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Nitrogen (N) is the most important nutrient in coffee, with a direct impact on productivity, quality, and sustainability. N uptake by the roots is dominated by ammonium (NH4+) and nitrates (NO3−), along with some organic forms at a lower proportion. From the perspective of mineral fertilizer, the most common N sources are urea, ammonium (AM), ammonium nitrates (AN), and nitrates; an appropriate understanding of the right balance between N forms in coffee nutrition would contribute to more sustainable coffee production through the better N management of this important crop. The aim of this research was to evaluate the influences of different NH4-N/NO3-N ratios in coffee from a physiological and agronomical perspective, and their interaction with soil water levels. Over a period of 5 years, three trials were conducted under controlled conditions in a greenhouse with different growing media (quartz sand) and organic soil, with and without water stress, while one trial was conducted under field conditions. N forms and water levels directly influence physiological responses in coffee, including photosynthesis (Ps), chlorophyll content, dry biomass accumulation (DW), nutrient uptake, and productivity. In all of the trials, the plants group in soils with N ratios of 50% NH4-N/50% NO3-N, and 25% NH4-N/75% NO3-N showed better responses to water stress, as well as a higher Ps, a higher chlorophyll content, a higher N and cation uptake, higher DW accumulation, and higher productivity. The soil pH was significantly influenced by the N forms: the higher the NO3−-N share, the lower the acidification level. The results allow us to conclude that the combination of 50% NH4-N/50% NO3-N and 25% NH4-N/75% NO3-N N forms in coffee improves the resistance capacity of the coffee to water stress, improves productivity, reduces the soil acidification level, and improves ion balance and nutrient uptake. [ABSTRACT FROM AUTHOR]

Hempseed has an excellent antioxidant content and is a rich source of essential amino acids and n-3 fatty acids. The objective of this paper consists on evaluating the hempseed Jubileu variety effects on performance, nitrogen (N) balance. The prediction of nitrous oxide (N2O) emissions was done as well. For 3 weeks of trial, a total of 15 pigs (39 kg ± 0.32) were randomly allocated individually in digestibility cages. Following a 7-day adaption period, there were two balancing periods where urine and feces were quantitatively collected. Two types of diet were used: Control group received a classical diet and Experimental group which received the same diet, supplemented with 5% hempseed. The growth parameter and carcass quality were not significantly altered by hempseed addition; however, a slight increased of ADG and feed conversion was noticed. Due to the significantly decreased of N concentration in the urine, TNO value was lower as well (P<0.05). A decline of N digestibility was noticed for HS group diet (P<0.001). Average value of N2O estimated was lower in HS fed group (P = 0.03). In conclusion, hempseed is a proteo-oleaginous source, which can be added in pigs' diet with beneficial effect on performance, N metabolism indicators and N2O emissions. [ABSTRACT FROM AUTHOR]

The high value resource utilization of corn straw is a long-term problem at present and in the future. Biochar preparation is an important utilization way of corn straw. The research on city tail water treated by constructed wetland (CW) with biochar was carried out to further increase the wastewater treatment capacity of the CW. Surface characterization, structural characteristics, and adsorption of straw biochar modified by different acids were measured. The study found that the ability of H2SO4 to remove ash from biochar was stronger than other acids and H2SO4-biochar was easy to be cleaned without H2SO4 residue. The performance of biochar modified by H2SO4 was obviously better than other acids, and the biochar adsorption was enhanced. The modification of biochar substrate modified by H2SO4 in CW reduced the change of electrical conductivity (EC) and promoted denitrification. H2SO4-modified biochar promoted the absorption of N and P by Iris pseudacorus L. The compound modification effect of straw biochar was obvious. The results revealed the acid modification characteristics of straw biochar, which were beneficial for increasing the wastewater treatment rate by CW. This study will promote the sustainable development of CW. [ABSTRACT FROM AUTHOR]

Question: Legumes are a key component of rangelands because they play an important role in animal nutrition and the entrance of nitrogen (N) into ecosystems through symbiotic fixation. Legume abundance is commonly low in N‐enriched environments because of competition with grasses and non‐legume forbs. Both haying and livestock grazing remove plant biomass and reduce light limitation to plant growth, with the difference that livestock may selectively consume legumes. This study examines how legumes respond to grazing, haying and fertilization, and what mechanisms explain legume abundance in rangelands. Location: Flooding Pampa, Argentina. Methods: We performed two manipulation field experiments over 3 years. First, a factorial of rangeland management (intact, haying, or grazing) under two nutrient levels (ambient and increased N, phosphorus [P] and potassium [K]); and second, a factorial of rangeland management (intact or haying) and N × P addition. We evaluated legume, grass and non‐legume forb abundance and ground‐level light in three to five replicates of our experiments over 3 years. Results: NPK fertilization increased legume abundance consistently under grazing, and temporarily under haying, but had no effect in the intact grassland. Also, P addition increased legume abundance only under haying when N was not added. Temporal changes in legume abundance were positively associated with changes in ground‐level light, which increased with haying and grazing, but decreased with fertilization in the intact grassland, and negatively with grass abundance. Conclusions: The negative effects of nutrients on legume abundance were offset by the positive effects of livestock. The reduction in grass competition and increase in ground‐level light due to grazing and haying explained the positive responses of legume abundance to nutrients in this temperate grassland. Our results highlight the importance of considering the interactive response of legume abundance to grazing and fertilization, which are becoming common practices in rangelands. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal (AM) fungi establish root symbioses that can improve acquisition of nutrients such as nitrogen (N) from soils, leading to improvements in host plant growth. Previously, we showed that applying AM fungal necromass to the rhizosphere could stimulate plant growth. Here we investigated the interactions between AM fungi (living or dead) and ammonia oxidizers (AO), a key group of soil prokaryotes involved in soil N cycling, to understand the effects of these interactions on plant N levels. We were interested in whether the necromass contained any significant biological nitrification inhibitory (BNI) activity that could account for the previously suggested antagonism between AM fungi and AO. Methods: We set up a compartmented pot experiment with Andropogon gerardii as a host plant, which included rhizosphere (amended with living and/or dead AM fungal biomass) and a root-free zone. The latter contained a mesh bag with 15N-labelled plant litter. Results: Inoculation with living AM fungus enhanced plant biomass and nutrient acquisition, including increased transfer of 15N from the mesh bags to the plants. Additionally, AO bacteria but not archaea were significantly suppressed in the mesh bags. In contrast, AM fungal necromass had minimal effect on plant biomass and nutrient acquisition. Surprisingly, it stimulated the growth of both AO bacteria and archaea in the rhizosphere of non-mycorrhizal plants. Conclusions: Based on the above, we found no support for AM fungi suppressing the AO through an elusive BNI production. Rather, it seems that the main mechanism of AM fungal-AO interaction is substrate competition. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is the most important nutrient in coffee, with a direct impact on productivity, quality, and sustainability. N uptake by the roots is dominated by ammonium (NH4+) and nitrates (NO3−), along with some organic forms at a lower proportion. From the perspective of mineral fertilizer, the most common N sources are urea, ammonium (AM), ammonium nitrates (AN), and nitrates; an appropriate understanding of the right balance between N forms in coffee nutrition would contribute to more sustainable coffee production through the better N management of this important crop. The aim of this research was to evaluate the influences of different NH4-N/NO3-N ratios in coffee from a physiological and agronomical perspective, and their interaction with soil water levels. Over a period of 5 years, three trials were conducted under controlled conditions in a greenhouse with different growing media (quartz sand) and organic soil, with and without water stress, while one trial was conducted under field conditions. N forms and water levels directly influence physiological responses in coffee, including photosynthesis (Ps), chlorophyll content, dry biomass accumulation (DW), nutrient uptake, and productivity. In all of the trials, the plants group in soils with N ratios of 50% NH4-N/50% NO3-N, and 25% NH4-N/75% NO3-N showed better responses to water stress, as well as a higher Ps, a higher chlorophyll content, a higher N and cation uptake, higher DW accumulation, and higher productivity. The soil pH was significantly influenced by the N forms: the higher the NO3−-N share, the lower the acidification level. The results allow us to conclude that the combination of 50% NH4-N/50% NO3-N and 25% NH4-N/75% NO3-N N forms in coffee improves the resistance capacity of the coffee to water stress, improves productivity, reduces the soil acidification level, and improves ion balance and nutrient uptake.

The terrestrial gross primary productivity (GPP) plays a crucial role in regional or global ecological environment monitoring and carbon cycle research. Many previous studies have produced multiple products using different models, but there are still significant differences between these products. This study generated a global GPP dataset (NI-LUE GPP) with 0.05° spatial resolution and at 8 day-intervals from 2001 to 2018 based on an improved light use efficiency (LUE) model that simultaneously considered temperature, water, atmospheric CO2 concentrations, radiation components, and nitrogen (N) index. To simulate the global GPP, we mapped the global optimal ecosystem temperatures ( T opt eco ) using satellite-retrieved solar-induced chlorophyll fluorescence (SIF) and applied it to calculate temperature stress. In addition, green chlorophyll index (CIgreen), which had a strong correlation with the measured canopy N concentrations (r = 0.82), was selected as the vegetation index to characterize the canopy N concentrations to calculate the spatiotemporal dynamic maximum light use efficiency (εmax). Multiple existing global GPP datasets were used for comparison. Verified by FLUXNET GPP, our product performed well on daily and yearly scales. NI-LUE GPP indicated that the mean global annual GPP is 129.69 ± 3.11 Pg C with an increasing trend of 0.53 Pg C/yr from 2001 to 2018. By calculating the SPAtial Efficiency (SPAEF) with other products, we found that NI-LUE GPP has good spatial consistency, which indicated that our product has a reasonable spatial pattern. This product provides a reliable and alternative dataset for large-scale carbon cycle research and monitoring long-term GPP variations. [ABSTRACT FROM AUTHOR]

This field experimental work was conducted during successive seasons (2021 and 2022) to explore the effect of different fertilizer ratios between nitrogen (N), phosphorus (P) and potassium (K) on the vegetative growth of Cleopatra mandarin rootstock seedlings (Citrus reshni L.). The seedlings were subjected to different fertilizer ratios between N, P and K (2:1:1 and 1:1:2) as well as the control (1:1:1) for investigating their effect on some growth parameters of Cleopatra mandarin rootstock seedlings. All fertilizer ratios were applied at the beginning of April and during the experimental seasons using 0.5 g of N, P, and K mixed with ratios different (1:1:1, 2:1:1 and 1:1:2) for every litter of irrigation water. The treatments were distributed as randomized complete block designs with 3 replicates for each treatment. The results obtained during both experimental seasons revealed obviously that all treatments have significantly increased growth parameters as compared to control. Generally, N, P and K with a ratio 2:1:1 particularly were statistically the most effective in this study. [ABSTRACT FROM AUTHOR]

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C. korshinskii is one of the most widely-planted sand-fixing legumes in northwest China and exploring its rhizosphere microbiome is of great ecological importance. However, the effect of long-term sand fixation on the composition, diversity, and underlying functions of microbes in the C. korshinskii rhizosphere in dryland ecosystems remain unclear. Here, we performed high-throughput sequencing using a 16S rRNA (absolute quantification) and bacterial functional annotation of prokaryotic taxa (FAPROTAX) analysis and an ITS (relative quantification) and fungal functional guild (FUNGuild) analysis to investigate the C. korshinskii rhizosphere microbiome and metabolic functional groups at different sand-fixing ages (six years, CK6; twelve years, CK12; and eighteen years, CK18) and determined the physicochemical properties of the rhizosphere soil. Results showed that the key bacterial taxa of the rhizosphere were significantly more abundant in CK18 than in CK12 and CK6 at the phylum-classgenus level, and that fungal Glomeromycota was also significantly more abundant in the CK18 rhizosphere compared to CK12 and CK6. Among these bacterial taxa, the enrichment effect of key, functional, genus-level species of bacteria was the most obvious, including Rhizobium, Ensifer, Neorhizobium, Mesorhizobium, Streptomyces, Sphingomonas, and Flavobacterium, which are N-fixing and/or phosphate-solubilizing groups. The significant improvement seen in the physicochemical properties of the CK18 rhizosphere soil, including the higher total nitrogen (TN), available nitrogen (AN), pH, electrical conductivity (EC), higher N:P ratio, and lower C:N ratio, all demonstrated the relationship between the rhizosphere microbes and soil carbon (C) and nitrogen (N) cycling. A redundancy analysis (RDA) of different taxonomic levels indicated a close positive relationship between rhizosphere microbes and AN. In addition, the functional groups of the C. korshinskii rhizosphere bacteria were closely related to soil AN and were mainly composed of chemoheterotrophy and aerobic chemoheterotrophy. A Spearman correlation analysis revealed that these functional groups were mainly identified from bacterial Actinobacteria, Proteobacteria, Verrucomicrobia, Bacteroidetes, and fungal Glomeromycota. Our study provides evidence that the rhizosphere microbes of C. korshinskii are closely related to the accumulation of N in the restoration of desert ecosystems, and that the ecological functional processes they are involved in mainly involve C and N cycles, which play an important role in desertification reversal. [ABSTRACT FROM AUTHOR]

Nitrogen (N), a macronutrient, is often a limiting factor in plant growth, development, and productivity. To adapt to N-deficient environments, plants have developed elaborate N starvation responses. Under N-deficient conditions, older leaves exhibit yellowing, owing to the degradation of proteins and chlorophyll pigments in chloroplasts and subsequent N remobilization from older leaves to younger leaves and developing organs to sustain plant growth and productivity. In recent years, numerous studies have been conducted on N starvation-induced leaf senescence as one of the representative plant responses to N deficiency, revealing that leaf senescence induced by N deficiency is highly complex and intricately regulated at different levels, including transcriptional, post-transcriptional, post-translational and metabolic levels, by multiple genes and proteins. This review summarizes the current knowledge of the molecular mechanisms associated with N starvation-induced leaf senescence. [ABSTRACT FROM AUTHOR]

• Dam-induced conditions result in primarily phosphorus limitation in the subtropical deep Lake Qiandaohu. • Nitrogen and phosphorus co-limitation is also identified in Lake Qiandaohu's riverine zones. • A nearly 1:1 linear relationship between chlorophyll a and total phosphorus concentrations is observed. • The study establishes control targets for total phosphorus concentration and loading in Lake Qiandaohu. Impoundments play a vital role as nutrient sinks, capable of retaining and exporting nitrogen (N) and phosphorus (P) at different rates. The imbalance in N and P stoichiometry relative to phytoplankton demand often determines the limiting nutrient of phytoplankton biomass in these systems. This critical factor has a substantial impact on the management of eutrophication, encompassing the formulation of nutrient control strategies and the setting of regulatory thresholds. Nonetheless, research remains relatively limited on phytoplankton limiting factors and nutrient stoichiometry interactions in subtropical impoundment reservoirs. This study fills a critical gap in the current research by providing a comprehensive assessment of the influences of N and P on phytoplankton biomass in Lake Qiandaohu, China. Through field monitoring, nutrient addition experiments, and novel constraint line regression model, we provide new insights into the nutrient-phytoplankton dynamics within the lake. Both bioassay experiments and statistics indicated primarily P-limitation in Lake Qiandaohu owing to its dam-induced deep-water conditions, characterized by a nearly 1:1 linear relationship between chlorophyll a (Chl a) and total P (TP) concentrations. This underscores the pivotal role of P management plays in controlling algal blooms. Utilizing the constraint line equation that relates TP to Chl a , we have proposed TP thresholds designed to keep Chl a within the specified target ranges, specifically below 10, 12, 20, 24, 40, and 60 μg/L. Furthermore, leveraging Vollenweider's models with these TP concentration thresholds, we established TP loading targets that accommodate a range of hydrological conditions, from normal to wet and dry years. Furthermore, both nutrient addition experiments and constraint line regression model indicates potential N and P co-limitation in specific regions, particularly the riverine zone, where the unsettled particulate matter results in relatively lower N:P ratios. To address this, we introduces TN thresholds and suggests localized control measures, including the use of floating macrophytes beds, as effective alternatives. Considering the uniform nutrient management policy currently applied across Chinese lakes and reservoirs, which may lead to under- or over-protection for individual water bodies, our research provides a flexible cost-effective eutrophication management framework tailored for the China's subtropical region. [ABSTRACT FROM AUTHOR]

Returning crop straw to the field not only improves the nitrogen (N) supplying capacity and N retention of soil but also decreases the amount of rural organic waste and prevents air pollution. Therefore, understanding the mechanisms of the N release and re-adsorption dynamics on crop straw residue during straw decomposition in agricultural soil is important, and this understanding can help us strengthen N fertilizer management during the crop growth period. An on-farm incubation experiment was conducted in the Jianghan Plain in Central China under flooded conditions using the nylon mesh bag method. Results showed that the decomposition rate of crop straw was much faster at the beginning of the incubation stage, whereas it was steady during the later stage with no observed differences among the three types of crop straw. After 120 d of incubation, the cumulative decomposition proportion of rice straw, wheat straw and rape straw was 72.9, 56.2, and 66.9%, respectively. The proportion of N that released from the three crop straws was 52.0, 54.4 and 54.9%, respectively. The zeta potentials and Brunauer, Emmett and Teller (BET) surface area of the rice, wheat and rape straw residues increased gradually as the decomposition period progressed. The water adsorption capacity of the rice straw was significantly affected during the decomposition period. The saturated water adsorption capacity of rice straw was the highest at 30 d of decomposition (4.17 g g–1) and then decreased slightly. The saturated water adsorption of wheat and rape straws reached the lowest value at 30 d and then gradually increased and became stable. All the results demonstrated that crop straw and straw residue can re-adsorb NH4+ ions from the surrounding solution. The re-adsorption was affected by the decomposition period and concentration of exogenous NH4+ and was independent of the crop species via the combined efforts of physical and chemical adsorption, ion exchange and water retention on residue surfaces. Future studies will focus on straw returning and N fertilizer application at different levels of moisture content of the soil reduce potential negative effects such as water-logging and excess N caused by the straw substrate.

Purpose: The ecological importance of arbuscular mycorrhizal fungi (AMF) in plant acquisition of inorganic and organic sources of nitrogen (N) is not clear. To improve understanding of the plant N nutrition ecology, we tested the effect of intraspecific competition and AMF in plant N source use in growth and N acquisition. Methods: Solidago virgaurea was grown in microcosms in a fully factorial experiment under greenhouse conditions. The factors tested were intraspecific competition between seedlings and adult plants (yes, no), N source (NH4, glycine) and AMF (inoculated with Glomus hoi, not inoculated). Results: When grown separately, non-mycorrhizal seedling growth was highest when grown with ammonium, but non-mycorrhizal adults grew best with glycine as the sole N source. Mycorrhizal symbiosis with Glomus hoi evened out this initial niche partitioning in terms of differences in N source use and all mycorrhizal plants grew best with ammonium. Competition shaped plant benefit from mycorrhizal symbiosis depending on the N source. Competition reduced mycorrhizal growth benefit in glycine-grown seedlings, but not in adults. Plant performance did not show uniform relationship with δ15N, but δ15N was affected by life stage, competition and mycorrhiza. Conclusions: Plant competition and AMF shape plant N source use. Plant and AMF benefit of the symbiosis depend on the N source. [ABSTRACT FROM AUTHOR]

The terrestrial gross primary productivity (GPP) plays a crucial role in regional or global ecological environment monitoring and carbon cycle research. Many previous studies have produced multiple products using different models, but there are still significant differences between these products. This study generated a global GPP dataset (NI-LUE GPP) with 0.05° spatial resolution and at 8 day-intervals from 2001 to 2018 based on an improved light use efficiency (LUE) model that simultaneously considered temperature, water, atmospheric CO2 concentrations, radiation components, and nitrogen (N) index. To simulate the global GPP, we mapped the global optimal ecosystem temperatures (Topteco) using satellite-retrieved solar-induced chlorophyll fluorescence (SIF) and applied it to calculate temperature stress. In addition, green chlorophyll index (CIgreen), which had a strong correlation with the measured canopy N concentrations (r = 0.82), was selected as the vegetation index to characterize the canopy N concentrations to calculate the spatiotemporal dynamic maximum light use efficiency (εmax). Multiple existing global GPP datasets were used for comparison. Verified by FLUXNET GPP, our product performed well on daily and yearly scales. NI-LUE GPP indicated that the mean global annual GPP is 129.69 ± 3.11 Pg C with an increasing trend of 0.53 Pg C/yr from 2001 to 2018. By calculating the SPAtial Efficiency (SPAEF) with other products, we found that NI-LUE GPP has good spatial consistency, which indicated that our product has a reasonable spatial pattern. This product provides a reliable and alternative dataset for large-scale carbon cycle research and monitoring long-term GPP variations.

Summary: Ectomycorrhizal plants trade plant‐assimilated carbon for soil nutrients with their fungal partners. The underlying mechanisms, however, are not fully understood. Here we investigate the exchange of carbon for nitrogen in the ectomycorrhizal symbiosis of Fagus sylvatica across different spatial scales from the root system to the cellular level.We provided 15N‐labelled nitrogen to mycorrhizal hyphae associated with one half of the root system of young beech trees, while exposing plants to a 13CO2 atmosphere. We analysed the short‐term distribution of 13C and 15N in the root system with isotope‐ratio mass spectrometry, and at the cellular scale within a mycorrhizal root tip with nanoscale secondary ion mass spectrometry (NanoSIMS).At the root system scale, plants did not allocate more 13C to root parts that received more 15N. Nanoscale secondary ion mass spectrometry imaging, however, revealed a highly heterogenous, and spatially significantly correlated distribution of 13C and 15N at the cellular scale.Our results indicate that, on a coarse scale, plants do not allocate a larger proportion of photoassimilated C to root parts associated with N‐delivering ectomycorrhizal fungi. Within the ectomycorrhizal tissue, however, recently plant‐assimilated C and fungus‐delivered N were spatially strongly coupled. Here, NanoSIMS visualisation provides an initial insight into the regulation of ectomycorrhizal C and N exchange at the microscale. [ABSTRACT FROM AUTHOR]

Summary: Nitrogen (N) is an essential nutrient that limits plant growth in many ecosystems. Here we investigate an overlooked component of the terrestrial N cycle – subsurface ammonia (NH3) gas transport and its contribution to plant and mycorrhizal N acquisition.We used controlled mesocosms, soil incubations, stable isotopes, and imaging to investigate edaphic drivers of NH3 gas efflux, track lateral subsurface N transport originating from 15NH3 gas or 15N‐enriched organic matter, and assess plant and mycorrhizal N assimilation from this gaseous transport pathway.NH3 is released from soil organic matter, travels belowground, and contributes to root and fungal N content. Abiotic soil properties (pH and texture) influence the quantity of NH3 available for subsurface transport. Mutualisms with arbuscular mycorrhizal (AM) fungi can substantially increase plant NH3‐N uptake. The grass Brachypodium distachyon acquired 6–9% of total plant N from organic matter‐N that traveled as a gas belowground. Colonization by the AM fungus Rhizophagus irregularis was associated with a two‐fold increase in total plant N acquisition from subsurface NH3 gas.NH3 gas transport and uptake pathways may be fundamentally different from those of more commonly studied soil N species and warrant further research. [ABSTRACT FROM AUTHOR]

Chemical responses of tundra vegetation and tundra soil to environmental changes are likely to differ, with implications for ecosystem functioning, yet they are rarely compared. Here, we aimed at comparing sensitivity and magnitude of short‐term carbon and nitrogen responses of three main tundra ecosystem compartments: vascular plants, mosses, and soil, to two environmental perturbations: herbivore disturbance and warming. In a full‐factorial field experiment in the high‐Arctic Svalbard, we simulated herbivore disturbance as spring grubbing activity by pink‐footed geese (Anser brachyrhynchus) and passively increased summer temperatures using open‐top chambers. Manipulations were set up within three habitats that differ in soil moisture and carried out for two consecutive growing seasons. Overall, we found small and few significant responses to herbivore disturbance and warming, suggesting that carbon and nitrogen contents of high‐Arctic ecosystems are relatively resistant to these perturbations, at least in the short term. However, the three ecosystem compartments still differed in their sensitivity to perturbations (vascular plants > soil > mosses), and this was exacerbated by their differential sensitivity across habitats (mesic > moist > wet). Also, while vascular plants responded to herbivore disturbance in mesic and wet habitats and to warming in mesic and moist habitats, soil and mosses only responded to herbivore disturbance in mesic and wet habitats, respectively. Responses to treatments were generally consistent across the two growing seasons, despite great differences in temperature conditions and large between‐year variations in the chemical composition of the three ecosystem compartments. These findings highlight the potential for environmental perturbations to have small, yet differential short‐term impacts on the carbon and nitrogen contents of vascular plants, mosses, and soil, both within and between tundra habitats. Our results imply that assessments of a single ecosystem compartment in a given context cannot be extrapolated to the whole ecosystem, thus stressing the importance of considering both vegetation and soil carbon and nitrogen responses, and how they display across habitats, in order to better understand how environmental changes might affect biogeochemical processes in the tundra. Longer‐term studies should dig deeper into the relative role of (simulated) global change drivers vs. natural inter‐annual climatic fluctuations for tundra ecosystem carbon and nitrogen dynamics. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of three N fertilization levels 60 (low), 120 (medium), and 180 (high) kg N ha−1 and soil moisture content gradients created by a line-source sprinkler on the expression of plasticity in lateral root branching and dry matter production (DMP) of upland new rice for Africa (NERICA) 1 and 4. There were no significant differences in DMP between NERICA 1 and 4 under well-watered, mild drought, and severe drought conditions regardless of N level. In contrast, under moderate drought (12–21% v/v of soil moisture content [SMC] in 2011 and 16–24% v/v of SMC in 2012), NERICA 1 had significantly higher shoot dry weight, total root length (TRL), lateral root length, and branching index than NERICA 4 at medium and high N; however, there was no significant difference between the two NERICAs in DMP at low N. TRL of NERICA 1 was significantly higher under moderate drought than well-watered conditions, but only with medium and high N. Regardless of N level, moderate drought did not enhance NERICA 4’s root system. Thus, NERICA 1’s root system exhibited plastic development, promoting lateral root branching at medium and high N. These morphological changes were associated with the greater DMP in NERICA 1 than NERICA 4 under moderate drought, whereas the lack of such plasticity at low N meant genotypic differences in DMP were obscured. Our findings implied that N application can improve upland NERICA productivity under moderate drought conditions, but differences in variety and field conditions may influence efficacy.

Foliar application of nutrient is more efficient than soil-applied. In this project the effect of calcium nitrate and potassium nitrate on qualitative and quantitative traits was investigated in seedless barberry (Berberis vulgaris L.). Seedless barberry shrubs with different reproductive statuses (ON and OFF) were treated with spraying of calcium nitrate (Ca(NO3)2) or potassium nitrate (KNO3) solutions at concentration of 0.5% and distilled water (as control) four times during different fruit growth and development stages. The results showed that foliar application of both chemical salts significantly increased the number of clusters per branch, the number of berries per branch and the number of berries per cluster in 2017. The highest and the lowest number of clusters per branch, and the number of berries per branch were obtained in KNO3 and control treatments, respectively in 2018. Also, the greatest number of berries per cluster was recorded in treated plants with Ca(NO3)2 in 2018. The nitrogen content of fruit was higher in Ca(NO3)2 treatment. The highest fruit calcium content was obtained in Ca(NO3)2 treatment in both seasons. Berries treated with distilled water (control) were redder, and the fruits treated with Ca(NO3)2 and KNO3 (0.5%) were brighter in the 2017 season. However, the quality of treated fruit with Ca(NO3)2 and KNO3 (0.5%) was higher than the control in both years. The results showed that foliar spraying with Ca(NO3)2 and KNO3 significantly improved the qualitative and quantitative characteristics of barberry fruit compared to the control. [ABSTRACT FROM AUTHOR]

Cereal cyst nematode (CCN) (Heterodera avenae) is a major root parasite of wheat throughout the world. A pot experiment was conducted in screen house in CCS Haryana Agricultural University, Hisar during 2016–2017 for studying the nutrient uptake by wheat plants infected with H. avenae. Urea, single super phosphate (SSP), Muriate of potash (MOP), and zinc sulfate (Zn SO4) were applied singly and in combinations, and compared with a control without fertilizers. H. avenae reduced the uptake of nutrients (nitrogen (N), phosphorous (P), potassium (K), and Zn) as compared to uninfested soil. Improved nutrients uptake was found in the treatment where all nutrients were applied in soil. Lesser uptake was recorded in the treatment where no nutrient was applied in soil. In the soil, more nutrients were recorded in infested soil as compared to uninfested soil and, nutrients were also more in soil in the treatments where individual nutrients were applied than their combined application. [ABSTRACT FROM AUTHOR]

In the long‐term, herbivores can alter nutrient dynamics in terrestrial ecosystems by changing the functional composition of plant communities. Here, we ask to what extent herbivores can affect plant‐community nutrient dynamics in the short‐term. We provide theoretical expectations for immediate effects of herbivores on tundra‐grassland plant‐community nutrient levels throughout a single growing season and empirically evaluate these predictions. We established an experiment within two forb‐dominated and two grass‐dominated tundra‐grassland communities. We selected tundra‐patches disturbed by small rodents during the previous winter, and neighbouring undisturbed tundra‐patches. Within each tundra‐patch, we set up a reindeer‐open and a reindeer‐exclusion plot. Throughout the summer, we randomly collected over 2800 leaf samples from 34 vascular plant species/genera and analysed their nitrogen and phosphorus contents. Plant‐community nutrient levels were consistently higher in tundra‐patches affected by small rodents, both across tundra‐grassland types and throughout the growing season. Forbs and grasses growing in small‐rodent disturbed tundra‐patches had 11% and 25% higher nutrient content, respectively, compared to undisturbed tundra‐patches. Reindeer affected only grasses growing in grass‐dominated tundra‐grasslands and the outcome was dependent on small‐rodent winter disturbance. Reindeer increased grass nitrogen content in undisturbed tundra‐patches (+7%) and weakened the positive effects of small rodents in disturbed tundra‐patches (from 25% to 15% higher nutrient content [both nitrogen and phosphorus]). By enhancing plant nutrient levels throughout a single growing season, herbivores were key, immediate modifiers of plant‐community nutrient dynamics in tundra‐grasslands. Higher nutrient contents still detected in senescent leaves at the end of the summer in herbivore‐affected tundra suggest that herbivory is accelerating short‐term tundra‐grassland nutrient cycling rates. Our findings from tundra‐grassland communities align with theoretical expectations of positive herbivore effects on nutrient cycling in relatively productive ecosystems. [ABSTRACT FROM AUTHOR]

Fully mycoheterotrophic plants are thought to obtain carbon exclusively from their root‐associated fungal partners. The general enrichment of these plants in the heavy isotopes 13C and 15N suggests that fungi are the main nutrient source for these plants. Yet, the majority of studies have targeted mycoheterotrophic plants associated with ectomycorrhizal, orchid mycorrhizal and saprotrophic fungi, while mycoheterotrophic plants living on arbuscular mycorrhizal fungi remain understudied.Here, we sampled 13 species of arbuscular mycorrhizal fully mycoheterotrophic plants from five families and co‐occurring autotrophic reference plants growing in forests of tropical South America, tropical South East Asia and temperate Australasia. We measured stable isotope natural abundances (δ13C, δ15N, δ2H and δ18O), determined total nitrogen concentrations and used high‐throughput DNA sequencing to characterize the arbuscular mycorrhizal fungal communities associated with the sampled mycoheterotrophic plants.We observed a general enrichment in 13C and 15N isotopes across mycoheterotrophic plant families and geographic regions. We confirm cases where no 15N enrichment is present, but we show that in general arbuscular mycoheterotrophic plants are enriched in 15N. Moreover, we demonstrate for the first time that these plants are significantly enriched in 2H but not in 18O in relation to their autotrophic references. The fungal communities targeted by the mycoheterotrophs mainly consist of Glomeraceae and show strong association with the isotopic signatures and geographic origin of the plants.Synthesis. Our findings enlarge the limited knowledge on the multi‐element stable isotopic signatures of mycoheterotrophic plants living on arbuscular mycorrhizal fungi. We show that these plants are enriched in 13C and 2H as expected due to their mycoheterotrophic nutrition, and that in general they are also enriched in 15N, despite some exceptions. Variation in stable isotope signatures is likely influenced by plant taxonomy, geography and fungal community composition. [ABSTRACT FROM AUTHOR]

The contents and forms of nitrogen (N), phosphorus (P), and organic carbon (C) were determined with 40 cm (approximately 1600 s) core sediments from Erhai Lake on the Yungui Plateau of China as the sample. The vertical distribution characteristics, coupling relationships and ecological indicator significance of C–N–P were studied and identified. The results showed that the total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) contents were in the ranges of 1436–8255 mg·kg−1, 1287–5462 mg·kg−1, and 870.26–1507.74 mg·kg−1, respectively. In the Erhai Lake sediments, the main forms of TOC, organic nitrogen (ON) and organic phosphorus (OP) were humus, TN, and TP, respectively. The deposition of C, N, and P in the Erhai Lake sediments was divided into four periods. In the initial development period (from 40 to 23 cm), C, N and P were deposited and released synchronously; the main form of N was nontransferable total nitrogen (NTN), and that of P was inorganic phosphorus (IP). In the ecological recovery period (from 22 to 14 cm), C and N were deposited synchronously, and their deposition amounts were more than that of P. C, N and P were released synchronously. The main form of N was transferable total nitrogen (TTN), and that of P was IP. In the rapid economic growth period (from 13 to 0 cm), C, N, and P were deposited and released synchronously; the main form of N was NTN, and that of P was OP. In comparison to the other periods, this period was a period of higher active soil organic carbon (ASOC). In the integrated management period (surface sediment), C and N were deposited and released synchronously, and their deposition amounts were greater than that of P. The main form of N was NTN, that of P was OP, and the ASOC content was high. When exogenous inputs were the main sources of C, N, and P, the deposition forms of P and N were mainly OP and NTN, respectively, and those of IP and TTN were calcium-bound P (Ca–P) and ion-exchange form N (IEF–N), respectively. When endogenous inputs were the main sources of C, N and P, the deposition forms of P and N were mainly IP and TTN, respectively, and those of IP and TTN were Fe/Al–P and weak acid extractable form (WAEF–N), respectively. The content ratio of Ca–P and Fe/Al–P, as well as that of IEF–N and WAEF–N, could reflect the changes in the contribution of endogenous and exogenous sources to the Erhai Lake sediments. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is the most important nutrient for plant production and therefore it is necessary to fertilize with quantities of it that allow ensuring the proper development of crops. Currently, chemical synthesis fertilizers containing ammonium (NH4+), nitrate (NO3-) or urea (CO(NH2)2), are the most commonly used. However, the way in which they are dosed and applied to soils is not suitable, since they are used in high quantities with little efficiency, generating a high environmental impact by causing salinity, toxicity and pollution problems in soils and water, which in turn has effects on ecosystems and health. Recognizing this problem, and taking into account the need to continue generating both products and mechanisms, that allow to guarantee the productivity of agricultural systems and their contribution to the economy and food security of countries in a sustainable way, they have been raised varied solutions in this regard. This paper sought to analyze the effects generated by nitrogen fertilizers in soil and water, as well as the alternatives proposed by several authors that minimize the impact of these compounds on the environment.After conducting a systematic review of various studies on the subject, it it was observed that in the literature of the last 20 years, the use of microorganisms for bioremediation is highlighted, as well as the application of biofertilizers as the most relevant and efficient alternatives to counteract in a sustainable way the contaminating effects with nitrogen fertilizers. [ABSTRACT FROM AUTHOR]

Background: Cattle manure (CM) is the most common organic fertilizer used by farmers. However, its usually slow decomposition leads to the use of chemical fertilizers. Therefore, experiments on nano- and micro-sized particles of CM were conducted to evaluate the possibility of accelerating its decomposition in soil. Methods: The effects of a sole application of CM in different sizes (nano-, micro-, and natural-sized particles) in two ranges (5 and 20 Mg ha-1) and the combined application of CM and chemical fertilizers on the plant growth characteristics of soybean (cv. JS 335) were studied at Gorgan University. Nano- and micro-sized particles of CM were produced using a ball mill, and their half-life in soil was measured. Soil properties were measured before planting. Grain yield, 1000 grain weight, number of pods per plant, biological yield, plant height, and nutrient contents in plant shoot material were measured. Results: The results showed that the use of nano-sized particles of CM (nCM) caused a significant increase in yield and yield components. Increasing the amount of crushing resulted in an increased rate of CM mineralization and in proper nitration before the formation of nodes in the roots. A significantly higher yield was obtained with nCM than with chemical fertilizer, and due to the nCM particles’ half-life in soil, the plants were allowed to absorb nutrients for a longer time period. Conclusion: The nCM has two major advantages over chemical fertilizers in that it does not release nutrients as quickly as chemical fertilizers and the loss of nutrients from soil is low.

Background: The application of biochar as a soil amendment has achieved popularity and has been found to improve considerably soil nutrient status and plant productivity in low fertile soils. Methods: This study used two different methods to apply sewage sludge and sewage sludge biochar with three replicates in a completely randomized block design. The experiment included (1) control, (2) mulch biochar (20 t/ha), (3) incorporated biochar (20 t/ha), (4) mulch sewage sludge (45 t/ha), and (5) incorporated sewage sludge (45 t/ha). This study aimed to investigate the potential benefits of sewage sludge and its biochar as mulch and incorporated into the top-soil for soil fertility, growth, yield, and shoot nutrient concentration of soybean and the effects of treatments on dry bulk density, water content, and mechanical resistance. Results: The results showed higher values of height, biological yield, grain yield, and number of pods in the biochar mulch treatments (116.5, 10627.01, 4180, and 71.2, respectively). Moreover, it was determined that the addition of biochar and sewage sludge to soil resulted in increased shoot nitrogen (N), phosphorous (P), and potassium (K) concentrations, soil P, soil K, and total soil N (TN) compared with the control plots. Results from this study also showed that biochar and sewage sludge had positive impacts on the physical properties of soil. Bulk density and soil mechanical resistance were decreased, and volumetric water content was increased. Conclusion: Heating sludge removed all pathogens. It is recommended that short- and long-term studies be conducted in the region to investigate further increases in the combined biochar and sewage sludge application rates.

Clinoptilolite zeolite coated with hydrous ferric oxide (FeZeo) may improve nutrient retention when blended into sand-based root zones. The objective of this study was to evaluate the effects of nutrient-charged FeZeo on nitrogen (N) and phosphorus (P) leaching and on growth of creeping bentgrass (Agrostis palustris Huds.). FeZeo was pre-loaded with 255 mg kg−1 N and 224 mg kg−1 P using a water-soluble fertilizer. Then, root zone mixes (RZM) containing 0, 5, 10, and 20% fertilizer-loaded FeZeo were packed into lysimeters and seeded with creeping bentgrass at a rate of 49 kg ha−1. RZMs with 20% FeZeo received no additional fertilization whereas those containing 0, 5, and 10% FeZeo received four additional fertilizer applications during the next 8 months so that the cumulative N and P rates for every lysimeter were equivalent to 149 kg ha−1 and 131 kg ha−1, respectively. Lysimeters were irrigated every 2 to 3 days and leachate was collected and analyzed. Compared to putting green sand, the 5, 10 and 20% FeZeo treatments reduced the quantity of leached P by 96.2%, 91.3%, and 90.3%, and the quantity of leached N by 88.6%, 82.7% and 76.7%, respectively. Results suggest that pre-fertilized FeZeo applied to sand-based root zone mixes at 5 to 10% can significantly reduce nutrient leaching while maintaining acceptable plant growth, but higher rates of FeZeo can reduce plant growth. An alternative use for higher rates of FeZeo might include a filtering material for agricultural tile drainage. Abbreviations: cation exchange capacity (CEC), electrical conductivity (EC), iron-oxide coated clinoptilolite zeolite FeZeo, nitrogen (N), RZM, root zone mix [ABSTRACT FROM AUTHOR]

Two field trials were conducted on the Research Farm of the Institute of Food Security, Environmental Resources and Agricultural Research, Nigeria during the late cropping seasons (Jun.–Nov.) of 2014 and 2015 to evaluate the agronomic performance of four recently released sunflower varieties (SAMSUN-1, SMASUN-2, SAMSUN-3 and SAMSUN-4) to three fertilizer regimes: Control, Split application of 30 kg N + 28 kg P2O5 at 21 days after sowing (DAS) and at anthesis and Single application of 60 kg N and 56 kg P2O5 at 21DAS. The experiment was laid out in a randomized complete block design using a 3 × 4 factorial arrangement and replicated three times. Data were collected on phenology, plant height, seed yield and yield attributes, and quality. The varietal effect was only significant in 2015 for head weight, a number of achene per head and 100 achene weight. Application of N and P fertilizer either as split or single significantly (P ≤ 0.05; F-test) enhanced plant height at R5 and R9, 100 achene weight, achene weight per head and grain yield in both years. Single application resulted in significantly (P ≤ 0.05) higher grain yield in 2014 than the split and control and was on par with a split. Significant variety × fertilizer regime was recorded for protein content in 2014 and 2015, and oil content in 2015. Therefore, a single application of N and P fertilizers at 21 WAS is recommended for adoption in the humid tropics to enhance seed and oil production of SAMSUN-3 and SAMSUN-4. [ABSTRACT FROM AUTHOR]

Abstract Over the last 30 years, Denmark has implemented a series of environmental action plans involving regulation of agricultural nitrogen (N) use and management in order to minimize the N pollution of the environment. The local effects of these action plan initiatives depend on various factors such as the efficiency of the implemented measures, and in particular, the hydrogeological structures and geochemical conditions of the subsurface that control the transport and fate of N. In this study, the effects of the Danish agricultural N regulations on shallow oxic groundwater are compared among five small agricultural catchments underlain by two types of lithology (sandy vs. loamy). Long-term spatially dense groundwater monitoring data is compared with monitoring data of nitrate in the root zone leaching and in stream. The results show clear improvements in the environmental state of shallow oxic groundwater in the first two decades since 1989 where the number of monitoring points with significant decreasing nitrate trends gradually increased for both soil types. Such improvements can be attributed to the effects of N mitigation measures implemented as a general regulation all over the country. However, deteriorations have been recorded in the last decade until 2016 where 26–35% of the monitoring points exhibited significant upward nitrate trends in both types of catchments. It is noteworthy that for sandy soils, the major part (93%) of the monitoring points showing significant upward trends in the period 2009–2016, also had concentrations above the groundwater standard of 50 mg/l nitrate in 2016. Altogether, the oxic groundwater in the sandy catchments was more responsive to N regulations than that in the loamy catchments. This might be due to efficient N regulation through statutory norms for the utilization of N in manure, increasing the N use efficiency in areas with a relatively high livestock density. Another reason is the nitrate vulnerability of the aquifers in sandy areas, with widespread oxic conditions from the top soil to the saturated zone. In the loamy catchments, nitrate may be reduced in near-surface localized reduced zones, and the reaction is often fast and the travel time from the root zone to the stream often relatively short. Therefore, stream nitrate concentrations were higher in the loamy catchments than in the sandy catchments. This is attributed to different hydrogeological pathways. Thus, in sandy catchments, deep groundwater is an important pathway, while in loamy catchments tile drains deliver nitrate directly to the streams. Our results indicate that N mitigation measures will help improve groundwater quality in sandy soils, while in loamy soils they will help to reduce surface water N loads. This implies that to achieve optimal environmental N reduction, agricultural N regulations should be strategically implemented according to farming characteristics and site-specific hydrogeological and geochemical conditions of the subsurface. Highlights • Clear nitrate response in shallow groundwater on agricultural N regulation. • In sandy sites, groundwater is more responsive to the agricultural N regulations. • In sandy sites, groundwater is nitrate vulnerable. • In loamy site, surface water is nitrate vulnerable. • Target N regulation should be adjusted to hydro-geochemical site characteristics. [ABSTRACT FROM AUTHOR]

The production of agricultural wastes is problematic. Without proper disposal, many aspects of the environment may be affected by these wastes. This study attempted to harness rice straw and sugar cane bagasse wastes for the enhancement of Triticum aestivum cultivation through cellulase production by the fungus Aspergillus niger. The FPase and CMCase activities (representing the cellulytic activity) of A. niger were found to be enhanced until the fifth day of incubation. The maxima of the FPase and CMCase activities were 89.0 ± 2.0 and 3.3 ± 0.4 U mL−1 for the rice straw; and 91.0 ± 2.1 and 4.1 ± 0.4 U mL−1 for the sugar cane bagasse, respectively. A pot experiment was conducted to evaluate the effectiveness of cellulase-digested wastes on the growth and biochemical constituents of wheat cultivars. The plant height, fresh weight, and pigment constitution of wheat cultivars were enhanced compared to sand soil and compost fertilized soil treatments. Moreover, the total soluble carbohydrate, nitrogen and phosphorus contents of T. aestivum shoots showed promising results using these wastes. Our results show that rice straw and sugar cane bagasse can be suitable substrates for wheat cultivation. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of three N fertilization levels 60 (low), 120 (medium), and 180 (high) kg N ha−1 and soil moisture content gradients created by a line-source sprinkler on the expression of plasticity in lateral root branching and dry matter production (DMP) of upland new rice for Africa (NERICA) 1 and 4. There were no significant differences in DMP between NERICA 1 and 4 under well-watered, mild drought, and severe drought conditions regardless of N level. In contrast, under moderate drought (12–21% v/v of soil moisture content [SMC] in 2011 and 16–24% v/v of SMC in 2012), NERICA 1 had significantly higher shoot dry weight, total root length (TRL), lateral root length, and branching index than NERICA 4 at medium and high N; however, there was no significant difference between the two NERICAs in DMP at low N. TRL of NERICA 1 was significantly higher under moderate drought than well-watered conditions, but only with medium and high N. Regardless of N level, moderate drought did not enhance NERICA 4's root system. Thus, NERICA 1's root system exhibited plastic development, promoting lateral root branching at medium and high N. These morphological changes were associated with the greater DMP in NERICA 1 than NERICA 4 under moderate drought, whereas the lack of such plasticity at low N meant genotypic differences in DMP were obscured. Our findings implied that N application can improve upland NERICA productivity under moderate drought conditions, but differences in variety and field conditions may influence efficacy. [ABSTRACT FROM AUTHOR]

Abstract The maintenance and accumulation of soil organic carbon (SOC) is critical to the agricultural sustainability and environmental stability in oasis-desert belts. The objective of this study was to determine the effects of oasis formation on SOC and aggregate structure, as well as the linkage between them, throughout a 0–200 cm soil profile. The investigation was conducted in five oases at the northern foot of the Tianshan Mountains in Central Asia. Oasis farmlands reclaimed 3, 5, 10, 20, 50, and >100 years ago were compared with the desert pairs they originated from. The SOC content significantly increased throughout the whole profile after 20 years of reclamation, despite a loss in the first 10 years of reclamation. The values reached maxima at 50 years of reclamation, which increased by 67–135% compared to initial values. The macro-aggregate (diameter > 0.25 mm) fraction with high carbon (C) concentration significantly increased throughout the soil profile after reclamation, and showed the greatest variation during oasis formation, compared with the other aggregate fractions (0.25–0.053 and <0.053 mm). These changes were significantly correlated with increases in soil nutrients and microbial biomass and decreases in soil pH and salt during oasis formation. In conclusion, the oasis formation enhanced SOC accumulation not only in topsoil but also in deep soil, and soil aggregate structure was improved by increased macro-aggregates. The formation of macro-aggregates and the increase in their associated C had significant correlations with SOC accumulation. Fertilization, especially inorganic nitrogen, very likely promoted the SOC accumulation and soil aggregation in concert with annual input of crop residues into the originally poor desert soils during oasis formation. Highlights • SOC contents (0–200 cm) significantly increased at 20 years of desert reclamation. • SOC contents reached maxima at 50 years of reclamation. • Oasis formation improved soil aggregate structure by increasing macro-aggregates. • The increase in SOC content promoted soil aggregation during oasis formation. • Soil N contents had the most significant correlation with SOC contents. [ABSTRACT FROM AUTHOR]

Summary: Nitrous oxide (N2O) is a potent, globally important, greenhouse gas, predominantly released from agricultural soils during nitrogen (N) cycling. Arbuscular mycorrhizal fungi (AMF) form a mutualistic symbiosis with two‐thirds of land plants, providing phosphorus and/or N in exchange for carbon. As AMF acquire N, it was hypothesized that AMF hyphae may reduce N2O production.AMF hyphae were either allowed (AMF) or prevented (nonAMF) access to a compartment containing an organic matter and soil patch in two independent microcosm experiments. Compartment and patch N2O production was measured both before and after addition of ammonium and nitrate.In both experiments, N2O production decreased when AMF hyphae were present before inorganic N addition. In the presence of AMF hyphae, N2O production remained low following ammonium application, but increased in the nonAMF controls. By contrast, negligible N2O was produced following nitrate application to either AMF treatment.Thus, the main N2O source in this system appeared to be via nitrification, and the production of N2O was reduced in the presence of AMF hyphae. It is hypothesized that AMF hyphae may be outcompeting slow‐growing nitrifiers for ammonium. This has significant global implications for our understanding of soil N cycling pathways and N2O production. [ABSTRACT FROM AUTHOR]

The Substance Flow Analysis (SFA) concept has been widely used for the sustainability of material flow management in agriculture of many South-east Asia studies including Malaysia. Focusing on agricultural land, this paper emphasises the dynamic analysis of nitrogen flux from sectors, processes and flows that enter, leave, circulate and also accumulate in the metabolism of agricultural land. SubSTance Flow Analysis software (STAN 2.5) and Microsoft Excel have been used to complete the nitrogen equilibrium calculation in four selected subsystems which are subsystem market use, crop production, livestock production and environment, in six districts in Terengganu. In the present study, intensive use of nitrate fertilisers (5835 tons N per year), crop harvesting (3645 tonnes per year), and water absorbing into underground systems (1969 tons per year), have been identified as the major contributors to environmental degradation. The results of the present study found that the SFA method is very practical to estimate the amount of agricultural nutrient load, to identify the contribution of agricultural activity, the level of land use, and also to analyse the pattern of agricultural nutrient release space in Terengganu. Some innovative proposals are also offered and hopefully this study can be used as a reference for any sustainable management plan for other scientific studies. [ABSTRACT FROM AUTHOR]

Summary: The emission of isoprenoids (e.g. isoprene and monoterpenes) by plants plays an important defensive role against biotic and abiotic stresses. Little is known, however, about the functional traits linked to species‐specific variability in the types and rates of isoprenoids emitted and about possible co‐evolution of functional traits with isoprenoid emission type (isoprene emitter, monoterpene emitter or both).We combined data for isoprene and monoterpene emission rates per unit dry mass with key functional traits (foliar nitrogen (N) and phosphorus (P) concentrations, and leaf mass per area) and climate for 113 plant species, covering the boreal, wet temperate, Mediterranean and tropical biomes.Foliar N was positively correlated with isoprene emission, and foliar P was negatively correlated with both isoprene and monoterpene emission rate. Nonemitting plants generally had the highest nutrient concentrations, and those storing monoterpenes had the lowest concentrations. Our phylogenetic analyses found that the type of isoprenoid emission followed an adaptive, rather than a random model of evolution.Evolution of isoprenoids may be linked to nutrient availability. Foliar N and P are good predictors of the type of isoprenoid emission and the rate at which monoterpenes, and to a lesser extent isoprene, are emitted. See also the Editorial by Kessler, 220: 655–658. [ABSTRACT FROM AUTHOR]

Summary: Boreal trees rely on their ectomycorrhizal fungal symbionts to acquire growth‐limiting nutrients, such as nitrogen (N), which mainly occurs as proteins complexed in soil organic matter (SOM). The mechanisms for liberating this N are unclear as ectomycorrhizal fungi have lost many genes encoding lignocellulose‐degrading enzymes present in their saprotrophic ancestors. We hypothesized that hydroxyl radicals (˙OH), produced by the ectomycorrhizal fungus Paxillus involutus during growth on SOM, are involved in liberating organic N. Paxillus involutus was grown for 7 d on N‐containing or N‐free substrates that represent major organic compounds of SOM. ˙OH production, ammonium assimilation, and proteolytic activity were measured daily. ˙OH production was strongly induced when P. involutus switched from ammonium to protein as the main N source. Extracellular proteolytic activity was initiated shortly after the oxidation. Oxidized protein substrates induced higher proteolytic activity than unmodified proteins. Dynamic modeling predicted that ˙OH production occurs in a burst, regulated mainly by ammonium and ferric iron concentrations. We propose that the production of ˙OH and extracellular proteolytic enzymes are regulated by similar nutritional signals. Oxidation works in concert with proteolysis, improving N liberation from proteins in SOM. Organic N mining by ectomycorrhizal fungi has, until now, only been attributed to proteolysis. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) concentrations and N:P ratios critically influence periphyton productivity and nutrient cycling in aquatic ecosystems. In coastal wetlands, variations in hydrology and water source (fresh or marine) influence nutrient availability, but short-term effects of drying and rewetting and long-term effects of nutrient exposure on periphyton nutrient retention are uncertain. An outdoor microcosm experiment simulated short-term exposure to variation in drying-rewetting frequency on periphyton mat nutrient retention. A 13-year dataset from freshwater marshes of the Florida Everglades was examined for the effect of long-term proximity to different N and P sources on mat-forming periphyton nutrient standing stocks and stoichiometry. Field sites were selected from one drainage with shorter hydroperiod and higher connectivity to freshwater anthropogenic nutrient supplies (Taylor Slough/Panhandle, TS/Ph) and another drainage with longer hydroperiod and higher connectivity to marine nutrient supplies (Shark River Slough, SRS). Total P, but not total N, increased in periphyton mats exposed to both low and high drying-rewetting frequency with respect to the control mats in our experimental microcosm. In SRS, N:P ratios slightly decreased downstream due to marine nutrient supplies, while TS/Ph increased. Mats exposed to short-term drying-rewetting had higher nutrient retention, similar to nutrient standing stocks from long-term field data. Periphyton mat microbial communities may undergo community shifts upon drying-rewetting and chronic exposure to nutrient loads. Additional work on microbial species composition may further explain how periphyton communities interact with drying-rewetting dynamics to influence nutrient cycling and retention in wetlands. [ABSTRACT FROM AUTHOR]

Contents Summary 68 I. Introduction 68 II. Have ECM fungi retained genes with lignocellulolytic potential from saprotrophic ancestors? 69 III. Are genes with saprotrophic function expressed by ECM fungi when in symbiosis? 71 IV. Do transcribed enzymes operate to obtain N from SOM? 71 V. Is the organic N derived from SOM transferred to the plant host? 71 VI. Concluding remarks 72 Acknowledgements 72 References 72 Summary: The view that ectomycorrhizal (ECM) fungi commonly participate in the enzymatic liberation of nitrogen (N) from soil organic matter (SOM) has recently been invoked as a key mechanism governing the biogeochemical cycles of forest ecosystems. Here, we provide evidence that not all evolutionary lineages of ECM have retained the genetic potential to produce extracellular enzymes that degrade SOM, calling into question the ubiquity of the proposed mechanism. Further, we discuss several untested conditions that must be empirically validated before it is certain that any lineage of ECM fungi actively expresses extracellular enzymes in order to degrade SOM and transfer N contained therein to its host plant. [ABSTRACT FROM AUTHOR]

• Total STXs of A. pacificum increased with increasing NO 3 − concentrations, while the excessive supplementation (8.82 mM) reduced the cellular toxicity. • A. pacificum toxicity profile was influenced by the changes in nitrate availability. • The correlation between sxtA4, sxtB and sxtI was demonstrated by a significant increase of the transcript abundance in cultures with high NO 3 − concentrations. • The novel sxtI was identified in this study, and its expression levels parallel to that of sxt implies its pivotal role in STX biosynthesis. • The toxin production in A. pacificum is linked to physiological and molecular processes in the cells, influenced by N availability. The dinoflagellate Alexandrium pacificum (group IV) is of particular interest because of its involvement in harmful algal blooms and production of saxitoxin (STX), which causes paralytic shellfish poisoning. The toxicity from STX and its analogues (STXs) is suspected to be affected by nitrogen (N) availability. However, the toxicity-associated behavior and STX-biosynthesis gene responses of the toxic A. pacificum under N fluctuations have not been sufficiently investigated. In the present study, we identified the sxtI gene involved in sxt biosynthesis pathway and evaluated the effects of nitrate (NO 3 −) on STXs production and the expression of four sxt core genes (sxtA4, sxtG, sxtB, and sxtI). Quantification of total STXs levels in the cultures under different NO 3 − regimes showed that NO 3 − concentration influenced STXs production. In addition, the proportion and concentration of STXs varied depending on the NO 3 − concentration. Core sxt transcript abundance was also influenced by available NO 3 − in a time-dependent manner. Expressional levels and patterns of sxtI were correlated with those of sxtA and sxtB. The relationship between the toxins and sxt responses in A. pacificum under various NO 3 − regimes suggests the direct involvement of N in the STXs biosynthesis pathway. Understanding this link would provide a tool to understand the toxin dynamics of dinoflagellates following N shifts in marine environments. [ABSTRACT FROM AUTHOR]

China is undergoing a rapid transition from a rural to an urban society. This societal change is a consequence of a national drive toward economic prosperity. However, accelerated urban development resulting from rapid population migration from rural to urban lands has led to high levels of untreated sewage entering aquatic ecosystems directly. Consequently, many of these regions have been identified as hot spots of riverine nitrogen (N) pollution because of the increasing level of urban point-source discharge. In order to address this concern, we assessed effects of urban development on ammonia-nitrogen (AN) loads using a panel data regression model. The model, expressed as an exponential function of anthropogenic N inputs multiplied by a power function of streamflow, was applied to 20 subwatersheds of the Huai River Basin for the years 2003-2010. The results indicated that this model can account for 81% of the variation in annual AN fluxes over space and time. Application of this model to three scenarios of urban development and sewage treatment (termed urbanization priority, sustainable development, and environmental priority) suggests that future N pollution will inevitably deteriorate if current urban environmental management and investment are not significantly improved. Stronger support for environmental management is very critical to alleviate N pollution and improve water quality. More effort should focus on improving sewage treatment and the N removal rate of the current sewage system in light of the increasing degree of urbanization. [ABSTRACT FROM AUTHOR]

Soil salinity and sodicity can not only directly restrain crop growth by osmotic and specific ion stresses, it also may reduce grain yield indirectly by impacting plant absorption of essential nutrients. Ensuring adequate nitrogen is an important management aspect of rice production in saline-sodic soils. The objective of this study was to investigate the interaction of soil pH, salinity and nitrogen application on rice yield and nutrient absorption. We conducted a rice experiment in containers in a greenhouse. The soils were first leached with 9 target salt solutions of pH 7, 8 and 9 and electrical conductivity (EC) of 2, 6 and 10 dS m −1 . Nitrogen application rates were 100, 200 and 300 kg N ha −1 . Rice grain yield and shoot weight significantly decreased with increasing soil pH and increasing soil EC, and significantly increased with increasing nitrogen application ( P < 0.001). However, at high EC and/or high pH yield was not significantly increased by increased N. High pH and high EC in soil significantly influenced the mineral nutrient content of rice shoots ( P < 0.05). High soil pH and soil EC stresses were superimposed on each other, the negative effects on rice were compounded. The results by stepwise regression analysis showed that soil pH very significantly and adversely impacts grain yield and was the major factor impacting rice grain yield (R 2 = 0.565, P < 0.001). Nitrogen application provided a positive response under control and pH 7 at all salinity values, and at pH 8 under low salinity only. There was no significant response to additional N under pH 8 and elevated EC and no significant response at pH 9 for all EC values. Thus, adequate nitrogen application is an important technical measure for improving rice yield and promoting nutrient absorption in rice of high EC soils but not of high pH soils where pH is the major limiting factor for rice production in saline-sodic soils. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity represents one of the main yield-limiting factors for crops in acid soils. Silicon (Si) is known to increase tolerance in higher plants. This study was conducted to determine whether treatment with Si could improve nutrient uptake by peanut under Al stress. Peanut (Arachis hypogaeaL. cv Zhonghua 4) was raised with or without Si (1.5 mM) in the growth chamber under 0 and toxic Al (0.3 mM) levels. Aluminum stress significantly decreased the root- and total-dry weight by 52.4% and 32.0%, respectively. The content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) was significantly decreased, but that of Al increased markedly in shoots and roots after Al exposure at seedling, flower-needle, and pod-setting stage. Silicon alleviates Al toxicity in peanut plants in relation to Al distribution and allocation of tissue P, K, Ca, and Mg by favoring the partitioning of dry mass to roots. [ABSTRACT FROM AUTHOR]