Nitrogen Deposition Research Articles

Modified Biochar Materials From Eucalyptus globulus Wood as Efficient CO2 Adsorbents and Recyclable Catalysts

AbstractHighly porous carbon materials derived from renewable resources constitute a promising and sustainable strategy regarding the enhancement of CO2 capture technologies. In this work, the valorization of Eucalyptus globulus wood, a forest invasive species present in European forests, is performed through its transformation in biochar. The deposition of nitrogen and different metals (aluminum, copper and chromium) onto biochar is performed, using the magnetron sputtering as a pioneering technique, to produce coated biochar nanoparticles with improved properties. The resultant modified biochar particles maintain a highly porous structure and present a remarkable CO2 adsorption capacity (up to 4.80 mmol g−1 for N@BC), which is attributed to the synergy of their large total surface area (527 m2 g−1) and microporosity (pore diameter = 21 Å), with a high content of nitrogen and oxygen heteroatom moieties (40.4% N, 11.4% O). Their application as heterogeneous bifunctional catalysts in CO2 cycloaddition to epichlorohydrin is performed, in the absence of any solvent or co‐catalyst, under moderate conditions (20 bar CO2, 120 °C), leading to good conversions (up to 58% conversion) and excellent selectivity for cyclic carbonates. Cu‐coated biochar is shown to be more stable than non‐modified material, being recycled and reused along 4 consecutive runs without loss of catalytic activity or selectivity.

Warming, nitrogen deposition, and provenance shift above-belowground insect interactions and host compensatory growth.

Above-belowground insect herbivore interactions and plant compensatory growth are crucial for reshaping the fitness of invasive plants, and it is likely that climate warming, nitrogen (N) deposition, and plant provenance influence this interaction and growth in a complex way. We performed an experiment with Solidago canadensis from home and introduced ranges, leaf-chewing Spodoptera litura, and root-feeding Protaetia brevitarsis under climate warming and N deposition, and addressed how these abiotic stressors and plant provenance jointly shaped the reciprocal effects between S. litura and P. brevitarsis and the compensatory growth of S. canadensis after herbivory. Under ambient conditions, S. litura and P. brevitarsis inhibited each other on the basis of growth; warming, N addition or warming plus N addition shifted or even reversed this competition depending on provenance. While the survival-based above-belowground interactions differed from growth-based ones, warming or warming plus N addition also shifted or even reversed the neutralism or amensalism detected under ambient conditions depending on provenance. S. canadensis from its home range was more tolerant of herbivory than from its introduced range under ambient conditions; warming, N addition or warming plus N addition decreased the plant compensatory growth of native S. canadensis, but increased that of invasive S. canadensis relative to ambient conditions. These findings suggest that climate warming and N deposition could enhance positive above-belowground insect interactions, increasing insect pressures on S. canadensis, and that plant provenance might be important in mediating climate change effects on insect interactions and host compensatory growth under plant invasions.

Unveiling the Hidden Responses: Metagenomic Insights into Dwarf Bamboo (Fargesia denudata) Rhizosphere under Drought and Nitrogen Challenges.

Dwarf bamboo (Fargesia denudata) is a crucial food source for the giant pandas. With its shallow root system and rapid growth, dwarf bamboo is highly sensitive to drought stress and nitrogen deposition, both major concerns of global climate change affecting plant growth and rhizosphere environments. However, few reports address the response mechanisms of the dwarf bamboo rhizosphere environment to these two factors. Therefore, this study investigated the effects of drought stress and nitrogen deposition on the physicochemical properties and microbial community composition of the arrow bamboo rhizosphere soil, using metagenomic sequencing to analyze functional genes involved in carbon and nitrogen cycles. Both drought stress and nitrogen deposition significantly altered the soil nutrient content, but their combination had no significant impact on these indicators. Nitrogen deposition increased the relative abundance of the microbial functional gene nrfA, while decreasing the abundances of nirK, nosZ, norB, and nifH. Drought stress inhibited the functional genes of key microbial enzymes involved in starch and sucrose metabolism, but promoted those involved in galactose metabolism, inositol phosphate metabolism, and hemicellulose degradation. NO3--N showed the highest correlation with N-cycling functional genes (p < 0.01). Total C and total N had the greatest impact on the relative abundance of key enzyme functional genes involved in carbon degradation. This research provides theoretical and technical references for the sustainable management and conservation of dwarf bamboo forests in giant panda habitats under global climate change.

The Responses of Soil Extracellular Enzyme Activities and Microbial Nutrients to the Interaction between Nitrogen and Phosphorus Additions and Apoplastic Litter in Broad-Leaved Korean Pine Forests in Northeast China

The impact of nitrogen and phosphorus deposition alternations, as well as apoplastic litter quality and quantity, on soil nutrient cycling and soil carbon pool processes in forest ecosystems is of considerable importance. Soil ecological enzyme chemistry is a powerful tool for elucidating the nutrient limitations of microbial growth and metabolic processes. In order to explore the responding mechanisms of soil ecological enzyme chemistry to the simultaneous changes in apoplast input and nitrogen and phosphorus deposition in temperate coniferous and broad-leaved mixed forests, an outdoor simulating experiment was conducted. The results demonstrate that the treatments involving apoplastic material and nitrogen and phosphorus additions had significantly impacted soil nutrient levels across different forest types. Apoplastic treatments and N-P additions had a significant effect on the soil total organic carbon (TOC), dissolved organic carbon (DOC), soil total soluble nitrogen (TSN), soil available phosphorus (SAP), soil total nitrogen (TN), soil total phosphorus (TP), and microbial biomass carbon (MBC). However, the effects on soil microbial biomass (MBN) and microbial biomass phosphorus (MBP) were insignificant. The apomictic treatments with N and P addition did not result in a statistically significant change in soil C-hydrolase activities (β-1,4-glucosidase BG, β-1,4-xylosidase BX, cellobiohydrolase CBH, phenol oxidase POX, and peroxidase PER), N-hydrolase activities (β-1,4-N-acetylglucosaminidase NAG and L-leucine aminopeptidase LAP), or P-hydrolase activities (Acid phosphatase AP). Although the apomictic treatments did not yield a significant overall impact on carbon hydrolase activity, they influenced the activity of specific enzymes, such as CBH, LAP, and PER, to varying degrees. The effects on BG, BX, CBH, AP, and C-hydrolase activities were significant for different stand types. The impact of apomictic treatments and N-P additions on soil nitrogen hydrolase activities was inconsequential with a minimal interactive effect. The highest correlation between PER, LAP, and N-hydrolase activities was observed in conjunction with elevated levels of nitrogen and phosphorus addition (N3L0, original litter treatment, and high amounts of N and P addition). These findings may provide a theoretical foundation for the management of ecosystem function in broad-leaved Korean pine forests.

Plant production and community structure in a mesic semi-natural grassland: Moderate soil textural variation has a much stronger influence than experimentally increased atmospheric nitrogen deposition

Plant production and community structure in a mesic semi-natural grassland: Moderate soil textural variation has a much stronger influence than experimentally increased atmospheric nitrogen deposition

Changes in the Phylogenetic Structure of Alpine Grassland Plant Communities on the Qinghai-Tibetan Plateau with Long-Term Nitrogen Deposition.

Nitrogen (N) deposition rates have notably increased around the world, especially in high-altitude regions like the Qinghai-Tibetan Plateau (QTP). We conducted a six-year comprehensive experiment to simulate nitrogen deposition in an alpine grassland area near Qinghai Lake. Four levels of nitrogen depositions, i.e., 0 (CK), 8 kg N ha-1year-1 (N1), 40 kg N ha-1year-1 (N2), and 72 kg N ha-1year-1 (N3), with three replicates for each N treatment, were tested annually in early May and early July, with the meticulous collection of plant and soil samples during the peak growth period from 15 July to 15 August. We used the null model to evaluate the impact of environmental filtration and interspecific competition on the dynamics of the plant community was assessed based on the level of discrete species affinities within the plant community by constructing a phylogenetic tree. The results showed that the environmental filter was the predominant driver for the change of community's genealogical fabric. The N2 and N3 treatments increased the influence of soil factors on the change of plant community structure. Climatic factors played a crucial role on the change of plant community in the CK grassland area, while soil factors were dominant in the N1- and N3-treated grasslands.

Co-fermentation with multiple-strains and cellulase enhances the nutritional quality of hot-pressed rapeseed meal by modifying its physicochemical properties

The thermal damage of proteins and the presence of anti-nutritional factors seriously affect the quality of hot-pressed rapeseed meal (RSM), thereby limiting its utilization in the feed and food industry. Previously, we developed a co-fermentation method with multi-strains and cellulase that can simultaneously degrade the protein and anti-nutrient components in hot-pressed RSM. This study aimed to evaluate the impact of fermentation on the physicochemical properties and nutritional value of hot-pressed RSM. After fermentation, the levels of neutral detergent fiber (NDF) and glucosinolate (GLS) in hot pressed RSM decreased by 41.47% and 77.30%, respectively, and the trichloroacetic acid-soluble protein (TASP) and lysine contents increased by 1007.62% and 65.25%, respectively. During the fermentation process, the extensive hydrolysis of rapeseed protein resulted in a 49.11% yield of peptides < 3K Da, and intensified the umami, saltiness, sweetness, and bitterness of fermented rapeseed meal (FRSM). Animal experiments demonstrated that co-fermentation effectively enhances the ileal digestibility of most amino acids in hot-pressed RSM, as well as the deposition of nitrogen and energy, thereby improving the growth of growing pigs. Overall, the co-fermentation with microbes and cellulase is an effective strategy for enhancing the quality of hot-pressed RSM.

Foraminiferal denitrification and deep bioirrigation influence benthic biogeochemical cycling in a seasonally hypoxic fjord

Benthic macro- and micro-biota often play significant roles in controlling the biogeochemical dynamics in sediments. Their activity can be influenced by oxygen availability and impacted by the rise in global hypoxia in coastal regions over the last decades. To understand how these organisms interact with coastal hypoxia and influence sediment biogeochemistry, we undertook a study of early diagenesis in Bedford Basin, a seasonally hypoxic fjord on the West Atlantic coast in Nova Scotia, Canada, using a combination of observations and reaction-transport modeling. We observed that the seafloor was a source of ammonium and sink of nitrate with average fluxes of 2.2 ± 1.8 and −0.9 ± 0.7 mmol m−2 d−1 respectively. The diffusive oxygen uptake was 14 ± 4.6 mmol m−2 d−1 and the total organic carbon content in collected sediment cores was 5–7 % with a C/N ratio of ∼10. The pyrite content increased steadily from 0.5 wt% Fe at surface to ∼2 wt% Fe at 20 cm depth. Hydrogen sulfide was negligible down to 25 cm depth most of the time. The sediment was inhabited by tube-forming polychaete Spiochaetopterus sp. that formed tubes up to ∼30 cm in length. The living foraminiferal assemblage in the top 5 cm sediment was found to be dominated (>85 %) by nitrate-storing and denitrifying benthic foraminifera Stainforthia fusiformis. These observations were used to develop and constrain a biogeochemical reaction-transport model. The model results suggest that the observed decrease in porewater concentrations of ammonium and dissolved inorganic carbon below 5 cm depth, was due to deep bioirrigation by tubeworms, accounting for almost 50 % of the benthic efflux. The model further revealed that the deep bioirrigation along with bioturbation and iron cycling prevented accumulation of free sulfide in the top 25 cm sediment despite oxygen penetration depths of ∼1 mm. Modelled organic carbon and nitrogen deposition was 25.2 and 2.9 mmol m−2 d−1 with burial efficiencies of 23 % and 17 %, respectively. The model indicated a total denitrification rate of 1.3 mmol N m−2 d−1 that was largely (∼70 %) driven by benthic foraminifera. This study reports the first evidence of foraminiferal denitrification in western Atlantic coastal sediments, and suggests that eukaryote mediated denitrification is an important driver of sediment N-loss in seasonally hypoxic environments, a process that has been traditionally assumed to be carried out by prokaryotic microbes.

Rising CO2 and land use change amplify the increase in terrestrial and riverine export of dissolved organic carbon over the past four decades

The lateral transport of dissolved organic carbon (DOC) from land to rivers and oceans is a significant but overlooked component of the global carbon cycle. However, there are still large uncertainties in the magnitude and trend of global DOC export fluxes, as well as their response to environmental change. In this study, several simulations were conducted using a developed land surface model that considered riverine DOC transport and anthropogenic disturbance to investigate the terrestrial DOC loading and riverine DOC export, and to quantify the relative contributions of natural and anthropogenic factors over the past four decades (1981–2016). These factors include climate change, nitrogen deposition, land use change, atmospheric CO2 concentration, anthropogenic water regulation, and fertilizer and manure application. Results showed that the average global annual terrestrial DOC loading was about 432.30 ± 53.59 Tg C yr−1, and rivers exported about 209.73 ± 36.58 Tg C yr−1 to oceans over the past four decades. Simultaneously, a significant increase in terrestrial DOC loading and riverine DOC export fluxes (3.36 Tg C yr−2 and 2.99 Tg Cyr−2, p < 0.01) was found, which increased by 26.88 % and 47.02 %, respectively. According to our factorial analysis, the interannual variability in DOC fluxes in most regions was mainly attributed to climate change and contributed more than 60 % of the long-term increase. In addition, rising atmospheric CO2 and land use change amplified the increase in terrestrial DOC loading, with the area dominated by the two factors expanding from 7.94 % in the 1980s to 23.84 % in the 2010s, and riverine DOC export showed a similar pattern, which may be related to the increased soil DOC sources. Anthropogenic water regulation and nitrogen addition have led to a slight increase in DOC fluxes, which should not be ignored, otherwise carbon fluxes may be underestimated.

Nutrient Addition Enhances the Temperature Sensitivity of Soil Carbon Decomposition Across Forest Ecosystems.

Atmospheric nitrogen (N) and phosphorus (P) depositions have been shown to alter nutrient availability in terrestrial ecosystems and thus largely influence soil carbon cycling processes. However, the general pattern of nutrient-induced changes in the temperature response of soil carbon decomposition is unknown. Yet, understanding this pattern is crucial in terms of its effect on soil carbon-climate feedback. Here, we report that N and P additions significantly increase the temperature sensitivity of soil organic carbon decomposition (Q10) by sampling soils from 36 sites across China's forests. We found that N, P, and their co-addition (NP) significantly increased the Q10 by 11.3%, 11.5%, and 23.9%, respectively. The enhancement effect of nutrient addition on Q10 was more evident in soils from warm regions than in those from cold regions. Moreover, we found that nutrient-induced changes in substrate availability and initial substrate and nutrient availability mainly regulated nutrient addition effects. Our findings highlight that N and P deposition enhances the temperature response of soil carbon decomposition, suggesting that N and P deposition should be incorporated into Earth system models to improve the projections of soil carbon feedback to climate change.

Effects of Nitrogen Forms on Soil Enzyme Activities in a Saline-Alkaline Grassland.

Global climate change and agricultural practices have increased atmospheric nitrogen (N) deposition, significantly affecting the nitrogen cycling process in grasslands. The impact of different N forms on key soil enzyme activities involved in N nitrification, particularly in the saline-alkali grasslands of the Hexi Corridor, using natural grassland as a control (CK) and adding three N treatments: inorganic N (IN), organic N (ON) and a mixed N treatment (MN, with a 4:6 ratio of organic to inorganic N). Our study assessed the effects of these N forms on soil properties and enzyme activities crucial for N cycling. The findings indicate that different N forms significantly enhance soil mineral N content, with ON treatment leading to the highest increases in nitrate and ammonium content 92.44% and 35.6%, respectively, compared to CK. Both IN and ON treatments significantly boosted soil nitrate reductase and urease activities (p < 0.05), while MN treatment decreased nitrate reductase activity, with ON treatment showing the greatest sensitivity to enzyme activity changes. Soil pH slightly increased with N addition, but soil nitrite reductase activity remained relatively unchanged (0.372-0.385 mg g-1). Correlation analysis revealed that soil mineral N content and pH are key regulators of enzyme activities in saline-alkaline grasslands. These results suggest that different N forms should be considered in nutrient cycling models, with organic N addition potentially enhancing soil N conversion and mitigating nutrient limitations in grassland ecosystems.

Influence of Various Methods of Processing Soybeans on Protein Digestibility and Reduction of Nitrogen Deposits in the Natural Environment – A Review

Abstract Soybean meal (SBM) is a significant source of protein for poultry due to its high concentration of protein and amino acids profile. The primary objective of SBM processing is the reduction and deactivation of anti-nutritional factors (ANFs) to enhance nutrient digestibility. However, eliminating ANFs does not necessarily correlate with increased protein and amino acid content. Several processing methods, such as soaking, cooking, and commercial techniques, improve SBM protein digestibility. To sustain feeding qualities, soybeans must undergo heating to remove inherent chemicals that interfere with poultry digestion. However, both under and over-processing can impair meal digestibility. Extrusion heating significantly contributes to protein and starch digestibility while reducing certain ANFs. Thermomechanical and enzyme-assisted procedures reduce heat-resistant proteins more efficiently than extraction methods, producing soy protein concentrate (SPC) and fermentation. These techniques reduce ANFs in SBM, activating digestive enzymes and alleviating digestive tract pressure, leading to decreased endogenous protein deficits. Exogenous enzyme supplementation is a biotechnological approach for enhancing the nutritional content of SBM and certain other protein-rich products. However, different processing methods not only affect protein digestibility but also impact poultry production, gastrointestinal health, and the environment due to higher nitrogen excrement. Ammonia (NH3) emissions are a significant environmental concern in chicken farming, resulting from uric acid production during protein consumption. It has a negative impact on the environment and the health of birds/humans. This review investigates the impact of several processing techniques on the digestibility of SBM protein and the reduction of N2 regarding one health concept. Future research should focus on identifying optimal processing methods maximizing protein digestibility while minimizing environmental nitrogen impacts.

Ectomycorrhizal fungi and the nitrogen economy of Nothofagus in southern Patagonia.

Subantarctic Nothofagus forests are the southernmost forests in the world, with negligible atmospheric nitrogen (N) deposition. Most paradigms about the role of ectomycorrhizal (ECM) fungi in N cycling and plant N uptake at high latitudes have been tested in boreal coniferous forests, while in the southern hemisphere, ECM hosts are primarily angiosperms. Using ITS1 meta-barcoding, we characterized ECM and saprotrophic fungal communities in evergreen and deciduous Nothofagus forests forming monodominant and mixed stands in the archipelago of Tierra del Fuego (Chile and Argentina). We assessed the N economy of Nothofagus by correlating host species with fungal relative abundances, edaphic variables, net N mineralization, microbial biomass N and the activity of eight extracellular soil enzymes activities. The N economy of deciduous N. pumilio forests was strikingly similar to boreal coniferous forests, with the lowest inorganic N availability and net N mineralization, in correlation to higher relative abundances of ECM fungi with enzymatic capacity for organic N mobilization (genus Cortinarius). In contrast, the N economy of evergreen N. betuloides forests was predominantly inorganic and correlated with ECM lineages from the family Clavulinaceae, in acidic soils with poor drainage. Grassy understory vegetation in deciduous N. antarctica forests likely promoted saprotrophic fungi (i.e., genus Mortierella) in correlation with higher activities of carbon-degrading enzymes. Differences between Nothofagus hosts did not persist in mixed forests, illustrating the range of soil fertility of these ECM angiosperms and the underlying effects of soil and climate on Nothofagus distribution and N cycling in southern Patagonia.

Nitrogen deposition contributed to a global increase in nitrous oxide emissions from forest soils

Nitrous oxide is a potent greenhouse gas. Anthropogenically enhanced nitrogen deposition causes natural forest soils to release more nitrous oxide, exacerbating global warming. We used data from nitrogen addition experiments conducted in forests worldwide to quantify the spatially varying sensitivity of soil nitrous oxide emission to nitrogen deposition, thereby inferring soil nitrous oxide emission dynamics from nitrogen deposition data. From 1985 to 2015, nitrous oxide emitted from global forest soils increased from 3.55 to 3.85 teragrams of nitrogen per year. Nitrogen deposition contributed directly to 9.0% of global forest soil nitrous oxide emissions. The derived country-specific sensitivities of soil nitrous oxide emission to nitrogen deposition could be employed as localized emission factors for forestland nitrous oxide emission inventories. This study sheds light on a process-augmented data-driven approach to estimating global nitrous oxide emissions by synthesizing experimental and observational data.

Diverse effects of climate changes and anthropogenic activities on sedimentary nitrogen isotope (δ15Nsed.) in lakes across different regions of China since the late Holocene

Nitrogen plays a vital role in the Earth's systems. Nitrogen isotopes have been widely used in environmental and climatic research. Various biogeochemical processes and nitrogen sources contribute to the sedimentary organic matter. Therefore, environmental implications of sedimentary nitrogen isotope (δ15Nsed.) require further investigation. In this study, we report and compile the δ15Nsed. records from eight lakes in China influenced by either climate changes or anthropogenic activities since the late Holocene to determine the major forcing factors of δ15Nsed.. Our results showed that: (1) During the late Holocene, lacustrine δ15Nsed. was mainly regulated by natural climate changes, such as temperature, precipitation, or both as anthropogenic activities were weak. (2) The impact of gradually increasing anthropogenic disturbances on δ15Nsed. in the different lakes varied. Globally, the declining lacustrine δ15Nsed. values could be attributed to atmospheric reactive nitrogen deposition. However, on the regional catchment scale, the increased δ15Nsed. values in lakes may be related to increased nutrient input and higher primary production caused by increased anthropogenic activities, whereas the rapid decline of δ15Nsed. values in lakes is possibly related to more nutrient input and 15N-depleted organic matter input resulting excessive anthropogenic activities. Our study suggests that the impact of anthropogenic activities on lake ecosystems gradually increased in recent decades, and the amplitudes in variations of δ15Nsed. values in some lakes exceeded those during periods of weak anthropogenic disturbances. If not properly managed, anthropogenic disturbances may outweigh nature (i.e., temperature, precipitation) as the leading cause of lake ecosystem changes in the future.

Photocatalytic NOx degradation and [formula omitted] adsorption by mortar modified with S-g-C3N4/MgAl-CLDH: Influence factors and stability

NOx is a harmful gas that causes respiratory diseases and acid rain. Commonly used photocatalysts for degrading NOx such as UV responsive TiO2 show weak photocatalytic degradation efficiency under visible light. Furthermore, the great concern is that the degradation product, nitrates (NO3-), from NOx could be washed away and increase the nitrogen deposition and eutrophication in the surrounding soil and aquatic environments, resulting in serious secondary pollution. To address these issues, this study proposes a novel solution by incorporating S-g-C3N4/MgAl-CLDH nanocomposites into a cementitious system which features high NOx degradation efficiency under visible light condition and the efficient capture and adsorption of NO3- in situ. The NOx degradation was comprehensively studied, encompassing the influencing factors and stability. The mechanism for NO3- adsorption process was expounded using the isothermal model. The results show that the amount of exposed S-g-C3N4/MgAl-CLDH and the contact area between S-g-C3N4/MgAl-CLDH and NOx are the essential reasons affecting the NOx degradation. The NOx degradation ability of photocatalytic mortar exhibits excellent stability with the NOx removal ratio decreasing by only 4.8 % and 14.5 % after ten consecutive tests and 120 min of ultrasonic washing, respectively. Furthermore, S-g-C3N4/MgAl-CLDH increases the NO3- adsorption capacity of photocatalytic mortar by about 1.5 times, and the adsorption process of NO3- follows the Freundlich isotherm. The study offers an alternate method for designing innovative nanocomposites in cement-based materials to control environmental pollution.

Growth and physiological metabolic regulation mechanisms of the dominant plant Leymus secalinus in alpine meadow under nitrogen deposition

Nitrogen (N) deposition is an important pathway that affects the growth and development of alpine grassland plants. Under N deposition, Leymus secalinus has become the most dominant species in the alpine meadow of the Qinghai-Tibetan Plateau. However, its adaptive mechanisms to N deposition are still unknown. Therefore, we analyzed the physiological indices of Leymus secalinus under different N deposition levels (CK, 0 kg N ha−1 yr−1; N1, 8 kg N ha−1 yr−1; N3, 40 kg N ha−1 yr−1; N5, 72 kg N ha−1 yr−1) and focused on its growth and metabolism. The results indicated that the leaf carbon (C), N, amino acid (AA), and photosynthetic pigment contents in Leymus secalinus were significantly increased under N deposition, its endogenous hormone levels were regulated and the activities of N metabolism-related enzymes were enhanced. Metabolomics analysis further showed that the metabolites changed significantly and were mostly enriched in the amino acid metabolic pathway. Among them, glutamine and aspartic acid played key roles in N deposition for dominant growth of Leymus secalinus by regulating N and amino acid metabolism. These analyses unveiled the physiological and biochemical changes of dominant species in response to N deposition, identifying critical metabolites involved in this process. Furthermore, these findings provide substantial evidence explaining the ecological phenomenon of Leymus secalinus emerging as a dominant species under N deposition, serving as a data reference for understanding the physiological response and adaptation to N deposition in alpine grassland plants.

Water controls the divergent responses of terrestrial plant photosynthesis under nitrogen enrichment

Abstract Quantifying leaf photosynthetic response to nitrogen (N) deposition under contrasting water conditions is important for reliably modelling terrestrial carbon and water cycles, a topic that has not been well understood. Here, we analysed 737‐paired observations from 102 publications to assess the response of 11 leaf photosynthesis‐related properties to N addition under different water conditions. Our research includes global experiments, with 19 conducted in the field and 83 in greenhouses. Treatments without water reduction were classified as ‘no water change’, while those with reduced water or precipitation causing physiological drought were categorized as ‘drought’. We found that, compared to the control group, N addition significantly increased leaf photosynthetic rate (Pn; 20.9%), leaf transpiration (E; 8.3%) and stomatal conductance (gs; 14.1%). However, the decrease in Pn (−11.6%), E (−24.7%) and gs (−23.9%) under the combination of N addition and drought indicated that N addition could not offset the negative effects of drought. Furthermore, N addition significantly enhanced water‐use efficiency (WUE) by 19.8% under no water change conditions and by 21.1% under drought conditions. Within plant functional groups, herbaceous species exhibited greater susceptibility to N addition than woody species, especially under drought conditions. The observed patterns of increase in Pn with longer experimental duration and WUE with higher N rate under drought conditions showed that plants would gradually adapt to long‐term water stress in the context of N deposition. Furthermore, our results showed that drought could strengthen the correlations between leaf photosynthetic properties. Lastly, our study demonstrated that N addition and drought significantly impacted leaf nitrogen content and SPAD, respectively, and further affected gs, Pn and WUE. Synthesis. Our results emphasize the crucial role of water conditions in shaping the response of leaf photosynthesis to nitrogen (N) enrichment and also acknowledge the significance of leaf functional traits in regulating the dynamics of leaf photosynthetic processes.

Bilberry Expansion in the Changing Subalpine Belt.

Bilberry (Vaccinium myrtillus L.) expansion in subalpine and alpine ecosystems is increasing due to climate change and reduced land management. This review examines bilberry traits, environmental responses, and ecosystem impacts. As a stress-tolerant chamaephyte, bilberry thrives in acidic, nutrient-poor soils across various habitats. It propagates effectively through rhizomes and demonstrates a phalanx growth form. Bilberry's growth and distribution are influenced by elevation, soil structure, pH, water availability, and nitrogen content. Mycorrhizal associations play a crucial role in nutrient uptake. The species modifies the microclimate, facilitates litter accumulation, and influences soil microbial communities, affecting nutrient turnover and biodiversity. Bilberry shows moderate tolerance to herbivory and frost, with the ability to recover through rapid emergence of new ramets. However, severe or repeated disturbances can significantly impact its abundance and reproductive success. Climate warming and atmospheric nitrogen deposition have accelerated bilberry growth in treeline ecotones. The management of bilberry expansion requires a nuanced approach, considering its resilience, historical land-use changes, and environmental factors. The goal should be to limit, not eliminate, bilberry, as it is a natural part of subalpine communities. Long-term comparative monitoring and experimental manipulation are necessary for effective management strategies.

Temporal-scale-dependent mechanisms of forest soil nitrous oxide emissions under nitrogen addition

Nitrous oxide (N₂O) emissions from forest soils are typically intensified under elevated anthropogenic nitrogen (N) deposition, likely due to increased N availability. However, the extent to which these emissions are linked to N availability across different timescales remains poorly understood. Here we investigated the temporal-scale-dependent mechanisms of N₂O emissions in a subalpine forest under N-addition, using hourly-resolved N₂O measurements. Our findings revealed that N-addition induced both pulse emissions and a long-lasting effect on soil N₂O emissions. The pulse emissions occurred immediately after each N-addition, indicating a strong linkage between the pulse events and elevated N availability. However, variations in annual N₂O emissions were not directly regulated by N availability but were instead explained by denitrifying microbial functional genes ratio. A global meta-analysis further confirmed the importance of microbial functional genes in regulating N2O emissions in natural terrestrial ecosystems. Our results suggest a crucial role of microbial functional genes in predicting annual N2O emissions from forest soils.