Silicon has opposite effects on the accumulation of inorganic and methylated arsenic species in rice

Background and aims

Rice (Oryza sativa) is a main source of human exposure to inorganic arsenic and mitigation measures are needed to decrease As accumulation in this staple crop. It has been shown that silicon decreases the accumulation of arsenite but, unexpectedly, increases the accumulation of dimethylarsinic acid (DMA) in rice grain. The aim of this study was to investigate why Si increases DMA accumulation.

Methods

Pot and incubation experiments were conducted to investigate how the addition of sparingly soluble silicate gel affected As speciation in the soil solution and the accumulation of different As species in rice tissues.

Results

Silicon addition significantly decreased the concentration of inorganic As (mainly arsenite) but increased the concentration of DMA in both the vegetative and reproductive tissues of rice. Silicon increased the concentration of DMA in the soil solution, whereas autoclaving soil decreased DMA concentration. Less DMA was adsorbed by the soil than arsenate and Si addition significantly inhibited DMA adsorption.

Conclusions

Silicon increased DMA accumulation and decreased arsenite accumulation in rice through different mechanisms. Silicic acid released from the silicate gel increased the availability of DMA for rice uptake by inhibiting DMA adsorption on the soil solid phase or by displacing adsorbed DMA. Although silicic acid also increased the concentration of inorganic As in the soil solution, this effect was much smaller than the inhibitory effect of Si on arsenite uptake by rice roots.     

2-h postchallenge plasma glucose predicts cardiovascular events in patients with myocardial infarction without known diabetes mellitus

Background

Non-enzymatic glycation increases hemoglobin-oxygen affinity and reduces oxygen delivery to tissues by altering the structure and function of hemoglobin.

Objectives

We investigated whether an elevated blood concentration of glycosylated hemoglobin (HbA1c) could induce falsely high pulse oximeter oxygen saturation (SpO₂) in type 2 diabetic patients during mechanical ventilation or oxygen therapy.

Methods

Arterial oxygen saturation (SaO₂) and partial pressure of oxygen (PO₂) were determined with simultaneous monitoring of SpO₂ in 261 type 2 diabetic patients during ventilation or oxygen inhalation.

Results

Blood concentration of HbA1c was >7% in 114 patients and????7% in 147 patients. Both SaO₂ (96.2?±?2.9%, 95% confidence interval [CI] 95.7-96.7% vs. 95.1?±?2.8%, 95% CI 94.7-95.6%) and SpO₂ (98.0?±?2.6%, 95% CI 97.6-98.5% vs. 95.3?±?2.8%, 95% CI 94.9-95.8%) were significantly higher in patients with HbA1c >7% than in those with HbA1c????7% (Data are mean?±?SD, all p?<?0.01), but PO₂ did not significantly differ between the two groups. Bland-Altman analysis demonstrated a significant bias between SpO₂ and SaO₂ (1.83 ±0.55%, 95% CI 1.73% -1.94%) and limits of agreement (0.76% and 2.92%) in patients with HbA1c >7%. The differences between SpO₂ and SaO₂ correlated closely with blood HbA1c levels (Pearson??s r?=?0.307, p?<?0.01).

Conclusions

Elevated blood HbA1c levels lead to an overestimation of SaO₂ by SpO₂, suggesting that arterial blood gas analysis may be needed for type 2 diabetic patients with poor glycemic control during the treatment of hypoxemia.     

Root-induced changes in radial oxygen loss, rhizosphere oxygen profile, and nitrification of two rice cultivars in Chinese red soil regions

Aims

To evaluate the external and internal morphological differences of roots that might influence rice root radial oxygen loss (ROL) and the corresponding rhizosphere nitrification activity, growth characteristics and nitrogen nutrition of rice.

Methods

The root ROL and rhizosphere oxygen profile were determined using a miniaturised Clark-type oxygen microelectrode system, and the rhizosphere nitrification activity was studied with a short-term nitrification activity assay.

Results

The rice biomass, nitrogen accumulation and nitrogen use efficiency (NUE) of ZH (high yield) were significantly higher than those of HS (low yield). The root biomass, number, diameter and porosity of ZH were also much greater than those of HS. The inner and surface oxygen concentrations of the root of ZH were significantly higher than those of HS. The order of paddy soil oxygen penetration depth was ZH?>?HS?>?CK, and the order of the oxygen concentrations detected in the water layer and rhizosphere soil was the same. The rhizosphere nitrification activity and nitrate concentration of ZH were significantly higher than those of HS.

Conclusions

More porous and thicker roots improved the individual root ROL, and more adventitious root numbers enhanced the entire plant ROL and correspondingly improved the rhizosphere nitrification activity, which might influence the growth and nitrogen nutrition of rice.     

Selection of phosphate-solubilizing diazotrophic Herbaspirillum and Burkholderia strains and their effect on rice crop yield and nutrient uptake

Background and Aims

Plant growth-promoting bacteria, mainly diazotrophs and phosphate solubilizers, can reduce the use of chemical fertilizers for rice crops. Here, diazotrophic bacteria isolated from rice were screened for their ability to solubilize inorganic P (P_i) in vitro and in association with rice plants cultivated in pots.

Methods

Forty-nine isolates were tested for the ability to solubilize P_i on NBRIP and GL agar plate media and seven selected strains were further evaluated in NBRIP liquid medium. Three of these strains were inoculated in rice plants grown in soil pots containing ¹⁵N-labeled fertilizer and two sources of P: tricalcium phosphate (TCP) or simple superphosphate (SSP). The dry matter, yield, N, P, and the ¹⁵N content accumulated in plant tissues were measured at 135 days after planting.

Results

Seven strains belonging to the genera Herbaspirillum and Burkholderia formed a halo of solubilized P_i on agar plates. The Burkholderia strains showed peak soluble P (around 200 mg P L^?1) on the fifth day when grown in NBRIP liquid medium for 14 days. Inoculation of Herbaspirillum strains (H18, ZA15) and a Burkholderia vietaminensis strain (AR114) increased rice grain yield from 33 to 47 % with TCP and 18 to 44 % with TSS, respectively. The bacterial inoculation led to enhanced N-use efficiency of the ¹⁵N-labeled fertilizer.

Conclusion

These results suggest that the selection and use of P-solubilizing diazotrophic bacteria are a good strategy to promote P solubilization and/or N use efficiency in rice plants.     

Does radial oxygen loss and iron plaque formation on roots alter Cd and Pb uptake and distribution in rice plant tissues?

Background and Aims

Metal (e.g. Cd and Pb) pollution in agricultural soils and crops have aroused considerable attention in recent years. This study aimed to evaluate the effects of ROL and Fe plaque on Cd and Pb accumulation and distribution in the rice plant.

Methods

A rhizobag experiment was employed to investigate the correlations among radial oxygen loss (ROL), Fe plaque formation and uptake and distribution of Cd and Pb in 25 rice cultivars.

Results

Large differences between the cultivars were found in rates of ROL (1.55 to 6.88 mmol O₂ kg^?1 root d.w. h^?1), Fe plaque formation (Fe: 6,117–48,167 mg kg^?1; Mn: 127–1,089 mg kg^?1), heavy metals in shoot (Cd: 0.13–0.35 mg kg^?1; Pb: 4.8–8.1 mg kg^?1) and root tissues (Cd: 1.1–3.5 mg kg^?1; Pb: 45–199 mg kg^?1), and in Fe plaque (Cd: 0.54–2.6 mg kg^?1; Pb: 102–708 mg kg^?1). Rates of ROL were positively correlated with Fe plaque formation and metal deposition on root surfaces, but negatively correlated with metal transfer factors of root/plaque and distributions in shoot and root tissues.

Conclusions

ROL-induced Fe plaque promotes metal deposition on to root surfaces, leading to a limitation of Cd and Pb transfer and distribution in rice plant tissues.     

Occluded C in rice phytoliths: implications to biogeochemical carbon sequestration

Aims

Carbon (C) bio-sequestration within the phytoliths of plants, a mechanism of long-term biogeochemical C sequestration, may play a major role in the global C cycle and climate change. In this study, we explored the potential of C bio-sequestration within phytoliths produced in cultivated rice (Oryza sativa), a well known silicon accumulator.

Methods

The rice phytolith extraction was undertaken with microwave digestion procedures and the determination of occluded C in phytoliths was based on dissolution methods of phytolith-Si.

Results

Chemical analysis indicates that the phytolith-occluded C (PhytOC) contents of the different organs (leaf, stem, sheath and grains) on a dry weight basis in 5 rice cultivars range from 0.4 mg?g^?1 to 2.8 mg?g^?1, and the C content of phytoliths from grains is much lower than that of leaf, stem and sheath. The data also show that the PhytOC content of rice depends on both the content of phytoliths and the efficiency of C occlusion within phytoliths during rice growth. The biogeochemical C sequestration flux of phytoliths in 5 rice cultivars is approximately 0.03–0.13 Mg of carbon dioxide (CO₂) equivalents (Mg-e-CO₂) ha^?1?year^?1. From 1950 to 2010, about 2.37?×?10⁸?Mg of CO₂ equivalents might have been sequestrated within the rice phytoliths in China. Assuming a maximum phytoliths C bio-sequestration flux of 0.13 Mg-e-CO₂ ha^?1?year^?1, the global annual potential rate of CO₂ sequestrated in rice phytoliths would approximately be 1.94?×?10⁷?Mg.

Conclusions

Therefore rice crops may play a significant role in long-term C sequestration through the formation of PhytOC.     

Background nitrous oxide emissions in agricultural and natural lands: a meta-analysis

Aim

This study aimed at better characterising background nitrous oxide (N₂O) emissions (BNE) in agricultural and natural lands.

Methods

We compiled and analysed field-measured data for annual background N₂O emission in agricultural (BNEA) and natural (BNEN) lands from 600 and 307 independent experimental studies, respectively.

Results

There were no significant differences between BNEA (median: 0.70 & mean: 1.52 kg N₂O???N ha^?1 yr^?1) and BNEN (median:0.31 & mean:1.75 kg N₂O???N ha^?1 yr^?1) (P?>?0.05). A simultaneous comparison across all BNEA and BNEN indicated that BNEs from riparian, vegetable crop fields and intentional fallow areas were significantly higher than from boreal forests (P?<?0.05). Correlation and regression analyses supported the underlying associations of soil organic carbon (C), nitrogen (N), pH, bulk density (BD),and/or air temperature (AT) with BNEs to a varying degree as a function of land-use or ecosystem type (Ps?<?0.05).

Conclusions

Although overall BNEN tended to be lower than BNEA on median basis, results in general suggest that land-use shifts between natural and managed production systems would not result in consistent changes in BNE.     

Aluminium speciation and phytotoxicity in alkaline soils

Aim

Highly alkaline soils (pH?>?9.0) may adversely affect agricultural crop productivity. Problems encountered include poor structure and nutrient deficiency. Research based on solution cultures suggests that aluminium (Al) phytotoxicity may occur in soils with pH?>?9.0, but little research has been undertaken on actual soils under controlled conditions. The nature of the Al species responsible and the pH regime of the soils when this occurs are unknown.

Methods

The charge and species of Al responsible for this toxicity was investigated using Zeta Potential measurement, Nuclear Magnetic Resonance (NMR) spectroscopy, Al precipitation characteristics and electrical conductivity as a function of pH. An anion exchange resin was used to evaluate Al availability to plants at alkaline pH. To verify Al phytotoxicity, a pot experiment was performed with plants grown at near neutral and high pH, with and without Al.

Results

The anionic aluminate species of aluminium was ubiquitous at highly alkaline pH, and was the dominant charged species at pH 9.2. Aluminium was phytotoxic at high pH, significantly reducing the stem and root development of field pea test plants over and above that caused by alkalinity alone. The effects of both alkalinity in general and aluminium in particular became noticeable at pH 9.0 and debilitating at pH?>?9.2.

Conclusion

As this corresponds to the pH where aluminate becomes dominant, it is probably responsible for the phytotoxicity.     

The effects of postprandial glucose and insulin levels on postprandial endothelial function in subjects with normal glucose tolerance

Background

Type 2 diabetes mellitus (T2DM) patients are at increased risk of developing cardiovascular events. Unfortunately traditional risk assessment scores, including the Framingham Risk Score (FRS), have only modest accuracy in cardiovascular risk prediction in these patients.

Methods

We sought to determine the prognostic values of different non-invasive markers of atherosclerosis, including brachial artery endothelial function, carotid artery atheroma burden, ankle-brachial index, arterial stiffness and computed tomography coronary artery calcium score (CACS) in 151 T2DM Chinese patients that were identified low-intermediate risk from the FRS recalibrated for Chinese (<20% risk in 10?years). Patients were prospectively followed-up and presence of atherosclerotic events documented for a mean duration of 61?±?16?months.

Results

A total of 17 atherosclerotic events in 16 patients (11%) occurred during the follow-up period. The mean FRS of the study population was 5.0?±?4.6% and area under curve (AUC) from receiver operating characteristic curve analysis for prediction of atherosclerotic events was 0.59?±?0.07 (P?=?0.21). Among different vascular assessments, CACS?>?40 had the best prognostic value (AUC 0.81?±?0.06, P?<?0.01) and offered significantly better accuracy in prediction compared with FRS (P?=?0.038 for AUC comparisons). Combination of FRS with CACS or other surrogate vascular markers did not further improve the prognostic values over CACS alone. Multivariate Cox regression analysis identified CACS?>?40 as an independent predictor of atherosclerotic events in T2DM patients (Hazards Ratio 27.11, 95% Confidence Interval 3.36-218.81, P?=?0.002).

Conclusions

In T2DM patients identified as low-intermediate risk by the FRS, a raised CACS?>?40 was an independent predictor for atherosclerotic events.     

Computational investigations on the electronic and structural properties of the unsaturated silylenoid HP=SiLiF

The structures of unsaturated silylenoid HP=SiLiF were studied by density functional theory at the B3LYP/6-311+G(d,P) level. Four equilibrium structures, the three-membered ring (1), the four-membered ring (2), the “classical” silane (3), and the linear (4) structures, were located. Their energies are in the order of 4?>?3?>?1?>?2. To exploit the stability of HP=SiLiF, the insertions reaction of 2 and HP=Si into C-Cl have been investigated, respectively. The results show that the insertion of HP=Si is more favorable. To compare with the saturated silylenoid, the insertion reaction of H₂SiLiF was also investigated. The calculations indicate that the insertion of HP=SiLiF (2) is more favorable. The unsaturated siylenoid HP=SiLiF has similar reaction characters to saturated silylenoid H₂SiLiF and silylene HP=Si.     

Root and shoot biomasses in the tropical dry forest of semi-arid Northeast Brazil

Aims

Root and shoot biomasses and their ratio (R:S) were determined for three stages of forest regeneration (18, 40 and >?60 years.), and for open and dense vegetation, in four soil classes in the semi-arid region of Northeast Brazil.

Methods

Shoot biomasses were estimated by allometry and roots were collected in 0.7?×?0.7?×?1 m trenches.

Results

Root and shoot biomasses and the R:S ratio were over double in the >60 year-old vegetation (R:S?=?0.67) when compared to more recent regenerated areas (0.32). In dense vegetation the biomass of roots and shoots were also more than the double of those in open vegetation but the R:S ratios were not significantly different (0.51 and 0.49). Litholic Neosols had lower ratio (0.22) than the other soil classes (0.53 to 0.63) and dense and open vegetation did not differ. In all areas except in deep sandy Quartzarenic Neosols most of the roots (> 90 %) were in the upper 40-cm layer of the soil profile, and consisted of coarse roots.

Conclusion

Root biomass accumulates more slowly than aboveground biomass and it takes several decades to stabilize in shallower soils. The R:S ratios are higher when compared to other dry land forests, probably due to low water availability.     

Minor contribution of leaf litter to N nutrition of beech (Fagus sylvatica) seedlings in a mountainous beech forest of Southern Germany

Aims

Our aims were to characterize the fate of leaf-litter-derived nitrogen in the plant-soil-microbe system of a temperate beech forest of Southern Germany and to identify its importance for N nutrition of beech seedlings.

Methods

¹⁵N-labelled leaf litter was traced in situ into abiotic and biotic N pools in mineral soil as well as into beech seedlings and mycorrhizal root tips over three growing seasons.

Results

There was a rapid transfer of ¹⁵N into the mineral soil already 21 days after tracer application with soil microbial biomass initially representing the dominant litter-N sink. However, ¹⁵N recovery in non-extractable soil N pools strongly increased over time and subsequently became the dominant ¹⁵N sink. Recovery in plant biomass accounted for only 0.025 % of ¹⁵N excess after 876 days. After three growing seasons, ¹⁵N excess recovery was characterized by the following sequence: non-extractable soil N?>>?extractable soil N including microbial biomass?>>?plant biomass?>?ectomycorrhizal root tips.

Conclusions

After quick vertical dislocation and cycling through microbial N pools, there was a rapid stabilization of leaf-litter-derived N in non-extractable N pools of the mineral soil. Very low ¹⁵N recovery in beech seedlings suggests a high importance of other N sources such as root litter for N nutrition of beech understorey.     

Successive straw biochar application as a strategy to sequester carbon and improve fertility: A pot experiment with two rice/wheat rotations in paddy soil

Aims

A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.

Methods

We adopted 4.5 t ha^?1, 9.0 t ha^?1 biochar and 3.75 t ha^?1 straw for each crop season with an identical dose of NPK fertilizers.

Results

We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH₄ emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N₂O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH₃ volatilization in the rice season, but stimulated it in the wheat season.

Conclusions

Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH₄ mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH₃ volatilization differently in the flooded rice and upland wheat seasons, respectively.     

Effect of selenium fertilization on the accumulation of cadmium and lead in rice plants

Background and Aims

The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated.

Methods

Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg^?1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS.

Results

Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg^?1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively.

Conclusions

The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice.     

Spatial and temporal patterns of carbon storage from 1992 to 2002 in forest ecosystems in Guangdong, Southern China

Aims

The overall goal of this study was to examine the spatial and temporal patterns of C storage from 1992 to 2002 in forest ecosystems in Guangdong, China.

Methods

We used 2237, 2103, and 1978 plot data from three continuous forest inventory in 1992, 1997, and 2002, respectively, four TM images and one soil survey data in Guangdong to examine the spatial and temporal patterns of C storage in forest ecosystems during 1992–2002. The uncertainty analysis of forest C storage in Guangdong in 1992 and 2002 was also conducted to provide the range of estimations.

Results

The forest coverage percent in Guangdong increased from 37.1 % in 1992 to 57.2 % in 2002 while the total forest C storage in Guangdong increased from 144.73?±?6.20 Tg in 1992 to 215.03?±?8.48 Tg in 2002. The order of average forest biomass C storage increase during 1992–2002 among the four regions is Western Guangdong (GW)?>?Eastern Guangdong (GE)?>?the Pearl River Delta (PRE)?>?Northern Guangdong (GN). The factors including tree species and altitude and slope aspect can explain 58–67 % variation of Veg C storage multiple regression model in Guangdong. However, the multiple regression model for SOC storage can only explain about 18–39 % variation of SOC storage in Guangdong. Total ecosystem C is mainly determined by SOC storage.

Conclusions

The total forest C storage in Guangdong increased about 49 % from 1992 to 2002 partially due to the increasing forest coverage percent over the period. The spatial distribution of forest C storage in Guangdong was uneven and this pattern reflects differences in forest management and economic and social development. Future forest management should focus on the selection of tree species, management of forest stand structures and implementation of sustainable practices so that Veg C sequestration potentials can be maximized.     

Energy-dispersive X-ray fluorescence analysis of zinc and iron concentration in rice and pearl millet grain

Background and aims

Rice (Oryza sativa L.) and pearl millet (Pennisetum glaucum L.) biofortification breeding programs require accurate and convenient methods to identify nutrient dense genotypes. The aim of this study was to investigate energy-dispersive X-ray fluorescence spectrometry (EDXRF) for the measurement of zinc (Zn) and iron (Fe) concentration in whole grain rice and pearl millet.

Methods

Grain samples were obtained from existing biofortification breeding programs. Reference Zn and Fe concentrations obtained by inductively-coupled plasma-optical emission spectroscopy (ICP-OES) were used to calibrate the EDXRF instrument. Calibration was performed with 24 samples and separate calibrations were developed for rice and pearl millet. To validate calibrations, EDXRF analyses were conducted on an additional 40 samples of each species.

Results

EDXRF results were highly correlated with ICP-OES values for both Zn and Fe in both species (r²?=?0.79 to 0.98). EDXRF predicted Zn and Fe in rice to within 1.9 and 1.6?mg?kg^?1 of ICP-OES values, and Zn and Fe in pearl millet to within 7.6 and 12.5?mg?kg^?1 of ICP-OES values, at a 95% confidence level.

Conclusion

EDXRF offers a convenient, economical tool for screening Zn and Fe concentration in rice and pearl millet biofortification breeding programs.     

Impact of elevated temperatures on greenhouse gas emissions in rice systems: interaction with straw incorporation studied in a growth chamber experiment

Aims

Two pot experiments in a “walk-in” growth chamber with controlled day and night temperatures were conducted to investigate the influence of elevated temperatures along with rice straw incorporation on methane (CH₄) and nitrous oxide (N₂O) emissions as well as rice yield.

Methods

Three temperature regimes–29/25, 32/25, and 35/30 °C (Exp. I) and 29/22, 32/25, and 35/28 °C (Exp. II), representing daily maxima/minima were used in the study. Two amounts of rice straw (0 and 6 t ha^?1) were applied with four replications in each temperature regime. CH₄ and N₂O emissions as well as soil redox potential (Eh) were monitored weekly throughout the rice-growing period.

Results

Elevated temperatures increased CH₄ emission rates, with a more pronounced effect from flowering to maturity. The increase in emissions was further enhanced by incorporation of rice straw. A decrease in soil Eh to <?100 mV and CH₄ emissions was observed early in rice straw–incorporated pots while the soil without straw did not reach negative Eh levels (Exp. I) or showed a delayed decrease (Exp. II). Moreover, soil with high organic C (Exp. II) had higher CH₄ emissions. In contrast to CH₄ emissions, N₂O emissions were negligible during the rice-growing season. The global warming potential (GWP) was highest at high temperature with rice straw incorporation compared with low temperature without rice straw. On the other hand, the high temperature significantly increased spikelet sterility and reduced grain yield (p?<?0.05).

Conclusions

Elevated temperature increased GWP while decreased rice yield. This suggests that global warming may result in a double negative effect: higher emissions and lower yields.     

Nitrous oxide emissions and nitrate leaching from a rain-fed wheat-maize rotation in the Sichuan Basin, China

Aims

A 3-year field experiment (October 2004–October 2007) was conducted to quantify N₂O fluxes and determine the regulating factors from rain-fed, N fertilized wheat-maize rotation in the Sichuan Basin, China.

Methods

Static chamber-GC techniques were used to measure soil N₂O fluxes in three treatments (three replicates per treatment): CK (no fertilizer); N150 (300 kg N fertilizer ha^?1 yr^?1 or 150 kg N?ha^?1 per crop); N250 (500 kg N fertilizer ha^?1 yr^?1 kg or 250 kg N?ha^?1 per crop). Nitrate (NO ₃ ^? ) leaching losses were measured at nearby sites using free-drained lysimeters.

Results

The annual N₂O fluxes from the N fertilized treatments were in the range of 1.9 to 6.7 kg N?ha^?1 yr^?1 corresponding to an N₂O emission factor ranging from 0.12 % to 1.06 % (mean value: 0.61 %). The relationship between monthly soil N₂O fluxes and NO ₃ ^- leaching losses can be described by a significant exponential decaying function.

Conclusions

The N₂O emission factor obtained in our study was somewhat lower than the current IPCC default emission factor (1 %). Nitrate leaching, through removal of topsoil NO ₃ ^? , is an underrated regulating factor of soil N₂O fluxes from cropland, especially in the regions where high NO ₃ ^- leaching losses occur.     

Transgenic Bt rice has adverse impacts on CH4 flux and rhizospheric methanogenic archaeal and methanotrophic bacterial communities

Background and Aims

The effect of transgenic insect-resistant crops on soil microorganisms has become an issue of public concern. The goal of this study was to firstly realize the variation of in situ methane (CH₄) emission flux and methanogenic and methanotrophic communities due to planting transgenic Bt rice (Bt) cultivar.

Methods

CH₄ emitted from paddy soil was collected by static closed chamber technique. Denaturing gradient gel electrophoresis and real-time PCR methods were employed to analyze methanogenic archaeal and methanotrophic bacterial community structure and abundance.

Results

Results showed that planting Bt rice cultivar effectively reduced in situ CH₄ emission flux and methanogenic archaeal and methanotrophic bacterial community abundance and diversity. Data analysis showed that in situ CH₄ emission flux increased significantly with the increase of methanogenic archaeal abundance (R ² ?=?0.839, p?<?0.001) and diversity index H′ (R ² ?=?0.729, p?<?0.05), whereas was not obviously related to methanotrophic bacterial community.

Conclusions

Our results suggested that the lower in situ CH₄ emission flux from Bt soil may result from lower methanogenic archaeal community abundance and diversity, lower methanogenic activity and higher methanotrophic activity. Moreover, our results inferred that specific functional microorganisms may be a more sensitive indicator than the total archaeal, bacterial or fungal population to assess the effects of transgenic insect-resistant plants on soil microorganisms.     

Development of a microarray for two rice subspecies: characterization and validation of gene expression in rice tissues

Background

Rice is one of the major crop species in the world helping to sustain approximately half of the global population’s diet especially in Asia. However, due to the impact of extreme climate change and global warming, rice crop production and yields may be adversely affected resulting in a world food crisis. Researchers have been keen to understand the effects of drought, temperature and other environmental stress factors on rice plant growth and development. Gene expression microarray technology represents a key strategy for the identification of genes and their associated expression patterns in response to stress. Here, we report on the development of the rice OneArray® microarray platform which is suitable for two major rice subspecies, japonica and indica.

Results

The rice OneArray® 60-mer, oligonucleotide microarray consists of a total of 21,179 probes covering 20,806 genes of japonica and 13,683 genes of indica. Through a validation study, total RNA isolated from rice shoots and roots were used for comparison of gene expression profiles via microarray examination. The results were submitted to NCBI’s Gene Expression Omnibus (GEO). Data can be found under the GEO accession number GSE50844 (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE50844). A list of significantly differentially expressed genes was generated; 438 shoot-specific genes were identified among 3,138 up-regulated genes, and 463 root-specific genes were found among 3,845 down-regulated genes. GO enrichment analysis demonstrates these results are in agreement with the known physiological processes of the different organs/tissues. Furthermore, qRT-PCR validation was performed on 66 genes, and found to significantly correlate with the microarray results (R?=?0.95, p?<?0.001***).

Conclusion

The rice OneArray® 22 K microarray, the first rice microarray, covering both japonica and indica subspecies was designed and validated in a comprehensive study of gene expression in rice tissues. The rice OneArray® microarray platform revealed high specificity and sensitivity. Additional information for the rice OneArray® microarray can be found at http://www.phalanx.com.tw/index.php.