Relationship of Nitrogen Deficiency-Induced Leaf Senescence with ROS Generation and ABA Concentration in Rice Flag Leaves

Nitrogen (N) deficiency is one of the critical environmental factors that induce leaf senescence, and its occurrence may cause the shorten leaf photosynthetic period and markedly lowered grain yield. However, the physiological metabolism underlying N deficiency-induced leaf senescence and its relationship with the abscisic acid (ABA) concentration and reactive oxygen species (ROS) burst in leaf tissues are not well understood. In this paper, the effect of N supply on several senescence-related physiological parameters and its relation to the temporal patterns of ABA concentration and ROS accumulation during leaf senescence were investigated using the premature senescence of flag leaf mutant rice (psf) and its wild type under three N treatments. The results showed that N deficiency hastened the initiation and progression of leaf senescence, and this occurrence was closely associated with the upregulated expression of 9-cis-epoxycarotenoiddioxygenase genes (NCEDs) and with the downregulated expression of two ABA 8′-hydroxylase isoform genes (ABA8ox2 and ABA8ox3) under LN treatment. Contrarily, HN supply delayed the initiation and progression of leaf senescence, concurrently with the suppressed ABA biosynthesis and relatively lower level of ABA concentration in leaf tissues. Exogenous ABA incubation enhanced ROS generation and MDA accumulation in a dose-dependent manner, but it decreased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in detached leaf. These results suggested that the participation of ABA in the regulation of ROS generation and N assimilating/remobilizing metabolism in rice leaves was strongly responsible for induction of leaf senescence by N deficiency.

     

Weight gains of meat goat kids on wheat (Triticum aestivum L.) pastures fertilized at different nitrogen levels

Wheat (Triticum aestivum L.) pastures are increasingly being used for cool-season forages to complement range-based goat production systems in southern USA. Because goats are more selective than cattle, ideal nitrogen (N) fertilizer rates already established for wheat grazed by cattle may be different for goats. Weight gains of Boer X Spanish doe kids (average 17 kg) as well as forage yields and crude protein (CP), acid detergent fiber (ADF) and acid detergent lignin (ADL) concentrations were measured for two winter seasons on replicated wheat paddocks fertilized with 0, 56, 112 and 224 kg N/ha per season in split autumn/spring applications at Stephenville, TX, USA. Animals were stocked in the pasture at 20 head/ha from January to April 2003 (478 mm rainfall from September to March) and 2004 (355 mm rainfall). Available forage ranged from 50 to 200 kg/ha in January and from 2300 to 6300 kg/ha in April in the 0 and 224 kg N/ha paddocks, respectively. Crude protein dry matter (DM) concentration ranged from 25 to 34% (0 and 224 kg N/ha, respectively) in January, but down to 13 and 22% across treatments in April. Average daily gains (ADG) over the 90-day trial were similar both years, 68 g per head per day for the 0 N treatment and undifferentiated among the fertilized paddocks, all near 90 g per head per day. Results indicate that N fertilizer rates above 56 kg/ha per season do not increase ADG/kid, but will increase ADG/ha if stocking rates are adjusted for forage production.     

Soil nitrogen dynamics in a holm oak forest

Soil nitrogen (N) dynamics were studied in a dense, holm oak (Quercus ilex ssp. ilex) stand in the Montseny mountains to determine annual and seasonal patterns of N availability and uptake in an undisturbed Mediterranean forest on acidic soil. Soil mineral N content, net N mineralization (NNM), and net nitrification (NN) were determined by monthly sampling at two soil depths followed by in situ incubation in polyethylene bags. NNM per unit of soil mass was much higher at 0–5 cm than at 5–20 cm (annual means 24 and 2.5 mg N/kg, respectively) but on an area basis NNM was similar at both depths. A total of 80 kg N/ha/yr were mineralized from the first 20 cm of soil. NN amounted to only 9% of the annual NNM (7.5 kg N/ha/yr) and it occurred only in the upper 5 cm. NNM was maximum in June and July, while the NN peaked in May. Despite favourable soil temperature and moisture, NNM was negative in autumn because of microbial immobilization. Seasonal and depth variations of NNM appeared to be controlled more by substrate quality than by organic matter quantity, temperature or moisture. NN was not limited by ammonium availability. Calculated N uptake amounted to 91 kg/ha yr, peaking in June and July. The investigated stand showed a moderately high N availability, but ammonium was the major form of mineral N supply for holm oak.     

黄河口新生湿地土壤磷赋存形态及其动态变化对外源氮输入的响应

选择黄河口新生湿地为研究对象,基于野外原位氮输入模拟试验,探讨了不同氮输入梯度下(NN:对照处理;LN:低氮处理;MN:中氮处理;HN:高氮处理)湿地土壤磷赋存形态的动态变化特征。结果表明,不同氮处理下土壤中闭蓄态磷(HCl-P_i和Residual-P)均是TP的主体(87.75%—90.04%),而活性磷(Resin-P、NaHCO_3-P_i和NaHCO_3-P_o)和中等活性磷(NaOH-P_i、NaOH-P_o、Sonic-P_i和Sonic-P_o)占TP的比例均较低,分别为4.81%—5.58%和5.14%—6.57%。相对于NN处理,MN和HN处理下的活性磷含量分别增加了9.16%和12.44%,而LN、MN和HN处理下的中等活性磷含量分别增加了2.25%,6.92%和24.24%,说明外源氮输入整体增加了土壤中的活性磷含量。与之相比,闭蓄态磷含量在LN、MN和HN处理下均呈降低趋势,其值相对于NN处理分别降低了3.08%、3.08%和5.22%。尽管不同氮处理下土壤养分条件、水盐及酸碱状况均是影响不同磷形态赋存的关键因素,但随着氮输入量的增加,影响磷赋存形态的养分类型发生了明显改变,即由NN和LN处理下主要受N和S影响逐步转变为MN和HN处理下主要受P影响。研究发现,外源氮输入不但可能影响不同磷形态之间的转化,而且亦可能通过改变植物生长节律以及土壤养分及酸碱状况来影响土壤中各形态磷的赋存。     

Assessing the impacts of biochar-blended urea on nitrogen use efficiency and soil retention in wheat production

Improving nitrogen (N) use efficiency (NUE) in crop plants is important to reduce the negative impact of excessive N on the environment. Although biochar-blended fertilizer had been increasingly tested in crop production, the fate of fertilized N in soil and plant had not been elucidated in field conditions. In this study, a novel biochar-blended urea (BU) was prepared by pelleting maize straw biochar, bentonite, sepiolite, carboxymethylcellulose sodium, and chitosan with urea (commercial urea without biochar [CU]). N fertilization in a winter wheat field was treated with BU and CU at both 265 kg N ha^?1 (HL) and 186 kg N ha^?1 (LN). Within a treatment plot, a microplot was fertilized with ¹⁵N-labeled urea at a relevant N level. We investigated the influence of fertilizer management on biomass, grain yield, bioaccumulation of nutrient, soil properties, ¹⁵N isotopic abundance, and greenhouse gas emissions. Microscopic and spectroscopic analysis showed that micro/nanonetwork of biochar could bind N to form a loss control agglomerated particle, and organo-mineral coatings on BU may protect N from quick release. Compared with CU, BU significantly increased grain yield by 13% and 38%, and grain N allocation by 19% and 55%, respectively, at HN and LN level. The total recovery of urea ¹⁵N in wheat plant (¹⁵N based NUE) was 32.8% under CU regardless of N rates but increased to 41.7% (HN rate) and 56.3% (LN rate) under BU. Whereas, the soil proportion (soil residual ¹⁵N) was 20.1% and 13.4% under CU but 32.5% and 18.8% under BU, in 0-20cm topsoil, respectively, at HN and LN rate. Compared with the CU, BU had no effect on CO₂ and CH₄ emissions but significantly reduced the total N₂O emission by 23%–28%. These important findings suggested that BU can be beneficial to uplift plant NUE to reduce reactive N loading but boost crop production.     

Mapping QTLs for nitrogen uptake in relation to the early growth of wheat (Triticum aestivum L.)

The objective of this study was to map QTLs for N uptake (NUP) in wheat, and to investigate factors influencing NUP. Two independent field trials with low N (LN) and high N (HN) treatments were conducted in the growing seasons of 2002–2003 (trial 1) and 2003–2004 (trial 2) to measure NUP per plant (N accumulated in the aerial part at maturity stage) of a doubled haploid (DH) population consisting of 120 DH lines derived from winter wheat varieties Hanxuan 10 and Lumai 14. A hydroponic culture with all nutrients supplied sufficiently was conducted to investigate shoot dry weight (SDW), root dry weight (RDW), tiller number (TN) and NUP (total plant N uptake) per plant of this mapping population at seedling stage. SDW, RDW, TN and NUP investigated in the hydroponic culture were significantly and positively correlated with each other, and with NUP under both LN and HN conditions in the field trials. Nine and eight QTLs for NUP were detected under LN and HN conditions in the field trials, respectively. Four to five QTLs for SDW, RDW, TN and NUP were detected in the hydroponic culture. One SDW QTL, three RDW QTLs, two TN QTLs detected in the hydroponic culture were linked with QTLs for NUP under LN or HN condition in the field trials. The positive correlation and genetic linkage for the traits between the field trials and the hydroponic culture demonstrated that greater seedling vigor of root and shoot is an important factor influencing N uptake in wheat. Diaoguo An and Junying Su: These authors contributed equally to this work. Section Editor: H.J. Kronzucker     

Fast chlorophyll fluorescence transient and nitrogen fixing ability of chickpea nodulation variants

High nodulating (HN) selections of the cultivars ICC 4948 and ICC 5003 had the highest nodule number and nodule dry mass followed by low nodulating (LN) selections of the same cultivar. Both non-nodulating (NN) selections of cv. ICC 4993 and ICC 4918 did not show any nodule. Using N-difference method the HN selection of cv. 1CC 4948 was able to meet 73 % of its demand of N through biological fixation of N₂ [P(fix)], while 27 % of N demand was met by uptake from the soil, whereas its LN selection was able to meet only 54 % of its demand of N through biological fixation of N₂. Similarly in cv. ICC 5003 HN and LN selections the P(fix) was 76 and 64 %, respectively. Fast chlorophyll (Chl) fluorescence transient data analysis showed that performance index PI(abs) was 62.0 in cv. ICC 4948 HN selection and 44.5 in its respective LN selections. Corresponding values for cv. ICC 5003 were 32.4 and 28.4. In NN selections of ICC 4993 and ICC 4918 it was 12.6 and 30.7, respectively. Structure function index of the plants SFI(abs) and driving force for photosynthesis (DF) were highest in the HN selections followed by LN selections and lowest in the NN selections. The total uptake of N by chickpea plants was significantly and positively correlated with the density of reaction centres ABS/CS₀, TR₀/CS₀, and DI₀/CS_M, whereas total N uptake by chickpea seeds was significantly positively correlated with N and TR₀/CS₀. The percentage of P(fix) was highly significantly positively correlated with N, the so-called turnover number which indicates how many times Q_A has been reduced in the time span from 0 to t_Fmax and TR₀/CS₀. Fast Chl a fluorescence measurement can be used as a model system to assess the N fixation ability in chickpea.     

Comparative transcriptomic analysis reveals that multiple hormone signal transduction and carbohydrate metabolic pathways are affected by Bacillus cereus in Nicotiana tabacum

Bacillus cereus is thought to be a beneficial bacterium for plants in several aspects, such as promoting plant growth and inducing plant disease resistance. However, there is no detailed report on the effect of Bacillus cereus acting on Nicotiana tabacum. In the present study, RNA-based sequencing (RNA-seq) was used to identify the molecular mechanisms of the interaction between B. cereus CGMCC 5977 and N. tabacum. A total of 7345 and 5604 differentially expressed genes (DEGs) were identified from leaves inoculated with Bacillus cereus at 6 and 24 hpi, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the most DEGs could be significantly enriched in hormone signal transduction, the MAPK signaling pathway, photosynthesis, oxidative stress, and amino sugar, and nucleotide sugar metabolism. Furthermore, glycolysis/gluconeogenesis was severely affected by inoculation with Bacillus cereus. In the hormone signal pathway, multiple DEGs were involved in plant defense-related major hormones, including activation of jasmonic acid (JA), salicylic acid (SA), and ethylene (Eth). Further analyses showed that other hormone-related genes involved in abscisic acid (ABA), gibberellin (GA), auxin (AUX), and cytokinin (CK) also showed changes. Notably, a large number of genes associated with glycolysis/gluconeogenesis, catabolism of starch and oxidative stress were induced. In addition, the majority of DEGs related to nucleic acid sugar metabolism were also significantly upregulated. Biochemical assays showed that the starch content of B. cereus-treated leaves was reduced to 2.51 mg/g and 2.38 mg/g at 6 and 24 hpi, respectively, while that of the control sample was 5.42 mg/g. Overall, our results demonstrated that multiple hormone signal transduction and carbohydrate metabolic pathways are involved in the interaction of tobacco and B. cereus.     

Effects of Nitrogen Nutrition Level on Photosynthesis of Wheat Under Rapid Water Stress

Effects of nitrogen (N) nutrition level on photosynthesis of wheat were studied using method of quick drying of detached leaves, under rapid water stress. The results showed that in the case, leaf water potential (Ψw), net photosynthetic rate (Pn) and stomatal conductance (Gs) of high N (HN) leaves decreased more quickly than that of low N (LN) leaves. Therefore, the difference of Pn between HN and LN leaves became less and less with increasing water stress. Under severe water stress, the Pn of HN leaves were lower than that of LN leaves. The intercellular concentration of CO2 (Ci) of HN leaves were lower than that of LN leaves, and the value of stomatal limitation of photosynthesis (Ls) of HN leaves were higher during rapid water stress. However, the mesophllous conductance of CO2 (Gm) and photosynthetic activity of mesophyll of HN leaves were still higher than that of LN leaves.     

滇中亚高山人工林凋落物分解对模拟氮沉降的响应

2018年2月至2019年1月,利用尼龙网袋法对滇中亚高山华山松和云南松两种人工林开展模拟氮(N)沉降下凋落叶和凋落枝原位分解试验,N沉降水平分别为对照(CK, 0 g N·m^-2·a^-1)、低N(LN, 5 g N·m^-2·a^-1)、中N(MN, 15 g N·m^-2·a^-1)和高N(HN, 30 g N·m^-2·a^-1)。结果表明: 华山松凋落叶和凋落枝年分解率分别为34.8%和18.0%,分别高于云南松凋落叶的32.2%和凋落枝的16.1%。模拟N沉降下,LN处理使华山松凋落叶、枝分解95%所需时间较对照分别减少0.202和1.624年,MN处理分别减少0.045和1.437年,HN处理则分别增加0.840和2.112年;LN处理使云南松凋落叶、枝分解95%所需时间较对照分别减少0.766和4.053年,MN处理分别增加0.366和0.455年,HN处理分别增加0.826和0.906年。经过1年的分解,低N处理促进了华山松和云南松凋落物(叶、枝)的分解,而高N处理表现为抑制作用;N沉降对两种林型凋落物分解的影响与凋落物中纤维素和木质素含量密切相关。可见,凋落物基质质量在一定程度上决定了凋落物分解对N沉降的响应情况,尤其是纤维素和木质素含量。     

Prenatal and early postnatal dietary sodium restriction sensitizes the adult rat to amphetamines

Acute sodium deficiency sensitizes adult rats to psychomotor effects of amphetamine. This study determined whether prenatal and early life manipulation of dietary sodium sensitized adult offspring to psychomotor effects of amphetamine (1 or 3 mg/kg ip) in two strains of rats. Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) dams were fed chow containing low NaCl (0.12%; LN), normal NaCl (1%; NN), or high NaCl (4%; HN) throughout breeding, gestation, and lactation. Male offspring were maintained on the test diet for an additional 3 wk postweaning and then fed standard chow thereafter until testing began. Overall, blood pressure (BP), total fluid intake, salt preference, and adrenal gland weight were greater in SHR than in WKY. WKY LN offspring had greater water intake and adrenal gland weight than did WKY NN and HN offspring, whereas WKY HN offspring had increased BP, salt intake, and salt preference compared with other WKY offspring. SHR HN offspring also had increased BP compared with other SHR offspring; all other measures were similar for SHR offspring. The low-dose amphetamine increased locomotor and stereotypical behavior compared with baseline and saline injection in both WKY and SHR offspring. Dietary sodium history affected the rats' psychomotor response to the higher dose of amphetamine. Injections of 3 mg/kg amphetamine in both strains produced significantly more behavioral activity in the LN offspring than in NN and HN offspring. These results show that early life experience with low-sodium diets produce long-term changes in adult rats' behavioral responses to amphetamine.     

The effect of fertilizer‐N on the inter‐specific competition among three wheat aphids under elevated CO2

Increasing atmospheric carbon dioxide (ab. CO₂) and fertilizer‐nitrogen (ab. N) applications may have marked direct effects on the plant growth of agricultural crops, and in turn affect the higher trophic level of insect herbivores. In this study, the effects of elevated CO₂ (i.e., 650 µl/L vs. ambient 400 µl/L) and fertilizer‐N (0, 50, 100, 200 kg/ha) on the population abundances and the inter‐specific competition among three co‐occurring species of wheat aphids, Sitobion avenae, Rhopalosiphum padi and Schizaphis graminum, were studied. The grain weight per ear and the 1,000‐grain weight were generally increased when grown under elevated CO₂ and showed a significant effect at the 100 kg/ha (grain weight per ear) and 0, 50 and 100 kg/ha (1,000‐grain weight) N. These two yield indexes increased with increasing fertilizer‐N levels within reasonable limits and reached a maximum at 100 kg/ha. Elevated CO₂ combined with fertilizer‐N levels formed complex indirect effects on the three wheat aphids through the wheat crops they fed on. Elevated CO₂ significantly decreased the niche overlap index (ab. NOI) between S. avenae and R. padi under 0 and 100 kg/ha and that between R. padi and S. graminum under 0 kg/ha, while significantly increased the three NOIs under 50 kg/ha and that between R. padi and S. graminum under 100 and 200 kg/ha. S. avenae and R. padi had the larger population and stronger competition in low‐N condition (0 and 50 kg/ha), which was harmful to wheat yield and quality when combined with its own poor nutrition. Overall, the 100 kg/ha N level was the best option based on the aphid population, competition and wheat yields. Therefore, the balanced relationship formed among fertilizers, plants and insects under 100 kg/ha N was vital for the interactive ecosystem.