Spatially distinct responses within willow to bark stripping by deer: effects on insect herbivory

Plant volatiles and priority effects interactively determined initial community assembly of arthropods on multiple willow species

Plant traits, which are often species specific, can serve as environmental filtering for community assembly on plants. At the same time, the species identity of the initially colonizing arthropods would vary between plant individuals, which would subsequently influence colonizing arthropods and community development in the later stages. However, it remains unclear whether interindividual divergence due to priority effects is equally important as plant trait-specific environmental filtering in the initial stages. In this study, we propose that plant volatile organic compounds (PVOCs) may play a crucial role as an environmental filter in the initial stages of community assembly, which can prevent the community assembly process from being purely stochastic. To test this hypothesis, we conducted short term but highly frequent monitoring (19 observations over 9 days) of arthropod community assembly on intact individuals of six willow species in a common garden. PVOC compositions were analyzed before starting the experiment and compared with arthropod compositions occurring on Days 1-2 of the experiment (earliest colonizer community) and those occurring on Days 8-9 of the experiment (subsequent colonizer community). Unintentionally, deer herbivory also occurred at night of Day 2. Distance-based statistics demonstrated that PVOC compositions were plant species specific, but neither the earliest colonizer nor the subsequent colonizer community composition could be explained by plant species identity. Rather, Procrustes analysis showed that both the PVOC composition and that of the earliest colonizer community can be used to explain the subsequent colonizer community. In addition, the linkage between PVOCs and the subsequent colonizer community was stronger on individuals with deer herbivory. These findings indicate that PVOCs have widespread effects on initial community assembly, as well as priority effects brought on by stochastic immigration, and that plant species identity only has weak and indirect effects on the actual composition of the community.

Root climbers may alter invertebrate communities on tree trunks: an indirect effect of lianas

Root climbers are a group of lianas which typically climb the host tree using adhesive roots and do not compete with the host for light. They are relatively more abundant in high-latitude forests and were recently documented to have no harmful effect on their host trees. Although previous studies have examined the direct negative effects of lianas on their host trees, little is known about potential indirect effects via effects on the animal and plant communities. Here, we aimed to determine the effects of root climbers on the animal and plant community composition of their host trunk and whether these alterations indirectly affect host trees. To answer these questions, we compared the invertebrate community, herbaceous plant presence, moss cover and herbivory rates in more than 22 pairs of host and control trees in cool-temperate forests in Hokkaido, Japan. We selected Quercus crispula Blume and Hydrangea petiolaris Sieb. et Zucc. as the study species. Generalised linear mixed models (GLMMs) were used to determine the influence of lianas on tree trunk communities and host trees. Our results showed that the presence of root climbers increased the abundance of Araneae and herbaceous plants and reduced the abundance of Formicidae on host trees, implying a reduction of herbivory on hosts. These results imply that liana presence may reduce the herbivory rate on the host tree, potentially by altering the trunk animal and plant community structure. Our results have implications for the understanding of the effects of lianas on host trees and their function in high-latitude forests.

Differential Impacts of Willow and Mineral Fertilizer on Bacterial Communities and Biodegradation in Diesel Fuel Oil-Contaminated Soil

Despite decades of research there is limited understanding of how vegetation impacts the ability of microbial communities to process organic contaminants in soil. Using a combination of traditional and molecular assays, we examined how phytoremediation with willow and/or fertilization affected the microbial community present and active in the transformation of diesel contaminants. In a pot study, willow had a significant role in structuring the total bacterial community and resulted in significant decreases in diesel range organics (DRO). However, stable isotope probing (SIP) indicated that fertilizer drove the differences seen in community structure and function. Finally, analysis of the total variance in both pot and SIP experiments indicated an interactive effect between willow and fertilizer on the bacterial communities. This study clearly demonstrates that a willow native to Alaska accelerates DRO degradation, and together with fertilizer, increases aromatic degradation by shifting microbial community structure and the identity of active naphthalene degraders.