Root-derived carbon in soil respiration and microbial biomass determined by 14C and 13C

Two approaches to quantitatively estimating root-derived carbon in soil CO₂ efflux and in microbial biomass were compared under controlled conditions. In the ¹⁴C labelling approach, maize (Zea mays) was pulse labelled and the tracer was chased in plant and soil compartments. Root-derived carbon in CO₂ efflux and in microbial biomass was estimated based on a linear relationship between the plant shoots and the below-ground compartment. Since the maize plants were grown on C₃ soil, in a second approach the differences in ¹³C natural abundance between C₃ and C₄ plants were used to calculate root-derived carbon in the CO₂ efflux and in the microbial biomass. The root-derived carbon in the total CO₂ efflux was between 69% and 94% using the ¹⁴C labelling approach and between 86% and 94% in the natural ¹³C labelling approach. At a ¹³C fractionation measured to be 5.2‰ between soil organic matter (SOM) and CO₂, the root-derived contribution to CO₂ ranged from 70% to 88% and was much closer to the results of the ¹⁴C labelling approach. Root-derived contributions to the microbial biomass carbon ranged from 2% to 9% using ¹⁴C labelling and from 16% to 36% using natural ¹³C labelling. At a 3.2‰ ¹³C fractionation between SOM and microbial biomass, both labelling approaches yielded an equal contribution of root-derived C in the microbial biomass. Both approaches may therefore be used to partition CO₂ efflux and to quantify the C sources of microbial biomass. However, the assumed ¹³C fractionation strongly affects the contributions of individual C sources.     

Stimulation of root exudation of rice seedlings by Azospirillum strains: carbon budget under gnotobiotic conditions

Summary The association of rice seedlings (cv. Delta) with different strains of Azospirillum was studied under monoxenic conditions in the dark. Axenic 3-day-old seedlings were obtained on a C- and N-free medium and inoculated with 6 · 10⁷ bacteria per plant in a closed vial. Seven days later, different components of a carbon budget were evaluated on them and on sterile controls: respired CO₂, carbon of shoot and roots, bacterial and soluble carbon in the medium. Two strains (A. lipoferum 4B and A. brasilense A95) isolated from the rhizosphere of rice caused an increase in exudation, + 36% and + 17% respectively compared with sterile control. Shoot carbon incorporation and respiration were reduced by inoculation. A third strain (A. brasilense R07) caused no significant change in exudation. A. lipoferum B7C isolated from maize did not stimulate rice exudation either. We further investigated a possible effect of nitrogen fixation on this phenomenon: inhibition of nitrogen fixation by 10% C₂H₂ did not modify the extent of C exudation by rice associated with A. lipoferum 4B or with the non-motile A. lipoferum 4T.     

Silicon induced cadmium tolerance of rice seedlings

Cadmium (Cd²⁺) toxicity and effects of silicon (Si) applications on the cellular and intracellular accumulations and distributions of Cd were investigated by conventional electron microscopy and EDX analysis. The Si‐deprived rice (Oryza sativa L.) plants (‐Si) differ greatly from Si‐replete ones in cell walls and vacuoles distributions of Ca in their leaves and roots. Energy dispersive x‐ray microanalysis revealed that considerable amounts of Cd could be detected in the cytoplasm, vacuole or cellular organelles in ‐Si rice plants, while very little to be found in +Si ones. From the nanochemical and nanobiological points of views, cell wall templates mediated the formation of colloidal silica with the high specific adsorption property to prevent the uptake of Cd into the cell.     

Enantioselective separation and phytotoxicity on rice seedlings of paclobutrazol

The environmental significance of enantioselectivity in chiral insecticides and herbicides has been widely studied. However, little information is currently available on the enantioselective behavior of chiral plant growth regulators. In this study, paclobutrazol enantiomers were resolved and prepared by chiral high-performance liquid chromatography with a Sino-chiral OJ column. The relationship among absolute configuration, optical activity and circular dichroism of paclobutrazol enantiomers was established. The enantioselective behavior of paclobutrazol, including enantioselective effect of paclobutrazol on the growth of rice seedlings and cyanobacteria and enantioselective loss of paclobutrazol in rice seedling growth media, in rice culture system was studied. The (2S,3S)-(-)-enantiomer was almost 3.1 times more active than the (2R,3R)-(+)-enantiomer toward shoot growth as measured by 7 day EC50 values. Enantioselectivity could not be determined with respect to root growth of rice seedlings because a typical dosage response was not observed in the range of the concentrations studied. The dissipation of paclobutrazol in rice growth medium is not enantioselective. Enantiomers and diastereoisomer of paclobutrazol all facilitated the growth of cyanobacteria, which increase the effectiveness of rice biofertilizers. The (2S,3S)-(-)-enantiomer showed stronger stimulatory activity on Microcystis aeruginosa cyanobacteria than the (2R,3R)-(+)-enantiomer, whereas the latter was a more potent stimulator of Anabaena sp. growth. These observations indicate that application of the (2S,3S)-(-)-enantiomer of paclobutrazol and Microcystis aeruginosa in rice cultivation is a good strategy for improving rice seedling performance.     

Release and activity of allelochemicals from allelopathic rice seedlings

3-Isopropyl-5-acetoxycyclohexene-2-one-1 (1), momilactone B (2), and 5,7,4'-trihydroxy-3',5'-dimethoxyflavone (3) were isolated and identified from an allelopathic rice accession PI312777. These three compounds at low concentrations could inhibit the growth of weeds Echinochloa crusgalli and Cyperus difformis associated with rice, especially mixtures of the compounds had stronger inhibitory activity than did individual compounds. Studies with hydroponic culture, continuous root exudates trapping system (CRETS), and direct resin adsorption methods showed that a total of 7.6 n moles 1, 2, and 3 were exuded from living roots of each seedling into the environment at 10 days after seedlings were transplanted. Furthermore, 1, 2, and 3 were found in the soil growing PI312777 seedlings at day 15 after seedlings emergence and reached a total of 39.5 microg/g soil at day 30. The results indicated that PI 312777 seedlings could release sufficient quantities of 1, 2, and 3 into the environment to act as allelochemicals inhibiting the growth of associated weeds. Investigations on the distribution of 1, 2, and 3 in PI 312777 plant, and its root exudates showed that the levels of 1, 2, and 3 were significantly higher in the shoots and root exudates than in the roots, and only trace 1 was observed in the roots. The results suggest that the roots of rice seedlings are not major site of synthesis or accumulation 1, 2, and 3, but a pathway for their release into the environment. The levels of 1, 2, and 3 in the root exudates were over 2-folds higher under direct resin adsorption than under hydroponic culture and CRETS, and hence, it is the preferred method to collect and identify active allelochemicals in rice exudates in future studies on rice allelopathy.     

水稻旱育壮秧的根际生态学特性分析

旱育秧是水稻高产栽培中的关键技术之一,具有省水、省种、省工、省肥、增产、早熟等特点。本研究采用大田试验,通过比较旱育秧与水育秧根际土壤生态因子及细菌群落多样性的变化,并结合地上部秧苗的形态特征,探讨旱育壮秧形成的根际生态学特性。研究结果表明,旱育方式下秧苗株高较水育秧苗矮32.31%,但植株地上部干重、根长、根干重、根冠比、白根数分别提高3.02%、21.99%、18.93%、15.10%、200.00%。根际土壤生态因子监测表明,旱育秧土壤含水量为15%~17%;与水育秧相比,土壤p H降低7.94%,电导率提高244.62%,温度上升2~3℃。旱育秧根际土壤中的磷酸单酯酶、蔗糖酶、脲酶、过氧化氢酶、脱氢酶活性分别比水育秧高166.66%、518.85%、131.98%、102.70%、84.36%,但硝酸盐还原酶活性却下降72.95%,这有利于土壤物能转化,提高土壤养分的有效性,表现为土壤有机质、硝态氮、铵态氮、速效钾、有效磷含量分别比水育秧高89.27%、320.11%、56.95%、50.85%、184.75%。细菌16S r DNA测序表明旱育秧苗根际土壤细菌Chao1指数和香农指数显著高于水育秧。菌群分析发现,旱育栽培下变形菌门α-变形菌纲和γ-变形菌纲,拟杆菌门,绿弯菌门,硝化螺旋菌门,酸杆菌门,芽单胞菌门,浮霉菌门和放线菌门比例上升,而厚壁菌门,变形菌门β-变形菌纲的比例下降。对土壤细菌优势群落的功能分析发现,旱育秧能够显著促进根际与土壤养分转化密切相关的硝化细菌、固氮菌、氨氧化菌、光合细菌、解磷菌、解钾菌的繁殖。同时,旱育秧根际土壤中与根系生长密切相关的根际促生菌的数量也显著提高。可见,旱育秧栽培方式通过控制土壤中水分的含量,调控秧苗根际土壤p H、电导率和温度,改善土壤生态环境,增强了根际土壤中与营养转化循环相关的优势菌群的数量比例,进而有利于健壮秧苗的形成。     

水稻秧苗抗拉力学特性及穴盘拔秧性能的力学试验研究

该文通过对水稻穴盘秧苗的抗拉力学特性和穴盘拔秧性能的试验研究,探讨水稻穴盘秧苗拔秧机理,为水稻穴盘秧苗拔秧机构的设计提供理论依据。试验结果表明：水稻秧苗的抗拉断力随秧苗秧龄、秧苗高度的增加而增大,随秧苗夹秧位置的提高而下降;秧苗所需从育秧穴盘中拔出的拔秧力与秧苗秧龄无明显关系,但受秧苗钵体湿度的影响较大,随秧苗钵体湿度的增加而减小,在相对湿度为40%～60%时,取得最小值;在正常条件下,单株或多株秧苗抗拉断力都远远大于从育秧穴盘拔取秧苗所需的拔秧力,采取拔取的方式将秧苗从育秧穴盘取出是可行的。     

Enantiomeric resolution and growth-retardant activity in rice seedlings of uniconazole

The increasing application of chiral pesticides has enhanced interest in their enantioselectivity. However, little relevant information is currently available for enantioselective activity of chiral plant growth regulators. In an attempt to screen active enantiomers of uniconazole, this work investigated enantiomeric separation and the enantioselective effect of uniconazole on the growth of rice seedlings and cyanobacteria. Baseline resolution of uniconazole enantiomers was achieved on a Chiralpak AD column by chiral high-performance liquid chromatography (HPLC). The relationship among circular dichroism (CD), optical rotation (OR), and absolute configuration was successfully established by coupling of CD and OR detection. The t test at the 95% level of confidence indicated significant differences between the enantiomers in their retardant activity toward growth of rice seedlings and stimulation effect on growth of cyanobacteria, the natural biofertilizers in rice paddy fields. The S-(+)-enantiomer was more active than the R-(-)-enantiomer in retarding growth of rice seedlings and stimulating growth of Microcystis aeruginosa . This special enantiomeric selectivity was further elucidated by probing the binding mode of enantiomers to gibberellin (GA) 20-oxidase by molecular docking. The S-(+)-enantiomer was found to bind tightly with GA 20-oxidase. The results suggested that the S-(+)-enantiomer instead of a racemate of uniconazole should be used to improve rice seedling quality.     

Effect of Azospirillum brasilense inoculation on root morphology and respiration in tomato seedlings

Summary The level of Azospirillum brasilense strain Cd colonization in the rhizosphere of some vegetables was 10⁴–10⁵ colony-forming units (CFU) per root of one plant in 2-week-old plants inoculated with 5 × 10⁸ Azospirillum cells. Significant increases in root length (35%) and in top (90%) and root (50%) dry weight and total leaf area (90%) were observed in 18-day-old inoculated tomato plants compared with non-inoculated controls. An inoculum concentration of 1 × 10⁸ to 5 × 10⁸ CFU/ml stimulated the appearance of root hairs. Large numbers of bacteria (1 × 10⁹ CFU/ml) caused asymmetrical growth of the root tip. In a petri dish system, Azospirillum (1 × 10⁸ CFU/ml) increased root dry weight (150%), protein content (20%), respiration rate per root (70%) and the specific activity of malate dehydrogenase (45%–65%) over non-inoculated controls. The specific respiration rate, expressed as micromol of O₂ per minute per milligram of dry weight of roots, was significantly lower in inoculated roots, suggesting that less energy was spent for accumulation of more dry material.     

不同品种辣椒幼苗光合与呼吸对弱光的响应

分别在300μmol／m2·s和100μmol／m2·s的人工光源下。研究了“中椒5号”、“中椒6号”、“中椒10号”和“红英达”4个辣椒品种光合和呼吸特性对弱光的响应。结果表明,弱光下幼苗净光合速率(Pn)、暗呼吸速率(Rd)、夜闻呼吸速率(Rn)、饱和光强(SL)、光补偿点(LCP)、光饱和光合速率(Pmax)下降,表观量子效率(AQY)上升。弱光下辣椒Pn的下降是非气孔限制的结果,较低的Rubisco羧化活性是辣椒Pmax下降的一个重要原因。弱光下辣椒叶片叶绿素(Chl．)含量上升,Chl．a／b值和比叶重(SLM)下降。供试品种中“中椒10号”在弱光下具有较低的LCP、Rd、Rn以及较高的AQY,表现出较强的弱光耐受性。     

PGPR对水稻塑盘旱育秧苗素质的影响

采用水稻抛秧塑盘(434孔)旱育秧方法,研究3株PGPR(Bacillus sp.RBB1、Bacillus sp.WP8和Pseudomonassp.RBP1)对水稻旱育秧苗素质的作用,比较PGPR不同接种方式及施用壮秧剂对促生效果的差异,以及PGPR对土壤细菌群落结构的影响。结果表明:①RBP1和WP8可不同程度地促进秧苗生长,主要表现在促使秧苗矮壮、增加干物质积累;②PGPR拌土普遍优于浸种方式;③PGPR的有效性受是否与壮秧剂混用的影响,其次是接种方式;④地上部干物重对PGPR不同处理方式较为敏感,是评价促生效果的理想指标;⑤PGPR对土壤细菌群落结构有一定的影响,但不十分明显。通过研究,明确WP8和RBP1具有开发成水稻育秧专用微生物肥料的潜力。     

Low phosphorus effects on the metabolism of rice seedlings

Abstract

Phosphorus‐stress‐induced (Psi) changes in shoot and root phosphorus (P) content (SPC and RPC) and use efficiency (SPUE and RPUE) defined as dry biomass production per unit of absorbed P, root acid phosphatase activity (RAPA), and excreted acid phosphatase activity (EAPA), were investigated for 5 rice genotypes under P‐sufficient (10 ppm Pi) and P‐stressed (0.5 ppm Pi) solution culture conditions. Genotypic tolerance to P‐stress was assessed based on less decrease in shoots and roots P content and larger increase in shoots and roots P use efficiency with decreasing P concentration from 10 ppm to 0.5 ppm in the culture solution. Plants were harvested 2 and 4 weeks after growing, respectively, for the parameter measurements. Significant (#0.01) genotypic differences in SPC and RPC were observed under P‐sufficient and P‐stressed conditions with the differences decreasing with length of growing period. On the contrary, significant (#0.01) genotypic differences in SPUE and RPUE were only found under P‐stress condition, but not under P‐sufficient condition, suggesting that genotypic variation in tolerance to P‐stress in terms of PUE could be screened under P‐stress conditions. More than 2‐fold genotypic differences in Psi‐RAPA and Psi‐EAPA were obtained after 2 weeks, followed by a decrease in Psi‐EAPA, but not in Psi‐RAPA. After 2 weeks, Psi‐EAPA was highly correlated to decrease in SPC and decrease in RPC measured after 2 and 4 weeks, respectively. Significant negative correlations were also found between decrease in SPC and increase in RPUE, and between decrease in SPC and decrease in RPC. The implications of these results in evaluating rice genotypic tolerance to P‐stress is discussed.     

Phosphine-induced phosphorus mobilization in the rhizosphere of rice seedlings

Purpose

The aim of this study was to evaluate the role of phosphine in the mobilization of phosphorus in the rhizosphere soil of rice seedlings and to determine the relative efficiency of phosphine in plant P acquisition.

Materials and methods

An indoor simulation experiment was conducted and the matrix-bound phosphine (MBP), phosphorus fractions, and phosphatase activity in the rhizosphere soil samples from rice cultivation, biomass, the plant P, and the root system activity were measured under different phosphine concentrations (0, 1.4, 4.2, and 7.0 mg m^?3) for a period of 30 days.

Results and discussion

The results indicated that phosphine treatments enhanced MBP, inorganic P (resin–P_i, NaHCO₃–P_i, and NaOH–P_i), and phosphatase activity, as well as the root system activity, and the content of P in the rice seedlings was stimulated with increasing phosphine concentrations. However, organic P (NaHCO₃–P_o and NaOH–P_o) accumulation occurred in the rhizosphere of the rice seedlings. In addition, the content of organic P in the soil samples decreased with increased phosphine concentration.

Conclusions

Therefore, relatively high concentrations of phosphine in paddy field could have a positive impact on the effectiveness of phosphorus in rice plants via influencing the rhizosphere properties.

     

乳芽直播种植技术条件下水稻生长特性的研究

为了探索水稻直播的最佳种植工艺及其相应的机械化生产，采用田间试验方法，在辽阳市景尔屯村的20 hm²水田进行了乳芽直播、常规插秧和抛秧3个处理的水稻种植对比试验。对培育期乳芽的根长、根数和高度等生长特征的研究结果表明，练苗环节对根长和乳芽高度的增长速度有明显的抑制作用，但对乳芽根数的增加无影响。对秧苗生长中期的性状特征研究结果表明，与其它2个处理相比，乳芽直播的秧苗在5月20～7月27日期间生长较快，分蘖和抽穗开始时间早，分蘖节位低，但由于播种密度太大，有效分蘖率较低。对3个处理的产量形成指标检测结果表明，乳芽直播处理的穗数密度为538.7万穗/hm²，每穗结实粒数为76.8粒，千粒重为0.0246 kg。     

pH值对水稻幼苗吸收NO3——的影响

运用微电极技术研究了改变细胞内外pH值对常规籼稻(杨稻6号)NO3-吸收的影响。结果表明:1)未经NO3-培养的水稻根表皮细胞吸收NO3-会引起细胞膜电位瞬时的去极化或超级化。当水稻根系吸收NO3-时,表皮细胞膜电位改变的程度随外界NO3-浓度的增大而增大;在浓度为0.5.mmol/L时达到最大,而后表皮细胞膜电位的变化基本维持不变。2)外界不同pH(4.4、5.5、7.0)条件下,表皮细胞膜电位对NO3-的响应随着外界pH的升高而有所降低,并且表皮细胞膜电位对NO3-的响应在pH.8.0受抑制程度不大。3)5.mmol/L丁酸钠和3.mmol/L普鲁卡因可以使细胞内pH分别降低0.16个单位和升高0.2个单位;改变细胞内pH值对水稻吸收NO3-时引起表皮细胞膜电位的变化几乎没有明显的影响。4)不同pH条件下,培养2周左右的水稻地上部干鲜重差异显著,以pH.5.5时为最高;组织中NO3-和NH4+的含量也在pH.5.5时最高。由于细胞内pH是受系统严格调控的,具有极强的缓冲能力,因此,NO3-的吸收主要受外界pH的影响。酸性可以促进NO3-的内流;而微碱性增加了NO3-的外流,降低了NO3-的净吸收。     

Seed priming improves growth of nursery seedlings and yield of transplanted rice

Abstract

An attempt to improve the performance of rice (Oryza sativa L.) nursery seedlings through seed priming and its effect on the yield after transplantation was made in a field trial. Priming tools employed during the investigation include pre-germination, hydropriming for 48 h, osmohardening with KCl and CaCl₂ (ψs-1.25 MPa) for 24 h, vitamin priming with 10 ppm ascorbic acid for 48 h and seed hardening for 24 h. All the priming techniques resulted in improved germination speed and spread, seedling fresh and dry weight, root and shoot length, number of secondary roots, seedling nitrogen, total sugars and α-amylase activity. Osmohardening with CaCl₂ resulted in the best performance as indicated by improved germination speed and spread, seedling vigour and starch metabolism, followed by hardening and osmohardening with KCl. However, improved starch metabolism in coarse rice was observed in osmohardening with KCl. Higher K and Ca contents were observed in seeds osmohardened with KCl and CaCl₂, respectively. Maximum straw and kernel yield and harvest index were recorded from osmohardening with CaCl₂ in fine and osmohardening with KCl in coarse rice. Increased number of secondary roots and α-amylase activity were accompanied with increased seedling nitrogen and reducing sugars, respectively.     

Soil carbon dioxide flux and rice photosynthesis

Measurement of CO₂ concentration in air at 25 em below and 100 em above the canopy of a good rice crop indicated that a severe CO₂ deficit occurred around the photosynthetic surface of crop when light intensity was high. Soil CO₂ flux as measured by the soda lime method in a closed system ranged from 3.9 to 5.7 g.m^-2. day^-1 under flooded conditions and from 6.0 to 8,6g.m^-2 .day^-1 under drained conditions. Cropped soil released more CO₂ than bare soil under both flooded and drained conditions. The estimated contribution of soil CO₂ to gross photosynthesis was 6%, for the flooded soil and 7% for the drained soil or a contribution of 9 and 12% to net dry matter production. These results together with other information indicate that atmospheric CO₂ is the most important source of CO₂, in crop photosynthesis, soil CO₂ released into atmosphere Is second most important, and soil CO₂ absorbed by plant roots is almost negligible.     

穴盘水稻秧苗通过分秧滑道的运动仿真与分析

为了研究所设计的分秧滑道的性能,利用Pro/E和ADAMS软件对穴盘水稻秧苗通过分秧滑道运动进行了仿真。建立了2种秧苗营养土钵模型,球体模型和实际尺寸营养土钵模型。结果发现秧苗在通过分秧滑道圆弧段时其速度、加速度和接触力会发生突变;秧苗通过7条滑道需要的时间最长为0.633 s,最短为0.463 s;当滑道相对竖直平面倾斜2°布置时,秧苗通过滑道的通过性与滑道竖直布置时的差异不大。通过仿真可得到7穴秧苗不同时间点在7条滑道中的运动轨迹,以及在滑道运动的状态下,秧苗通过2组分秧滑道后在田间的定植情况。研究结果为今后分秧机构的进一步优化设计和试验研究提供了参考依据。     

水稻钵苗空气整根气吸式有序移栽机的研究

采用空气整根育秧技术对水稻钵苗进行育秧试验,提出了水稻钵苗空气整根育秧、气吸取苗和投苗的有序移栽方案。试验结果表明,采用空气整根培育钵苗,根系遍布整个钵腔,生物学特性优于常规钵育秧,且移栽时钵体不易破碎和倒伏。采用空气整根钵盘,以较小的吸力,钵苗就可从钵腔底部取出,实现不伤苗和根的钵苗有序移栽。对气吸式水稻钵苗有序移栽机的总体方案设计、横纵向移箱装置、投苗装置进行了分析和研究,研制了样机。试验结果表明,由步进电机驱动齿轮齿条机构控制横纵向送秧箱,驱动曲柄摆杆机构控制吸气活门,由电磁铁控制导苗管投苗活门的单