Patterns and drivers of prokaryotic communities in thermokarst lake water across Northern Hemisphere

13 páginas.- 5 figuras.- 81referencias.Aim: The formation of thermokarst lakes could make a large amount of carbon accessible to microbial degradation, potentially intensifying the permafrost carbon-climate feedback via carbon dioxide/methane emissions. Because of their diverse functional roles, prokaryotes could strongly mediate biogeochemical cycles in thermokarst lakes. However, little is known about the large-scale patterns and drivers of these communities. Location: Permafrost regions in the Northern Hemisphere. Time period: Present day. Major taxa studied: Prokaryotes. Methods: Based on a combination of large-scale measurements on the Tibetan Plateau and data syntheses in pan-Arctic regions, we constructed a comprehensive dataset of 16S rRNA sequences from 258 thermokarst lakes across Northern Hemisphere permafrost regions. We also used the local contributions to beta diversity (LCBD) to characterize the variance of prokaryotic species composition and screened underlying drivers by conducting a random forest modelling analysis. Results: Prokaryotes in thermokarst lake water were dominated by the orders Burkholderiales, Micrococcales, Flavobacteriales and Frankiales. The relative abundance of dominant taxa was positively associated with dissolved organic matter (DOM) properties, especially for the chromophoric/aromatic compounds. Microbial structure differed between high-altitude and high-latitude thermokarst lakes, with the dominance of Flavobacterium in high-altitude lakes, and the enrichment of Polynucleobacter in high-latitude lakes. More importantly, climatic variables were among the main drivers shaping the large-scale variation of prokaryotic communities. Specifically, mean annual precipitation was the best predictor for prokaryotic beta diversity across the Northern Hemisphere, as well as in the high-altitude permafrost regions, while mean annual air temperature played a key role in the high-latitude thermokarst lakes. Main conclusions: Our findings demonstrate significant associations between dominant taxa and DOM properties, as well as the important role of climatic factors in affecting prokaryotic communities. These findings suggest that climatic change may alter DOM conditions and induce dynamics in prokaryotic communities of thermokarst lake water in the Northern Hemisphere. © 2023 John Wiley & Sons Ltd.This work was supported by the National Key Research and Development Program of China (2022YFF0801903), National Natural Science Foundation of China (31988102, and 31825006), and Tencent Foundation through the XPLORER PRIZE. M.D‐B. acknowledges support from TED2021‐130908B‐C41/AEI/10.13039/501100011033/Unión Europea NextGenerationEU/PRTR and from the Spanish Ministry of Science and Innovation for the I + D + i project PID2020‐115813RA‐I00 funded by MCIN/AEI/10.13039/501100011033.Peer reviewe

Decadal soil carbon accumulation across Tibetan permafrost regions

Acknowledgements We thank the members of Peking University Sampling Teams (2001–2004) and IBCAS Sampling Teams (2013–2014) for assistance in field data collection. We also thank the Forestry Bureau of Qinghai Province and the Forestry Bureau of Tibet Autonomous Region for their permission and assistance during the sampling process. This study was financially supported by the National Natural Science Foundation of China (31670482 and 31322011), National Basic Research Program of China on Global Change (2014CB954001 and 2015CB954201), Chinese Academy of Sciences-Peking University Pioneer Cooperation Team, and the Thousand Young Talents Program.Peer reviewedPostprintPostprin

Linkage of plant and abiotic properties to the abundance and activity of N-cycling microbial communities in Tibetan permafrost-affected regions

AimsAmmonia oxidation and denitrification are crucial for nitrogen (N) availability and nitrous oxide production in N-limited permafrost soils. However, it remains unclear about the relative roles of abiotic and biotic properties in controlling the abundance and activity of ammonia-oxidizing and denitrifying microorganisms in permafrost-affected soils.MethodsWe analysed the potential ammonia oxidation and denitrification rates (PAO and PDR), the abundance of archaeal amoA, bacterial amoA, nirK, nirS and nosZ genes, soil characteristics, climatic and plant properties across two vegetation types in Tibetan permafrost-affected soils. The relative importance of abiotic and biotic properties in driving functional N gene abundance, PAO and PDR were assessed using variation partition analysis (VPA) and random forest (RF) model.ResultsThe functional N gene abundance and PDR were lower in alpine steppe than in alpine meadow. Variations in the PAO and PDR and functional N gene abundance were mainly explained by abiotic variables such as organic carbon and total N, then by plant properties such as plant N concentration, plant species richness and productivity based on the VPA. The RF model showed that abiotic properties (e.g., precipitation) and plant properties (e.g., plant N concentration or plant productivity) predicted the PDR and the abundance of functional N genes. Both VPA and RF model showed that the PAO and PDR could be determined by the abundance of functional N genes such as archaeal amoA gene and nosZ gene, respectively.ConclusionsOur study highlights that abiotic and plant properties are important predictors of the abundance and activity of ammonia-oxidizing and denitrifying communities in permafrost-affected regions, implying that plant properties, which were previously overlooked, should be incorporated into ecosystem models for improved prediction of belowground N process rates in a changing environment

Changes in above-/below-ground biodiversity and plant functional composition mediate soil respiration response to nitrogen input

1. Biodiversity loss and changes in plant community composition induced by anthropogenic nitrogen (N) deposition exert profound effects on ecosystem functions. However, limited studies have considered the joint effects of plant community composition, plant species richness, plant functional diversity and soil biodiversity on the dynamics of soil autotrophic and heterotrophic respiration under extra N input. 2. We addressed this issue by conducting a multilevel N-manipulation experiment in a Tibetan alpine steppe. Based on soil respiration observations as well as biotic and abiotic measurements under this N addition experiment, we quantified the relative and interactive effects of above-/below-ground biodiversity, plant community composition and other explanatory variables (environmental factors, plant and microbial properties) on autotrophic and heterotrophic respiration. 3. Our results showed that the effects of N enrichment via plant productivity, root amount, the proportion of sedge biomass and plant functional diversity explained 71% of the N-induced variations in autotrophic respiration. With regard to heterotrophic respiration, the combination of N addition, soil pH, plant functional diversity and soil biota diversity accounted for 78% of its variations along the N addition gradient. Further analyses showed that above-/below-ground diversity loss and changes in plant community composition explained similar variation to that contributed by other factors in both autotrophic and heterotrophic respiration. The declined plant functional diversity and the increased proportion of sedge biomass promoted autotrophic respiration. Conversely, the loss of soil biodiversity together with the decreased plant functional diversity led to the decline of heterotrophic respiration along the experimental N gradient. 4. Our results highlight that the indirect regulation of N input on ecosystem function through changes in plant community composition and above-/below-ground biodiversity loss should be considered for better understanding the responses of terrestrial ecosystems to atmospheric N deposition

SWAMP: A new experiment for simulating permafrost warming and active layer deepening on the Tibetan Plateau

Abstract Our knowledge on the responses of permafrost ecosystems to climate warming is critical for assessing the direction and magnitude of permafrost carbon‐climate feedback. However, most of the previous experiments have only been able to warm the air and surface soil, with limited effects on the permafrost temperature. Consequently, it remains challenging to realistically simulate permafrost thawing in terms of increased active layer (a layer freezing and thawing seasonally above permafrost) thickness under climate warming scenarios. Here, we presented the experimental design and warming performance of a novel experiment, Simulate Warming at Mountain Permafrost (SWAMP), the first one to successfully simulate permafrost warming and the subsequent active layer deepening in a swamp meadow situated on the Tibetan Plateau. Infrared heating was employed as above‐ground warming to elevate the temperature of the air and surface soil, and heating rods were inserted vertically in the soil to provide below‐ground warming for transmitting heat to the deep active layer and even to permafrost deposits. In 3 m diameter warmed circular plots, the air and the entire soil profile (from surface soil to 120 cm) was effectively heated, with an increase of approximately 2°C in the upper 60 cm, which progressively weakened with soil depth. Warming increased soil moisture across the growing season by inducing an earlier thawing of the soil. Values varied from 1.8 ± 1.8 to 12.3 ± 2.3% according to the soil depth. Moreover, during the growing season, the warmed plots had greater thaw depths and a deeper active layer thickness of 12.6 ± 0.8 cm. In addition, soil thawing duration was prolonged by the warming, ranging from 22.8 ± 3.3 to 49.3 ± 4.5 days depending on the soil depth. The establishment of SWAMP provides a more realistic simulation of warming‐induced permafrost thaw, which can then be used to explore the effect of climate warming on permafrost ecosystems and the potential permafrost carbon‐climate feedback. Notably, our experiment is more advantageous for investigating how deep soil processes respond to climate warming and active layer deepening, compare with experiments which use passive warming techniques such as open top chambers (OTCs)

Trajectory of Topsoil Nitrogen Transformations Along a Thermo-Erosion Gully on the Tibetan Plateau

Permafrost thaw, especially thermokarst formation, that is, ground collapse due to thawing of ice-rich permafrost, is expected to alter soil gross nitrogen (N) transformations, which can regulate plant productivity and ecosystem carbon cycle. However, it remains unclear how thermokarst formation modifies soil N processes in permafrost ecosystems. Here N-15 pool dilution techniques were used to evaluate changes in topsoil gross N transformations during various thaw stages (early, middle, and late stages) along a thermo-erosion gully on the Tibetan Plateau. Structural equation modeling was then conducted to explore the relative importance of biotic and abiotic factors in affecting soil gross N transformations. The results showed that topsoil gross N mineralization (GNM) decreased at the three stages, reflecting declined inorganic N production after permafrost collapse. In contrast, topsoil gross nitrification increased only during the early stage. Additionally, the ratio of microbial N immobilization to GNM was enhanced during the middle and late stages, indicating a stronger microbial N limitation after thermokarst formation. The structural equation modeling analysis revealed that soil moisture played an important role in modulating gross N transformations. For GNM, decreased soil moisture had inhibiting effects via regulating the microbial biomass, microbial community, and enzyme activities along the thaw sequence. For gross nitrification, declined soil moisture exerted facilitating effects directly by improving oxygen availability and indirectly by modulating the abundances of ammonia-oxidizing archaea and bacteria during the early stage. Overall, these results demonstrated that thermokarst formation altered soil N processes, potentially triggering interactions between ecosystem N and carbon cycles after permafrost thaw

Data from: Trait identity and functional diversity co-drive response of ecosystem productivity to nitrogen enrichment

1. Exploring the mechanisms underlying the change in ecosystem productivity under anthropogenic nitrogen (N) inputs is of fundamental ecological interest. It has been proposed that functional traits, environmental factors, and species richness are central drivers linking ecosystem productivity with environmental change. However, few studies have considered the joint effects of functional traits, environmental factors, and species richness on ecosystem productivity under increasing N inputs. 2. We established a N-manipulation experiment in a Tibetan alpine steppe in 2013. Using structural equation models, we assessed the effects of N-induced changes in environmental factors, species richness, and trait metrics (the mean, variance, skewness and kurtosis of trait distribution) on gross ecosystem productivity as well as three resource use efficiencies (water, light, and phosphorus (P) use efficiencies), based on measurements during the peak growing season in 2016. 3. We found that both light and P use efficiencies decreased under N enrichment, largely due to the N-induced decline in functional diversity of leaf P concentration. However, both gross ecosystem productivity and water use efficiency exhibited initial increases and subsequent slight decreases with N addition. These nonlinear patterns were closely associated with both the increased morphological trait (i.e., mean-leaf area) and decreased diversity of leaf P concentration. 4. Synthesis. Our results illustrate how N-induced changes in functional traits may have dual effects on ecosystem productivity: the stimulating effects of the dominant trait identity via increasing canopy light interception vs. the inhibiting effect of decreasing trait diversity via declining resource use efficiencies. Our results highlight the importance of including functional traits in land surface models to improve predictions of the response of ecosystem function to N inputs

Trait identity and functional diversity co-drive response of ecosystem productivity to nitrogen enrichment

1. Exploring the mechanisms underlying the change in ecosystem productivity under anthropogenic nitrogen (N) inputs is of fundamental ecological interest. It has been proposed that functional traits, environmental factors and species richness are central drivers linking ecosystem productivity with environmental change. However, few studies have considered the joint effects of functional traits, environmental factors and species richness on ecosystem productivity under increasing N inputs. 2. We established a N-manipulation experiment in a Tibetan alpine steppe in 2013. Using structural equation models, we assessed the effects of N-induced changes in environmental factors, species richness and trait metrics (mean, variance, skewness and kurtosis of trait distribution) on gross ecosystem productivity as well as three resource use efficiencies (water, light and phosphorus (P) use efficiencies), based on measurements during the peak growing season in 2016. 3. We found that both light and P use efficiencies decreased under N enrichment, largely due to the N-induced decline in functional diversity of leaf P concentration. However, both gross ecosystem productivity and water use efficiency exhibited initial increases and subsequent slight decreases with N addition. These nonlinear patterns were closely associated with both the increased morphological trait (i.e. mean of leaf area) and decreased diversity of leaf P concentration. 4. Synthesis. Our results illustrate how N-induced changes in functional traits may have dual effects on ecosystem productivity: the stimulating effects of the dominant trait identity via increasing canopy light interception versus the inhibiting effect of decreasing trait diversity via declining resource use efficiencies. Our results highlight the importance of including functional traits in land surface models to improve predictions of the response of ecosystem function to N inputs

Data from: Trait identity and functional diversity co-drive response of ecosystem productivity to nitrogen enrichment

1. Exploring the mechanisms underlying the change in ecosystem productivity under anthropogenic nitrogen (N) inputs is of fundamental ecological interest. It has been proposed that functional traits, environmental factors, and species richness are central drivers linking ecosystem productivity with environmental change. However, few studies have considered the joint effects of functional traits, environmental factors, and species richness on ecosystem productivity under increasing N inputs. 2. We established a N-manipulation experiment in a Tibetan alpine steppe in 2013. Using structural equation models, we assessed the effects of N-induced changes in environmental factors, species richness, and trait metrics (the mean, variance, skewness and kurtosis of trait distribution) on gross ecosystem productivity as well as three resource use efficiencies (water, light, and phosphorus (P) use efficiencies), based on measurements during the peak growing season in 2016. 3. We found that both light and P use efficiencies decreased under N enrichment, largely due to the N-induced decline in functional diversity of leaf P concentration. However, both gross ecosystem productivity and water use efficiency exhibited initial increases and subsequent slight decreases with N addition. These nonlinear patterns were closely associated with both the increased morphological trait (i.e., mean-leaf area) and decreased diversity of leaf P concentration. 4. Synthesis. Our results illustrate how N-induced changes in functional traits may have dual effects on ecosystem productivity: the stimulating effects of the dominant trait identity via increasing canopy light interception vs. the inhibiting effect of decreasing trait diversity via declining resource use efficiencies. Our results highlight the importance of including functional traits in land surface models to improve predictions of the response of ecosystem function to N inputs

Above- and below-ground resource acquisition strategies determine plant species responses to nitrogen enrichment

Background and Aims: Knowledge of plant resource acquisition strategies is crucial for understanding the mechanisms mediating the responses of ecosystems to external nitrogen (N) input. However, few studies have considered the joint effects of above-ground (light) and below-ground (nutrient) resource acquisition strategies in regulating plant species responses to N enrichment. Here, we quantified the effects of light and non-N nutrient acquisition capacities on species relative abundance in the case of extra N input. Methods: Based on an N-manipulation experiment in a Tibetan alpine steppe, we determined the responses of species relative abundances and light and nutrient acquisition capacities to N enrichment for two species with different resource acquisition strategies (the taller Stipa purpurea, which is colonized by arbuscular mycorrhizal fungi, and the shorter Carex stenophylloides, which has cluster roots). Structural equation models were developed to explore the relative effects of light and nutrient acquisition on species relative abundance along the N addition gradient. Key Results: We found that the relative abundance of taller S. purpurea increased with the improved light acquisition along the N addition gradient. In contrast, the shorter C. stenophylloides, with cluster roots, excelled in acquiring phosphorus (P) so as to elevate its leaf P concentration under N enrichment by producing large amounts of carboxylate exudates that mobilized moderately labile and recalcitrant soil P forms. The increased leaf P concentration of C. stenophylloides enhanced its light use efficiency and promoted its relative abundance even in the shade of taller competitors. Conclusions: Our findings highlight that the combined effects of above-ground (light) and below-ground (nutrient) resources rather than light alone (the prevailing perspective) determine the responses of grassland community structure to N enrichment