Nitrogen (N2) fixation is a major source of available N in ecosystems that receive low amounts of atmospheric N deposition. In boreal forest and subarctic tundra, the feather moss Hylocomium ...splendens is colonized by N2 fixing cyanobacteria that could contribute fundamentally to increase the N pool in these ecosystems. However, N2 fixation in mosses is inhibited by N input. Although this has been shown previously, the ability of N2 fixation to grow less sensitive towards repeated, increased N inputs remains unknown. Here, we tested if N2 fixation in H. splendens can recover from increased N input depending on the N load (0, 5, 20, 80, 320 kg N ha(-1) yr(-1)) after a period of N deprivation, and if sensitivity towards increased N input can decrease after repeated N additions. Nitrogen fixation in the moss was inhibited by the highest N addition, but was promoted by adding 5 kg N ha(-1) yr(-1), and increased in all treatments during a short period of N deprivation. The sensitivity of N2 fixation towards repeated N additions seem to decrease in the 20 and 80 kg N additions, but increased in the highest N addition (320 kg N ha(-1) yr(-1)). Recovery of N in leachate samples increased with increasing N loads, suggesting low retention capabilities of mosses if N input is above 5 kg N ha(-1) yr(-1). Our results demonstrate that the sensitivity towards repeated N additions is likely to decrease if N input does not exceed a certain threshold.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit ...BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or both.
BNF in dominant mosses was measured with the acetylene reduction assay (ARA) at different time intervals following Mo and P additions, in both laboratory microcosms with mosses from a boreal spruce forest and field plots in subarctic tundra. We further used a 15N2 tracer technique to assess the ARA to N2 fixation conversion ratios at our subarctic site.
BNF was up to four-fold higher shortly after the addition of Mo, in both the laboratory and field experiments. A similar positive response to Mo was found in moss colonizing cyanobacterial biomass. As the growing season progressed, nitrogenase activity became progressively more P limited. The ARA: 15N2 ratios increased with increasing Mo additions.
These findings show that N2 fixation activity as well as cyanobacterial biomass in dominant feather mosses from boreal forests and subarctic tundra are limited by Mo availability.
Background and aims Nitrogen fixation associated with cryptogams is potentially very important in arctic and subarctic terrestrial ecosystems, as it is a source of new nitrogen (N) into these highly ...N limited systems. Moss-, lichen-and legume-associated N₂ fixation was studied with high frequency (every second week) during spring, summer, autumn and early winter to uncover the seasonal variation in input of atmospheric N₂ to a subarctic heath with an altered climate. Methods We estimated N₂ fixation from ethylene production by acetylene reduction assay in situ in a field experiment with the treatments: long-vs. short-term summer warming using plastic tents and litter addition (simulating expansion of the birch forest). Results N₂ fixation activity was measured from late April to mid November and 33 % of all N₂ was fixed outside the vascular plant growing season (Jun-Aug). This substantial amount underlines the importance of N₂ fixation in the cold period. Wanning increased N₂ fixation two-to fivefold during late spring. However, longterm summer warming tended to decrease N₂ fixation outside the treatment (tents present) period. Litter alone did not alter N₂ fixation but in combination with warming N₂ fixation increased, probably because N₂ fixation became phosphorus limited under higher temperatures, which was alleviated by the P supply from the litter. Conclusion In subarctic heath, the current N₂ fixation period extends far beyond the vascular plant growing season. Climate warming and indirect effects such as vegetation changes affect the process of N₂ fixation in different directions and thereby complicate predictions of future N cycling.
Many Arctic regions are currently experiencing substantial summer and winter climate changes. Litter decomposition is a fundamental component of ecosystem carbon and nutrient cycles, with fungi being ...among the primary decomposers. To assess the impacts of seasonal climatic changes on litter fungal communities and their functioning, Betula glandulosa leaf litter was surface‐incubated in two adjacent low Arctic sites with contrasting soil moisture regimes: dry shrub heath and wet sedge tundra at Disko Island, Greenland. At both sites, we investigated the impacts of factorial combinations of enhanced summer warming (using open‐top chambers; OTCs) and deepened snow (using snow fences) on surface litter mass loss, chemistry and fungal decomposer communities after approximately 1 year. Enhanced summer warming significantly restricted litter mass loss by 32% in the dry and 17% in the wet site. Litter moisture content was significantly reduced by summer warming in the dry, but not in the wet site. Likewise, fungal total abundance and diversity were reduced by OTC warming at the dry site, while comparatively modest warming effects were observed in the wet site. These results suggest that increased evapotranspiration in the OTC plots lowered litter moisture content to the point where fungal decomposition activities became inhibited. In contrast, snow addition enhanced fungal abundance in both sites but did not significantly affect litter mass loss rates. Across sites, control plots only shared 15% of their fungal phylotypes, suggesting strong local controls on fungal decomposer community composition. Nevertheless, fungal community functioning (litter decomposition) was negatively affected by warming in both sites. We conclude that although buried soil organic matter decomposition is widely expected to increase with future summer warming, surface litter decay and nutrient turnover rates in both xeric and relatively moist tundra are likely to be significantly restricted by the evaporative drying associated with warmer air temperatures.
Soil microbial biomass in arctic heaths has been shown to be largely unaffected by treatments simulating climate change with temperature, nutrient and light manipulations. Here, we demonstrate that ...more than 10 years is needed for development of significant responses, and that changes in microbial biomass are accompanied with strong alterations in microbial community composition. In contrast to slight or nonsignificant responses after 5, 6 and 10 treatment years, 15 years of inorganic NPK fertilizer addition to a subarctic heath had strong effects on the microbial community and, as observed for the first time, warming and shading also led to significant responses, often in opposite direction to the fertilization responses. The effects were clearer in the top 5 cm soil than at the 5-10 cm depth. Fertilization increased microbial biomass C and more than doubled microbial biomass P compared to the non-fertilized plots. However, it only increased microbial biomass N at the 5-10 cm depth. Fertilization increased fungal biomass and the relative abundance of phospholipid fatty acid (PLFA) markers of gram-positive bacteria. Warming and shading decreased the relative abundance of fungal PLFAs, and shading also altered the composition of the bacterial community. The long time lag in responses may be associated with indirect effects of the gradual changes in the plant biomass and community composition. The contrasting responses to warming and fertilization treatments show that results from fertilizer addition may not be similar to the effects of increased nutrient mineralization and availability following climatic warming.
BackgroundIn the context of rising costs of raw materials and environmental degradation caused by livestock farming, the agri-food sector faces significant challenges in sourcing sustainable ...proteins. Grain legumes have emerged as cost-effective protein sources, with lower water footprint and GHG emissions compared to animal sources. However, their cultivation is threatened by strong yield fluctuations. Leveraging intra-specific diversity through cultivar mixtures in cropping systems can effectively buffer biotic and abiotic stresses, hence increasing yield stability. In this study, we investigate the effect of intra-specific diversity on lentil nitrogen uptake under pot (2020) and field conditions (2021). We hypothesize that cultivars with higher affinity for nitrogen fixation influence the other components of the mixture, and that nitrogen uptake dynamics are a possible driver in modulating cultivar mixture behaviour. We designed two-, three-, and four-cultivar mixtures with a trait-blind approach and compared them to sole cultivars.Results and conclusionsOur results show inconsistencies across the two experimental years, indicating that lentils may shift their nitrogen source from the atmosphere to the soil when grown in pots. Mixtures 15N enrichment was not always consistent with pure stand performance, suggesting that cultivar mixtures may have an unpredictable cumulative effect on nitrogen uptake. Regarding correlations with agronomic parameters, we observed a significant correlation between nodules number and nitrogen concentration, regardless of experimental conditions. Finally, we found that 15N excess emerged as a significant predictor for pure stands’ yield, but the differences were diluted with the increase in diversity levels. The findings on 15N enrichment responses, cultivar impacts, and complex mixture effects on soil microbiota underscore the need for further research.
Warming occurs in the Arctic twice as fast as the global average, which in turn leads to a large enhancement in terpenoid emissions from vegetation. Volatile terpenoids are the main class of biogenic ...volatile organic compounds (VOCs) that play crucial roles in atmospheric chemistry and climate. However, the biochemical mechanisms behind the temperature‐dependent increase in VOC emissions from subarctic ecosystems are largely unexplored. Using 13CO2‐labeling, we studied the origin of VOCs and the carbon (C) allocation under global warming in the soil–plant–atmosphere system of contrasting subarctic heath tundra vegetation communities characterized by dwarf shrubs of the genera Salix or Betula. The projected temperature rise of the subarctic summer by 5°C was realistically simulated in sophisticated climate chambers. VOC emissions strongly depended on the plant species composition of the heath tundra. Warming caused increased VOC emissions and significant changes in the pattern of volatiles toward more reactive hydrocarbons. The 13C was incorporated to varying degrees in different monoterpene and sesquiterpene isomers. We found that de novo monoterpene biosynthesis contributed to 40%–44% (Salix) and 60%–68% (Betula) of total monoterpene emissions under the current climate, and that warming increased the contribution to 50%–58% (Salix) and 87%–95% (Betula). Analyses of above‐ and belowground 12/13C showed shifts of C allocation in the plant–soil systems and negative effects of warming on C sequestration by lowering net ecosystem exchange of CO2 and increasing C loss as VOCs. This comprehensive analysis provides the scientific basis for mechanistically understanding the processes controlling terpenoid emissions, required for modeling VOC emissions from terrestrial ecosystems and predicting the future chemistry of the arctic atmosphere. By changing the chemical composition and loads of VOCs into the atmosphere, the current data indicate that global warming in the Arctic may have implications for regional and global climate and for the delicate tundra ecosystems.
We studied the origin of biogenic volatile organic compounds (VOCs) and carbon (C) allocation under global warming in subarctic heath tundra ecosystem using isotope labeling of 13CO2. Our results show the importance of de novo monoterpene biosynthesis and the impact of warming in vegetation communities characterized by Salix spp. (willows) or Betula spp. (birch). Warming increased overall VOC emissions and altered the composition of the volatile blend toward more reactive compounds. Analyses of above‐ and belowground 12/13C suggest shifts of C allocation and negative effects of warming on C sequestration in these delicate tundra ecosystems.
Emissions of biogenic volatile organic compounds (BVOCs) from terrestrial ecosystems are important for the atmospheric chemistry and the formation of secondary organic aerosols, and may therefore ...influence the climate. Global warming is predicted to change patterns in precipitation and plant species compositions, especially in arctic regions where the temperature increase will be most pronounced. These changes are potentially highly important for the BVOC emissions but studies investigating the effects are lacking. The aim of this study was to investigate the quality and quantity of BVOC emissions from a high arctic soil moisture gradient extending from dry tundra to a wet fen. Ecosystem BVOC emissions were sampled five times in the July-August period using a push-pull enclosure technique, and BVOCs trapped in absorbent cartridges were analyzed using gas chromatography–mass spectrometry. Plant species compositions were estimated using the point intercept method. In order to take into account important underlying ecosystem processes, gross ecosystem production, ecosystem respiration and net ecosystem production were measured in connection with chamber-based BVOC measurements. Highest emissions of BVOCs were found from vegetation communities dominated by Salix arctica and Cassiope tetragona, which had emission profiles dominated by isoprene and monoterpenes, respectively. These results show that emissions of BVOCs are highly dependent on the plant cover supported by the varying soil moisture, suggesting that high arctic BVOC emissions may affect the climate differently if soil water content and plant cover change.
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•Biogenic volatile organic compound (BVOC) emissions from the Arctic are poorly understood•We assessed BVOC emissions over a soil moisture gradient in the High Arctic•BVOC measurements were coupled with CO2 exchange, vegetation and soil analyses•BVOC emissions were dependent on the vegetation composition controlled by soil moisture
High-altitude and alpine areas are predicted to experience rapid and substantial increases in future temperature, which may have serious impacts on soil carbon, nutrient and soil fauna. Here we ...report the impact of 20 years of experimental warming on soil properties and soil mites in three contrasting plant communities in alpine/subarctic Sweden. Long-term warming decreased juvenile oribatid mite density, but had no effect on adult oribatids density, total mite density, any major mite group or the most common species. Long-term warming also caused loss of nitrogen, carbon and moisture from the mineral soil layer in mesic meadow, but not in wet meadow or heath or from the organic soil layer. There was a significant site effect on the density of one mite species, Oppiella neerlandica, and all soil parameters. A significant plot-scale impact on mites suggests that small-scale heterogeneity may be important for buffering mites from global warming. The results indicated that juvenile mites may be more vulnerable to global warming than adult stages. Importantly, the results also indicated that global warming may cause carbon and nitrogen losses in alpine and tundra mineral soils and that its effects may differ at local scale.
Climate change may alter nutrient cycling in Arctic soils and plants. Deeper snow during winter, as well as summer warming, could increase soil temperatures and thereby the availability of otherwise ...limiting nutrients such as nitrogen (N). We used fences to manipulate snow depths in Svalbard for 9 consecutive years, resulting in three snow regimes: 1) Ambient with a maximum snow depth of 35 cm, 2) Medium with a maximum of 100 cm and 3) Deep with a maximum of 150 cm. We increased temperatures during one growing season using Open Top Chambers (OTCs), and sampled soil and vascular plant leaves throughout summer 2015. Labile soil N, especially inorganic N, during the growing season was significantly greater in Deep than Ambient suggesting N supply in excess of plant and microbial demand. However, we found no effect of Medium snow depth or short-term summer temperature increase on soil N, presumably due to minor impacts on soil temperature and moisture. The temporal patterns of labile soil N were similar in all snow regimes with high concentrations of organic N immediately after snowmelt, thereafter dropping towards peak growing season. Concentrations of all N forms increased at the end of summer. Vascular plants had high N at the start of growing season, decreasing as summer progressed, and leaf N concentrations were highest in Deep, corresponding to the higher soil N availability. Short-term summer warming was associated with lower leaf N concentrations, presumably due to growth dilution. Deeper snow enhanced labile soil organic and inorganic N pools and plant N uptake. Leaf 15N natural abundance levels (δ15N) in Deep indicated a higher degree of utilization of inorganic than organic N, which was especially pronounced in mycorrhizal plants.
•Enhanced snow regimes cause high amounts of labile soil N during growing season.•Common tundra plants acquire more N in enhanced than in ambient snow regimes.•Common tundra plants acquire more inorganic N in enhanced snow regimes.
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