Nitrogen Inputs Research Articles

Association between CH4 uptake and N2O emission in grassland depends on nitrogen inputs

Association between CH4 uptake and N2O emission in grassland depends on nitrogen inputs

Fertilization effects on symbiotic and free-living biological nitrogen fixations: Similar effects but different mechanisms

Biological nitrogen fixation (BNF) by N-fixing microorganisms (NFMs) is one of the critical nitrogen input pathways in terrestrial ecosystems and is primarily affected by human activity during fertilization. However, the responses and underlying mechanisms of symbiotic and free-living BNFs to fertilization remain unclear. This study conducted a global meta-analysis to reveal the responses and mechanisms of symbiotic and free-living BNFs to inorganic N, phosphorus (P), potassium (K), and organic (O) fertilizers in agroecosystems. The results showed that symbiotic and free-living BNFs responded similarly to different fertilizers. Specifically, N fertilization significantly decreased the symbiotic BNF (absolute N fixation rate: −43.32%) and free-living BNF (absolute N fixation rate: −53.10%), and P, K, and O fertilizers had opposite effects. However, the regulatory mechanisms underlying similar responses were different. The negative effect of N fertilization on symbiotic BNF was due to the decrease in weight and number of nodules, whereas the negative effect of N fertilization on free-living BNF was due to the free-living NFMs preference for soil N, decreased soil pH and C/N ratio, and increased NH4+ concentration. The P, K, and O fertilizers promoted symbiotic BNF by directly or indirectly stimulating root nodule growth, whereas P, K, and O fertilizers increased free-living BNF by promoting the abundance of free-living NFMs and mitigating the decrease in soil pH and C/N ratio caused by N fertilization. These results indicate that inappropriate fertilization can lead to soil inactivation by suppressing NFMs. Optimizing fertilization strategies is critical to achieving high yields by exploiting BNFs and maintaining sustainable soil health.

Nitrogen fertilization and soil nitrogen cycling: Unraveling the links among multiple environmental factors, functional genes, and transformation rates

Anthropogenic nitrogen (N) inputs substantially influence the N cycle in agricultural ecosystems. However, the potential links among various environmental factors, nitrogen functional genes, and transformation rates under N fertilization remain poorly understood. Here, we conducted a five-year field experiment and collected 54 soil samples from three 0–4 m boreholes across different treatments: control, N-addition (nitrogen fertilizer) and NPK-addition (combined application of nitrogen, phosphorus and potassium fertilizers) treatments. Our results revealed pronounced variations in soil physiochemical parameters, metal concentrations and antibiotic levels under both N and NPK treatments. These alternations induced significant shifts in bacterial and fungal communities, altered NFG abundance and composition, and greatly enhanced rates of nitrate reduction processes. Notably, nutrients, antibiotics and bacteria exerted a more pronounced influence on NFGs and nitrate reduction under N treatment, whereas nutrients, metals, bacteria and fungi had a significant impact under NPK treatment. Furthermore, we established multidimensional correlations between nitrate reduction gene profiles and the activity rates under N and NPK treatments, contrasting with the absence of significant relationships in the control treatment. These findings shed light on the intricate relationships between microbial genetics and ecosystem functions in agricultural ecosystem, which is of significance for predicting and managing metabolic processes effectively.

Core Bacterial Taxa Determine Formation of Forage Yield in Fertilized Soil.

Understanding the roles of core bacterial taxa in forage production is crucial for developing sustainable fertilization practices that enhance the soil bacteria and forage yield. This study aims to investigate the impact of different fertilization regimes on soil bacterial community structure and function, with a particular focus on the role of core bacterial taxa in contributing to soil nutrient content and enhancing forage yield. Field experiments and high-throughput sequencing techniques were used to analyze the soil bacterial community structure and function under various fertilization regimes, including six treatments, control with no amendment (CK), double the standard rate of organic manure (T01), the standard rate of organic manure with nitrogen input equal to T04 (T02), half the standard rate of inorganic fertilizer plus half the standard rate of organic manure (T03), the standard rate of inorganic fertilizer reflecting local practice (T04), and double the standard rate of inorganic fertilizer (T05). The results demonstrated that organic manure treatments, particularly T01, significantly increased the forage yield and the diversity of core bacterial taxa. Core taxa from the Actinomycetota, Alphaproteobacteria, and Gammaproteobacteria classes were crucial in enhancing the soil nutrient content, directly correlating with forage yield. Fertilization significantly influenced functions relating to carbon and nitrogen cycling, with core taxa playing central roles. The diversity of core microbiota and soil nutrient levels were key determinants of forage yield variations across treatments. These findings underscore the critical role of core bacterial taxa in agroecosystem productivity and advocate for their consideration in fertilization strategies to optimize forage yield, supporting the shift towards sustainable agricultural practices.

Modelling analysis of nitrogen removal from paddy water with high infiltration rate

AbstractAn understanding of nitrogen processes in a paddy field, characterised by large water flux for irrigation and outflows under continuous irrigation, is required to manage adequate nitrogen inputs and outputs. This study identifies the effect of large water flux, especially high infiltration rate, on nitrogen processes in a paddy field under continuous irrigation. The developed nitrogen process model in this study was applied to two paddy fields having different infiltration rates (216 and 106 mm day− 1 on average), and simulated physicochemical and biological nitrogen processes in ponded water, soil water and soil, including whole water flows as well as organic, and inorganic nitrogen forms. In each field, irrigation was found to be the major nitrogen input (153.2–461.5 kg N ha− 1 year− 1), and nitrogen outflow (65.2–284.3 kg N ha− 1 year− 1) found to be smaller than the input from irrigation. The irrigation water was primarily contaminated by dissolved organic nitrogen (DON) and nitrate. Nitrogen transportation from ponded water to soil water was four times greater under high infiltration condition than under low infiltration condition. High nitrogen transport to the soil layer increased air emission via denitrification and decreased outflows. In particular, DON and ammonium transported to soil water are sources of nitrite and nitrate, and denitrification was five times higher under high infiltration than low infiltration. The results of this study imply that paddy fields with high infiltration rates have a greater possibility of nitrogen removal from paddy water, rather than being a pollutant source for the water environment.

A multi-spatial scale analysis of anthropogenic nitrogen and phosphorus inputs in a large river basin: environmental effect and policy impact

A multi-spatial scale analysis of anthropogenic nitrogen and phosphorus inputs in a large river basin: environmental effect and policy impact

Soil Health Intensification through Strengthening Soil Structure Improves Soil Carbon Sequestration

Intensifying soil health means managing soils to enable sustainable crop production and improved environmental impact. This paper discusses soil health intensification by reviewing studies on the relationship between soil structure, soil organic matter (SOM), and ecosystem carbon budget. SOM is strongly involved in the development of soil structure, nutrient and water supply power, and acid buffering power, and is the most fundamental parameter for testing soil health. At the same time, SOM can be both a source and a sink for atmospheric carbon. A comparison of the ratio of soil organic carbon to clay content (SOC/Clay) is used as an indicator of soil structure status for soil health, and it has shown significantly lower values in cropland than in grassland and forest soils. This clearly shows that depletion of SOM leads to degradation of soil structure status. On the other hand, improving soil structure can lead to increasing soil carbon sequestration. Promoting soil carbon sequestration means making the net ecosystem carbon balance (NECB) positive. Furthermore, to mitigate climate change, it is necessary to aim for carbon sequestration that can improve the net greenhouse gas balance (NGB) by serving as a sink for greenhouse gases (GHG). The results of a manure application test in four managed grasslands on Andosols in Japan showed that it was necessary to apply more than 2.5 tC ha−1 y−1 of manure to avoid reduction and loss of SOC in the field. Furthermore, in order to offset the increase in GHG emissions due to N2O emissions from increased manure nitrogen input, it was necessary to apply more than 3.5 tC ha−1y−1 of manure. To intensify soil health, it is increasingly important to consider soil management with organic fertilizers that reduce chemical fertilizers without reducing yields.

To Eat or Not to Eat: Novel Stable Isotope Models Reveal a Shift in Carnivory with Nutrient Availability for Aquatic Utricularia spp.

Freshwater nitrogen inputs are increasing globally, altering the structure and function of wetland ecosystems adapted to low nutrient conditions. Carnivorous wetland plants, Utricularia spp., are hypothesised to reduce their reliance on carnivory and increase their assimilation of environmental nutrients when the supply of ambient nutrients increases. Despite success in using stable isotope approaches to quantify carnivory of terrestrial carnivorous plants, quantifying carnivory of aquatic Utricularia requires improvement. We developed stable isotope mixing models to quantify aquatic plant carnivory and used these models to measure dietary changes of three Utricularia species: Utricularia australis, U. gibba, and U. uliginosa in 11 wetlands across a 794 km gradient in eastern Australia. Diet was assessed using multiple models that compared variations in the natural abundance nitrogen isotope composition (δ15N) of Utricularia spp. with that of non-carnivorous plants, and environmental and carnivorous nitrogen sources. Carnivory supplied 40 - 100 % of plant nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon. Our findings suggest that Utricularia populations may adapt to high nutrient environments by shifting away from energetically costly carnivory. This has implications for species conservation as anthropogenic impacts continue to affect global wetland ecosystems.

Dynamic responses of soil microbial communities to seasonal freeze-thaw cycles in a temperate agroecosystem

Soil freeze-thaw cycles (FTCs) are common in temperate agricultural ecosystems during the non-growing season and are progressively influenced by climate change. The impact of these cycles on soil microbial communities, crucial for ecosystem functioning, varies under different agricultural management practices. Here, we investigated the dynamic changes in soil microbial communities in a Mollisol during seasonal FTCs and examined the effects of stover mulching and nitrogen fertilization. We revealed distinct responses between bacterial and fungal communities. The dominant bacterial phyla reacted differently to FTCs: for example, Proteobacteria responded opportunistically, Actinobacteria, Acidobacteria, Choroflexi and Gemmatimonadetes responded sensitively, and Saccharibacteria exhibited a tolerance response. In contrast, the fungal community composition remained relatively stable during FTCs, except for a decline in Glomeromycota. Certain bacterial OTUs acted as sensitive indicators of FTCs, forming keystone modules in the network that are closely linked to soil carbon, nitrogen content and potential functions. Additionally, neither stover mulching nor nitrogen fertilization significantly influenced microbial richness, diversity and potential functions. However, over time, more indicator species specific to these agricultural practices began to emerge within the networks and gradually occupied the central positions. Furthermore, our findings suggest that farming practices, by introducing keystone microbes and changing interspecies interactions (even without changing microbial richness and diversity), can enhance microbial community stability against FTC disturbances. Specifically, higher nitrogen input with stover removal promotes fungal stability during soil freezing, while lower nitrogen levels increase bacterial stability during soil thawing. Considering the fungal tolerance to FTCs, we recommend reducing nitrogen input for manipulating bacterial interactions, thereby enhancing overall microbial resilience to seasonal FTCs. In summary, our research reveals that microbial responses to seasonal FTCs are reshaped through land management to support ecosystem functions under environmental stress amid climate change.

Sea Level Modulation of Atlantic Nitrogen Fixation Over Glacial Cycles

AbstractN2 fixation in low‐latitude surface waters dominates the input of fixed nitrogen (N) to the global ocean, sustaining ocean fertility. In the Caribbean Sea, higher foraminifera‐bound (FB‐)δ15N indicates a decline in N2 fixation during ice ages, but its cause and broader implications are unclear. Here, we report three additional Atlantic FB‐δ15N records, from the subtropical North and South Atlantic gyres (MSM58‐50 and DSDP Site 516) and the equatorial Atlantic (ODP Site 662). Similar glacial and interglacial δ15N in the equatorial Atlantic suggests a stable δ15N for the nitrate below the gyre thermoclines. The North Atlantic record shows a FB‐δ15N rise during the ice ages, resembling a previously published FB‐δ15N record from the South China Sea. The commonality among the FB‐δ15N records is that they resemble sea level‐driven variation in regional shelf area, with high FB‐δ15N (inferred reduction in N2 fixation) during periods of low shelf area. The South China Sea shows the largest δ15N signal, the subtropical North Atlantic shows less, and the South Atlantic shows the least, the same ordering as the ice age reductions in continental shelf area in the different regions. Reduced shelf sedimentary denitrification would have increased the nitrogen‐to‐phosphorus ratio of the nutrient supply to open ocean surface waters, leading to decreased N2 fixation and thus higher gyre thermocline nitrate δ15N, explaining the higher FB‐δ15N of peak ice ages. These observations identify shelf sediment denitrification as an important regional driver of modern N2 fixation and imply strong basin‐scale coupling of fixed nitrogen losses and inputs.

Enhanced nitrous oxide emission factors due to climate change increase the mitigation challenge in the agricultural sector.

Effective nitrogen fertilizer management is crucial for reducing nitrous oxide (N2O) emissions while ensuring food security within planetary boundaries. However, climate change might also interact with management practices to alter N2O emission and emission factors (EFs), adding further uncertainties to estimating mitigation potentials. Here, we developed a new hybrid modeling framework that integrates a machine learning model with an ensemble of eight process-based models to project EFs under different climate and nitrogen policy scenarios. Our findings reveal that EFs are dynamically modulated by environmental changes, including climate, soil properties, and nitrogen management practices. Under low-ambition nitrogen regulation policies, EF would increase from 1.18%-1.22% in 2010 to 1.27%-1.34% by 2050, representing a relative increase of 4.4%-11.4% and exceeding the IPCC tier-1 EF of 1%. This trend is particularly pronounced in tropical and subtropical regions with high nitrogen inputs, where EFs could increase by 0.14%-0.35% (relative increase of 11.9%-17%). In contrast, high-ambition policies have the potential to mitigate the increases in EF caused by climate change, possibly leading to slight decreases in EFs. Furthermore, our results demonstrate that global EFs are expected to continue rising due to warming and regional drying-wetting cycles, even in the absence of changes in nitrogen management practices. This asymmetrical influence of nitrogen fertilizers on EFs, driven by climate change, underscores the urgent need for immediate N2O emission reductions and further assessments of mitigation potentials. This hybrid modeling framework offers a computationally efficient approach to projecting future N2O emissions across various climate, soil, and nitrogen management scenarios, facilitating socio-economic assessments and policy-making efforts.

Biochar effects on crop yield variability

Context or ProblemNumerous studies have demonstrated that biochar application can increase crop yield by improving soil properties and health. Yet, these studies, however, neglected how biochar alters yield variability across years – reflecting the yield stability. Objective or Research questionThis study aimed to investigate the effects of biochar application on crop yield variability. MethodsPublished data from 38 experimental sites were collected from the Web-of-Science. Two-thirds of the data were originated from three main staple crops: maize, wheat, and rice. The remaining were from rapeseed, soybean, sweet potato, and peppermint. Biochar effects on crop yield and its variability as well as their driving factors were analyzed by linear mixed models depending on soil conditions, field management practices, and climate types. ResultsBiochar increased the crop yield globally by 14 %, especially in soils with low pH (< 5.5), low nitrogen (N) and phosphorus (P) inputs (≤ 120 kg N ha−1, < 35 kg P ha−1), with high biochar inputs (≥ 20 Mg ha−1), and under crop rotation. Biochar increased crop yields by 12 % in short-term (≤ 5 years) and 21 % in long-term (> 5 years) experiments. Biochar increased yield variability by 42 % in acidic soils (pH < 5.5) and by 24 % with low N inputs (≤ 120 kg N ha−1), mainly because its liming and fertilization effects were short-lasting within the first few years. The yield variability after biochar application decreased with the increase in mean annual temperature, inter-annual variabilities of temperature and precipitation, but with the decrease in mean annual precipitation in the growing season. Yield variability under biochar increased in short-term experiments by 27 %, but there was no change (0 %) in long-term experiments because of the higher yield gains and resistance to fluctuating weather conditions. Therefore, crop yield variability decreased with increasing yield in long-term experiments. ConclusionsBiochar application increased short-term variability of crop yields, but its long-term variability remained unaffected. Implications or SignificanceThis study highlights that biochar can support steadily future crop production in the long run.

Nutrient regime and balance of nutrients in soil under forage crops under application of different types of fertilizers (on the example of Kyzylorda region)

Modern agriculture is facing a number of challenges, among which the efficient use of fertilisers to provide plants with the necessary nutrients is of particular importance. In particular, the growing focus on sustainable agriculture and the need to preserve soil resources underline the relevance of research into optimising fertiliser use. The purpose of the study was to identify effective methods of fertiliser use to provide plants with nutrients. To achieve this goal, the effectiveness of green manure, organic (manure) and mineral fertilisers under Sorghum and perennial grasses (Medicago sativa, Elytrigia, Agropyron) on saline soil was investigated. The study founded that organic fertilisers, such as manure and green manure, contribute to a more even supply of nutrients to plants compared to mineral fertilisers. This is particularly important in the context of nitrogen and phosphorus balance, where Medicago sativa has a positive nitrogen balance due to its ability to symbiotically fix nitrogen. Other crops studied, such as Elytrigia, Agropyron and Sorghum, showed a negative nitrogen balance on the control variant, but the application of N100P50K110 mineral fertiliser resulted in a positive nitrogen balance. The replacement of mineral fertilisers with organic fertilisers such as manure and green manure increased nitrogen inputs but also increased nitrogen removal from the soil due to the increase in phytomass yields. The results of the study confirmed the importance of transitioning to a more sustainable and environmentally friendly way of production in agriculture, which will ensure the development of the industry and increase its competitiveness in the international market. The practical significance of the study is to provide farmers with the opportunity to increase the yield of their crops and at the same time preserve soil fertility through the optimal use of nutrients contained in fertilisers

Assessment of moss-associated biological nitrogen fixation of dominant moss species in mature black spruce forests in Eastern Canada

Biological nitrogen fixation (BNF) by bryophytes is an essential source of new nitrogen in nitrogen-limited boreal ecosystems. This assessment is, however, primarily based on reports from northern Europe and, to a lesser extent, Western North America. A more systematic and extensive evaluation of nitrogen fixation by moss is required to close current gaps in records of moss BNF and better assess the importance of bryophytes on N input in boreal ecosystems. Here, we evaluated nitrogen fixation activity and contribution to N input of dominant bryophyte species in black spruce forests from Eastern Canada. We assessed the relative abundance, BNF activity, and relative contribution to nitrogen input on five sites along a 600 km transect. We report that several moss species contribute to nitrogen input but that Ptilium crista-castrensis is the main contributor. Estimated nitrogen input by mosses (≪ 1 kg·ha−1·year−1) is in the low range of N inputs reported in the literature and is consistent with activities reported elsewhere for similar species, N deposition, and forest age. Results show that atmospheric deposition, while low, remains a more significant source of exogenous N to mature black spruce forests than bryophytes.

Reducing Application of Nitrogen Fertilizer Increases Soil Bacterial Diversity and Drives Co-Occurrence Networks.

Reducing nitrogen fertilizer application highlights its role in optimizing soil bacterial communities to achieve sustainable agriculture. However, the specific mechanisms of bacterial community change under these conditions are not yet clear. In this study, we employed long-term field experiments and high-throughput sequencing to analyze how varying levels of nitrogen application influence the soil bacterial community structure and co-occurrence networks. The results show that reducing the nitrogen inputs significantly enhances the diversity and evenness of the soil bacterial communities, possibly due to the diminished dominance of nitrogen-sensitive taxa, which in turn liberates the ecological niches for less competitive species. Furthermore, changes in the complexity and stability of the bacterial co-occurrence networks suggest increased community resilience and a shift toward more mutualistic interactions. These findings underline the potential of reduced nitrogen application to alleviate competitive pressures among bacterial species, thereby promoting a more diverse and stable microbial ecosystem, highlighting the role of competitive release in fostering microbial diversity. This research contributes to our understanding of how nitrogen management can influence soil health and offers insights into sustainable agricultural practices.

Long-term effects of nitrogen and phosphorus fertilization on profile distribution and characteristics of dissolved organic matter in fluvo-aquic soil

Dissolved organic matter (DOM) drives numerous biogeochemical processes (e.g. carbon cycling) in agro-ecosystems and is sensitive to fertilization management. Nevertheless, changes in the quantity and quality of DOM in the vertical soil profile following long-term continuous nitrogen (N) and phosphorus (P) inputs remain unclear. In this study, the contents and optical characteristics of DOM along a 2-m soil profile were investigated using a 40-year wheat/maize rotation combined with experiments using different N and P fertilization rates in the North China Plain. The results revealed that the dissolved organic carbon (DOC) content decreased with an increase in soil depths. Compared with that in the control (no fertilization), 40-year N, P, and N + P additions increased the soil DOC content by 26%–69%, except for 270-kg N, and 67.5-kg P treatments. N + P application resulted in higher DOC contents than N-alone and P-alone applications. N, P, and N + P inputs increased or did not affect the aromaticity and hydrophobicity of DOM at 0–40 cm but reduced them from 40 to 200 cm. Compared with that in the control, N, P, and N + P inputs enhanced the content of humic acid-like substances (C1+C2+C3+C4) and decreased the content of protein-like substance (C5). C1 was the dominant component among the five DOM, representing the microbial humic component. Optical indices also indicated that soil DOM primarily originated from microbial sources. Nutrient addition accelerated transformation between complex C1 and simple C5 via promoting microbial activities. These results imply that N and P fertilizers increased the DOM content and altered its composition, thereby potentially affecting the stability of soil organic matter in the agroe-cosystems.

Improving the value of planting and breeding waste compost in agricultural applications: A zucchini cultivation case and circular agricultural models analysis

An important way of utilizing agricultural wastes to improve soil quality is the use of planting and breeding waste compost (PBWC). However, the impact of compost on agricultural production systems is unclear. Therefore, in order to study the effect of PBWC on crop growth, soil environment, and circular agriculture, PBWC [sheep manure (SM): tail vegetable (TV): corn straw (CS) = 6: 3: 1] was used based on chemical fertilizer reduction for zucchini production. In zucchini production systems, R9 (chemical fertilizer reduction by 30 % + 9,000 kg ha−1 PBWC) treatment was most effective in improving the quality and yield of zucchini fruits, mainly by improving the soil microenvironment, manifested in (1) increasing soil alkali-hydrolyzable nitrogen (AN) available potassium(AK), and soil organic matter (SOM), reducing EC, and improving C/N. (2) Increasing the richness and metabolic capacity of bacterial community. (3) Increasing the abundance of Proteobacteria, a phylum with absolute dominance (up to 32.46 %). Then, an optimization model of “summer corn − greenhouse zucchini − fattened sheep” was constructed to analyze the effect of changes in fertilizer dosage usage on the whole model. Compared with the local traditional recycling model, the optimized system reduced the ratio of inorganic to organic nitrogen input from 2.8:1 to 1.4:1, increased the recycling rate of nitrogen (N), phosphorus (P), and potassium (K) by 31.28 %, 50.84 %, and 30.25 %, respectively, and the net energy yield ratio (EYR) increased by 1.04. The optimized recycling system had significant economic and environmental benefits, which would become the basis for moving towards more sustainable farming. Overall, the circular agriculture model with PBWC returning as the core achieves sustainable production by improving material recycling and soil microenvironment. Therefore, chemical fertilizer reduction by 30 % combined with 9000 kg ha−1 PBWC can be used in practical production to improve the productivity of the circular agriculture model and achieve high yield and high quality crops.

Crop Diversification and Fertilization Strategies in a Rainfed System with Drought Periods

Crop diversification and the reduction of nitrogen (N) inputs are key issues in the EU for more sustainable agriculture. An experiment was set up in a semiarid rainfed Mediterranean system. Our hypothesis was that these challenges could be addressed by introducing new crops and using pig slurries (PSs). The experimental factors were N fertilization at sowing (with or without PS) combined (according to a split-block design) with N fertilization as topdressing (the control, two N mineral rates, and two N rates from PS). Barley, rapeseed, and pea performances were evaluated in two different crop sequences: (i) barley–rapeseed or rapeseed–barley after a fallow season, and (ii) barley–pea or pea–barley after a fallow season followed by a non-fertilized barley crop. The results of the four-year study demonstrated that under a spring drought risk, barley performed better than peas in terms of relative crop yield maintenance. After fallow, N can be saved while maintaining the yields and total biomass of barley and rapeseed. In the second crop sequence, maximum pea and barley yields were associated with a minimum topdressing of 60 or 120 kg mineral N ha−1, respectively. However, slurry fertilization at sowing also allowed the highest yields for barley. Rapeseed and peas can be introduced to reduce N fertilization inputs. However, the obtained yield plateau for pea and rapeseed (3 and 4 Mg ha−1, respectively) and the effect of a yield spring drought on pea yields (50% reduction) might be a constraint for the success of EU policies on crop diversification.

Nine-year fertilization promoted C sink and mediated microbial nutrient utilization in alpine meadow soil aggregates

Increased nitrogen (N) and phosphorus (P) inputs to terrestrial ecosystems, which are caused by human activities and atmospheric deposition, significantly affect soil nutrient cycling. However, information on the variations of fertilization treatments on the nutrient utilization and carbon (C) storage mechanisms in alpine meadow soil aggregates is limited. Here, we investigated the responses of microbial nutrient utilization and C storage dynamics in soil aggregates to nine-year fertilization (N, P, and NP addition) in an alpine meadow. The results demonstrated that nine-year fertilization did not affect soil aggregate stability, however, they promoted soil organic C (SOC), total N (TN), and total P (TP) accumulation and altered the microbial nutrient-limitation patterns of soil aggregates in the alpine meadow. Compared to N and NP treatments, the P addition was optimal for improving soil aggregate-associated C storage and soil C pool management index (CMI). Furthermore, the NP treatment significantly exacerbated the microbial C limitation and microbial P limitation was significantly greater with N addition alone than with P addition alone, which was consistent with the resource allocation theory. The enhanced microbial carbon limitation caused by fertilization had no significant impact on soil aggregate-associated C storage and CMI. Simultaneously, soil nutrients and enzyme activities increased with decreasing soil aggregate size. However, these changes did not affect the microbial nutrient limitation patterns and CMI, which may have been related to the stronger nutrient protection ability of microaggregates. Therefore, nine years of fertilization increased the soil aggregate-associated C sink functions and affected soil microbial nutrient-limitation patterns by altering the soil C, N and P stoichiometry in the alpine meadow. These findings provide technical support for future alpine meadow management.

Novel lanthanum and waste lye modified fly ash zeolite for nitrogen and phosphorus removal: mechanisms and application in the constructed wetland

Excess inputs of nitrogen (N) and phosphorus (P) can lead to imbalance in water ecosystems and thus trigger eutrophication. In this study, a novel Lanthanum and waste lye modified zeolite synthesized from fly ash (LZFA) was prepared and used as a modified substrate for constructed wetland (CW) to enhance N and P removal. Single-factor and response surface methodology (RSM) were used to optimize the preparation process. The results showed that the maximum adsorption capacities of N and P were 17.26 mg/g and 21.48 mg/g, respectively. Compared to solely zeolite synthesized from fly ash (ZFA), the decreased N sorption capacity in LZFA was attributed to a reduction in the surface negative charge and cation exchange capacity. The mechanism of P adsorption was attributed to the formation of La-O-P monodentate, bidentate mononuclear or bidentate binuclear inner-sphere complexation. Meanwhile, the introduction of Ca from waste lye was also involved in the P reaction. The N and P removal rates of LZFA modified subsurface flow constructed wetland (SFCW) were 2.67 % and 7.33 % higher than SFCW modified with gravel. In practical production, if a circular chain from coal ash production to use for green plant fertilizer can be established, the cost of treating P can be significantly reduced.