Complementarity of dung beetle species with different functional behaviours influence dung–soil carbon cycling

Decomposition of large ungulate herbivore dung and its subsequent incorporation into the soil play key roles in carbon and nutrient cycling and are important for grassland productivity. Dung beetles contribute to the initial breakdown and transport of organic matter from the dung into the soil but how they interact with the microbial community to modify decomposition processes remains poorly understood. Using a mesocosm experiment, we investigated the individual and interactive effect of two dung beetle species with contrasting functional behaviour (dweller species: Agrilinus ater (De Geer 1774) vs. tunneler species: Typhaeus typhoeus (Linneaus 1758)) on dung C cycling (CO2 fluxes and C transfer through the soil profile) and resultant effects on microbial activity and biomass in the soil. Both dung beetle species contributed significantly to dung removal, reducing the C lost through microbial respiration from the whole mesocosm. However, C concentrations measured in leachates from the mesocosm were only significantly higher in the presence of the tunneler species, indicating that tunnelling activity was required to increase C transfer down the soil profile. The combined effect of the two dung beetle species resulted in the highest soil microbial respiration from the soil and in particular in the 2–10 cm depth increment, suggesting positive complementarity effects between species with different functional behaviour. We conclude that the return of C in the form of dung in grasslands, coupled with the activity of a functionally diverse dung beetle assemblage, could result in short term fluctuations in soil microbial activity with important consequences for soil C cycling

Biogeographic differences in soil biota promote invasive grass response to nutrient addition relative to co-occurring species despite lack of belowground enemy release

Multiple plant species invasions and increases in nutrient availability are pervasive drivers of global environmental change that often co-occur. Many plant invasion studies, however, focus on single-species or single-mechanism invasions, risking an oversimplifcation of a multifaceted process. Here, we test how biogeographic diferences in soil biota, such as belowground enemy release, interact with increases in nutrient availability to infuence invasive plant growth. We conducted a greenhouse experiment using three co-occurring invasive grasses and one native grass. We grew species in live and sterilized soil from the invader’s native (United Kingdom) and introduced (New Zealand) ranges with a nutrient addition treatment. We found no evidence for belowground enemy release. However, species’ responses to nutrients varied, and this depended on soil origin and sterilization. In live soil from the introduced range, the invasive species Lolium perenne L. responded more positively to nutrient addition than co-occurring invasive and native species. In contrast, in live soil from the native range and in sterilized soils, there were no diferences in species’ responses to nutrients. This suggests that the presence of soil biota from the introduced range allowed L. perenne to capture additional nutrients better than co-occurring species. Considering the globally widespread nature of anthropogenic nutrient additions to ecosystems, this efect could be contributing to a global homogenization of fora and the associated losses in native species diversity

Belowground competition drives invasive plant impact on native species regardless of nitrogen availability

Plant invasions and eutrophication are pervasive drivers of global change that cause biodiversity loss. Yet, how invasive plant impacts on native species, and the mechanisms underpinning these impacts, vary in relation to increasing nitrogen (N) availability remains unclear. Competition is often invoked as a likely mechanism, but the relative importance of the above and belowground components of this is poorly understood, particularly under differing levels of N availability. To help resolve these issues, we quantified the impact of a globally invasive grass species, Agrostis capillaris, on two co-occurring native New Zealand grasses, and vice versa. We explicitly separated above- and belowground interactions amongst these species experimentally and incorporated an N addition treatment. We found that competition with the invader had large negative impacts on native species growth (biomass decreased by half), resource capture (total N content decreased by up to 75%) and even nutrient stoichiometry (native species tissue C:N ratios increased). Surprisingly, these impacts were driven directly and indirectly by belowground competition, regardless of N availability. Higher root biomass likely enhanced the invasive grass’s competitive superiority belowground, indicating that root traits may be useful tools for understanding invasive plant impacts. Our study shows that belowground competition can be more important in driving invasive plant impacts than aboveground competition in both low and high fertility ecosystems, including those experiencing N enrichment due to global change. This can help to improve predictions of how two key drivers of global change, plant species invasions and eutrophication, impact native species diversity

Appendix A. Effects of warming and plant functional groups on litter mass loss.

Effects of warming and plant functional groups on litter mass loss

Appendix B. Effects of vegetation diversity (number of plant functional groups).

Effects of vegetation diversity (number of plant functional groups)

Appendix C. Effects of warming and plant functional groups on soil fauna and microbes.

Effects of warming and plant functional groups on soil fauna and microbes

Vegetation exerts a greater control on litter decomposition than climate warming in peatlands

Historically, slow decomposition rates have resulted in the accumulation of large amounts of carbon in northern peatlands. Both climate warming and vegetation change can alter rates of decomposition, and hence affect rates of atmospheric CO2 exchange, with consequences for climate change feedbacks. Although warming and vegetation change are happening concurrently, little is known about their relative and interactive effects on decomposition processes. To test the effects of warming and vegetation change on decomposition rates, we placed litter of three dominant species (Calluna vulgaris, Eriophorum vaginatum, Hypnum jutlandicum) into a peatland field experiment that combined warming with plant functional group removals, and measured mass loss over two years. To identify potential mechanisms behind effects, we also measured nutrient cycling and soil biota. We found that plant functional group removals exerted a stronger control over short-term litter decomposition than did ~1°C warming, and that the plant removal effect depended on litter species identity. Specifically, rates of litter decomposition were faster when shrubs were removed from the plant community, and these effects were strongest for graminoid and bryophyte litter. Plant functional group removals also had strong effects on soil biota and nutrient cycling associated with decomposition, whereby shrub removal had cascading effects on soil fungal community composition, increased enchytraeid abundance and increased rates of N mineralization. Our findings demonstrate that, in addition to litter quality, changes in vegetation composition plays a significant role in regulating short-term litter decomposition and below-ground communities in peatland, and that these impacts can be greater than moderate warming effects. Our findings, albeit from a relatively short-term study, highlight the need to consider both vegetation change, and its impacts below-ground, alongside climatic effects when predicting future decomposition rates and carbon storage in peatlands