Climate change induced range-expanding plants : aboveground and belowground interactions

Burning of fossil fuels has raised the level of atmospheric carbon dioxide, which contributes to global climate warming. As a result the mean earth surface temperature has increased faster in the past decades than in the previous thousands of years before. This rapid climate warming together with habitat fragmentation and other land use changes puts a major pressure on many plants and animals. They should either adapt to the warmer climate conditions or disperse in order to keep up with their optimal climatic conditions. Range expansion brings new interactions within the ecosystem in the new range. This can lead to potential benefits, for example range shifting species that do not encounter natural enemies in the new range might become invasive. Although invasive species are a well-studied phenomenon, there is relatively little known about the general mechanisms of biological invasions under climate change. In this thesis I focus on plant species that expand range due to current climate warming. I examined how these range-expanding plants interact with aboveground herbivorous insects and - mostly - how they establish belowground interactions with components of the soil food web. I examined how these interactions in the new range may play a role in the successful establishment of climate change induced range-expanding plants in plant communities of the new range. The focus of my study was on riverine (riparian) areas along the great rivers in the Netherlands, which are well connected with southern Europe by the Rhine and Rhine-Danube canal. In the first experiment we examined exotic plant exposure to aboveground and belowground enemies. We used plants that originated from Eurasia (intra-continental range expanders) and plants that originated from other continents (inter-continental range expanders). We compared these exotic plants with phylogenetically related natives. We grew the plants with and without non-coevolved polyphagous (generalist) herbivores, a locust Schistocerca gregaria and an aphid Myzus persicae. We also exposed all plants to a general soil community from the invaded range and compared their plant-soil feedback responses. Then I tested how individual plants responded to aboveground and belowground plant enemies and I compared this to their combined effects. I also tested whether the strength of aboveground control by generalist shoot-feeding insects was indicative of the strength of belowground control by plant-soil feedback. In the next study I examined how the soil nematode community from the new range responds to exotic plant species compared to related native plants species. As a follow up, I determined the rhizosphere community composition of bacteria, fungi, arbuscular mycorrhizal fungi (AMF) and fusaria. All groups of microbes were analyzed qualitatively and the non-mycorrhizal fungal biomass and fusaria were also analyzed quantitatively. I tested the hypothesis that range-expanding plant species have a different rhizosphere microbial community composition than natives. Finally, I compared the early establishment of range-expanding exotics and phylogenetically related plant species that are native in the invaded habitats. In a greenhouse I grew five range-expanding plant species and five related natives in sterilized and non-sterile inoculated soils from the new range, both alone and with a background community of plant species present in the invaded habitat. In the field, I grew the same plants species in artificially created sparse and dense plant communities. I tested whether range-expanding exotic plant species establish better under competition with native vegetation than phylogenetically related natives, because exotics may benefit from less negative interactions with the soil community compared to natives.</p

Biomechanics in Paralympics: Implications for Performance

Purpose: To provide an overview of biomechanical studies in Paralympic research and their relevance for performance in Paralympic sports. Methods: The search terms paralympic biomechanics, paralympic sport performance, paralympic athlete performance, and paralympic athlete were entered into the electronic database PubMed. Results: Thirty-four studies were found. Biomechanical studies in Paralympics mainly contributed to performance enhancement by technical optimization (n = 32) and/or injury prevention (n = 6). In addition, biomechanics was found to be important in understanding activity limitation caused by various impairments, which is relevant for evidence-based classification in Paralympic sports (n = 6). Distinctions were made between biomechanical studies in sitting (41%), standing (38%), and swimming athletes (21%). In sitting athletes, mostly kinematics and kinetics in wheelchair propulsion were studied, mainly in athletes with spinal-cord injuries. In addition, kinetics and/or kinematics in wheelchair basketball, seated discus throwing, stationary shot-putting, hand-cycling, sit-skiing, and ice sledge hockey received attention. In standing sports, primarily kinematics of athletes with amputations performing jump sports and running and the optimization of prosthetic devices were investigated. No studies were reported on other standing sports. In swimming, mainly kick rate and resistance training were studied. Conclusions: Biomechanical research is important for performance by gaining insight into technical optimization, injury prevention, and evidence-based classification in Paralympic sports. In future studies it is advised to also include physiological and biomechanical measures, allowing the assessment of the capability of the human body, as well as the resulting movement

Will fungi solve the carbon dilemma?

Environmental Biolog

Herbivory and dominance shifts among exotic and congeneric native plant species during plant community establishment

Invasive exotic plant species often have fewer natural enemies and suffer less damage from herbivores in their new range than genetically or functionally related species that are native to that area. Although we might expect that having fewer enemies would promote the invasiveness of the introduced exotic plant species due to reduced enemy exposure, few studies have actually analyzed the ecological consequences of this situation in the field. Here, we examined how exposure to aboveground herbivores influences shifts in dominance among exotic and phylogenetically related native plant species in a riparian ecosystem during early establishment of invaded communities. We planted ten plant communities each consisting of three individuals of each of six exotic plant species as well as six phylogenetically related natives. Exotic plant species were selected based on a rapid recent increase in regional abundance, the presence of a congeneric native species, and their co-occurrence in the riparian ecosystem. All plant communities were covered by tents with insect mesh. Five tents were open on the leeward side to allow herbivory. The other five tents were completely closed in order to exclude insects and vertebrates. Herbivory reduced aboveground biomass by half and influenced which of the plant species dominated the establishing communities. Exposure to herbivory did not reduce the total biomass of natives more than that of exotics, so aboveground herbivory did not selectively enhance exotics during this early stage of plant community development. Effects of herbivores on plant biomass depended on plant species or genus but not on plant status (i.e., exotic vs native). Thus, aboveground herbivory did not promote the dominance of exotic plant species during early establishment of the phylogenetically balanced plant communities

The Role of Plant Litter in Driving Plant-Soil Feedbacks

Most studies focusing on plant-soil feedbacks (PSFs) have considered direct interactions between plants, abiotic conditions (e. g., soil nutrients) and rhizosphere communities (e.g., pathogens, mutualists). However, few studies have addressed the role of indirect interactions mediated by plant litter inputs. This is problematic because it has left a major gap in our understanding of PSFs in natural ecosystems, where plant litter is a key component of feedback effects. Here, we propose a new conceptual framework that integrates rhizosphere- and litter-mediated PSF effects. Our framework provides insights into the relative contribution of direct effects mediated by interactions between plants and soil rhizosphere organisms, and indirect effects between plants and decomposer organisms mediated by plant root and shoot litter. We distinguish between three pathways through which senesced root and shoot litter may influence PSFs. Specifically, we examine: (1) physical effects of litter (layer) traits on seed germination, soil structure, and plant growth; (2) chemical effects of litter on concentrations of soil nutrients and secondary metabolites (e.g., allelopathic chemicals); and (3) biotic effects of saprotrophic soil communities that can perform different functional roles in the soil food web, or that may have specialized interactions with litter types, thereby altering soil nutrient cycling. We assess the role of litter in PSF effects via physical, chemical and biotic pathways to address how litter-mediated feedbacks may play out relative to, and in interaction with, feedbacks mediated through the plant rhizosphere. We also present one of the first experimental studies to show the occurrence and species-specificity of litter-mediated feedbacks and we identify critical research gaps. By formally incorporating the plant-litter feedback pathway into PSF experiments, we will further our understanding of PSFs under natural conditions

Exogenous carbon turnover within the soil food web strengthens soil carbon sequestration through microbial necromass accumulation

Exogenous carbon turnover within soil food web is important in determining the trade-offs between soil organic carbon (SOC) storage and carbon emission. However, it remains largely unknown how soil food web influences carbon sequestration through mediating the dual roles of microbes as decomposers and contributors, hindering our ability to develop policies for soil carbon management. Here, we conducted a 13C-labeled straw experiment to demonstrate how soil food web regulated the residing microbes to influence the soil carbon transformation and stabilization process after 11 years of no-tillage. Our work demonstrated that soil fauna, as a “temporary storage container,” indirectly influenced the SOC transformation processes and mediated the SOC sequestration through feeding on soil microbes. Soil biota communities acted as both drivers of and contributors to SOC cycling, with 32.0% of exogenous carbon being stabilizing in the form of microbial necromass as “new” carbon. Additionally, the proportion of mineral-associated organic carbon and particulate organic carbon showed that the “renewal effect” driven by the soil food web promoted the SOC to be more stable. Our study clearly illustrated that soil food web regulated the turnover of exogenous carbon inputs by and mediated soil carbon sequestration through microbial necromass accumulation