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Nitrogen (N) and carbon (C) inputs substantially affect soil microbial functions. However, the influences of long-term N and C additions on soil microbial resource limitation and heterotrophic respiration-fundamental microbial functional traits-remain unclear, impeding the understanding of how soil C dynamics respond to global change. In this study, the responses of soil microbial resource limitation and heterotrophic respiration (Rh) to 7-year N and biochar (BC) additions in a subtropical Moso bamboo (Phyllostachys edulis) plantation were investigated. We used eight treatments: Control, no N and BC addition; N30, 30 kg N (ammonium nitrate)·hm -2 ·a -1 ; N60, 60 kg N·hm -2 ·a -1 ; N90, 90 kg N·hm -2 ·a -1 ; BC20, 20 t BC (originating from Moso bamboo chips) hm -2 ; N30 + BC20, 30 kg N·hm -2 ·a -1  + 20 t BC hm -2 ; N60 + BC20, 60 kg N·hm -2 ·a -1  + 20 t BC hm -2 ; and N90 + BC20, 90 kg N·hm -2 ·a -1  + 20 t BC hm -2 . Soil microbes were co-limited by N and phosphorus (P) and not limited by C in the control treatments. Long-term N addition enhanced soil microbial N and P limitation but significantly reduced soil Rh by 15.1 %-20.0 % relative to that in the control treatments. BC amendment alleviated soil microbial N and P limitation and significantly decreased C use efficiency by 10.9 %-42.1 % but increased Rh by 33.6 %-91.6 % in the long-term N-free and N-supplemented treatments (P < 0.05). Soil C- and N-acquisition enzyme activities were the dominant drivers of soil microbial resource limitation. Furthermore, microbial resource limitation was a more reliable predictor of Rh than soil resources or microbial biomass. The results suggested that long-term N and BC additions affect Rh by regulating microbial resource limitation, highlighting its significance in understanding soil C cycling under environmental change., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Forests harbor extensive biodiversity and act as a strong global carbon and nitrogen sink. Although enhancing tree diversity has been shown to mitigate climate change by sequestering more carbon and nitrogen in biomass and soils in manipulative experiments, it is still unknown how varying environmental gradients, such as gradients in resource availability, mediate the effects of tree diversity on carbon and nitrogen accrual in natural forests. Here, we use Canada's National Forest Inventory data to explore how the relationships between tree diversity and the accumulation of carbon and nitrogen in tree biomass and soils vary with resource availability and environmental stressors in natural forests. We find that the positive relationship between tree functional diversity (rather than species richness) and the accumulation of carbon in tree biomass strengthens with increasing light and soil nutrient availability. Moreover, the positive relationship between tree functional diversity and the accumulation of carbon and nitrogen in both organic and mineral soil horizons is more pronounced at sites with greater water and nutrient availabilities. Our results highlight that conserving and promoting functionally diverse forests in resource-rich environments could play a greater role than in resource-poor environments in enhancing carbon and nitrogen sequestration in Canada's forests., (© 2024. The Author(s).)

Atmospheric nitrogen (N) deposition inevitably alters soil nutrient status, subsequently prompting plants to modify their root morphology (i.e., adopting a do-it-yourself strategy), mycorrhizal symbioses (i.e., outsourcing strategy), and root exudation (i.e., nutrient-mining strategy) linking with resource acquisition. However, how N deposition influences the integrated pattern of these resource-acquisition strategies remains unclear. Furthermore, most studies in forest ecosystems have focused on understory N and inorganic N deposition, neglecting canopy-associated processes (e.g., N interception and assimilation) and the impacts of organic N on root functional traits. In this study, we compared the effects of canopy vs understory, organic vs inorganic N deposition on eight root functional traits of Moso bamboo plants. Our results showed that N deposition significantly decreased arbuscular mycorrhizal fungi (AMF) colonization, altered root exudation rate and root foraging traits (branching intensity, specific root area, and length), but did not influence root tissue density and N concentration. Moreover, the impacts of N deposition on root functional traits varied significantly with deposition approach (canopy vs. understory), form (organic vs. inorganic), and their interaction, showing variations in both intensity and direction (positive/negative). Furthermore, specific root area and length were positively correlated with AMF colonization under canopy N deposition and root exudation rate in understory N deposition. Root trait variation under understory N deposition, but not under canopy N deposition, was classified into the collaboration gradient and the conservation gradient. These findings imply that coordination of nutrient-acquisition strategies dependent on N deposition approach. Overall, this study provides a holistic understanding of the impacts of N deposition on root resource-acquisition strategies. Our results indicate that the evaluation of N deposition on fine roots in forest ecosystems might be biased if N is added understory., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Increasing soil carbon and nitrogen storage can help mitigate climate change and sustain soil fertility 1,2 . A large number of biodiversity-manipulation experiments collectively suggest that high plant diversity increases soil carbon and nitrogen stocks 3,4 . It remains debated, however, whether such conclusions hold in natural ecosystems 5-12 . Here we analyse Canada's National Forest Inventory (NFI) database with the help of structural equation modelling (SEM) to explore the relationship between tree diversity and soil carbon and nitrogen accumulation in natural forests. We find that greater tree diversity is associated with higher soil carbon and nitrogen accumulation, validating inferences from biodiversity-manipulation experiments. Specifically, on a decadal scale, increasing species evenness from its minimum to maximum value increases soil carbon and nitrogen in the organic horizon by 30% and 42%, whereas increasing functional diversity enhances soil carbon and nitrogen in the mineral horizon by 32% and 50%, respectively. Our results highlight that conserving and promoting functionally diverse forests could promote soil carbon and nitrogen storage, enhancing both carbon sink capacity and soil nitrogen fertility., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Soil microbes make up a significant portion of the genetic diversity and play a critical role in belowground carbon (C) cycling in terrestrial ecosystems. Soil microbial diversity and organic C are often tightly coupled in C cycling processes; however, this coupling can be weakened or broken by rapid global change. A global meta-analysis was performed with 1148 paired comparisons extracted from 229 articles published between January 1998 and December 2021 to determine how nitrogen (N) fertilization affects the relationship between soil C content and microbial diversity in terrestrial ecosystems. We found that N fertilization decreased soil bacterial (-11%) and fungal diversity (-17%), but increased soil organic C (SOC) (+19%), microbial biomass C (MBC) (+17%), and dissolved organic C (DOC) (+25%) across different ecosystems. Organic N (urea) fertilization had a greater effect on SOC, MBC, DOC, and bacterial and fungal diversity than inorganic N fertilization. Most importantly, soil microbial diversity decreased with increasing SOC, MBC, and DOC, and the absolute values of the correlation coefficients decreased with increasing N fertilization rate and duration, suggesting that N fertilization weakened the linkage between soil C and microbial diversity. The weakened linkage might negatively impact essential ecosystem services under high rates of N fertilization; this understanding is important for mitigating the negative impact of global N enrichment on soil C cycling., (© 2022 John Wiley & Sons Ltd.)

Nitrous oxide and ammonia emissions from farmland need to be abated as they directly or indirectly affect climate warming and crop yield. We conducted a two-year field experiment to investigate the effect of biochar applied at two rates (no biochar application vs. biochar applied at 10 t ha -1 ) on gaseous nitrogen (N) losses (N 2 O emissions and NH 3 volatilization), plant N uptake, residual soil mineral N, and peanut (Arachis hypogaea L.) yield under three irrigation regimes: furrow irrigation (FI), drip irrigation (DI), and mulched drip irrigation (MDI). We found that MDI reduced residual (post-harvest) soil mineral N, cumulative N 2 O emissions, and yield-scaled N 2 O emissions as compared to FI. Biochar application increased residual soil NO 3 - -N and decreased yield-scaled N 2 O emissions as compared with the control without biochar application. Under the three irrigation regimes, biochar application decreased cumulative NH 3 volatilization and increased plant N uptake and yield compared with the control. Biochar application improved the sustainability of peanut production and could be used to alleviate the environmental damage associated with gaseous N emissions. Where possible, biochar application under MDI in peanut fields is recommended as a management strategy to minimize gaseous N losses., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

Soil gross nitrogen (N) mineralization (GNM), a key microbial process in the global N cycle, is mainly controlled by climate and soil properties. This study provides for the first time a comprehensive analysis of the role of soil physicochemical properties and climate and their interactions with soil microbial biomass (MB) in controlling GNM globally. Through a meta-analysis of 970 observations from 337 published papers from various ecosystems, we found that GNM was positively correlated with MB, total carbon, total N and precipitation, and negatively correlated with bulk density (BD) and soil pH. Our multivariate analysis and structural equation modeling revealed that GNM is driven by MB and dominantly influenced by BD and precipitation. The higher total N accelerates GNM via increasing MB. The decrease in BD stimulates GNM via increasing total N and MB, whereas higher precipitation stimulates GNM via increasing total N. Moreover, the GNM varies with ecosystem type, being greater in forests and grasslands with high total carbon and MB contents and low BD and pH compared to croplands. The highest GNM was observed in tropical wet soils that receive high precipitation, which increases the supply of soil substrate (total N) to microbes. Our findings suggest that anthropogenic activities that affect soil microbial population size, BD, soil substrate availability, or soil pH may interact with changes in precipitation regime and land use to influence GNM, which may ultimately affect ecosystem productivity and N loss to the environment., (© 2021 John Wiley & Sons Ltd.)

Both soil microbial nitrate (NO 3 - -N immobilization while stimulate denitrification nitrogen (N) loss remains unclear. Here, 3 - -N immobilization while stimulate denitrification nitrogen (N) loss remains unclear. Here, 15 N tracing coupled with acetylene inhibition methods were used to assess the effect of adding glucose, wheat straw and peanut straw on NO 3 - -N immobilization and denitrification under aerobic conditions in an upland soil, in which NO 3 - -N immobilization has been previously demonstrated to be negligible. The organic C sources (5 g C kg -1 soil) were added in a factorial experiment with 100, 500, and 1000 mg N kg -1 soil (as K 15 NO 3 ) in a 12-d laboratory incubation. Microbial NO 3 - -N immobilization in the 12-d incubation in the three N treatments was 5.5, 7.7, and 8.2 mg N kg -1 d -1 , respectively, in the glucose-amended soil, 5.9, 4.2, and 2.4 mg N kg -1 d -1 , respectively, in the wheat straw-amended soil, and 4.9, 5.1 and 4.4 mg N kg -1 d -1 , respectively, in the peanut straw-amended soil. Therefore, under sufficient NO 3 - -N substrate, the higher microbial NO 3 - -N immobilization in the glucose than in the crop residue treatments was likely due to the slow decomposition of the latter that provided low available C. The 15 N recovery in the N 2 O + N 2 pool over the12-day incubation was <2% for all treatments, indicating negligible denitrification N loss due to low denitrification rates in the aerobic incubation in spite of increasing C availability. We conclude that external C addition can enhance microbial NO 3 - -N immobilization without causing large N losses through denitrification. This has significant implications for reducing soil NO 3 - -N accumulation by enhancing microbial NO 3 - -N immobilization through increasing C inputs using organic materials and subsequently mitigating nitrate pollution of water bodies., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Plant invasion can markedly alter soil fungal communities and nitrogen (N) availability; however, the linkage between the fungal decomposition capacity and N mineralization during plant invasion remains largely unknown. Here, we examined the relationship between net mineralization rates and relevant functional genes, as well as fungal species composition and function following Moso bamboo (Phyllostachys edulis) invasion of evergreen broadleaf forests, by studying broadleaf forests (non-invaded), mixed bamboo-broadleaf forests (moderately invaded) and bamboo forests (heavily invaded). Fungal species composition and functional genes involved in organic matter decomposition (laccase and cellobiohydrolase), N mineralization (alkaline peptidases) and nitrification (ammonia monooxygenase) were determined via high-throughput sequencing and real-time PCR. Both net ammonification and nitrification rates were generally increased with bamboo invasion into the broadleaf forest, where the net ammonification rate, on average, was 10.8 times higher than the nitrification rate across the three forest types. The fungal species composition and ecological guilds were altered with bamboo invasion, as demonstrated by the increased proportion of saprotrophs but decreased proportion of symbiotrophs in the bamboo forest. The increased net ammonification rate in bamboo forest was positively correlated with both fungal species composition and functional groups, and the fungal lcc gene (for lignin breakdown) abundance explained 67% of the variation of the net ammonification rate. In addition, the gene abundance of ammonia-oxidizing bacteria (AOB) explained 62% of the variation of net nitrification rate across the three forest types. The increased soil ammonification and nitrification rates following bamboo invasion of broadleaf forests suggest that the bamboo-invasion associated increase in soil N supply provided a positive feedback that facilitated bamboo invasion into broadleaf forests., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

Desert steppe, a unique ecotone between steppe and desert in Eurasia, is considered highly vulnerable to global change. However, the long-term impact of warming and nitrogen deposition on plant biomass production and ecosystem carbon exchange in a desert steppe remains unknown. A 12-year field experiment was conducted in a Stipa breviflora desert steppe in northern China. A split-design was used, with warming simulated by infrared radiators as the primary factor and N addition as the secondary factor. Our long-term experiment shows that warming did not change net ecosystem exchange (NEE) or total aboveground biomass (TAB) due to contrasting effects on C 4 (23.4% increase) and C 3 (11.4% decrease) plant biomass. However, nitrogen addition increased TAB by 9.3% and NEE by 26.0% by increasing soil available N content. Thus, the studied desert steppe did not switch from a carbon sink to a carbon source in response to global change and positively responded to nitrogen deposition. Our study indicates that the desert steppe may be resilient to long-term warming by regulating plant species with contrasting photosynthetic types and that nitrogen deposition could increase plant growth and carbon sequestration, providing negative feedback on climate change.

The effect of long-term nitrogen (N) and sulfur (S) deposition on litter mass loss and changes in carbon (C), N, and S composition and enzyme activities during litter decomposition was investigated in a boreal forest. This study included four N × S treatments: control (CK), N application (30 kg N ha -1 yr -1 ), S application (30 kg S ha -1 yr -1 ), and N plus S application (both at 30 kg ha -1 yr -1 ). Two experiments were conducted for 22 months: 1) a common litter decomposition experiment with litter bags containing a common litter (same litter chemistry) and 2) an in-situ litter decomposition experiment with litter from each treatment plot (and thus having different litter chemistry). Litterbags were placed onto the four treatment plots to investigate the direct effect of N and S addition and the combined effect of N and/or S addition and litter chemistry on litter decomposition, respectively. Regardless of the source of litter, N and/or S addition affected C, N and S composition at a certain period of the experiment but did not affect litter mass loss and enzyme activity throughout the experiment, indicating that the N and S addition rates were below the critical level required to affect C and N cycling in the studied ecosystem. However, the greater change in N composition per unit of litter mass loss in the N addition treatment than in the other treatments in the common litter but not in the in-situ litter experiment, suggests that the effect of N addition on N loss and retention depends on the initial litter chemistry. We conclude that the studied N and S addition rates did not affect litter decomposition and elemental cycling in the studied forest ecosystem even though the N and S addition rates were much greater than their ambient deposition rates., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Nitrogen (N) deposition has rapidly increased and is influencing forest ecosystem processes and functions on a global scale. Understanding process-specific N transformations, i.e., gross N transformations, in forest soils in response to N deposition is of great significance to gain mechanistic insights on the linkages between global N deposition and N availability or loss in forest soils. In this paper, we review factors controlling N mineralization, nitrification and N immobilization, particularly in relation to N deposition, discuss the limitations of net N transformation studies, and synthesize the literature on the effect of N deposition on gross N transformations in forest ecosystems. We found that more than 97% of published papers evaluating the effect of N deposition (including N addition experiments that simulate N deposition) on soil N cycle determined net rates of mineralization and nitrification, showing that N deposition significantly increased those rates by 24.9 and 153.9%, respectively. However, studies on net N transformation do not provide a mechanistic understanding of the effect of N deposition on N cycling. To date, a small number of studies (<20 published papers) have directly quantified the effect of N deposition on gross N transformation rates, limiting our understanding of the response of soil N cycling to N deposition. The responses to N deposition of specific N transformation processes such as autotrophic nitrification, heterotrophic nitrification, dissimilatory nitrate reduction to ammonium, N mineralization, and N immobilization are poorly studied. Future research needs to use more holistic approaches to study the impact of N deposition on gross N transformation rates, N loss and retention, and their microbial-driven mechanisms to provide a better understanding of the processes involved in N transformations, and to understand the differential responses between forest and other ecosystems., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The nitrogen (N) footprint is a novel approach to quantify losses to the environment of reactive N (Nr; all species of N except N2) derived from human activities. However, current N footprint models are difficult to apply to new countries due to the large data requirement, and sources of Nr included in calculating the N footprint are often incomplete. In this study, we comprehensively quantified the N footprint in China with an N mass balance approach. Results show that the per capita N footprint in China increased 68% between 1980 and 2008, from 19 to 32 kg N yr(-1). The Nr loss from the production and consumption of food was the largest component of the N footprint (70%) while energy and nonfood products made up the remainder in approximately equal portion in 2008. In contrast, in 1980, the food-related N footprint accounted for 86% of the overall N footprint, followed by nonfood products (8%) and energy (6%). The findings and methods of this study are generally comparable to that of the consumer-based analysis of the N-Calculator. This work provides policy makers quantitative information about the sources of China's N footprint and demonstrates the significant challenges in reducing Nr loss to the environment.

Hydrocarbon-contaminated wastes generated from oil and gas drilling activities may be used as a soil amendment once composted and further decomposition of residual hydrocarbons can be accomplished after the composts are applied to soils. To test if N fertilization may enhance hydrocarbon decomposition, we investigated the effects of N application on hydrocarbon degradation in different-aged composts (1-, 2-, 3-, and 4-year-old composts, coded as 1Y, 2Y, 3Y, and 4Y composts, respectively) through a pot experiment planted with white spruce (Picea glauca [Moench] Voss) seedlings. The percentage degradation of total petroleum hydrocarbon (TPH, C11 to C40) in the composts without N fertilization was correlated to initial NH4+ concentrations (R = 0.99, P < 0.001). The percentage degradation of TPH was highest in the 3Y compost (41.1%) that had an initial level of 325.3 mg NH4+ -N kg(-1) and the lowest in the IY compost (9.3%) that had an initial level of 8.3 mg NH4+ -N kg(-1). The degradation of TPH was enhanced by Nfertilization in the 1Y (from 9.3 to 15.3%) and 4Y composts (from 14.3 to 22.6%) that had low initial NH4+ concentrations. Our results show that application of NH4+ -based fertilizers may enhance the degradation of TPH when initial NH4+ concentrations in the compost are low.

Temporal changes in delta(15)N of cattle feedlot manure during its composting with either rice hull (RHM) or sawdust (SDM) as bedding materials were investigated. Regardless of the bedding material used, the delta(15)N of total N in the manure increased sharply from +7.6 per thousand to +9.9 per thousand and from +11.4 per thousand to +14.3 per thousand, respectively, in RHM or SDM, within 10 days from the commencement of composting. Such increases could be attributed primarily to N loss via NH(3) volatilization and denitrification based on the very high delta(15)N values (greater than +20 per thousand) of NH(4)(+) and NO(3)(-) in the co-composted manure. The delta(15)N of total N in RHM was substantially lower (by more than 3 per thousand) than that in SDM, suggesting that the delta(15)N of the composted manure was affected not only by N loss but also by the type of bedding material used. Specifically, the higher N concentration in the rice hull than in the saw dust could lead to a greater (15)N isotope dilution.

The lowering of the water table resulting from peatland drainage may dramatically alter C and N cycling in peatland ecosystems, which contain one-third of the total terrestrial C. In this study, tree annual ring width and C (delta(13)C) and N (delta(15)N) isotope ratios in soil and plant tissues (tree foliage, growth rings, and understory foliage) in a black spruce-tamarack (Picea mariana-Larix laricina) mixed-wood forest were examined to study the effects of drainage on tree growth and C and N dynamics in a minerotrophic peatland in west-central Alberta, Canada. Drainage increased the delta(15)N of soil NH4+ from a range of +0.6% per hundred to +2.9% per hundred to a range of +4.6% per hundred to +7.0% per hundred most likely through increased nitrification following enhanced mineralization. Plant uptake of 15N-enriched NH4+ in the drained treatment resulted in higher plant delta15N (+0.8% per hundred to +1.8% per hundred in the drained plots and -3.9% per hundred to -5.4% per hundred in the undrained plots), and deposition of litterfall N enriched with 15N increased the delta15N of total soil N in the surface layer in the drained (+2.9% per hundred) as compared with that in the undrained plots (+0.6% per hundred). The effect of drainage on foliar delta(13)C was species-specific, i.e., only tamarack showed a considerably less negative foliar delta(13)C in the drained (-28.1% per hundred) than in the undrained plots (-29.1% per hundred), indicating improved water use efficiency (WUE) by drainage. Tree ring area increments were significantly increased following drainage, and delta(13)C and delta(15)N in tree growth rings of both species showed responses to drainage retrospectively. Tree-ring delta(13)C data suggested that drainage improved WUE of both species, with a greater and more prolonged response in tamarack than in black spruce. Our results indicate that drainage caused the studied minerotrophic peatland to become a more open ecosystem in terms of C and N cycling and loss. The effects of forested peatland drainage or drying on C and N balances deserve further research in order to better understand their roles in future global change.

There are growing interests to use co-composted drilling wastes contaminated with hydrocarbons as growth media for planting in land reclamation. However, such use of the compost may have potential problems such as inherent toxicity of residual hydrocarbon and microbial N immobilization due to high compost C to N ratios. We investigated the growth, biomass production, N uptake, and foliar delta13C of white spruce (Picea glauca [Moench] Voss) seedlings in a pot experiment using 1-, 2-, 3-, and 4-yr-old composts (with different hydrocarbon concentrations and C to N ratios) and a local noncontaminated soil with (200 kg N ha(-1)) or without N fertilization. Growth and N content of seedlings (particularly N content in roots) were lower when grown in the compost media as compared with those grown in the soil. Within the compost treatments seedling growth was affected by compost age, but the magnitude of growth reduction was not linearly proportional to hydrocarbon concentrations. Plant N uptake increased with compost age, which corresponds with an increase in indigenous mineral N concentration. Effects of N fertilization on N uptake were curtailed by the presence of indigenous mineral N (e.g., in the 4-yr-old compost) and by fertilization-induced stimulation of microbial activities (e.g., in the 1-yr-old compost). The differences in foliar delta13C values between seedlings grown in compost and soil (P < 0.05) suggest that limitations on water uptake caused by the residual hydrocarbon might have been the predominant factor limiting seedling growth in the compost media. This study suggests that water stress caused by residual hydrocarbons may be a critical factor for the successful use of co-composted drilling wastes as a growth medium.

We assessed the response of soil microbial nitrogen (N) cycling and associated functional genes to elevated temperature at the global scale. A meta-analysis of 1,270 observations from 134 publications indicated that elevated temperature decreased soil microbial biomass N and increased N mineralization rates, both in the presence and absence of plants. These findings infer that elevated temperature drives microbially mediated N cycling processes from dominance by anabolic to catabolic reaction processes. Elevated temperature increased soil nitrification and denitrification rates, leading to an increase in N2 O emissions of up to 227%, whether plants were present or not. Rates of N mineralization, denitrification and N2 O emission demonstrated significant positive relationships with rates of CO2 emissions under elevated temperatures, suggesting that microbial N cycling processes were associated with enhanced microbial carbon (C) metabolism due to soil warming. The response in the abundance of relevant genes to elevated temperature was not always consistent with changes in N cycling processes. While elevated temperature increased the abundances of the nirS gene with plants and nosZ genes without plants, there was no effect on the abundances of the ammonia-oxidizing archaea amoA gene, ammonia-oxidizing bacteria amoA and nirK genes. This study provides the first global-scale assessment demonstrating that elevated temperature shifts N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification in terrestrial ecosystems. These findings infer that elevated temperatures have a profound impact on global N cycling processes with implications of a positive feedback to global climate and emphasize the close linkage between soil microbial C and N cycling.

Responses of the terrestrial biosphere to rapidly changing environmental conditions are a major source of uncertainty in climate projections. In an effort to reduce this uncertainty, a wide range of global change experiments have been conducted that mimic future conditions in terrestrial ecosystems, manipulating CO2, temperature, and nutrient and water availability. Syntheses of results across experiments provide a more general sense of ecosystem responses to global change, and help to discern the influence of background conditions such as climate and vegetation type in determining global change responses. Several independent syntheses of published data have yielded distinct databases for specific objectives. Such parallel, uncoordinated initiatives carry the risk of producing redundant data collection efforts and have led to contrasting outcomes without clarifying the underlying reason for divergence. These problems could be avoided by creating a publicly available, updatable, curated database. Here, we report on a global effort to collect and curate 57,089 treatment responses across 3644 manipulation experiments at 1145 sites, simulating elevated CO2, warming, nutrient addition, and precipitation changes. In the resulting Manipulation Experiments Synthesis Initiative (MESI) database, effects of experimental global change drivers on carbon and nutrient cycles are included, as well as ancillary data such as background climate, vegetation type, treatment magnitude, duration, and, unique to our database, measured soil properties. Our analysis of the database indicates that most experiments are short term (one or few growing seasons), conducted in the USA, Europe, or China, and that the most abundantly reported variable is aboveground biomass. We provide the most comprehensive multifactor global change database to date, enabling the research community to tackle open research questions, vital to global policymaking. The MESI database, freely accessible at doi.org/10.5281/zenodo.7153253, opens new avenues for model evaluation and synthesis‐based understanding of how global change affects terrestrial biomes. We welcome contributions to the database on GitHub. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition can profoundly alter soil N transformation processes and the long-term productivity of forest ecosystems. The response of soil gross N transformations to N deposition in forest ecosystems has been well studied through simulated N addition experiments. Simulated N addition experiments are conducted under a wide range of background N deposition rates. However, it remains unclear whether the response of soil gross N transformation rates to simulated N addition is dependent on background N deposition rates. Here, we collate results from the literature in forest ecosystems, and found, for the first time, that the responses of gross rates of N mineralization, nitrification, and NO3− immobilization to experimental N addition changed from positive to negative with increasing background N deposition rates with the thresholds for such changes were 3.23, 6.02, 1.90 kg N ha− 1 yr− 1, respectively. Our results suggest that background N deposition rates shall be incorporated into ecosystem models to better predict forest ecosystem N cycling under future N deposition scenarios. [ABSTRACT FROM AUTHOR]

Aims: Nitrogen (N) addition could affect litter decomposition through its direct effects on soil N availability and indirect effects on initial litter chemistry. The aim of this study was to evaluate the relative contribution of these direct and indirect effects to the decomposition of fine roots with different diameter classes.Methods: A two-year reciprocal replant-transplant field experiment was conducted in a Mongolian pine (Pinus sylvestris var. mongolica) plantation to examine the relative effect of exogenous and endogenous N enrichment induced by N addition (10 g N m−2 yr.−1) on the decomposition of fine roots with different diameter classes: < 0.5 mm (small fine root, SFR) and 0.5-2 mm (large fine root, LFR).Results: The LFR had significantly higher decomposition rates (k: 0.315-0.397 yr.−1) than the SFR (0.245-0.274 yr.−1) after 2 years of incubation. Exogenous N (i.e., increased soil N availability due to N addition) had no significant effect on the decomposition rates of fine roots, whereas endogenous N (i.e. increased N concentration in litter due to N addition) inhibited and accelerated the decomposition of SFR and LFR, respectively. Endogenous N decreased the net release of N but both endogenous and exogenous N increased the net release of phosphorus (P) from SFR. By contrast, exogenous and endogenous N decreased the net release of N and P from LFR.Conclusions: Our results suggest that N addition affected fine root decomposition indirectly by changing the chemical traits of fine roots rather than directly through changing soil N availability. Elevated input and decreased net N release of fine roots might be a potential mechanism explaining the increases of total organic carbon and total N in the semi-arid forest soil under N addition. Our study also suggests that SFR may be a more important source of stable soil organic matter relative to LFR. [ABSTRACT FROM AUTHOR]

Plant growth is often affected by low soil nitrogen (N) availability and soil salinity in the Athabasca oil sands region (AOSR) of Alberta, Canada, as the reclaimed cover soil of peat-mineral soil mix (PMM) releases N slowly, and may be affected by salts moving upward from the underlying saline tailings sand (TS) or overburden (OB) materials used for land reclamation. Whether soil salinity affects N transformation and thus N availability is not clear. We studied the effect of soil salinity on net and gross N transformation rates in a reclaimed boreal forest soil in an incubation experiment using the 15N isotopic pool dilution technique. To simulate the salinity in reclaimed soils, sodium chloride was added to a PMM soil to form five salinity levels represented by electrical conductivity (EC) of 2, 4, 6, and 8 dS m−1 (based on 1:2 w/v soil to water ratio) and the control. Gross N mineralization, nitrification, and immobilization rates were significantly different among salinity levels, with the rates suppressed by high soil salinity, but they were not completely inhibited even when soil EC reached 8 dS m−1. As the soil EC increased from 2 to 8 dS m−1, gross N immobilization rates decreased faster than gross N mineralization rates, resulting in less negative net N mineralization rates at high salinity levels. The immobilization of NH4+-N was a greater process for NH4+-N consumption than nitrification and possible NH3 volatilization, regardless of the salinity level. In contrast to gross nitrification rates, net nitrification rates were not affected by soil salinity in the studied soil, indicating that the influence of soil salinity on NO3−-N production and consumption was similar. We conclude that soil salinity had different effects on gross versus net rates of soil N transformation and reduced N mineralization and nitrification rates under high soil salinity would lower N availability and thus increase the need for N fertilization in reclaimed soils. [ABSTRACT FROM AUTHOR]

Question Global change is likely to strongly affect alpine and sub-alpine regions, in which bryophytes are important components. Global change effects on sub-alpine vegetation, bryophytes in particular, however, have been addressed in few studies. We ask if global warming and increased nitrogen (N) deposition, two of the most important components of global change, will have different effects on bryophyte communities and species in sub-alpine coniferous and shrubland ecosystems. Location Eastern slope of the Tibetan Plateau. Methods We established a warming by N deposition experiment, using a 2 × 2 factorial design, replicated three times, in each of two sub-alpine ecosystems. Effects on bryophytes at the community and species levels were evaluated after 4 (shrubland) and 5 (coniferous forest) years of warming and N deposition treatments. Results Bryophyte cover increased in the first two growing seasons and thereafter decreased until the end of the experiment in all treatments, most strongly in warming plots in both ecosystems and in N deposition plots in the coniferous forest. At the species level, the pleurocarpous bryophyte Pleurozium schreberi was resilient to warming but sensitive to N deposition, while the acrocarpous bryophytes Rhizomnium tuomikoskii and Racomitrium japonicum were resilient to N addition but sensitive to warming. Conclusions Effects of warming and increased N deposition on bryophytes were species- and to some extent also ecosystem-specific in the experiment in the sub-alpine region, indicating that bryophytes do not respond to global change as one single functional group. The observed species replacements in response to warming and N deposition may affect ecosystem processes. [ABSTRACT FROM AUTHOR]

Forest floor mineral soil mix (FMM) and peat mineral soil mix (PMM) are cover soils commonly used for reclamation of open-pit oil sands mining disturbed land in northern Alberta, Canada; coarse woody debris (CWD) is another source of organic matter for land reclamation. We investigated net nitrogen (N) transformation rates in FMM and PMM cover soils near and away from CWD 4-6 years after oil sands reclamation. Monthly net nitrification and N mineralization rates varied over time; however, mean rates across the incubation periods and microbial biomass were greater (p<0.05) in FMM than in PMM. Net N mineralization rates were positively related to soil temperature (p<0.001) and microbial biomass carbon (p=0.045). Net N transformation rates and inorganic N concentrations were not affected by CWD; however, the greater 15N isotope ratio of ammonium near CWD than away from CWD indicates that CWD application increased both gross N mineralization/nitrification (causing N isotope fractionation) and gross N immobilization (no isotopic fractionation).Microbial biomass was greater near CWD than away from CWD, indicating the greater potential for N immobilization near CWD. We conclude that (1)CWDapplication affected soil microbial properties andwould create spatial variability and diversemicrosites and (2) cover soil type and CWD application had differential effects on net N transformation rates. Applying FMM with CWD for oil sands reclamation is recommended to increase N availability and microsites. [ABSTRACT FROM AUTHOR]

Forest floor mineral soil mix (FMM) and peat mineral soil mix (PMM) are common cover soils and sources of organic matter for reclamation of open-pit mining disturbed land in the Athabasca oil sands region. Coarse woody debris (CWD) can be an additional source of organic matter and can provide nutrient and habitat for plant growth. However, the effect of CWD on nitrogen (N) cycling in reclaimed oil sands soils has not been studied. A laboratory incubation experiment was conducted to assess chemical effects of a CWD extract on gross and net N transformation rates in FMM and PMM using the 15 N pool dilution method. The CWD extract was used to simulate CWD leachates (with rainwater as a control) that are produced in the field. The effect of the simulated CWD leachate on the cover soils was studied in a 2 (FMM vs PMM) × 2 (CWD extract vs rainwater addition) factorial design. There was no difference in gross N mineralization rates between FMM and PMM, although net N mineralization rates were greater in FMM than in PMM ( p < 0.001) due to greater NH 4 + immobilization rates in PMM. Gross and net nitrification rates were greater in FMM than in PMM ( p < 0.001). The ratio of gross nitrification to gross NH 4 + immobilization rates (N/IA) was greater in FMM than in PMM ( p < 0.001), as the greater NH 4 + immobilization rates in PMM decreased gross nitrification rates by decreasing NH 4 + availability. Addition of the CWD extract decreased gross ( p < 0.01) and net ( p < 0.001) N mineralization rates, increased ( p < 0.001) NH 4 + immobilization and decreased ( p < 0.001) gross nitrification rates in both cover soils. The N/IA ratios were decreased by the CWD extract addition, indicating that heterotrophic NH 4 + immobilization was superior to autotrophic nitrification due to the high C/N ratio of the CWD extract. We conclude that FMM will have greater N availability for oil sands reclamation than PMM. Leachates from CWD would decrease N availability by decreasing gross N mineralization and nitrification rates and by increasing N immobilization rates. [ABSTRACT FROM AUTHOR]

Agroforestry land-use systems have significant potential for increasing soil carbon (C) storage and mitigating increases in atmospheric greenhouse gas (GHG) concentrations. We studied the impact of three agroforestry systems (hedgerow, shelterbelt, and silvopasture) on soil organic C (SOC) and nitrogen (N) in the 0-10 cm mineral layer, by comparing SOC and N distributions in whole soils and three particle-size fractions (<53, 53-250, 250-2000 μm) to assess the potential role of physical protection on soil C and N storage. We assessed thirty-five sites (12 hedgerows, 11 shelterbelts and 12 silvopastures), each comprised of 2 paired plots (forest and adjacent agricultural herbland), that were distributed along a 270 km long north-south soil/climate gradient in central Alberta, Canada. Across all sites, 48.4%, 28.5%, and 23.1% of SOC was found in the fine (<53 μm), medium (53-250 μm) and coarse fractions (250-2000 μm), respectively. Mean SOC in the whole soil was 62.5, 47.7 and 81.3 g kg-1 in hedgerow, shelterbelt and silvopasture systems, respectively. Soil C in the more stable fine fraction was 34.3, 28.8 and 29.3 g kg-1 in the hedgerow, shelterbelt and silvopasture systems, respectively. Within each agroforestry system, the forested land-use consistently had greater total SOC and SOC in all size fractions than the agricultural component. Our results demonstrate the potential for trees to increase soil C sequestration in agroforestry systems within the agricultural landscape. [ABSTRACT FROM AUTHOR]

Purpose: The chemistry of annual tree growth rings is affected by precipitation pH, and tree rings store information on environmental conditions at the time of ring formation. The purpose of this study was to evaluate the potential use of tree ring chemistry data in estimating historical precipitation pH using the relationship between precipitation pH and tree ring chemistry. Materials and methods: Red pine ( Pinus densiflora) stem disks were collected from a forest in southern Korea and analyzed for C isotope ratio (C/C, expressed as δC), N concentration, N isotope ratio (N/N, expressed as δN), and molar Ca/Al in annual growth rings. Correlation analysis was conducted for the relationship between tree ring chemistry and precipitation pH between 1992 and 2005 for which such data were available. A regression equation between precipitation pH and tree ring chemistry was then developed using stepwise multiple regression analysis. Results and discussion: We found that between 1992 and 2005, δN (−0.4‰ to −2.7‰) and Ca/Al (11.6 to 7.3) decreased in the growth rings (all significant at α = 0.05) with precipitation pH decreased from 5.7 to 5.0, while the amount of NO emission increased from 12.7 to 22.1 thousand tons between 1999 and 2005 in the study area. The decreased δN and Ca/Al in the tree rings associated with the decreasing precipitation pH seemed to reflect increased N deposition originated from NO emission that is known to be depleted in N relative to the soil mineral N and reduction in Ca availability due to soil acidification. The regression model indicated that mean annual precipitation pH values before the late 1990s at the study site fluctuated between 5.5 and 6.8; thereafter, it showed a decreasing pattern below 5.4 (the lowest measured and estimated pHs were 5.2 and 5.0, respectively) in the mid-2000s with increasing NO emission. Conclusions: The significant correlation of precipitation pH with δN and Ca/Al in tree rings suggested that it may be possible to use tree ring chemistry to estimate historical precipitation pH. However, δC and N concentration of tree rings were not useful as indicators of acid precipitation in this study, as δC is an integrator of many environmental factors that affect gas exchange and inter-ring movement of N towards the outermost ring may mask time-related information regarding N availability. Further research is needed to validate the model in regions where long-term precipitation pH records are available. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems are experiencing increased inputs of nitrogen (N) and temporal fluctuations in precipitation, causing flooding or drought, and this could strongly affect the fate of terrestrial plant species, as they might have different abilities to adapt to the changing environment. We grew Mosla dianthera (a widespread species) and M. hangchowensis (an endangered species) under three water treatments (drought, sufficient water, and waterlogging) in combination with three levels of N supply (low, intermediate, and sufficient N) to study the ecophysiological responses of the congeneric species to those simulated environmental changes. The two species showed different responses to waterlogging and drought treatments, particularly when there was abundant N supply in the system. For example, under sufficient N but drought or waterlogging conditions, M. dianthera increased root mass ratio (RMR) and decreased leaf mass ratio (LMR), total leaf area (LA), and leaf area ratio (LAR); such changes can enhance water acquisition and reduce water loss under both drought and waterlogging conditions, in contrast to the general lack of change in those parameters with M. hangchowensis. These differentiations in traits suggest that increased N availability might worsen drought and waterlogging injury to M. hangchowensis and thus accelerate the decline of this population. However, M. dianthera maybe better adapted to high N availability and both drought and waterlogging conditions. We hypothesize that the different adaptive abilities to high N availability and drought and waterlogging conditions are partly responsible for the ecological differentiation observed between these two species in the field and may determine their fate in their native habitat. Further research should test this hypothesis in field experiments. [ABSTRACT FROM AUTHOR]

The different responses to growth condition changes due to nitrogen deposition and rainfall variability among congeneric species may alter their differentiation pattern. We grew two Mosla species (Lamiaceae) under different nitrogen and water conditions. Under waterlogging, the two species showed similar positive growth responses to high nitrogen supply, implying potential chances to extend their populations in very wet habitats. However, under the wet and relatively dry conditions, M. dianthera was less tolerant to high nitrogen (biomass of M. dianthera was suppressed by high nitrogen more remarkably than that of M. cavaleriei) but more tolerant to nitrogen limitation than M. cavaleriei (with the decrease in water supply, root mass ratio of M. dianthera was increased by nitrogen limitation more noticeably than that of M. cavaleriei). Therefore, in relatively dry habitats, soil nitrogen addition might be unfavorable for M. dianthera. [ABSTRACT FROM AUTHOR]

How resource availabilities affect the competitiveness of Canada bluejoint grass [Calamagrostis canadensis (Michx.) P. Beauv., hereafter referred to as bluejoint] is poorly understood. Bluejoint is a widespread grass species in boreal forests and competes with tree species such as white spruce [Picea glauca (Moench) Voss] for belowground resources (e.g., soil N and water) when their supply is limited. In this greenhouse-based study, we tested the following hypotheses: (i) bluejoint competition reduces white spruce growth when belowground resource availabilities are limited; (ii) greater N and water availabilities may increase bluejoint competition and its adverse effects on white spruce growth; and (iii) white spruce foliar δ13C and δ15N are affected by soil N and water availabilities and bluejoint competition. A 2 × 2 2 (competition × N availability × water availability) factorial experiment was conducted using pots of planted white spruce seedlings with or without bluejoint. Bluejoint competition reduced the volume index (diameter² × height) of white spruce by 50%. The competitiveness of bluejoint appeared to be independent of resource availabilities, but bluejoint had greater growth response to increased N availability than white spruce. Bluejoint competition depleted white spruce foliar δ13C and δ13N by 1.2 and 1.2‰ respectively, even under adequate water supply, indicating that N deficiency caused by bluejoint competition had a dominant effect (increasing 13C discrimination during photosynthesis) compared with the potential effect of drought stress on foliar δ13, and that strong NH4 uptake by bluejoint may have prevented significant soil N losses and 15N enrichment through nitrification and subsequent denitrification. [ABSTRACT FROM AUTHOR]

Abstract: A better understanding of N availability in co-composted drilling wastes is required to evaluate the potential use of the composts as growth media. We investigated N dynamics in co-composted drilling wastes by examining the changes in the concentrations and partition of applied 15N in various soil N pools (, , dissolved organic N, microbial biomass N, and non-extractable N) in a 4-month greenhouse incubation experiment using 1-, 2-, 3-, and 4-year-old (referred to below as 1Y, 2Y, 3Y, and 4Y, respectively) composts, representing substrates with different quality. Regardless of compost age, after 4 months of incubation extractable N concentrations decreased (P<0.05), in contrast with the increasing pattern of the non-extractable N, indicating stabilization of the extractable N into the recalcitrant soil organic fraction. Fertilizer N application increased (P<0.05) extractable N concentrations. In the younger composts, a major part of the applied 15N was recovered in the non-extractable N fraction (44.0% for 1Y and 38.5% for 2Y) with little recovered as mineral N. On the other hand, a considerable percentage of the applied 15N (21.8% for 3Y and 18.8% for 4Y) was found in the pool in the older composts with relatively high mineral N but low organic C contents. This study shows that the dynamics of biologically available N and fate of applied N in the composts depend on compost quality such as mineral N and organic C contents, and compost C:N ratio. To use the co-composted drilling waste as growth media, different N management strategies need to be established for those composts with differed substrate quality. [Copyright &y& Elsevier]

Nitrogen (N) concentrations and stable N isotope abundances (δ15N) of common reed (Phragmites australis) planted in a constructed wetland were measured periodically between July 2001 and May 2002 to examine their seasonal variations in relation to N uptake and N translocation within common reed. Nitrogen concentrations in P. australis shoots were higher in the growing stage (7.5 to 24.8 g N kg-1)than in the senescence stage (4.2 to 6.8 g N kg-1), indicating N translocation from shoots to rhizomes. Meanwhile, the corresponding δ15N values were higher in the senescence stage (+12.2 to +22.4‰) than in the growing stage (+5.1 to +11.3‰). Coupled with the negative correlation (R² 0.24, P < 0.05, n 18) between N concentrations and δ15N values of shoots in the senescence stage, our results suggested that shoot N became enriched in δ15N due to N isotopic fractionation (with an isotopic fractionation factor, αs/p' of 1.012) during N translocation to rhizomes. However, the positive correlation between N concentrations and δ15N values in the growing stage (R² 0.19, P < 0.001, n 54) suggested that P. australis relies on N re-translocated from rhizome in the early growing stage and on mineral N in the sediment during the active growing stage. Therefore, seasonal δ15N variations provide N-isotopic evidence of N translocation within and N uptake from external N sources by common reed. [ABSTRACT FROM AUTHOR]

This article examines the white spruce response to co-composted hydrocarbon-contaminated drilling waste. There are growing interests to use co-composted drilling wastes contaminated with hydrocarbons as growth media for planting in land reclamation. However, such use of the compost may have potential problems such as inherent toxicity of residual hydrocarbon and microbial nitrogen (N) immobilization due to high compost carbon to nitrogen ratios. Growth and N content of seedlings were lower when grown in the compost media as compared with those grown in the soil. Within the compost treatments seedling growth was affected by compost age, but the magnitude of growth reduction was not linearly proportional to hydrocarbon concentrations. Plant N uptake increased with compost age, which corresponds with an increase in indigenous mineral N concentration. Effects of N fertilization on N uptake were curtailed by the presence of indigenous mineral N and by fertilization-induced stimulation of microbial activities.

Natural abundances of carbon-13 and nitrogen-15 were analyzed in 3-year bands of annual rings of three red pine ( Pinus densiflora Sieb. et Zucc.) trees in eastern Korea to elucidate their variations in relation to changing environmental conditions, particularly air pollution. Tree ring width had a trend to decrease with time ( r = −0.79, P < 0.001); however, tree-ring indices did not show any consistent pattern of change over time. Tree ring indices were correlated neither with the respective precipitation nor temperature. The δ13C (range: −25.7 to −24.4ä) of tree rings became less negative as tree ring indices increase ( r = 0.43, P < 0.05), suggesting that radial growth of trees might have been affected by environmental factors such as nutrient deficiency and acid rain that affect carboxylation efficiency. Increasing N concentration (range: 0.40 to 0.68 g N kg−1) with decreasing δ15N (range: +4.2 to −0.6ä) of tree rings ( r = −0.84, P < 0.01) during the period (since 1980s) of increasing NO x emission in Korea was consistent with the hypothesis that increasing deposition of N depleted in 15N may lead to 15N depletion in tree tissues. However, quantitative information on inter-ring translocation of N which may cause N isotopic fractionation is necessary to use the δ15N signal as a reliable indicator of air pollution. [ABSTRACT FROM AUTHOR]

In the initial online publication the figure legends for Figures 1 and 2 were reversed. The original article has been corrected. [ABSTRACT FROM AUTHOR]

Conservation agriculture through the use of crop residue retention and no-tillage (NT) has been widely practiced to improve agricultural soil quality, such as to increase soil organic carbon (C) content and the microbial population size. However, there has been no quantitative analysis on the effect of conservation agriculture, particularly in relation to crop residue retention, on soil microbial biomass C (C mic ) and nitrogen (N mic ), and the microbial quotient (qMIC, C mic -to-organic C ratio), which are frequently used as indicators of soil health under different agricultural practices. The objective of this study was to evaluate the influence of conservation agriculture practices on soil C mic , N mic and qMIC on a global scale using meta-analysis based on data from 96 recent publications. Relative to conventional tillage (CT) without residue retention, NT without residue retention (NTR0) increased C mic by 33% ( P  < 0.05), while NT with residue retention (NTR) increased ( P  < 0.05) C mic , N mic , and qMIC by 25, 64, and 57%, respectively. Greater C mic and N mic were found in the NT than in the CT treatment, regardless of the soil condition (e.g., soil pH and texture), experimental duration, and climate (e.g., mean annual temperature and precipitation). Particularly, NTR was a promising conservation agriculture practice to increase C mic and N mic in global farmlands, and NTR0 can be an alternate strategy for loam soils in the subhumid (600–1000 mm mean annual precipitation) region, or under long-term (>20 yr) conservation agriculture practices. We conclude that NTR should be an important strategy that could be used to increase C mic and N mic contents and improve soil quality in global farmlands. [ABSTRACT FROM AUTHOR]

Highlights • Effects of water and N input on maize yield and water productivity (WP) were assessed. • Effects of water and N input on maize nitrogen use efficiency (NUE) were studied. • Achieved values were lower than the attainable one by 28% (yield), 28 (WP), 21 (NUE). • Global mean water and N saving potentials was 10 and 18%. • Above-optimal water input increased both yield and WP by 3%. Abstract Global maize (Zea mays) yields are limited by water and nutrient availability. Although water and nitrogen (N) have long been recognized for their beneficial effects (alone or interactively) on maize production, synthetic analysis on the effects of water and N inputs on maize yield, water productivity (WP, yield per unit water usage) and N use efficiency (NUE, yield per unit N applied) at a global scale is lacking. The objectives of this study were to quantify the effects of water and/or N inputs on both yield, WP and NUE, and water and N saving potential. Based on yield (n = 1406), WP (n = 1406), and NUE (n = 1131) observations from 83 studies conducted in 15 countries, the meta-analysis found that the optimal maize yield was achieved when maize planting density (number of plants per unit area) was 8.7 plants m−2. Generally speaking, maize yield, WP, and NUE were inversely correlated to mean annual temperature. The positive effect of inputting either water or N on all variables faded away when the optimal input levels were exceeded. The achieved yield, WP, and NUE were significantly lower than the attainable values by 27.9%, 27.9%, and 20.5%, respectively. The overall global mean water and N saving potential was 10 and 18%, respectively. Meanwhile, optimizing water or N input separately did not consistently enhance yield, WP, or NUE, while above-optimal water input increased yield and WP more than below-optimal water input by 3.4% and 3.3%, respectively. These results showed that current water and N management practices have created large gaps between the actual and attainable productivity and efficiency indices (e.g. yield, WUE, and NUE), and that simultaneous optimization of water and fertilizer N inputs is crucial for achieving maximum maize yield. [ABSTRACT FROM AUTHOR]

The nitrogen (N) footprint is a novel approach to quantify losses to the environment of reactive N (Nr; all species of N except N2) derived from human activities. However, current N footprint models are difficult to apply to new countries due to the large data requirement, and sources of Nr included in calculating the N footprint are often incomplete. In this study, we comprehensively quantified the N footprint in China with an N mass balance approach. Results show that the per capita N footprint in China increased 68% between 1980 and 2008, from 19 to 32 kg N yr-1. The Nr loss from the production and consumption of food was the largest component of the N footprint (70%) while energy and nonfood products made up the remainder in approximately equal portion in 2008. In contrast, in 1980, the food-related N footprint accounted for 86% of the overall N footprint, followed by nonfood products (8%) and energy (6%). The findings and methods of this study are generally comparable to that of the consumer-based analysis of the N-Calculator. This work provides policy makers quantitative information about the sources of China's N footprint and demonstrates the significant challenges in reducing Nr loss to the environment. [ABSTRACT FROM AUTHOR]

Abstract: The effects of planting type and species richness on removal of BOD5, COD, nitrogen and phosphorus were studied in mesocosms with monocot alone (M), dicot alone (D) and mixed planting of M+D, where each planting type had four species richness levels. Above- and below-ground plant biomasses increased with the M and M+D species richness as shown by one-way ANOVA. The M+D type had the highest above-ground biomass, whereas the M type had the highest below-ground biomass among planting types. Carbon, nitrogen and phosphorus in the microbial biomass increased with the richness of the M and M+D type. Removals of BOD5, COD, inorganic P and total P did not change with the richness, but removals of NH4-N, NO3-N increased. Planting type impacted only removal of inorganic P, with higher removal of inorganic P in the M type. [Copyright &y& Elsevier]

Abstract: Spatial heterogeneities of vegetation and soil can strongly affect ecological functions of ecosystems, particularly for arid and semi-arid ecosystems where vegetation has a patchy distribution and livestock grazing is one of the major land use types. However, little is known about the impact of grazing on spatial patterns of vegetation and soil, even though grazing has variously been shown to create, maintain or destroy those patterns. We studied how grazing intensity affected the spatial patterns of vegetation and soil fertility at scales ranging from 0.1 to 18.7m in a desert steppe in Inner Mongolia, China. Increasing grazing intensity decreased the range of spatial autocorrelation of plant aboveground biomass at the fine scale (<2m), indicating that vegetation patches were more fragmented under higher grazing pressure. Spatial heterogeneity of soil water content and organic C concentration decreased along the gradient of increasing grazing intensity at the fine scale. Light grazing increased soil NH4 + availability and its overall variability. Soil NO3 − only had significant cross-correlation with aboveground biomass in un-grazed plots at the fine scale, suggesting that the spatial correlation between plant and soil fertility was affected by grazing. Spatial patterns of studied variables did not respond to grazing intensities at a coarse scale (1–18m). Our results demonstrated that the grazing intensity altered fine scale processes in this desert steppe and caused divergent responses of spatial distribution of vegetation and soil fertility. [Copyright &y& Elsevier]

Abstract: This study focused on the relationship between plant diversity (six species richness levels) and nutrient retention and enzyme activities associated with carbon, nitrogen and phosphorus cycling in a full-scale constructed wetland (CW) fed with post-treatment domestic wastewater. Effects of plant species richness on nutrient retention and enzyme activities were assessed using soil chemical and zymological methods, respectively. Retention of NH4–N and NO3–N in the wetland substrate increased with increasing species richness, while phosphorus retention significantly decreased under the richness level of 16 species per plot. Activities of enzymes such as dehydrogenase, β-glucosidase, invertase, phenol oxidase, l-arsparaginase, protease and nitrate reductase, while they were affected by plant species richness, were strongly depended on the presence or absence of plants in CW substrate, while activities of enzymes such as CM-cellulase, urease and acid phosphatase were strongly depended on plant species richness. We conclude that plant species richness influenced nutrient retention and enzyme activities in the substrate in our subtropical CW; increase plant species richness in CW will likely improve the efficiency of wastewater treatment. [Copyright &y& Elsevier]