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Chesapeake Bay tidal wetlands are experiencing a broad-scale, aggressive invasion by the non-native, clonal grass Phragmites australis. The grass is often managed with herbicides in efforts to restore native plant communities and wildlife habitat. Management efforts, however, can act as a disturbance, resulting in increased light availability, potentially fostering reinvasion from soil seedbanks. If native vegetation establishes quickly from seedbanks, the site should have greater resiliency against invasion, while disturbed sites where native plants do not rapidly establish may be rapidly colonized by australis. We surveyed the soil seedbank of three vegetation cover types in five Chesapeake Bay subestuaries: areas where P. australis had been removed, where P. australis was left intact, and with native, reference vegetation. We determined the total germination, the proportion of the seedbank that was attributable to invasive species, the richness, the functional diversity, and the overall composition of the seedbanks in each of the cover types (i.e., plots). After 2 years of herbicide treatment in the P. australis removal plots, vegetation cover type impacted the total germination or the proportion of invasive species in the seedbank. In contrast, we also found that seedbank functional composition in tidal brackish wetlands was not influenced by vegetation cover type in most cases. Instead, plots within a subestuary had similar seedbank functional composition across the years and were composed of diverse functional groups. Based on these findings, we conclude that plant community recovery following P. australis removal is not seed-limited, and any lack of native vegetation recruitment is likely the result of yet-to-bedetermined abiotic factors. These diverse seedbanks could lead to resilient wetland communities that could resist invasions. However, due to the prevalence of undesirable species in the seedbank, passive revegetation following invasive plant removal may speed up their re-establishment. The need for active revegetation will need to be assessed on a case-bycase basis to ensure restoration goals are achieved.

Aims Plant functional group (PFG) removal experiments are recognized as an effective way to explore the role of plant diversity and species traits in ecosystem functioning. To minimize soil physical disturbance in plant removal experiments, aboveground parts of targeted plant species are usually cut off without removing their roots from the soil. However, the potential effects of their remaining roots (partially as root litter) on soil nematode communities are still unclear. Methods We used a three-year PFG removal experiment in a Qinghai-Tibet alpine meadow and set up root-ingrowth mesh bags for one year where removal target plants’ roots existed only outside the mesh bags. Results We found that nematode communities outside the mesh bags had higher nematode channel ratio and lower channel index values, indicating that the root litter outside the mesh bags increased energy flux to bacterial-feeding nematodes over fungal-feeding nematodes. The relative abundance of plant-feeding nematodes was higher inside than outside the mesh bags, probably because of a higher ratio of living roots inside the mesh bags. Non-metric multidimensional scaling showed that the structure of nematode communities inside and outside of mesh bags was generally differentiated except for the no-removal control treatment. Conclusions We conclude that the remaining roots outside mesh bags could modify the relative abundance ratio of different nematode guilds and soil nematode community structures, suggesting legacy effects of target plants’ roots in PFG removal experiments.

Semi‐arid grasslands on the Mongolian Plateau are expected to experience high inputs of anthropogenic reactive nitrogen in this century. It remains unclear, however, how soil organisms and nutrient cycling are directly affected by N enrichment (i.e., without mediation by plant input to soil) vs. indirectly affected via changes in plant‐related inputs to soils resulting from N enrichment. To test the direct and indirect effects of N enrichment on soil organisms (bacteria, fungi and nematodes) and their associated C and N mineralization, in 2010, we designated two subplots (with plants and without plants) in every plot of a six‐level N‐enrichment experiment established in 1999 in a semi‐arid grassland. In 2014, 4 years after subplots with and without plant were established, N enrichment had substantially altered the soil bacterial, fungal and nematode community structures due to declines in biomass or abundance whether plants had been removed or not. N enrichment also reduced the diversity of these groups (except for fungi) and the soil C mineralization rate and induced a hump‐shaped response of soil N mineralization. As expected, plant removal decreased the biomass or abundance of soil organisms and C and N mineralization rates due to declines in soil substrates or food resources. Analyses of plant‐removal‐induced changes (ratios of without‐ to with‐plant subplots) showed that micro‐organisms and C and N mineralization rates were not enhanced as N enrichment increased but that nematodes were enhanced as N enrichment increased, indicating that the effects of plant removal on soil organisms and mineralization depended on trophic level and nutrient status. Surprisingly, there was no statistical interaction between N enrichment and plant removal for most variables, indicating that plant‐related inputs did not qualitatively change the effects of N enrichment on soil organisms or mineralization. Structural equation modelling confirmed that changes in soil communities and mineralization rates were more affected by the direct effects of N enrichment (via soil acidification and increased N availability) than by plant‐related indirect effects. Our results provide insight into how future changes in N deposition and vegetation may modify below‐ground communities and processes in grassland ecosystems. A plain language summary is available for this article. Plain Language Summary

1. Pollinator conservation is of increasing interest in the light of managed honeybee (Apis mellifera) declines, and declines in some species of wild bees. Much work has gone into understanding the effects of habitat enhancements in agricultural systems on wild bee abundance, richness and pollination services. However, the effects of ecological restoration targeting \"natural\" ecological endpoints (e.g. restoring former agricultural fields to historic vegetation types or improving degraded natural lands) on wild bees have received relatively little attention, despite their potential importance for countering habitat loss. 2. We conducted a meta-analysis to evaluate the effects of ecological restoration on wild bee abundance and richness, focusing on unmanaged bee communities in lands restored and managed to increase habitat availability and quality. Specifically, we assessed bee abundance and/or richness across studies comparing restored vs. unrestored treatments and studies investigating effects of specific habitat restoration techniques, such as burning, grazing, invasive plant removal and seeding. 3. We analysed 28 studies that met our selection criteria: these represented 11 habitat types and 7 restoration techniques. Nearly all restorations associated with these studies were performed without explicit consideration of habitat needs for bees or other pollinators. The majority of restorations targeted plant community goals, which could potentially have ancillary benefits for bees. 4. Restoration had overall positive effects on wild bee abundance and richness across multiple habitat types. Specific restoration actions, tested independently, also tended to have positive effects on wild bee richness and abundance. 5. Synthesis and applications. We found strong evidence that ecological restoration advances wild bee conservation. This is important given that habitat loss is recognized as a leading factor in pollinator decline. Pollinator responses to land management are rarely evaluated in non-agricultural settings and so support for wild bees may be an underappreciated benefit of botanically focused management. Future restoration projects that explicitly consider the needs of wild bees could be more effective at providing nesting, foraging and other habitat resources. We encourage land managers to design and evaluate restoration projects with the habitat needs of wild bee species in mind.

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 CO 2 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 play a significant role in regulating short-term litter decomposition and belowground 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.

1. Human-induced environmental change is occurring globally and alters ecosystem properties both directly, by changing abiotic conditions, and indirectly, by modifying community composition. The effects of changes in plant composition in determining ecosystem properties may be determined by the identity of the plants, their respective biomass in the community and also by the ability of remaining vegetation to compensate for their loss. 2. We used the graminoid removal treatment from a long-term (12 year) removal experiment to examine the role of graminoids in determining ecosystem properties and also the potential for biomass compensation by remaining species in a grassland in northern Canada. We conducted removals in both fertilized and nonfertilized environments to examine context-dependency of graminoid effects. 3. There was full biomass compensation for graminoid removal by the remaining functional groups (i.e., total biomass was equal to no-removal controls) after 5 years, and after 12 years fertilized plots showed overcompensation for removals. 4. After 12 years of graminoid removals, most ecosystem properties were not affected by removals in either fertilization environment. Similarly, there were few effects on microbial biomass or function with plant removal or fertilization treatments. 5. Comparison to earlier published responses in this experiment shows a strengthening of the responses of the plant community to graminoid removals over time while effects on ecosystem properties diminished. Full biomass compensation for removal of graminoids occurred after 5 years, and after 12 years of removals, fertilized plots had overcompensated for the loss of graminoids. In contrast, the shorter term (4 years) responses of soil available nutrients and soil moisture to removals have mainly disappeared after eight further years, likely because of the biomass compensation by the plant community. 6. Synthesis. Comparing the effects of graminoid removals on ecosystem structure and function after 4, 7, and now 10 and 12 years of removals, we now argue that, after over a decade of graminoid removal, recovery of plant biomass is required for the maintenance of most ecosystem properties and not functional group identity, as we concluded earlier. This highlights the importance of maintaining field experiments in the long term, particularly in northern ecosystems.

Woody plants (shrubs and trees) are encroaching across the globe, affecting livestock production and terrestrial ecosystem functioning. Despite the widespread practice, there has been no quantitative global assessment of whether removal of encroaching woody plants will re-instate productive grasslands and open savanna. Here we compiled a global database of 12,198 records from 524 studies on the ecosystem responses of both the encroachment and removal of woody plants, and show that removal fails to reverse encroachment impacts. Removing woody plants only reversed less than half of the reductions in herbaceous structure induced by encroachment, and woody expansion actually enhanced ecosystem functions (+8%). The effectiveness of removal varied with encroachment stage (that is, time since treatment) and the functional traits (for example, deciduousness and resprouting) of the focal woody species, and waned in drier regions. Our results suggest that assessment of woody plant communities before removal is critical to assess the likelihood of successful ecosystem recovery.A global synthesis reveals that removing woody plants cannot compensate for losses caused by their expansion. The effectiveness of removing woody plants depends on their identity and how long a site has been encroached.

1. Invasive species spread on natural ecosystems is one of the most important causes of biodiversity loss. To disentangle the invasive plant impact on communities it is essential to combine experimental and observation approaches, which enable the correct interpretations of results and lead to the right decisions for management. 2. We examined the invasion of southern Brazil's grasslands by Eragrostis plana, which is currently the most problematic invasive species in the region. By means of an experiment on invaded communities complemented by observation of non-invaded communities, we assessed E. plana impact on vegetation, evaluated community response to its removal and discussed the effectiveness of removal methods. Fifty permanent 1 × 1 m plots were located on natural grassland that was partially invaded by E. plana. Removal was done annually from 2012 to 2015 and consisted of five treatments (n = 10): (i) clipping above-ground biomass on one occasion; (ii) clipping above-ground biomass periodically; (iii) herbicide and (iv) hand-pulling, plus (v) control treatment with no-removal. In addition, 10 plots located in an adjacent noninvaded area were monitored. 3. All removal treatments reduced E. plana cover across years, but were not enough to eradicate it. Our results revealed not only differences between invaded and non-invaded communities, but also an effect of E. plana removal on resident species richness and total cover. 4. At the local scale, we demonstrated the impact of E. plana invasion on grassland vegetation, suggesting a reduction in resident species richness and total cover. Invasive species removal changed communities differently from invaded ones, but not resembling non-invaded references, suggesting that community recovery may need more time for reestablishment or that some restoration strategies are required. 5. Synthesis and applications. This study demonstrated the impact on vegetation of the most important invasive species in southern Brazil's natural grasslands. We highlighted the advantages of combining observations of non-invaded communities and experimental studies on invaded communities, with and without invasive removal, to help infer causal relationships in ecological invasion research.

The loss of aboveground plant diversity alters belowground ecosystem function; yet, the mechanisms underpinning this relationship and the degree to which plant community structure and climate mediate the effects of plant species loss remain unclear. Here, we explored how plant species loss through experimental removal shaped belowground function in ecosystems characterized by different climatic regimes and edaphic properties. We measured plant community composition as well as potential carbon (C) and nitrogen (N) mineralization and microbial extracellular enzyme activity in soils collected from four unique plant removal experiments located along an elevational gradient in Colorado, USA. We found that, regardless of the identity of the removed species or the climate at each site, plant removal decreased the absolute variation in potential N mineralization rates and marginally reduced the magnitude of N mineralization rates. While plant species removal also marginally reduced C mineralization rates, C mineralization, unlike N mineralization, displayed sensitivity to the climatic and edaphic differences among sites, where C mineralization was greatest at the high elevation site that receives the most precipitation annually and contains the largest soil total C pool. Plant removal had little impact on soil enzyme activity. Removal effects were not contingent on the amount of biomass removed annually, and shifts in mineralization rates occurred despite only marginal shifts in plant community structure following plant species removal. Our results present a surprisingly simple and consistent pattern of belowground response to the loss of dominant plant species across an elevational gradient with different climatic and edaphic properties, suggesting a common response of belowground ecosystem function to plant species loss regardless of which plant species are lost or the broader climatic context.

Mycorrhizal fungi enhance plant access to nitrogen (N) in nutrient-poor environments like the Arctic tundra by depolymerizing N-rich organic compounds into forms available to plants and microbes. As climate change reshapes plant communities and mycorrhizal associations, shifting dominance from herbaceous species to shrubs, changes in mycorrhizal type and plant species dominance may differentially stimulate N cycling. Both dominant and rare species, along with mycorrhizal associations, contribute to ecosystem processes and stability, though the specific roles of these components in N cycling and overall ecosystem functioning remain uncertain. We investigated how mycorrhizal associations and plant diversity affect gross N mineralization and nitrification rates in an Oroarctic ecosystem. Four years after a plant removal treatment, we measured these rates using in situ 15N labelling and quantified a selection of nitrification genes. Treatment plots included (1) unmanipulated (Control); or the removal of: (2) ectomycorrhizal (EcM) and ericoid mycorrhizal (ErM) plants, letting arbuscular mycorrhizal (AM) and non-mycorrhizal (NM) plants dominate (AM/NM); (3) AM and NM plants, letting EcM and ErM plants dominate (EcM/ErM); (4) low-abundance species, leaving the most abundant species (Dominant); and (5) high-abundance species, leaving only the low-abundance species (Rare). Gross N mineralization rates were 73 % and 78 % higher in EcM/ErM and Dominant, respectively, compared to Control, while AM/NM and Rare showed more moderate increases of 30 % and 46 %. Gross nitrification was also highest in EcM/ErM, with a 26 % increase over Control. Gene abundances did not mirror nitrification patterns. Archaeal ammonia oxidizers (AOA), Nitrospira-type nitrite oxidizers (NIS), and comammox clade A (ComaA) were consistently more abundant than bacterial ammonia oxidizers (AOB), Nitrobacter-type nitrite oxidizers (NIB), and comammox clade B (ComaB), suggesting a stable site-level nitrifier community. Dominant had the lowest gene copy numbers overall, except for AOB, which was highest. In addition, AOA gene abundance was significantly lower in Dominant compared to Control, with a marginal reduction observed for NIS. Our findings highlight the key role of EcM/ErM fungi in accelerating N cycling in Oroarctic soils, challenging traditional assumptions that N transformation rates are slow in EcM/ErM dominated ecosystems. These insights underscore the need to consider mycorrhizal associations and plant community composition when predicting tundra ecosystem responses to environmental change.