Effects of synthetic nitrogen fertilizer and manure on fungal and bacterial contributions to N2O production along a soil acidity gradient.

Reactive nitrogen (Nr) input often induces soil acidification, which may in turn affect bacterial and fungal nitrogen (N) transformations in soil and nitrous oxide (N2O) emissions. However, the interactive effects of soil acidity and Nr on the contributions of bacteria and fungi to N2O emissions remain unclear. We conducted a field experiment to assess the effects of anthropogenic Nr forms (i.e., synthetic N fertilizer and manure) on bacterial and fungal N2O emissions along a soil acidity gradient (soil pH = 6.8, 6.1, 5.2, and 4.2). The abundances and structure of bacterial and fungal communities were analyzed by real-time polymerase chain reaction and high-throughput sequencing techniques, respectively. Soil acidification reduced bacterial but increased fungal contributions to N2O production, corresponding respectively to changes in bacterial and fungal abundance. It also altered bacterial and fungal community structures and soil chemical properties, such as dissolved organic carbon and ammonia concentrations. Structural equation modeling (SEM) analyses showed that the soil properties and fungal community were the most important factors determining bacterial and fungal contributions to N2O emissions, respectively. The fertilizer form markedly affected N2O emissions from bacteria but not from fungi. Compared with synthetic N fertilizer, manure significantly lowered the bacterial contribution to N2O emissions in the soils with pH of 5.2 and 4.2. The manure application significantly increased soil pH but reduced nitrate concentration. The fertilizer form did not significantly alter the bacterial and fungal community structures. The SEM revealed that the fertilizer form affected the bacterial contribution to N2O production by changing the soil chemical properties. Together, these results indicated that soil acidification enhanced fungal dominance for N2O emission, and manure application has limited effects on fungal N2O emission, highlighting the challenges for mitigation of soil N2O emissions under future acid deposition and N enrichment scenarios.

Polyamine biosynthetic pathways and their relation with the cold tolerance of maize (Zea mays L.) seedlings.

BACKGROUND: The present study was designed to investigate the inhibition role of two polyamine biosynthesis inhibitors, i.e., D-arginine (D-Arg) and DL-α-difluoromethylornithine (DFMO), in polyamine biosynthesis under chilling stress in different tissues of two maize inbred lines - Huang C (chilling-tolerance) and Mo17 (chilling-sensitive). RESULTS: The results showed that exposure to the lower concentration of polyamine biosynthesis inhibitors improved seedlings growth, such as the root length, root and shoot fresh weight, chlorophyll a (chl a). The effectiveness of 10 µM D-Arg treatments was more prominent than those of 10 µM DFMO. However, the higher concentration of inhibitors suppressed seedlings growth, and the exposure to 100 µM DFMO caused stronger decreases in the photosynthetic pigments, such as chlorophyll a (chl a), chlorophyll b (chl b), total chlorophyll and carotenoids, than the other treatments. Meanwhile, the inhibitor treatments caused the lower content of putrescine (Put) in roots, mesocotyls and coleoptiles in both maize inbred lines as compared with untreated plants. However, the lower concentration (10 µM) of polyamine biosynthetic inhibitors improved the Spd content, except 10 µM D-Arg in root of Huang C, and 10 µM DFMO in coleoptiles of both Mo17 and Huang C. The correlation analysis found that Spd was positively significantly correlated with root length and shoot fresh weight of seedling. CONCLUSION: It was showed that the Spd played an important role in seedling growth improvement. At the same concentration of polyamine biosynthetic inhibitors, the Put contents in different tissues of the seedlings treated with DFMO were generally lower than those treated with D-Arg, except for Put contents in root of Mo17 with 10 µM treatment. Moreover, the treatments of 100 µM were more prominent than those of 10 µM treatments. Exposure to 100 µM D-Arg and 100 µM DFMO could each decrease the activities of Arginine decarboxylase (ADC), Ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) in all maize tissues. However, the decrease of the ADC activity was more prominent in 100 µM D-Arg-treated seedlings, while the decrease of SAMDC and ODC activities was prominent in 100 µM DFMO-treated seedlings. Genes involved in polyamine biosynthesis, such as ADC, ODC, SAMDC, and PAO, showed different expression patterns in response to chilling stress and polyamine biosynthesis inhibitors. This study suggested that Put was synthesized via both the ADC and ODC pathways after chilling stress, with the ODC pathway being the major one.

Physiological and transcriptional response to heat stress in heat-resistant and heat-sensitive maize (Zea mays L.) inbred lines at seedling stage.

To understand the molecular and physiological mechanism underlying the heat stress in maize, transcriptional and physiological response to heat stress in the heat-resistant Huangzaosi (HZS) and heat-sensitive Lv-9-Kuan (L9K) inbred lines at seedling stage were analyzed and compared at seedling stage. Our results indicated that MDA content of the two inbred lines increased significantly under heat stress; the values of MDA in L9K was significantly higher than that in HZS. The level of SOD, CAT, and POD enzyme activities in HZS was higher than those in L9K for both the heat-treated group and controls. The values of Fv/Fm, qP, and ФPSII reduced by heat stress in L9K were higher than the respective values in HZS. RNA-seq data showed that heat stress induced more heat stress-related genes in HZS (257 heat stress-related genes) than in L9K (224 heat stress-related genes). GO and KEGG enrichment analyses indicated that HZS and L9K changed their physiological and biochemical mechanisms in response to heat stress through different molecular mechanisms. Weighted Gene Co-expression Network Analysis showed that HZS might obtain stronger heat resistance than L9K through a unique transcriptional regulatory network. Our findings provide insights into the molecular networks that mediate the tolerance of maize heat stress and also help us to mine key heat stress-related genes.

A 4-year field measurement of N2O emissions from a maize-wheat rotation system as influenced by partial organic substitution for synthetic fertilizer.

Soil N2O emissions depend on the status of stoichiometric balance between organic C and inorganic N. As a beneficial management practice to sustain soil fertility and crop productivity, partial substitution of organic fertilizers (OFs) for synthetic fertilizers (SFs) can directly affect this balance status and regulate N2O emissions. However, no multi-year field studies of N2O emissions under different ratios of OFS to SFs have been performed. We conducted a 4-year experiment to measure N2O emissions in a maize-wheat rotation in central China. Six treatments were included: total SF (TS), total OF, no N fertilizer, and ratios of to SF with 1: 2 (LO), 1: 1 (MO), and 2: 1 (HO), based on N content. Two incubation experiments were performed to further interpret the field data. In the first year, cumulative N2O emissions (kg N ha-1) in LO, MO, and HO were 4.59, 4.68, and 3.59, respectively, significantly lower than in TS (6.67). However, from the second year onwards, organic substitution did not reduce N2O emissions and even significantly enhanced them in the fourth year relative to TS. Soil respiration under OF-amended soils increased over the course of the experiment. From the second year onwards, there was no marked difference in mineral N concentrations between OF- and SF-amended soils. OF caused a drop in soil pH. Cumulative N2O was negatively correlated with pH. Long-term organic substitution enhanced N2O emissions produced via denitrification rather than nitrification and resulted in higher temperature sensitivity of N2O emissions than TS. The enhanced N2O emissions from the OF-treated soils were mainly attributable to accelerated OF decomposition, increased denitrification-N2O emissions, and lessened N2O reduction due to lower pH and greater NO3-. These results indicate that OF substitution can reduce N2O emissions in the first year, but in the long-term it can increase emissions, especially as soils warm.

Changing roles of ammonia-oxidizing bacteria and archaea in a continuously acidifying soil caused by over-fertilization with nitrogen.

Nitrification coupled with nitrate leaching contributes to soil acidification. However, little is known about the effect of soil acidification on nitrification, especially on ammonia oxidation that is the rate-limiting step of nitrification and performed by ammonia-oxidizing bacteria (AOB) and archaea (AOA). Serious soil acidification occurs in Chinese greenhouses due to the overuse of N-fertilizer. In the present study, greenhouse soils with 1, 3, 5, 7, and 9 years of vegetable cultivation showed a consistent pH decline (i.e., 7.0, 6.3, 5.6, 4.9, and 4.3). Across the pH gradient, we analyzed the community structure and abundance of AOB and AOA by pyrosequencing and real-time PCR techniques, respectively. The recovered nitrification potential (RNP) method was used to determine relative contributions of AOA and AOB to nitrification potential. The results revealed that soil acidification shaped the community structures of AOA and AOB. In acidifying soil, soil pH, NH3 concentration, and DOC content were critical factors shaping ammonia oxidizer community structure. AOB abundance, but not AOA, was strongly influenced by soil acidification. When soil pH was below 5.0, AOA rather than AOB were responsible for almost all of the RNP. However, when soil pH ranged from 5.6 to 7.0, AOB were the major contributors to RNP. The group I.1a-associatied AOA had more relative abundance in low pH (pH<6.3), whereas group I.1b tended to prefer neutral pH. Clusters 2, 10, and 12 in AOB were more abundant in acidic soil (pH <5.6), while Nitrosomonas-like lineage and unclassified lineage 3 were prevailing in neutral soil and slightly acidic soil (pH, 6.0-6.5), respectively. These results suggested that soil acidification had a profound impact on ammonia oxidation and more specific lineages in AOB occupying different pH-associated niches required further investigation.

[Effect of precursor on growth and accumulation of alkaloids of Lycoris radiata suspension cells].

In order to investigate the effects of phenylalanine, tyrosine and tyramine on the growth of Lycoris radiata suspension cells and the accumulation of alkaloids, the growth quantity of the cells as well as the content of alkaloids in cells were determined, which were treated with above three kinds of precursors alone and phenylalanine combined with tyrosine respectively. The results indicate that the addition of phenylalanine alone and addition of phenylalanine on the basis of tyrosine at high concentration (200 micromol/L) had no significant effect on the growth of Lycoris radiata suspension cells and the content of alkaloids in cells; whereas tyrosine and tyramine promoted the growth of the cells and alkaloids accumulation. Treated with tyrosine at high concentration (200 micromol/L), the content of alkaloids of the cells was 2.56-fold higher than that of the control group, the amounts of lycoramine (3.77 mg/g) and galanthamine (4.46 mg/g) were 6.61-fold and 6.97-fold higher than that of the control group, respectively. When treated with tyramine (200 micromol/L), the amount of alkaloids in Lycoris radiata suspension cells was 2.63-fold higher than that of the control group, and the amounts of lycoramine (4.45 mg/g) and galanthamine (5.14 mg/g) were 9.08-fold and 9.18-fold higher than that of the control group, respectively. The above results demonstrate that adding tyrosine and tyramine in the media significantly promoted the growth of the Lycoris radiata suspension cells and alkaloids accumulation in the cells.

[Determination of five endogenous hormones in wheat by high performance liquid chromatography].

A high performance liquid chromatographic (HPLC) method was developed to determine the five endogenous hormones including indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellic acid (GA3 ), zeatin (ZT) and salicylic acid (SA) in wheat. The separation conditions were optimized, and methanol was chosen as the extraction solvent. Then the extract was extracted by petroleum ether and ethyl acetate, and purified with the Sep-Pak C18 column. The chromatographic conditions were as follows: Eclipse XDB-C18 reversed phase column (250 mm x 4.6 mm, 5 microm), the flow rate of 1 mL/min, the injection volume of 10 microL, and the detection wavelength of 240 nm were used for the separation of SA from 14.5 min to 18 min, while the detection at 254 nm used for the separation of the others. Methanol (A) and acetic acid aqueous solution (pH 3.6) (B) were used as the mobile phases with the linear gradient set as follows: 0-7 min 20% A, 7-10 min 20% A-28% A, 10-17 min 28% A, 17-19 min 28% A-40% A, 19-35 min 40% A. The results showed that: the hormones were separated well with the recoveries of 96.9% - 98%, and the RSDs were in the range of 1.54% to 2.29%. It is a reliable method for rapid, accurate separation and determination of the endogenous hormones in wheat.