taxa syndrome, but instead we suggest that there are four general urban trait syndromes, with resources associated with reproduction and diet likely to be driving patterns in traits associated with mobility and body size. Functional diversity measures showed a wide range of responses, leading to a shift in trait space that is most likely driven by the distribution and abundance of critical resources, and the urban trait syndrome displayed by individual species within a community. Further research is required to understand the interactions between the four general urban trait syndromes, resource distribution and abundance and changes in functional diversity of taxa at different spatial and temporal scales. Maximising opportunities to support species within taxa groups with different urban trait syndromes should be pivotal in conservation and management programmes within and among cities. This will reduce the likelihood of biotic homogenisation at the taxa level, and helps ensure that urban environments have the ecological capacity to respond to challenges such as climate change, further habitat fragmentation and loss, and other disruptions. These actions are critical if we are to reframe the role of cities in global biodiversity loss.

ecology↗