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

Greenhouse gas (CO2, CH4, and N2O) emissions after abandonment of agriculture

The GHG (CO2, CH4, N2O) emission potential along a chronosequence of former agricultural soils abandoned for 9 to 32 years were compared to an actively managed (on-going) agricultural soil (reference). The soils were incubated in mesocosms with and without manure amendment, and microbial functional groups involved in nitrous oxide emission were quantitatively assessed. Carbon dioxide emission significantly increased after agriculture abandonment (< 24 years) consistent with higher decomposition rate, but total emission decreased in the long term (> 29 years). With the cessation of agriculture, the abandoned sites generally became a net methane sink. Notably, total nitrous oxide emission showed a significant monotonic decrease over years of abandonment in response to manure amendment, possibly reflecting an altered capacity for (de)nitrification as indicated in the response of the (de)nitrifier abundance. Overall, our findings suggest that the GHG legacy of agriculture diminishes over time (> 29 years), with lowered GHG emissions and global warming potential (GWP) after abandonment of agriculture. © 2022, The Author(s)

Soil networks become more connected and take up more carbon as nature restoration progresses

Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered

Will fungi solve the carbon dilemma?

Soils are hotspots of diversity and sustain many globally important functions. Here we focus on the most burning issue: how to keep soils as carbon sinks while maintaining their productivity. Evidence shows that life in soils plays a crucial role in improving soil health yet soil ecological processes are often ignored in soil sciences. In this review, we highlight the potential of fungi to increase soil carbon sequestration while maintaining crop yield, functions needed to sustain human population on Earth and at same time keep the Earth livable. We propose management strategies that steer towards more fungal activity but also high functional diversity of fungi which will lead to more stable carbon sources in soil but also affects the structure of the soil food web up to ecosystem level. We list knowledge gaps that limit our ability to steer soil fungal communities such that stabilising carbon in top soils becomes more effective. Using the natural capacity of a biodiverse soil community to sequester carbon delivers double benefit: reduction of atmospheric carbon dioxide by storing photosynthesized carbon in soil and increasing agricultural yields by restoring organic matter content of degraded soils

Global soil map pinpoints key sites for conservation

A map of Earth reveals hotspots of soil biodiversity and regions to target for conservation. Many of these areas are currently unprotected, which suggests that it is time to rethink our soil management and conservation priorities

Network Analyses Can Advance Above-Belowground Ecology

An understanding of above-belowground (AG-BG) ecology is important for evaluating how plant interactions with enemies, symbionts, and decomposers affect species diversity and will respond to global changes. However, research questions and experiments often focus on only a limited number of interactions, creating an incomplete picture of how entire communities may be involved in AG-BG community ecology. Therefore, a pressing challenge is to formulate hypotheses of AG-BG interactions when considering communities in their full complexity. Here we discuss how network analyses can be a powerful tool to progress AG-BG research, link across scales from individual to community and ecosystem, visualize community interactions between the two (AG and BG) subsystems, and develop testable hypotheses

Appendix A. Individual plant shoot and root biomass responses to soil feedback and herbivory.

Individual plant shoot and root biomass responses to soil feedback and herbivory