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Abstract Nitrogen (N) availability is a well‐known driver of ecosystem structure and function, but as air quality regulations continue to reduce atmospheric N deposition, there is a need to understand how managed and unmanaged ecosystems respond to widespread decreases in terrestrial N availability. Historical N eutrophication, from pollution or fertilisation, may continue to constrain contemporary responses to decreases in available N because of altered plant and microbial feedbacks. Thus, while certain management practices like prescribed fire remove N from grassland ecosystems, the role of fire supporting ecosystems recovering from chronic N input is unknown.To address this knowledge gap, we ceased a 30‐year N‐fertilisation treatment at a field experiment in a tallgrass prairie ecosystem crossed with burned and fire‐suppressed (unburned) treatments. We established subplots within each previously fertilised, recovering plot, fertilised at the same historical rate (10 g N m⁻² year⁻¹as NH₄NO₃), to compare plant and soil properties in recovering plots with control (never‐fertilised) and still‐fertilised treatments within different fire regimes.We document different N‐fertilisation legacies among ecosystem properties in burned and unburned prairies recovering from N‐fertilisation. Soil N availability, nitrification and denitrification potentials in recovering plots remained higher than controls for 3–5 years—indicative of positive legacies—in both burned and unburned prairies, but burning did not reduce this legacy. In burned prairies, however, a positive legacy in above‐ground plant production persisted because a more productive grass species (switchgrass) replaced the previously dominant species (big bluestem) even though root C:N, but not soil C:N, increased to return back to control levels. Consequently, the main N loss pathways in burned and unburned prairies (pyrovolatilisation and microbially mediated processes, respectively) led to similar losses of soil total N (20–28 g N m⁻²) over 5 years.Synthesis: Our results indicate that N eutrophication induces positive legacies of ecosystem functions that can persist for at least half a decade. N‐induced legacies arise because of shifts in soil microbial N‐cycling and plant functional traits. As a result, different management practices may elicit similar trajectories of ecosystem recovery in terms of total and available soil N because of different plant and microbial feedbacks. 

Abstract Nitrogen (N) is a necessary element of soil fertility and a limiting nutrient in tallgrass prairie but grazers like bison and cattle can also recycle N. Bison and cattle impact the nitrogen (N) cycle by digesting forage that is consumed, and recycled back to the soil in a more available forms stimulating soil microbial N cycling activities. Yet we do not know how both grazers comparatively affect N cycling in tallgrass prairie. Thus, we investigated if bison and cattle had similar impacts on N cycling in annually burned tallgrass prairie relative to ungrazed conditions over a 3-year period (2020–2022) at the Konza Prairie Biological Station. We examined: soil pH, soil water content, mineralized N, nitrification potential, denitrification potential and extracellular enzyme assays. Interannual variability in precipitation controlled soil water and N cycling microbial activities but grazing effects had a stronger influence on N cycling. We found significant differences and increased soil pH, nitrification and denitrification potential and less N limitation in bison vs cattle grazed soils where bison grazed soils exhibited faster N cycling. Differences between the grazers may be attributed to the different management of bison and cattle as both can impact N cycling. Overall, these data provide some evidence that bison and cattle affect N cycling differently at this study site, and improve the ecological understanding of grazer impacts on N cycling dynamics within the tallgrass prairie ecosystem. 

Microbial communities display biogeographical patterns that are driven by local environmental conditions and dispersal limitation, but the relative importance of underlying dispersal mechanisms and their consequences on community structure are not well described. High dispersal rates can cause soil microbial communities to become more homogenous across space and therefore it is important to identify factors that promote dispersal. This study experimentally manipulated microbial dispersal within different land management treatments at a native tallgrass prairie site, by changing the relative openness of soil to dispersal and by simulating vector dispersal via bison dung addition. We deployed experimental soil bags with mesh open or closed to dispersal, and placed bison dung over a subset of these bags, to areas with three different land managements: active bison grazing and annual fire, annual fire but no bison grazing, and no bison grazing with infrequent fire. We expected microbial dispersal to be highest in grazed and burned environments, and that the addition of dung would consistently increase overall microbial richness and lead to homogenization of communities over time. Results show that dispersal rates, as the accumulation of taxa over the course of the 3-month experiment, increase taxonomic richness similarly in all land management treatments. Additionally, bison dung seems to be serving as a dispersal and homogenization vector, based on the consistently higher taxon richness and increased community similarity across contrasting grazing and fire treatments when dung is added. This finding also points to microbial dispersal as an important function that herbivores perform in grassland ecosystems, and in turn, as a function that was lost at a continental scale following bison extermination across the Great Plains of North America in the nineteenth century. This study is the first to detect that dispersal and vector dispersal by grazing mammals promote grassland soil microbial diversity and affect microbial community composition. 

The intensification of drought throughout the U.S. Great Plains has the potential to have large impacts on grassland functioning, as has been shown with dramatic losses of plant productivity annually. Yet, we have a poor understanding of how grassland functioning responds after drought ends. This study examined how belowground nutrient cycling responds after drought and whether legacy effects persist postdrought. We assessed the 2-year recovery of nutrient cycling processes following a 4-year experimental drought in a mesic grassland by comparing two different growing season drought treatments—chronic (each rainfall event reduced by 66%) and intense (all rain eliminated until 45% of annual rainfall was achieved)—to the control (ambient precipitation) treatment. At the beginning of the first growing season postdrought, we found that in situ soil CO2 efflux and laboratory-based soil microbial respiration were reduced by 42% and 22%, respectively, in the intense drought treatment compared to the control, but both measures had recovered by midseason (July) and remained similar to the control treatment in the second postdrought year. We also found that extractable soil ammonium and total inorganic N were elevated throughout the growing season in the first year after drought in the intense treatment. However, these differences in inorganic N pools did not persist during the growing season of the second year postdrought. The remaining measures of C and N cycling in both drought treatments showed no postdrought treatment effects. Thus, although we observed short-term legacy effects following the intense drought, C and N cycling returned to levels comparable to nondroughted grassland within a single growing season regardless of whether the drought was intense or chronic in nature. Overall, these results suggest that the key aspects of C and N cycling in mesic tallgrass prairie do not exhibit persistent legacies from 4 years of experimentally induced drought. 

ABSTRACT Fire can impact terrestrial ecosystems by changing abiotic and biotic conditions. Short fire intervals maintain grasslands and communities adapted to frequent, low-severity fires. Shrub encroachment that follows longer fire intervals accumulates fuel and can increase fire severity. This patchily distributed biomass creates mosaics of burn severities in the landscape—pyrodiversity. Afforded by a scheduled burn of a watershed protected from fires for 27 years, we investigated effects of woody encroachment and burn severity on soil chemistry and soil-inhabiting bacteria and fungi. We compared soils before and after fire within the fire-protected, shrub-encroached watershed and soils in an adjacent, annually burned and non-encroached watershed. Organic matter and nutrients accumulated in the fire-protected watershed but responded less to woody encroachment within the encroached watershed. Bioavailable nitrogen and phosphorus and fungal and bacterial communities responded to high-severity burn regardless of encroachment. Low-severity fire effects on soil nutrients differed, increased bacterial but decreased fungal diversity and effects of woody encroachment within the encroached watershed were minimal. High-severity burns in the fire-protected watershed led to a novel soil system state distinct from non-encroached and encroached soil systems. We conclude that severe fires may open grassland restoration opportunities to manipulate soil chemistry and microbial communities in shrub-encroached habitats.