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Forests have a substantial potential to contribute to climate change mitigation, depending on how they are managed. Forest fertilization with nitrogen is used to increase tree productivity in Fennoscandian forests, but it can also increase soil carbon stocks. However, such forests are often harvested through clearcutting, a practice known to impact soil carbon stocks, nitrogen mineralization and biodiversity. To test whether fertilizer-induced soil carbon stocks are persistent, we studied post-clearcut soil carbon and nitrogen stocks, soil respiration, tree growth, ground vegetation and soil fungal communities in 48 previously fertilized and unfertilized production forests in central Sweden. In the first year after clearcutting, clearcuts of previously fertilized forests stored 7 t (+30%) more carbon and 210 kg (+32%) more nitrogen per hectare in the soil organic layer than clearcuts of unfertilized forests. Four to 13 years after clearcutting, there was no significant difference in carbon and nitrogen stocks of the organic layer, or in soil CO2 efflux, between clearcuts of previously fertilized and unfertilized forests. Saprotrophic ascomycetes were more abundant in clearcuts of previously fertilized forests, independent of time since clearcutting. Previous fertilization did neither result in increased growth of regenerating trees nor alter understory vegetation. Synthesis and applications. Overall, the carry-over effects on biodiversity from forest fertilization into stands regenerating after clearcutting were limited. We conclude that soil organic carbon stores induced by fertilization are short-lived and do not persist after clearcutting. Consequently, the potential of forest fertilization to mitigate climate change is likely limited to increases in aboveground biomass and the products that can be produced with the harvested biomass. Our study raises questions about where the added nitrogen and the fertilizer-induced increase in soil carbon have ended up-knowledge that is essential for making well-informed decisions about future fertilization strategies. & Ouml;kad kolinlagring i skog har potential att bidra till att begr & auml;nsa klimatf & ouml;r & auml;ndringar, men omfattningen beror p & aring; hur skogen brukas. I Fennoskandien anv & auml;nds kv & auml;veg & ouml;dsling som en metod f & ouml;r att & ouml;ka skogsproduktionen. F & ouml;rutom att fr & auml;mja tr & auml;dens tillv & auml;xt kan g & ouml;dsling & auml;ven bidra till att & ouml;ka markens kollager. Den vanligaste avverkningsmetoden i Fennoskandien & auml;r kalavverkning, vilket p & aring;verkar markens kollager, kv & auml;vemineralisering och biologisk m & aring;ngfald. F & ouml;r att unders & ouml;ka de l & aring;ngsiktiga effekterna av g & ouml;dsling p & aring; kollagring studerade vi hur markens kol- och kv & auml;velager, markrespiration, tr & auml;dtillv & auml;xt samt sammans & auml;ttningen av markvegetation och svampsamh & auml;llen skilde sig efter kalavverkning mellan 24 tidigare g & ouml;dslade och 24 og & ouml;dslade produktionsskogar i centrala Sverige. Under det f & ouml;rsta & aring;ret efter avverkning inneh & ouml;ll det organiska markskiktet p & aring; hyggen fr & aring;n tidigare g & ouml;dslade skogar i genomsnitt 7 ton mer kol (+30 %) och 210 kg mer kv & auml;ve (+32 %) per hektar j & auml;mf & ouml;rt med hyggen fr & aring;n og & ouml;dslade skogar. Fyra till tretton & aring;r efter avverkning fanns det inga signifikanta skillnader i kol- och kv & auml;velager i det organiska markskiktet eller i markens CO2-avg & aring;ng mellan hyggen fr & aring;n tidigare g & ouml;dslade och og & ouml;dslade skogar. Oberoende av tid sedan avverkning var Saprotrofa spors & auml;ckssvampar mer vanligt f & ouml;rekommande p & aring; hyggen fr & aring;n tidigare g & ouml;dslade skogar. Tidigare g & ouml;dsling gav inte upphov till & ouml;kad tr & auml;dtillv & auml;xt eller f & ouml;r & auml;ndrad markvegetation i n & auml;stkommande skogsgeneration. Syntes och till & auml;mpningar. De l & aring;ngsiktiga effekterna av skogsg & ouml;dsling p & aring; biologisk m & aring;ngfald in i n & auml;sta skogsgeneration & auml;r begr & auml;nsade. P & aring; samma s & auml;tt leder g & ouml;dsling inte till en varaktig & ouml;kning av kolf & ouml;rr & aring;det i det organiska markskiktet. Vi drar d & auml;rf & ouml;r slutsatsen att potentialen f & ouml;r att l & aring;ngsiktigt & ouml;ka skogens kolf & ouml;rr & aring;d-och d & auml;rmed motverka klimatf & ouml;r & auml;ndringar-genom konventionell skogsg & ouml;dsling sannolikt & auml;r begr & auml;nsad till en & ouml;kning av kolf & ouml;rr & aring;det i ovanjordisk biomassa fram till avverkning samt i de produkter som framst & auml;lls fr & aring;n den avverkade biomassan. V & aring;r studie v & auml;cker fr & aring;gor om vart det tillsatta kv & auml;vet och den g & ouml;dselinducerade & ouml;kningen av markkolet tagit v & auml;gen - kunskap som beh & ouml;vs f & ouml;r att fatta v & auml;lgrundade beslut om framtida g & ouml;dslingsstrategier.

Sphagnum moss is the dominant plant genus in northern peatlands responsible for long-term carbon accumulation. Sphagnum hosts diverse microbial communities (microbiomes), and its phytobiome (plant host + constituent microbiome + environment) plays a key role in nutrient acquisition along with carbon cycling. Climate change can modify the Sphagnum-associated microbiome, resulting in enhanced host growth and thermal acclimation as previously shown in warming experiments. However, the extent of microbiome benefits to the host and the influence of host-microbe specificity on Sphagnum thermal acclimation remain unclear. Here, we extracted Sphagnum microbiomes from five donor species of four peatland warming experiments across a latitudinal gradient and applied those microbiomes to three germ-free Sphagnum species grown across a range of temperatures in the laboratory. Using this experimental system, we test if Sphagnum's growth response to warming depends on the donor and/or recipient host species, and we determine how the microbiome's growth conditions in the field affect Sphagnum host growth across a range of temperatures in the laboratory. After 4 weeks, we found that the highest growth rate of recipient Sphagnum was observed in treatments of matched host-microbiome pairs, with rates approximately 50% and 250% higher in comparison to maximum growth rates of non-matched host-microbiome pairs and germ-free Sphagnum, respectively. We also found that the maximum growth rate of host-microbiome pairs was reached when treatment temperatures were close to the microbiome's native temperatures. Our study shows that Sphagnum's growth acclimation to temperature is partially controlled by its constituent microbiome. Strong Sphagnum host-microbiome species specificity indicates the existence of underlying, unknown physiological mechanisms that may drive Sphagnum's ability to acclimatize to elevated temperatures. Together with rapid acclimation of the microbiome to warming, these specific microbiome-plant associations have the potential to enhance peatland resilience in the face of climate change.

Forest fertilization is a forest management practice that is often claimed to increase productivity in boreal forests. Although regarded as an efficient way to increase profitability, it is also costly, and associated with risks such as biodiversity loss and nitrogen leaching from the soil. To be both cost-efficient and sustainable, potential enhanced productivity due to fertilization should be balanced against the adverse environmental impact. One effective strategy is to limit fertilization to sites where it can most significantly increase tree productivity, while avoiding application in less suitable areas. However, the current understanding of the specific conditions under which forest fertilization optimally stimulates tree growth is limited. To clarify this, we analysed standing tree volume from 32,498 recently harvested fertilized and unfertilized stands from Sweden's largest forest owner. We applied generalized additive models to quantify the effect of fertilization on standing tree volume at harvest and how the fertilization effect depended on dominant tree species, stand characteristics (site index, stem density), climatic conditions (temperature sum), and management (thinning, stand age at harvest). We found that the effect of operational fertilization was highly context-dependent. In pine-dominated stands, fertilization failed to increase tree volumes in cold climates and low-productive stands. In spruce-dominated stands, fertilization did not result in increased tree volumes in low-productive and high-productive stands. For a more sustainable and cost-efficient application of this practice we suggest that the context dependency of the efficiency of fertilization is given more attention. Hence, we recommend to refrain from fertilizing pine-dominated stands situated on lowproductive land or in regions with cold climates, such as those found in northern Sweden.

Wildfire is the dominant disturbance in northern peatlands and can release large quantities of carbon to the atmosphere through combustion. Post-fire peat hydrophobicity can inhibit moss regeneration, thereby decreasing the potential for post-fire carbon sequestration. To investigate how to enhance post-fire recovery we assessed two moss restoration methods (plugs and fragments) in an Alberta poor fen two and three years following wildfire. We first characterized post-fire peat hydrophobicity and moss regeneration in four surface cover types: Severely Burned Feather moss hollows (SB-F), Severely Burned Sphagnum fuscum hummocks (SB-S), Lightly Burned S. fuscum hummocks (LB-S), and Lightly Burned Feather moss lawns (LB-F). Across burn severities, hydrophobicity was high in feather moss and relatively low in Sphagnum moss. Similarly, hydrophobicity increased with depth over the top several centimeters in feather moss, but not in Sphagnum moss surface cover. Peat hydrophobicity appears to limit post-fire regeneration. LB-S was the least hydrophobic of the four treatments and was the only cover type in which Sphagnum moss recovered to >10% surface area, though SB-F had marginal recovery of pioneer moss species. Consequently, we conducted experiments testing the success of moss plugs and fragments of varying moss species at LB-F and SB-F surface covers, which had high hydrophobicity and low post-fire moss recovery. Experimental results indicate that the species type used in transplants is less critical in their survival than the microenvironment into which they are transplanted (i.e., burn severity). Transplant success was slightly higher in plugs than fragments, and larger plug sizes (10–15 cm) were more successful than small plugs (<10 cm). Growth was greater in SB-F than LB-F surface cover, owing to differences in post-fire hydrophobicity, and thus moisture availability. We conclude that in appropriate areas post-fire, peatland management efforts could employ large mixed-moss or Sphagnum moss transplant units while accounting for pre-fire vegetation composition and burn severity to fast-track post-fire moss and ecosystem recovery.

Ponds are key elements for ecosystem functions in urban areas. However, little is known about pond biodiversity changes over time and the drivers underlying such changes. Here, we tested whether past species assemblages, land cover and pond environmental change influence pond macroinvertebrate species richness and temporal beta diversity. We also compared spatial and temporal beta diversity, and investigated species-specific colonization and extinction rates over time. We sampled for presence of Odonata and Trichoptera (larvae), and Coleoptera and Hemiptera (larvae and adults) species in 30 ponds in Stockholm, Sweden, in 2014 and 2019. Past species richness was the best predictor of current species richness, whereas temporal changes in land cover and pond environment were not significantly related to current species richness. No correlations between temporal beta diversity and land cover or pond environmental changes were detected. However, ponds showed large changes in their temporal beta diversity, with equal contributions from species gains and losses. The probability of species colonizing and going extinct from ponds revealed that more common species were more likely to colonize a pond, while uncommon species were more likely to go extinct in a pond. Within our 5-year study, we found (i) highly similar spatial and temporal beta diversity, (ii) that past species richness is a good predictor of current species richness; however, the same does not hold true for species composition. The high dynamics of urban pond communities suggest that a large number of ponds are required to maintain high species richness at a landscape level.

Premise: We assessed changes in traits associated with water economy across climatic gradients in the ecologically similar peat mosses Sphagnum cuspidatum and Sphagnum lindbergii. These species have parapatric distributions in Europe and have similar niches in bogs. Sphagnum species of bogs are closely related, with a large degree of microhabitat niche overlap between many species that can be functionally very similar. Despite this, ecologically similar species do have different distributional ranges along climatic gradients that partly overlap. These gradients may favor particular Sphagnum traits, especially in relation to water economy, which can be hypothesized to drive species divergence by character displacement.

Methods: We investigated traits relevant for water economy of two parapatric bryophytes (Sphagnum cuspidatum and S. lindbergii) across the border of their distributional limits. We included both shoot traits and canopy traits, i.e., collective traits of the moss surface, quantified by photogrammetry.

Results: The two species are ecologically similar and occur at similar positions along the hydrological gradient in bogs. The biggest differences between the species were expressed in the variations of their canopy surfaces, particularly surface roughness and in the responses of important traits such as capitulum mass to climate. We did not find support for character displacement, because traits were not more dissimilar in sympatric than in allopatric populations.

Conclusions: Our results suggest that parapatry within Sphagnum can be understood from just a few climatic variables and that climatic factors are stronger drivers than competition behind trait variation within these species of Sphagnum.

Changes in fire regime of boreal forests in response to climate warming are expected to impact postfire recovery. However, quantitative data on how managed forests sustain and recover from recent fire disturbance are limited.Two years after a large wildfire in managed even-aged boreal forests in Sweden, we investigated how recovery of aboveground and belowground communities, that is, understory vegetation and soil microbial and faunal communities, responded to variation in the severity of soil (i.e., consumption of soil organic matter) and canopy fires (i.e., tree mortality).While fire overall enhanced diversity of understory vegetation through colonization of fire adapted plant species, it reduced the abundance and diversity of soil biota. We observed contrasting effects of tree- and soil-related fire severity on survival and recovery of understory vegetation and soil biological communities. Severe fires that killed overstory Pinus sylvestris promoted a successional stage dominated by the mosses Ceratodon purpureus and Polytrichum juniperinum, but reduced regeneration of tree seedlings and disfavored the ericaceous dwarf-shrub Vaccinium vitis-idaea and the grass Deschampsia flexuosa. Moreover, high tree mortality from fire reduced fungal biomass and changed fungal community composition, in particular that of ectomycorrhizal fungi, and reduced the fungivorous soil Oribatida. In contrast, soil-related fire severity had little impact on vegetation composition, fungal communities, and soil animals. Bacterial communities responded to both tree- and soil-related fire severity.Synthesis: Our results 2 years postfire suggest that a change in fire regime from a historically low-severity ground fire regime, with fires that mainly burns into the soil organic layer, to a stand-replacing fire regime with a high degree of tree mortality, as may be expected with climate change, is likely to impact the short-term recovery of stand structure and above- and belowground species composition of even-aged P. sylvestris boreal forests.

Raised bogs are wetland ecosystems which, under the right climatic conditions, feature patterns of pool hollows and hummock ridges. The relative cover and the spatial arrangement of pool and ridge microforms are thought to be influential on peatland atmosphere carbon gas fluxes and plant biodiversity. The mechanisms responsible for the formation and maintenance of pools, and the stability of these features in response to warming climates, remain topics of ongoing research. We employed historical aerial imagery, combined with a contemporary uncrewed aerial vehicle survey, to study 61 years of changes in pools at a patterned raised bog in central Sweden. We used a pool inheritance method to track individual pools between image acquisition dates throughout the time series. These data show a rapid loss of open-water pool area during the study period, primarily due to overgrowth of open-water pools by Sphagnum. We postulate that these changes are driven by ongoing climate warming that is accelerating Sphagnum colonisation. Open-water pool area declined by 26.8% during the study period, equivalent to a loss of 1001 m2 y−1 across the 150-hectare site. This is contradictory to an existing theory that states pools are highly stable, once formed, and can only convert to a terrestrial state through catastrophic drainage. The pool inheritance analysis shows that smaller pools are liable to become completely terrestrialised and expire. Our findings form part of a growing body of evidence for the loss of open-water habitats in peatlands across the boreal and elsewhere.

Wild boar populations have increased worldwide, but the consequences of their disturbances on boreal forest ecosystems are largely unknown. We investigated how wild boars affect soil processes in a Swedish boreal forest. We estimated effects on ecosystem functioning using phospholipid fatty acid analyses (PLFA) to characterise microbial groups, and by measuring soil respiration, soil carbon (C), nitrogen (N) and phosphorus (P) concentrations, as well as the availability of NO3- and NH4+. We compared samples collected inside wild boar enclosures with adjacent reference areas without wild boar disturbance. We found no difference in soil microbial composition, except for a consistently higher fungi:bacteria ratio in the enclosures. These results are contrary to our hypothesis that rooting raises nitrogen levels, which in turn result in more bacteria. Soil nutrient levels showed inconsistent patterns, suggesting that substrate changes - as opposed to nutrient changes - stimulated fungal growth. Soil respiration was lower in the enclosures, contradicting earlier findings suggesting increased soil CO2 emissions from wild boar rooting. Overall, our study suggests that increased wild boar abundance has a minor impact on soil processes in boreal forests. Future studies should determine if the modest impacts remain across time and boreal forests.

The northern peatland carbon sink plays a vital role in climate regulation; however, the future of the carbon sink is uncertain, in part, due to the changing interactions of peatlands and wildfire. Here, we use empirical datasets from natural, degraded and restored peatlands in non-permafrost boreal and temperate regions to model net ecosystem exchange and methane fluxes, integrating peatland degradation status, wildfire combustion and post-fire dynamics. We find that wildfire processes reduced carbon uptake in pristine peatlands by 35% and further enhanced emissions from degraded peatlands by 10%. The current small net sink is vulnerable to the interactions of peatland degraded area, burn rate and peat burn severity. Climate change impacts accelerated carbon losses, where increased burn severity and burn rate reduced the carbon sink by 38% and 65%, respectively, by 2100. However, our study demonstrates the potential for active peatland restoration to buffer these impacts. Northern peatland carbon sink plays a vital role in climate regulation. Here, the authors show that wildfire reduced peatland carbon uptake and enhanced emissions from degraded peatlands; climate change impacts accelerated carbon losses where increased burn rate and severity reduced carbon sink.