Earthworm invasion causes declines across soil fauna size classes and biodiversity facets in northern North American forests

Multiple invasion routes have led to the pervasive introduction of earthworms in North America

Soil-dwelling organisms play a key role in ecosystem functioning and the delivery of ecosystem services. As a consequence, soil taxa such as earthworms are iconic in good land management practices. However, their introduction in places where species did not co-evolve with them can trigger catastrophic changes. This issue has been largely ignored so far in nature management policies because of the positive image of soil taxa and the lack of knowledge of the magnitude of soil fauna introductions outside their native range. Here we address this gap with a large spatio-temporal database of introduced alien earthworms. We show that 70 alien earthworm species have colonized the North American continent. They have larger geographical ranges than native species and novel ecological functions, representing a serious threat to the biodiversity and functioning of native ecosystems. The probably continuous introduction of alien earthworms, from a variety of sources and introduction pathways, into many distant and often empty niches, contrasts with the classical patterns of invasions in most aboveground taxa. This suggests that earthworms, and probably other soil organisms, constitute a major but overlooked pool of invasive species that are not adequately managed by existing control and mitigation strategies.

Different sets of traits determine transition of alien species along the invasion continuum

Invasive alien species are currently considered as one of the dominant drivers of global environmental change. Till now, the majority of studies have focused on single or a few traits of alien species that facilitate their invasion. Also inclusion of all the traits which determine the transition of aliens along the different stages of invasion continuum (casual, naturalised and invasive) has remained largely overlooked. In this study, we collected a comprehensive trait dataset on 144 alien plant species of Kashmir Himalaya - a global biodiversity hotspot region. To test which traits of alien species, individually or in combination along with anthropogenic factors, determine their transition along the invasion continuum, we employed chi-square tests, boosted regression trees and phylogenetic methods. We found the perennial life span, longer residence time, greater number of introduced regions, and better seed dispersal mechanism were critical in determining the transition from casual to naturalised. The herbaceous growth form, therophyte Raunkiaer life-form, annual life span, achene fruit, longer residence time and broader introduced range were the species' traits determining transition from naturalised to invasive. Aliens introduced as ornamentals have more propensity to become naturalised; whereas aliens introduced unintentionally show overrepresentation at the invasive stage. Phylogeny alone showed mixed results indicating both clustering and dispersion; however, in combination with other traits, it plays a significant role in determining the stage of invasion. Overall, our study disentangles the individual and interactive roles of multiple traits that determine the transition of alien species' along the invasion continuum. Further, we foresee the potential applicability of our findings in designing robust invasion risk analysis protocols and stage-specific invasion management strategies in this Himalayan region, with learnings for elsewhere in the world.

Invasive earthworms shift soil microbial community structure in northern North American forest ecosystems

Invasive earthworms colonize ecosystems around the globe. Compared to other species' invasions, earthworm invasions have received little attention. Previous studies indicated their tremendous effects on resident soil biota representing a major part of the terrestrial biodiversity. We investigated effects of earthworm invasion on soil microbial communities in three forests in North America by conducting DNA sequencing of soil bacteria, fungi, and protists in two soil depths. Our study shows that microbial diversity was lower in highly invaded forest areas. While bacterial diversity was strongly affected compared to fungi and protists, fungal community composition and family dominance were strongly affected compared to bacteria and protists. We found most species specialized on invasion in fungi, mainly represented by saprotrophs. Comparably, few protist species, mostly bacterivorous, were specialized on invasion. As one of the first observational studies, we investigated earthworm invasion on three kingdoms showing distinct taxa- and trophic level-specific responses to earthworm invasion.

A Modeling Approach for Assessing Ecological Risks of Neonicotinoid Insecticides from Emission to Nontarget Organisms: A Case Study of Cotton Plant

The use of neonicotinoid insecticides in agriculture has posed threats to ecological systems, and there is a need to assess the ecological risks of neonicotinoids from emission to nontarget organisms. We introduced a modeling approach to assess the ecological risks of neonicotinoids using honeybee and earthworm as model organisms, and the simulation was flexible under different environmental conditions. Using the cotton plant as an example, the simulation results demonstrated that under current recommended application rates, the use of common neonicotinoid insecticides posed no threat to earthworms, with the simulated risk quotients (RQs) much lower than 1. However, the simulation for some neonicotinoid insecticides (e.g., acetamiprid) indicated that using these insecticides on cotton plants could threaten honeybees, with simulated RQs higher than 1. The variability analysis showed that in high-latitude regions, the unacceptable risk to honeybees posed by insecticide application can be further elevated due to cold, wet weather that results in relatively high insecticide levels in pollen and nectar. The model evaluation showed large overlaps of simulated risk intervals between the proposed and existing (BeeREX) models. Because the proposed and existing models have different simulation mechanisms, we recommend that these two models be used together to complement each other in future studies. Environ Toxicol Chem 2023;42:928-938. © 2023 SETAC.

Non-native species change the tune of tundra soils: Novel access to soundscapes of the Arctic earthworm invasion

Over the last decade, an increasing number of studies have used soundscapes to address diverse ecological questions. Sound represents one of the few sources of information capable of providing in situ insights into processes occurring within opaque soil matrices. To date, the use of soundscapes for soil macrofauna monitoring has been experimentally tested only in controlled laboratory environments. Here we assess the validity of laboratory predictions and explore the use of soil soundscape proxies for monitoring soil macrofauna (i.e., earthworm) activities in an outdoor context. In a common garden experiment in northern Sweden, we constructed outdoor mesocosm plots (N = 36) containing two different Arctic vegetation types (meadow and heath) and introduced earthworms to half of these plots. Earthworms substantially altered the ambient soil soundscape under both vegetation types, as measured by both traditional soundscape indices and frequency band power levels, although their acoustic impacts were expressed differently in heath versus meadow soils. While these findings support the as-of-yet untapped promise of using belowground soundscape analyses to monitor soil ecosystem health, direct acoustic emissions from earthworm activities appear to be an unlikely proxy for tracking worm activities at daily timescales. Instead, earthworms indirectly altered the soil soundscape by 're-engineering' the soil matrix: an effect that was dependent on vegetation type. Our findings suggest that long-term (i.e., seasonal) earthworm activities in natural soil settings can likely be monitored indirectly via their impacts on soundscape measures and acoustic indices. Analyzing soil soundscapes may enable larger-scale monitoring of high-latitude soils and is directly applicable to the specific case of earthworm invasions within Arctic soils, which has recently been identified as a potential threat to the resilience of high-latitude ecosystems. Soil soundscapes could also offer a novel means to monitor soils and soil-plant-faunal interactions in situ across diverse pedogenic, agronomic, and ecological systems.

Evaluation of China's forest carbon sink service value

A study on the value accounting of forest carbon sink services can promote the rapid development of the carbon sink market and help better understand the impact of forest carbon sinks on climate change and economic development. However, few studies have evaluated the value of China's current forest carbon sink services. Based on research on carbon peak and carbon neutrality, according to the characteristics of China's forest ecosystems and forest resource inventory data, the stock volume method was used to measure the amount and value of forest carbon sinks in China in 2009-2013 and 2014-2018. The results showed that: (1) the physical amount of forest carbon aggregates in China increased from 2009 to 2013 and from 2014 to 2018. The carbon storage of natural and plantation forests both showed an upward trend. Among them, the growth rate of the carbon storage of plantation forests was higher than that of natural forests. (2) The state, adjoint, and coupling equations of forest carbon sinks were employed to ascertain the best price for China's forest carbon sinks in 2020. The results showed that the price of China's forest carbon sinks was slightly higher than the internationally accepted carbon sink price, reflecting that the changes in the value of China's forest carbon sinks and international carbon sinks were roughly the same. (3) We obtained an appropriate accounting model for China's forest carbon sinks. (4) The value of China's forest carbon sinks increased from 2009 to 2013 and from 2014 to 2018. Although the price of carbon sinks has declined, the overall forest resource stock has increased, especially in plantation forests. The increase in the value of carbon sinks was as high as 24.7%, resulting in an overall increase in the value of forest carbon sinks, which was also in line with the physical amount of forest carbon sinks. The measurement conclusions were consistent. Several key points to note based on these findings are as follows: (1) China's current forest carbon sink transactions are all project-level certified emission reduction transactions, and diversified non-market means should be constructed to comprehensively promote carbon sink transactions. (2) China's current carbon sink transactions are mainly clean development mechanism projects, with few transactions between enterprises, and the carbon trading market situation is not optimistic. (3) The key to effective forest carbon sequestration trading is the accurate accounting of forest carbon storage and carbon sequestration value. Thus, it is of great significance to establish a forest carbon sequestration measurement method that is economical, simple, and accurate. (4) The physical amount and value of carbon sequestration of China's forest resources are rising, and the contribution rate is increasing year by year. However, there is still a gap in per capita forest area and storage compared with those in other countries worldwide. Thus, China must be vigilant in times of peace and further strengthen the protection and construction of forest resources.

Aboveground impacts of a belowground invader: how invasive earthworms alter aboveground arthropod communities in a northern North American forest

Declining arthropod communities have recently gained a lot of attention, with climate and land-use change among the most frequently discussed drivers. Here, we focus on a seemingly underrepresented driver of arthropod community decline: biological invasions. For approximately 12 000 years, earthworms have been absent from wide parts of northern North America, but they have been re-introduced with dramatic consequences. Most studies investigating earthworm-invasion impacts focus on the belowground world, resulting in limited knowledge on aboveground-community changes. We present observational data on earthworm, plant and aboveground arthropod communities in 60 plots, distributed across areas with increasing invasion status (low, medium and high) in a Canadian forest. We analysed how earthworm-invasion status and biomass impact aboveground arthropod community abundance, biomass and species richness, and how earthworm impacts cascade across trophic levels. We sampled approximately 13 000 arthropods, dominated by Hemiptera, Diptera, Araneae, Thysanoptera and Hymenoptera. Total arthropod abundance, biomass and species richness declined significantly from areas of low to those with high invasion status, with reductions of 61, 27 and 18%, respectively. Structural equation models suggest that earthworms directly and indirectly impact arthropods across trophic levels. We show that earthworm invasion can alter aboveground multi-trophic arthropod communities and suggest that belowground invasions might be underappreciated drivers of aboveground arthropod decline.

Contrasting protist communities (Cercozoa: Rhizaria) in pristine and earthworm-invaded North American deciduous forests

Earthworms are considered ecosystem engineers due to their fundamental impact on soil structure, soil processes and on other soil biota. An invasion of non-native earthworm species has altered soils of North America since European settlement, a process currently expanding into still earthworm-free forest ecosystems due to continuous spread and increasing soil temperatures owing to climate change. Although earthworms are known to modify soil microbial diversity and activity, it is as yet unclear how eukaryote consumers in soil microbial food webs will be affected. Here, we investigated how earthworm invasion affects the diversity of Cercozoa, one of the most dominant protist taxa in soils. Although the composition of the native cercozoan community clearly shifted in response to earthworm invasion, the communities of the different forests showed distinct responses. We identified 39 operational taxonomic units (OTUs) exclusively indicating earthworm invasion, hinting at an earthworm-associated community of Cercozoa. In particular, Woronina pythii, a hyper-parasite of plant-parasitic Oomycota in American forests, increased strongly in the presence of invasive earthworms, indicating an influence of invasive earthworms on oomycete communities and potentially on forest health, which requires further research.