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Trichoderma can promote plant growth under saline stress, but the mechanisms remain to be revealed. In this study, we investigate photosynthetic gas exchange, photosystem II (PSII) performance, nitrogen absorption and accumulation in a medicinal plant wolfberry (Lycium chinense) in saline soil supplemented with Trichoderma biofertilizer (TF). Larger nitrogen and biomass accumulation were found in plants supplemented with TF than with organic fertilizer (OF), suggesting that Trichoderma asperellum promoted plant growth and nitrogen accumulation under saline stress. T. asperellum strengthened root nitrogen (N) absorption according to greater increased root NH4+ and NO3- influxes under supplement with TF than OF, while nitrogen assimilative enzymes such as nitrate reductase, nitrite reductase and glutamine synthetase activities in roots and leaves were also stimulated. Thus, the elevated N accumulation derived from the induction of T. asperellum on nitrogen absorption and assimilation. Greater increased photosynthetic rate (Pn) and photosynthetic N-use efficiency under supplement with TF than OF illustrated that T. asperellum enhanced photosynthetic capacity and N utilization under saline stress. Although increased leaf stomatal conductance contributed to carbon (C) isotope fractionation under TF supplement, leaf 13C abundance was significantly increased by supplement with TF rather than OF, indicating that T. asperellum raised CO2 assimilation to a greater extent, reducing C isotope preference. Trichoderma asperellum optimized electron transport at PSII donor and acceptor sides under saline stress because of lower K and J steps in chlorophyll fluorescence transients under supplement with TF than OF. The amount of PSII active reaction centers was also increased by T. asperellum. Thus, PSII performance was upgraded, consistent with greater heightened delayed chlorophyll fluorescence transients and I1 peak under supplement with TF than OF. In summary, TF acted to increase N nutrient acquisition and photosynthetic C fixation resulting in enhanced wolfberry growth under saline soil stress.

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It is very important to promote plant growth and decrease the nitrogen leaching in soil, to improve nitrogen (N) utilization efficiency. In this experiment, we designed a new fertilization strategy, fruit tree hole storage brick (FTHSB) application under subsurface drip irrigation, to characterise the effects of FTHSB addition on N absorption and utilization in grapes. Three treatments were set in this study, including subsurface drip irrigation (CK) control, fruit tree hole storage brick A (T1) treatment, and fruit tree hole storage brick B (T2) treatment. Results showed that the pore number and size of FTHSB A were significantly higher than FTHSB B. Compared with CK, T1 and T2 treatments significantly increased the biomass of different organs of grape, N utilization and 15N content in the roots, stems and leaves, along with more prominent promotion at T1 treatment. When the soil depth was 15-30 cm, the FTHSB application significantly increased the soil 15N content. But when the soil depth was 30-45 cm, it reduced the soil 15N content greatly. T1 and T2 treatments obviously increased the activities of nitrite reductase (NR) and glutamine synthetase (GS) in grape leaves, also the urease activity(UR) in 30 cm of soil. Our findings suggest that FTHSB promoted plant N utilization by reducing N loss in soil and increasing the enzyme activity related to nitrogen metabolism. In addition, this study showed that FTHSB A application was more effective than FTHSB B in improving nitrogen utilization in grapes.

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Plant roots and rhizosphere soils assemble diverse microbial communities, and these root-associated microbiomes profoundly influence host development. Modern wheat has given rise to numerous cultivars for its wide range of ecological adaptations and commercial uses. Variations in nitrogen uptake by different wheat cultivars are widely observed in production practices. However, little is known about the composition and structure of the root-associated microbiota in different wheat cultivars, and it is not sure whether root-associated microbial communities are relevant in host nitrogen absorption. Therefore, there is an urgent need for systematic assessment of root-associated microbial communities and their association with host nitrogen absorption in field-grown wheat. Here, we investigated the root-associated microbial community composition, structure, and keystone taxa in wheat cultivars with different nitrogen absorption characteristics at different stages and their relationships with edaphic variables and host nitrogen uptake. Our results indicated that cultivar nitrogen absorption characteristics strongly interacted with bacterial and archaeal communities in the roots and edaphic physicochemical factors. The impact of host cultivar identity, developmental stage, and spatial niche on bacterial and archaeal community structure and network complexity increased progressively from rhizosphere soils to roots. The root microbial community had a significant direct effect on plant nitrogen absorption, while plant nitrogen absorption and soil temperature also significantly influenced root microbial community structure. The cultivar with higher nitrogen absorption at the jointing stage tended to cooperate with root microbial community to facilitate their own nitrogen absorption. Our work provides important information for further wheat microbiome manipulation to influence host nitrogen absorption. KEY POINTS: • Wheat cultivar and developmental stage affected microbiome structure and network. • The root microbial community strongly interacted with plant nitrogen absorption. • High nitrogen absorption cultivar tended to cooperate with root microbiome.

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Blueberry roots are inefficient in taking up water and nutrients, a fact partially related to their scarcity of root hairs, but they improve nutrient uptake by associating with ericoid mycorrhizal and endophytic fungi. However, the benefits of this association are both cultivar- and fungus-dependent. Our objective was to assess the effect of inoculation with three native fungal strains (Oidiodendron maius A, O. maius BP, and Acanthomyces lecanii BC) on plantlet growth, plantlet survival, and nitrogen (N) absorption of the southern highbush blueberry (SHB) cultivars Biloxi and Misty. The fungal strains were inoculated into the peat-based substrate for growing blueberry cultivars, and plantlets produced by micropropagation were transplanted and grown for four months. The three inoculated strains positively affected the survival percentage in at least one of the cultivars tested, whereas O. maius BP positively affected plant biomass, N derived from fertilizer absorption, N content, and plant N recovery (%) in both Biloxi and Misty. Our results show that the O. maius BP strain may prove useful as a bio-inoculant to improve blueberry production during the nursery stage.

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Saline-alkaline stress suppresses rice growth and threatens crop production. Despite substantial research on rice's tolerance to saline-alkaline stress, fewer studies have examined the impact of magnetic water treatments on saline-alkaline-stressed rice plants. We explored the physiological and molecular mechanisms involved in saline-alkaline stress tolerance enhancement via irrigation with magnetized water using Nipponbare. The growth of Nipponbare plants was inhibited by saline-alkaline stress, but this inhibition was alleviated by irrigating the plants with magnetized water, as evidenced by greater plant height, biomass, chlorophyll content, photosynthetic rates, and root system in plants irrigated with magnetized water compared to those irrigated with non-magnetized water. Plants that were irrigated with magnetized water were able to acquire more total nitrogen. In addition, we proved that rice seedlings irrigated with magnetized water had a greater root NO3--nitrogen concentration and root NH4+-nitrogen concentration than plants irrigated with non-magnetized water. These findings suggest that treatment with magnetized water could increase nitrogen uptake. To test this hypothesis, we analyzed the expression levels of genes involved in nitrogen acquisition. The expression levels of OsNRT1;1, OsNRT1;2, OsNRT2;1, OsAMT1;2, OsAMT2;1, OsAMT2;2, OsAMT2;3, OsAMT3;1, OsAMT3;2, and OsAMT3;3 were higher in plants exposed to magnetized water medium compared to those exposed to non-magnetized water media. We further demonstrated that treatment with magnetized water increases available nitrogen, NO3--nitrogen content, and NH4+-nitrogen content in soil under saline-alkaline stress. Our results revealed that the increased resistance of rice seedlings to saline-alkaline stress may be attributable to a very effective nitrogen acquisition system enhanced by magnetized water.

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Feeding-derived amarula cake to growing pigs can overcome a narrow range of ingredients challenges and improve productivity. The objective of the current study was to determine the response in nitrogen (N) balance in slow-growing pigs fed on incremental levels of amarula nut cake (ANC). Thirty clinically healthy male growing Windsnyer (30.7 kg ± 6.57) (mean ± standard deviation) were individually assigned to separate pens in a completely randomized design, with six pigs per dietary treatment. Iso-energetic experimental diets were formulated to contain 0, 50, 100, 150, and 200 g/kg dry matter (DM) of ANC using the summit and dilution technique. Pigs were given 10 days of dietary adaptation and a collection period of 5 consecutive days after 31 days of feeding. Nitrogen intake increased linearly with incremental levels of ANC (P < 0.01). As ANC inclusion increased, the nitrogen (N) absorption, apparent N digestibility, and N retention in pigs increased until it reached a maximum, then started to decrease (P < 0.05). Nitrogen utilization increased at the rate of 0.63 g for each 1 g increase in ANC (P < 0.01). There was a linear decrease (P < 0.01) in total nitrogen excretion through urine and faeces with ANC inclusion. Urinary pH levels decreased quadratically in response to graded levels of ANC (P < 0.01). The relationship between urinary pH and ANC inclusion was Y = 0.0115x2 - 0.3491x + 4.872 (P < 0.01). The nitrogen balance responses were due to ANC inclusion in diets that were balanced for limiting amino acids. It can be concluded that ANC reduces N excretion, potentially minimizing ammonia volatilization, which makes it an alternative protein source for slow-growing pigs.

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Clarifying the pattern of nitrogen absorption and utilization of rice under the treatments of Astragalus sinicus combined with chemical fertilizer application and the pattern of absorption, utilization, distribution and residue of A. sinicus nitrogen in rice-soil system could provide basis to rational fertilization for rice planting area in southern Henan. In this study, undisturbed soil column simulation and isotope tracer technology of 15N were used to examine the differences of nitrogen uptake and utilization of rice, nitrogen nutrient balance of rice-soil system and nitrogen uptake, utilization, distribution and residue of A. sinicus nitrogen after mineralization and decomposition among seven treatments. The treatments involved 1) no fertilization (CK); 2) chemical fertilizer+22500 kg·hm-2 A. sinicus (FM1); 3) chemical fertilizer+30000 kg·hm-2 A. sinicus (FM2); 4) chemical fertilizer+37500 kg·hm-2 A. sinicus (FM3); 5) chemical fertilizer+22500 kg·hm-2 A. sinicus +lime (FM1+CaO); 6) chemical fertilizer+30000 kg·hm-2 A. sinicus lime (FM2+CaO); 7) chemical fertilizer+37500 kg·hm-2 A. sinicus +lime (FM3+CaO). Results showed that compared with CK, fertilization significantly increased nitrogen uptake of grain and rice stalks, apparent nitrogen loss, and nitrogen surplus. The grain nitrogen uptake, rice straw nitrogen uptake and nitrogen use efficiency of rice increased firstly and then decreased with the increasing A. sinicus application rates, while the apparent nitrogen loss and nitrogen surplus showed the opposite trend. The best performance was presented under the treatment of chemical fertilizer combined with 30000 kg·hm-2 of A. sinicus. Lime addition could increase grain nitrogen uptake, rice straw nitrogen uptake, and nitrogen use efficiency of rice, while reducing apparent nitrogen loss and nitrogen surplus, with the best performance of FM2+CaO. For all the treatments, the proportion of nitrogen absorbed by rice from A. sinicus was 6.3%-13.2%, while that from soil and chemical fertilizer was 86.8%-93.7%. The utilization ratio of A. sinicus nitrogen by rice was 23.8%-33.6%. The utilization ratio of A. sinicus nitrogen in different parts of rice was grain > stem and leaf > root. The residue rate of A. sinicus nitrogen in soil was 37.6%-62.4%. The loss rate of A. sinicus nitrogen was 7.8%-38.6%. Comprehensively considering nitrogen absorption and utilization of rice, nitrogen nutrient balance of rice-soil system, and the distribution situation of nitrogen from A. sinicus in rice, FM2+CaO was the optimum fertilization pattern in the study area.

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In the fabrication of 17-4 PH by laser powder bed fusion (L-PBF) the well-documented occurrence of large amounts of retained austenite can be attributed to an elevated concentration of nitrogen present in the material. While the effects of continuous wave (CW) laser processing on in-situ nitrogen absorption characteristics have been evaluated, power modulated pulsed wave (PW) laser processing effects have not. In this study the effects of PW L-PBF processing of 17-4 PH on nitrogen absorption, phase composition, and mechanical performance are explored using commercially available PW L-PBF equipment and compared to samples produced by CW L-PBF. PW L-PBF samples fabricated in cover gas conditions with varying amounts of nitrogen demonstrated reduced absorption levels compared to those produced by CW L-PBF with no effects on phase composition and minimal effects on mechanical performance.

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Based on the characteristics of natural polysaccharides in film-forming, chelating, and environmental friendly, a natural polysaccharide fertilizer agent was selected to increase the utilization of nitrogen fertilizer and increase plant growth. Five polysaccharides: xanthan gum, guar gum, fenugreek gum, welan gum and chitosan were screened for plant growth promoting effect. The results showed that welan gum had the most significant effect on promoting the growth of rice seedlings, and the concentrations of 0.1 mg mL-1 and 0.15 mg mL-1 showed the best growth effects. The effects of welan gum on nitrogen utilization in rice seedlings were investigated. Results showed welan gum increased the contents of ammonium, nitrate, free amino acids, and proteins in rice seedlings. There were four key enzymes of nitrogen metabolism which are nitrate reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase significantly enhanced by welan gum though up-regulating the transcriptional levels of these enzymes. Therefore, nitrogen uptake and nitrogen metabolism in rice seedlings were promoted to increase the biomass of rice seedlings. Based on the research, results showed that welan gum could constitute a promising fertilizer in the future.

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The limited availability of nitrogen (N) is a fundamental challenge for many crop plants. We have hypothesized that the relative crop photosynthetic rate (P) is exponentially constrained by certain plant-specific enzyme activities, such as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-G3PDH), 3-phosphoglyceric acid (PGA) kinase, and chloroplast fructose-1,6-bisphosphatase (cpFBPase), in Triticum aestivum and Oryza sativa. We conducted a literature search to compile information from previous studies on C3 and C4 crop plants, to examine the photosynthetic rate responses to limited leaf [N] levels. We found that in Zea mays, NADP-malic enzyme (NADP-ME), PEP carboxykinase (PCK), and Rubisco activities were positively correlated with P. A positive correlation was also observed between both phosphoenolpyruvate carboxylase (PEPC) and Rubisco activity with leaf [N] in Sorghum bicolor. Key enzyme activities responded differently to P in C3 and C4 plants, suggesting that other factors, such as leaf [N] and the stage of leaf growth, also limited specific enzyme activities. The relationships followed the best fitting exponential relationships between key enzymes and the P rate in both C3 and C4 plants. It was found that C4 species absorbed less leaf [N] but had higher [N] assimilation rates (A rate) and higher maximum photosynthesis rates (Pmax ), i.e., they were able to utilize and invest more [N] to sustain higher carbon gains. All C3 species studied herein had higher [N] storage (Nstore) and higher absorption of [N], when compared with the C4 species. Nstore was the main [N] source used for maintaining photosynthetic capacity and leaf expansion. Of the nine C3 species assessed, rice had the greatest Pmax , thereby absorbing more leaf [N]. Elevated CO2 (eCO2) was also found to reduce the leaf [N] and Pmax in rice but enhanced the leaf [N] and N use efficiency of photosynthesis in maize. We concluded that eCO2 affects [N] allocation, which directly or indirectly affects Pmax . These results highlight the need to further study these physiological and biochemical processes, to better predict how crops will respond to eCO2 concentrations and limited [N].

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The low nitrogen use efficiency (NUE) of fertilizers and aluminum toxicity are major limiting factors for crop development in red soil (acidic soil) of China. Biochar is a promising material for improving soil quality, alleviating aluminum and acidic toxicity. The present study was conducted on maize to evaluate the effects of biochar on NUE and soil quality under different applications of nitrogen fertilizer. Biochar was used in the following five levels in each pot; C0 (0 g), C1 (7.5 g), C2 (15 g), C3 (30 g), C4 (45 g), in combination with δ15N at two N levels: N0 (0 g kg-1) and N1 (0.2 g kg-1). The biochar increased soil nutrients, exchangeable cation, and SOM. Compared with C0, the K+, Ca2+, and Mg2+ were increased by 31.58%, 95.87%, and 463.75% while total Al3+ content of C4 treatment was decreased by 91.98%-93.30% in soil, respectively. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) showed that Al2SiO5 was adsorbed on the surface of biochar in the soil due to the special physical structure of biochar. Besides, the results showed that root and shoot biomass increased by 44.5% and 89.6%, respectively under biochar treatment. The nitrogen utilization rate of the plant was increased by 11.08% after the amendment of biochar to soil. The δ15N content was increased from 11.97 to 21.32 for root and from 50.84 to 82.33 mg kg-1 for the shoot. The use of biochar with N fertilizer showed a more positive effect on improving NUE of maize and facilitating soil quality. Our results suggest that biochar could be used to improve soil available nutrients, alleviate aluminum toxicity and acidic toxicity. Therefore, biochar could also increase the NUE of maize by adjusting soil quality.

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To determine the dynamic change characteristics of NO3-N in a rural-urban ecotone channel, five tracer tests were conducted in the Dongda Channel in the suburbs of Changchuan city, Jilin province, China, from October 2016 to April 2017. NaBr was used as conservative tracer and KNO3 served as an added nutritive salt. The kinetic features of NO3-N were simulated via the addition of tracers and by employing the spiralling curve characterization approach and the Michaelis-Menten (M-M) equation. The average absorption length of NO3--N background concentration (Sw-amb) is 199 m, which is much less than the discharge channel length (2.5 km), thereby suggesting that the channel has a strong NO3-N retention potential. Moreover, the M-M equation fits well the kinetic features of NO3-N adsorption. The average maximum absorption rate and subsaturation constant are 631 µg (m2 s)-1 and 1.46 mg L-1, respectively. The correlation analysis reveals that Sw-amb and NO3--N absorption rates (NO3-Namb) are significantly negatively correlated whereas the absorption rates of NO3--N background concentration (Uamb) and NO3-Namb are significantly positively correlated. The other spiralling indices show faint correlations with the background concentration of NO3-N. Meanwhile, the hydrological factors slightly influence NO3-N retention, but the geomorphic features of the channel, including (width residual) Фw and (cross-sectional area residual) ФA, have significant correlations with most spiralling indices, thereby highlighting the relatively important roles of geomorphic features in NO3-N retention.

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The effects of two nitrogen (N) concentrations combining with three phosphorus (P) concentrations on Isochrysis zhangjiangensis growth and formation of fatty acid (FA) were investigated in this study. Biomass concentration, mass fraction, and productivity of FA in I. zhangjiangensis were low in N-deprived media. Under both N and P sufficiency conditions, the intake of P and N was 40 times and 4.7 times of the normal algal growth condition, respectively, indicating I. zhangjiangensis had the potential for removing P and N from high concentrated N and P salinity wastewater. This study also showed that P deficiency in N sufficient medium increased the FA content, however, the difference between P limitation and P deprivation was not significant (P > 0.05). In N sufficient and P limitation medium, FA productivity was the highest, with a composition suitable for biofuel, so, this condition was the optimal condition for biodiesel production from I. zhangjiangensis.

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Modern rice cultivation relies heavily upon inorganic nitrogen fertilization. Effective fertilizer management is key to sustainable agricultural development. Field and pot trials were conducted in 2014-2016, including a 15N-labeled urea pot experiment (2014) to investigate mechanism by which optimized nitrogen fertilizer application (OFA) increases nitrogen utilization efficiency (NUE). Results showed that the applied nitrogen recovery efficiencies with OFA were 71.71%, 110.17%, and 51.38% higher than those obtained with traditional nitrogen fertilizer application (TFA) in 2014, 2015, and 2016, respectively. These improvements are attributed mainly to the high recovery efficiency rates derived from spikelet-developing and spikelet-promoting fertilizer applications at the jointing stage and 15-20 d after jointing. Under OFA, the amount of nitrogen fertilizer applied at the early stages was half that used in TFA, which not only promoted the absorption of soil nitrogen, but also reduced nitrogen loss to the environment, as the NUE of basal and tillering fertilizer was only about 22%. Nitrogen applied during the panicle differentiation stage increased the expression of ATM1;1, a NH4 + transporter in roots. This effect significantly improved the uptake of nitrogen derived from fertilizer from jointing to heading stage. Up-regulation of the expression and activity of GS and GOGAT at the panicle differentiation and grain-filling stages promoted nitrogen translocation from vegetative organs to reproductive organs. The uptake of nitrogen derived from fertilizer increased from 22.51% in TFA to 35.58% in OFA. Nevertheless, rice absorbs most of the nitrogen it requires from the soil. The OFA treatment could effectively utilize the environmental compensation effect, promote the absorption and transport of nitrogen, and ultimately lead to improvement in NUE. Future research should aim to understand the soil nitrogen supply capacity in order to apply nitrogenous fertilizer in such a way that it sustains the nitrogen balance.

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Microbial L-malate production from renewable feedstock is a promising alternative to petroleum-based chemical synthesis. However, high L-malate production of Aspergillus oryzae was achieved to date using organic nitrogen, with inorganic nitrogen still unable to meet industrial applications. In the current study, we constructed a screening system and nitrogen supply strategy to improve L-malate production with ammonium sulphate [(NH4)2SO4] as the sole nitrogen source. First, we generated and identified a high-producing mutant FMME218-37, which stably boosted L-malate production from 30.73 to 78.12 g/L, using a combined screening system with morphological characteristics. Then, by analyzing the fermentation parameters and physiological characteristics, we further speculated the key factor was the unbalance of carbon and nitrogen absorption. Finally, the titer and productivity of L-malate was increased to 95.2 g/L and 0.57 g/(L h) by regulating the nitrogen supply module to balance carbon and nitrogen absorption, which represented the highest level in A. oryzae with (NH4)2SO4 as nitrogen source achieved to date. Moreover, our findings using a low-cost substrate may lead to building an economical cell factory of A. oryzae for L-malate production.

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Globally, nitrogen deposition increment has caused forest structural changes due to imbalanced plant nitrogen metabolism and subsequent carbon assimilation. Here, a 2 consecutive-year experiment was conducted to reveal the effects of canopy addition of nitrogen (CAN) on nitrogen absorption, assimilation, and allocation in leaves of three subtropical forest woody species (Castanea henryi, Ardisia quinquegona, and Blastus cochinchinensis). We hypothesized that CAN altered leaf nitrogen absorption, assimilation and partitioning of different plants in different ways in subtropical forest. It shows that CAN increased maximum photosynthetic rate (Amax), photosynthetic nitrogen use efficiency (PNUE), and metabolic protein content of the two understory species A. quinquegona and B. cochinchinensis. By contrary, for the overstory species, C. henryi, Amax, PNUE, and metabolic protein content were significantly reduced in response to CAN. We found that changes in leaf nitrogen metabolism were mainly due to the differences in enzyme (e.g. Ribulose-1,5-bisphosphate carboxylase, nitrate reductase, nitrite reductase and glutamine synthetase) activities under CAN treatment. Our results indicated that C. henryi may be more susceptible to CAN treatment, and both A. quinquegona and B. cochinchinensis could better adapt to CAN treatment but in different ways. Our findings may partially explain the ongoing degradation of subtropical forest into a community dominated by small trees and shrubs in recent decades. It is possible that persistent high levels of atmospheric nitrogen deposition will lead to the steady replacement of dominant woody species in this subtropical forest.

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Cucumber (cv. Zhongnong 26) was used as material, the effects of NO3--N/NH4+-N ratios on growth and physiological characteristics of cucumber seedlings under suboptimal temperature and light intensity (18 ℃/10 ℃,180 ± 20 µmol·m-2·s-1) were studied. Total nitrogen in the nutrient solution was equal and three NO3--N/NH4+-N ratios, 26:2, 21:7 and 14:14, were applied as treatments. The results showed that cucumber treated by NO3--N/NH4+-N=21:7 had the longest total root length, the biggest root volume and root surface area, and the maximum number of root tips. H+-ATPase activity and relative expression of genes encoding nitrate transporter (NRT) and ammonium transporter (AMT) in cucumber roots were increased significantly by the treatment of NO3--N/NH4+-N=21:7. In addition, nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT) in cucumber leaves under the treatment of NO3--N/NH4+-N=21:7 were higher. As a result, the nitrogen content and biomass of cucumber were significantly increased. Compared with the plants under the treatment of NO3--N/NH4+-N=26:2 or 14:14, cucumber seedlings under the treatment of NO3--N/NH4+-N=21:7 had the highest biomass and total dry mass (DM) which were increased by 14.0% and 19.3% respectively under suboptimal temperature and light intensity. In conclusion, under suboptimal environmental conditions, NO3- -N/NH4+-N ratio could be adjusted to increase nitrogen absorption and metabolism of cucumber and alleviate the de-trimental effects caused by suboptimal conditions and promoted the cucumber growth.

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We examined the effect of planting an emergent aquatic plant (Phragmites australis) on nitrogen removal from sediments using a 42-d pot experiment. The experimental pot systems comprised two types of sediments planted with and without young P. australis. Total nitrogen (total N), total dissolved N, and NH4-N in the sediments decreased markedly after planting. In contrast, those levels decreased only slightly in the unplanted sediments. The decrease in total N in the P. australis-planted sediments was 7-20 times those in the unplanted sediments. Abundances of bacterial 16S rRNA, archaeal 16S rRNA, ammonia-oxidizing bacterial ammonia monooxygenase (amoA), ammonia-oxidizing archaeal amoA, and denitrifying bacterial nitrite reductase (nirK) genes increased significantly in sediments after planting. Phragmites australis appears to have released oxygen and created a repeating cycle of oxidizing and reducing conditions in the sediments. These conditions should promote mineralization of organic N, nitrification, and denitrification in the sediments. Phragmites australis absorbed bioavailable nitrogen generated by microbial nitrogen metabolism. During the 42-d period after planting, 31-44% of total N was removed by microbial nitrogen cycling, and 56-69% was removed via absorption by P. australis. These results suggest that planting P. australis can increase microbial populations and their activities, and that nitrogen removal can be accelerated by the combined functions of P. australis and microorganisms in the sediment. Thus, planting P. australis has considerable potential as an effective remediation technology for eutrophic sediments.

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BACKGROUND: Nitrogen absorption from the large intestine is considered of limited value for supporting body protein synthesis in animals and humans, but it may be of benefit when the dietary supply of nitrogen for synthesis of dispensable amino acids (DAAs) is deficient. OBJECTIVE: A whole-body nitrogen balance study was conducted to evaluate the impact of nitrogen absorption from the large intestine of pigs fed a diet deficient in DAA nitrogen. METHODS: Nine cecally cannulated barrows were fed a cornstarch and casein-based diet with a high indispensable amino acid (IAA) nitrogen to total nitrogen ratio (IAA:TN; 0.75). Pigs were randomly assigned to saline or 1 of 2 urea nitrogen infusion rates into the cecum (low and high, 1.5 and 3.0 g/d, respectively) following a 3 × 3 Latin square design. At the high urea nitrogen infusion rate, IAA:TN was 0.55. At slaughter, liver samples were taken to measure activity of carbamoyl phosphate synthetase I (CPS-I), glutamate dehydrogenase (GDH), and Gln synthetase (Gln-S). RESULTS: Whole-body nitrogen retention improved with urea infusion (4.86 ± 0.20 g/d, 6.40 ± 0.21 g/d, and 7.75 ± 0.19 g/d for saline and low and high infusion rates, respectively; P < 0.05), as well as body weight gain. The marginal efficiency of using nitrogen absorbed from the large intestine for improving nitrogen retention was not affected by urea nitrogen infusion rate (P > 0.10). Enzyme activity of CPS-I or Gln-S was not different between treatments (P > 0.10), but GDH showed a trend for a positive linear response with increasing urea nitrogen infusion rate (P = 0.06). CONCLUSION: These results indicate that urea nitrogen absorbed from the large intestine is efficiently used for increasing body protein deposition when feeding pigs a diet deficient in DAA nitrogen.

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To cope with environmental stress caused by global climate change and excessive nitrogen application, it is important to improve water and nitrogen use efficiencies in crop plants. It has been reported that higher nitrogen uptake could alleviate the damaging impact of drought stress. However, there is scant evidence to explain how nitrogen uptake affects drought resistance. In this study we observed that bZIP transcription factor AtTGA4 (TGACG motif-binding factor 4) was induced by both drought and low nitrogen stresses, and that overexpression of AtTGA4 simultaneously improved drought resistance and reduced nitrogen starvation in Arabidopsis. Following drought stress there were higher nitrogen and proline contents in transgenic AtTGA4 plants than in wild type controls, and activity of the key enzyme nitrite reductase (NIR) involved in nitrate assimilation processes was also higher. Expressions of the high-affinity nitrate transporter genes NRT2.1 and NRT2.2 and nitrate reductase genes NIA1 and NIA2 in transgenic plants were all higher than in wild type indicating that higher levels of nitrate transport and assimilation activity contributed to enhanced drought resistance of AtTGA4 transgenic plants. Thus genetic transformation with AtTGA4 may provide a new approach to simultaneously improve crop tolerance to drought and low nitrogen stresses.

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