Substrate-dependent biosynthesis of ethylene by rhizosphere soil fungi and its influence on etiolated pea seedlings

Several fungi were isolated from rhizosphere soils of various crops through enrichment on l-methionine (l-MET) as a sole C and N source. These fungi were examined for their C₂H₄ production potential in vitro. GC-FID analysis indicated that 78%, 83%, 89% and 72% of fungi isolated from rhizosphere soil of wheat, maize, potato and tomato, respectively, produced C₂H₄ from substrate l-MET. Eight of the most efficient C₂H₄-producing fungal isolates (two from each crop) were further tested for their ability to produce C₂H₄ from 2-keto-4-methylthiobutyric acid (KMBA) and α-ketoglutaric acid (α-KGA). Interestingly, all eight fungi produced C₂H₄ from KMBA, but none used α-KGA as C₂H₄ precursor. This result implies that the MET→KMBA→C₂H₄ pathway was most likely operating in these fungi. The most efficient C₂H₄ producer fungus (isolated from maize rhizosphere soil) was identified as Aspergillus terreus; this isolate was further studied to determine the optimal conditions for C₂H₄ production from l-MET. It was observed that a substrate (l-MET) concentration of 10 mmol l⁻¹, a glucose (C-source) concentration of 6.0 g L⁻¹, no nitrogen, a pH of 6.0, an incubation temperature of 30 °C and an incubation time of 72 h were optimal conditions for l-MET-derived C₂H₄ biosynthesis by Aspergillus terreus. In addition, C₂H₄ released from precursor (l-MET) by Aspergillus terreus significantly affected the seedling length and stem diameter of etiolated pea seedlings in both sterilized and non-sterilized soils compared to a control. C₂H₄-producing microflora may be ubiquitous in soil, and the availability of a substrate like l-MET could enhance C₂H₄ synthesis in the rhizosphere of a plant, in turn evoking a physiological response. As far as we know, this study represents the first comprehensive screening of rhizosphere fungi for their ability to produce C₂H₄ from l-MET and KMBA.     

Effect of acetylene and ethylene gases released from encapsulated calcium carbide on growth and yield of wheat and cotton

Calcium carbide (CaC₂) is a rich source of the nitrification inhibitor acetylene (C₂H₂) and plant hormone ethylene (C₂H₄). C₂H₄ formed from biotic reduction of C₂H₂ released from CaC₂ may accumulate in soil at physiologically active concentrations. Laboratory studies were conducted to evaluate the potential of encapsulated CaC₂ for gradually releasing C₂H₂ and its product C₂H₄ in soil. The GC-FID analysis revealed that encapsulated CaC₂ released a copious amount of C₂H₂ (up to 23700 nmol kg⁻¹ soil), which was gradually reduced to C₂H₄ over a period of time via a strictly biotic reaction as no C₂H₄ was detected in CaC₂-amended sterilized soil. Ammonium oxidation was suppressed by the encapsulated CaC₂ indicating that C₂H₂ acted as a nitrification inhibitor. Results of pot trials conducted in the net house indicated that encapsulated CaC₂ applied at 30 mg kg⁻¹ soil significantly increased the number of tillers (up to 45.5%), root weight (up to 14.9%), straw (up to 32.8%) and grain yield (up to 37.3%) of wheat over the fertilizer application alone. In the case of cotton, the number of bolls, root, shoot and seed weight were also significantly increased in response to the application of encapsulated CaC₂. Moreover, application of encapsulated CaC₂ resulted in greater N-use efficiency (NUE) (up to 61.1%) by both wheat and cotton crops than that observed at the same rates of N fertilizer alone. These findings imply that CaC₂ affects plant growth through hormonal action of C₂H₄ as well as improved NUE; however, the latter factor might be a relatively more contributing. It is desirable that CaC₂ is formulated for gradually slow release of C₂H₂ and C₂H₄ in soil air.     

Microbial ethylene production and inhibition of methanotrophic activity in a deciduous forest soil

Production of C₂H₄, but not of CH₄, was observed in anoxically incubated soil samples (cambisol on loamy sand) from a deciduous forest. Ethylene production was prevented by autoclaving, indicating its microbial origin. Ethylene production gradually decreased from 4 to 12 cm soil depth and was not affected by moisture or addition of methionine, a possible precursor of C₂H₄. Oxidation of atmospheric CH₄ in soil samples was inhibited by C₂H₄. Ethylene concentrations of 3, 6 and 10 μl l⁻¹ decreased CH₄ uptake by 21, 63 and 98%, respectively. Methionine and methanethiol, a possible product of methionine degradation, also inhibited CH₄ oxidation. Under oxic conditions, C₂H₄ was consumed in the soil samples. Ethylene oxidation kinetics exhibited two apparent K_m values of 40 μl l⁻¹ and 12,600 μl l⁻¹ suggesting the presence of two different types of C₂H₄-oxidizing microorganisms. Methanotrophic bacteria were most probably not responsible for C₂H₄ oxidation, since the maximum of C₂H₄ oxidation activity was localized in soil layers (2-8 cm depth) above those (8-10 cm depth) of CH₄ oxidation activity. Our observations suggest that C₂H₄ production in the upper soil layers inhibits CH₄ oxidation, thus being one reason for the localization of methanotrophic activity in deeper soil layers.     

Effectiveness of ACA Rates on Potatoes Raised in Irrigated Sandy Soil

Over a 5-year period, field evaluations of several rates of ACA, an acronym for Agricultural Crop Additive, were conducted on irrigated sandy Wisconsin soils using potato (Solanum tuberosum L.) as the test crop. In some years, statistically significant tuber total yield increases of about 4 Mg ha^?1 were seen for one rate, but not others, with the response rate varying between years. In 1 year, similarly sized yield increases were seen for all rates. In most years, the use of ACA (at one or more rates) increased the size of harvested tubers but did not affect other measured growth parameters including stem or tuber number, early-season vegetative or root growth, or midseason leaf nutrient concentrations. In the year when ACA was evaluated across three potato varieties, the responses appeared to be variety specific. No clear mode of action could be identified where the positive responses were seen other than the apparent influence of the additive on harvested tuber size.     

Promotion of plant growth by an auxin-producing isolate of the yeast Williopsis saturnus endophytic in maize (Zea mays L.) roots

A plant-growth-promoting isolate of the yeast Williopsis saturnus endophytic in maize roots was found to be capable of producing indole-3-acetic acid (IAA) and indole-3-pyruvic acid (IPYA) in vitro in a chemically defined medium. It was selected from among 24 endophytic yeasts isolated from surface-disinfested maize roots and evaluated for their potential to produce IAA and to promote maize growth under gnotobiotic and glasshouse conditions. The addition of l-tryptophan (L-TRP), as a precursor for auxins, to the medium inoculated with W. saturnus enhanced the production of IAA and IPYA severalfold compared to an L-TRP-non-amended medium. The introduction of W. saturnus to maize seedlings by the pruned-root dip method significantly (P<0.05) enhanced the growth of maize plants grown under gnotobiotic and glasshouse conditions in a soil amended with or without L-TRP. This was evident from the increases in the dry weights and lengths of roots and shoots and also in the significant (P<0.05) increases in the levels of in planta IAA and IPYA compared with control plants grown in L-TRP-amended or non-amended soil. The plant growth promotion by W. saturnus was most pronounced in the presence of L-TRP as soil amendment compared to seedlings inoculated with W. saturnus and grown in soil not amended with L-TRP. In the glasshouse test, W. saturnus was recovered from inside the root at all samplings, up to 8 weeks after inoculation, indicating that the roots of healthy maize may be a habitat for the endophytic yeast. An endophytic isolate of Rhodotorula glutinis that was incapable of producing detectable levels of IAA or IPYA in vitro failed to increase the endogenous levels of IAA and IPYA and failed to promote plant growth compared to W. saturnus, although colonization of maize root tissues by R. glutinis was similar to that of W. saturnus. Both endophytic yeasts, W. saturnus and R. glutinis, were incapable of producing in vitro detectable levels of gibberellic acid, isopentenyl adenine, isopentenyl adenoside or zeatin in their culture filtrates. This study is the first published report to demonstrate the potential of an endophytic yeast to promote plant growth. This is also the first report of the production of auxins by yeasts endophytic in plant roots.     

Growth and functioning of roots and of root systems subjected to soil compaction. Towards a system with multiple signalling?

The effect of soil mechanical impedance on root growth is discussed on several levels from the apex to the root system. At the individual root level, the balance of pressures on the root apex cannot account for observed reductions in root elongation rate. Furthermore, soil mechanical impedance affects the elongation rate of non-impeded organs, such as leaves or non-impeded roots. A chemical message originating in roots could account for such an effect, probably via changes in cell wall rheological properties in all growing zones of the plant. Changes in carbon allocation could also have a role. At a whole-plant level, indirect effects linked to changes in the plant structure contribute in a major way to the effect of mechanical impedance on root growth. Although only a small proportion of roots of fieldgrown plants are in contact with compact soil, geometrical characteristics of root systems are considerably affected. In particular, root deepening is delayed and roots tend to have a clumped spatial arrangement. Experimental evidence and modelling suggest that this change in root system architecture could cause water stress, even in relatively wet soil, because of an increase in resistance to the soil-root water flux. As a consequence, root water status and water flux decrease, and stomatal conductance is reduced as a consequence of a chemical message originating in the roots. This secondary message is superimposed onto the direct message linked to mechanical impedance. Under some climatic conditions, whole-plant growth rate, carbon allocation and phenologic development can then be significantly affected by a compaction in the ploughed layer, while only small changes can be expected under more favourable conditions.     

促早熟制剂对玉米农艺性状影响及避早霜害效果

2004—2005年利用3种玉米植物生长调节剂进行大田喷施试验，结果表明不同的制剂对玉米的农艺性状和避早霜害效果影响不同。玉黄金制剂（中国农业大学研制）可降低玉米株高、提前生育期和减少籽粒水分含量；玉米高梁制种丰产灵制剂（哈尔滨士林高科股份有限公司与吉林吉农高新技术发展股份有限公司联合研制）对玉米提早成熟和降低籽粒含水量也有一定影响，仅次于玉黄金。     

Changes in plant community structure and soil biota along soil nitrate gradients in two deciduous forests

Anthropogenic nitrogen (N) deposition is a serious threat to biodiversity and the functioning of many ecosystems, particularly so in N-limited systems, such as many forests. Here we evaluate the associations between soil nitrate and changes in plant community structure and soil biota along nitrate gradients from croplands into closed forests. Specifically, we studied the composition of the understory plant and earthworm communities as well as soil microbial properties in two deciduous forests (Echinger Lohe (EL) and Wippenhauser Forst (WF)) near Munich, Germany, which directly border on fertilized agricultural fields. Environmental variables, like photosynthetically active radiation, distance to the edge and soil pH were also determined and used as co-variates. In both forests we found a decrease in understory plant coverage with increasing soil nitrate concentrations. Moreover, earthworm biomass increased with soil nitrate concentration, but this increase was more pronounced in EL than in WF. Soil microbial growth after addition of a nitrogen source increased significantly with soil nitrate concentrations in WF, indicating changes in the composition of the soil microbial community, although there was no significant effect in EL. In addition, we found changes in earthworm community composition along the soil nitrate gradient in WF. Taken together, the composition and functioning of forest soil communities and understory plant cover changed significantly along soil nitrate gradients leading away from fertilized agricultural fields. Inconsistent patterns between the two forests however suggest that predicting the consequences of N deposition may be complicated due to context-dependent responses of soil organisms.     

Effects of phenolic acids on seed germination and seedling growth in soil

Summary It is commonly assumed that the adverse effect of plant residues on crop yields is largely or partly due to phytotoxic compounds leached from these residues or produced by their decomposition. There has been substantial support for the hypothesis that the phytotoxic compounds responsible for reduced crop yields are phenolic acids such as p-coumaric acid, p-hydroxybenzoic acid, and ferulic acid. To test the validity of this hypothesis, we studied the effects of nine phenolic acids (caffeic acid, chlorogenic acid, p-coumaric acid, ellagic acid, ferulic acid, gallic acid, p-hydroxybenzoic acid, syringic acid, and vanillic acid) on (1) seed germination of corn (Zea mays L.), barley (Hordeum vulgare L.), oats (Avena sativa L.), rye (Secale cereale L.), sorghum [Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.), and alfalfa (Medicago sativa L.) on germination paper and soil, (2) seedling growth of alfalfa, oats, sorghum, and wheat on germination paper and soil, and (3) early plant growth of corn, barley, oats, rye, sorghum, and wheat in soil. The results showed that although the phenolic acids tested affected germination and seedling growth on germination paper, they had no effect on seed germination, seedling growth, or early plant growth in soil even when the amounts applied were much greater than the amounts detected in soil. We conclude that the adverse effect of plant residues on crop yields is not due to phenolic acids derived from these residues.     

小桐子愈伤组织的诱导

本文以小桐子的叶片、叶柄、茎段及下胚轴和子叶作为外植体,研究不同外植体类型对愈伤组织诱导的影响,结果表明叶柄的诱导率最高,其次为茎段的诱导率。同时以小桐子的下胚轴作为外植体,研究植物生长调节剂种类及浓度配比对愈伤组织诱导的影响,结果显示6-BA与2,4-D的组合更适宜小桐子愈伤组织的诱导,MS＋6-BA0.5mg/L＋2,4-D0.1mg/L为小桐子愈伤组织诱导的最佳培养基,其愈伤组织诱导率高达96.7%。本研究为小桐子愈伤组织的分化、植株再生及相关的遗传转化研究提供了参考。     

春小麦穗发芽的化学控制初探

于春小麦各生育期(起身期、孕穗期、开花后10d、开花后18d、开花后25d)选用不同浓度6种植物生长调节化学药剂研究了化学控制穗发芽的可能性。结果表明,在保留现有春小麦品种的前提下,可采用化学药剂控制穗发芽,其中顺丁烯二酸马来酰肼(MH)效果最好,低浓度的α-萘乙酸(α-IAA)亦可抑制穗发芽,NaHSO₃一定程度上可减轻穗发芽损失。     

三种植物生长调节剂对降香黄檀种子发芽的影响

采用三种植物生长调节剂GA3、IBA和6-BA不同浓度按正交设计方法,搭配处理组合,对降香黄檀种子进行处理,通过对种子发芽率、发芽势和发芽指数指标的测定,研究不同浓度的植物生长调节剂对珍贵用材树种降香黄檀种子萌发的影响。结果表明：3种植物生长调节剂浸种对降香黄檀种子萌发以6-BA的促进效果较好,GA3次之,而IBA对降香黄檀种子的发芽促进作用不明显,以处理组合6-BA50mg/L6h为最优,显著提高种子的萌发率。     

Inhibiting soil loss and runoff from small plots induced by an individual freeze-thaw cycle using three rangeland species

This study investigated the role of three rangeland species viz. Agropyron trichophorum, Medicago sativa, and Lolium prenne on mitigating of effects of a freeze-thaw (FT) cycle on runoff generation and soil loss from small experimental plots. Small plots (0.5 × 0.5m) were prepared in three replicates for control (i.e., under a FT cycle only) and treatments (i.e., individually planted with the study species and subject to a FT cycle). The treated plots were then placed at a slope of 20% and subjected to simulated rainfall with intensity of 70 mm h⁻¹ and 30 min duration. The results of the study showed a significant effect (P < 0.05) of the plants on controlling runoff and soil loss after a FT cycle. Also, the detrimental effects of the FT cycle due to performance of ice lenses and formation of an active melting layer in the soil surface were ameliorated by the presence of litter on the soil and root-binding effect of the plants. Time to runoff increased by 54, 111 and 10%, runoff volume decreased by 27, 68 and 0.4% and soil loss changed by −34, −62, and +6.5% in the plots planted with A. trichophorum, L. prenne and M. sativa, respectively. The results of the current study indicated that L. prenne had the maximum benefit on reducing runoff and soil loss from the plots undergoing a FT cycle.     

开花后水分亏缺对小麦生理影响与化学调控的补偿效应

旱棚PVC管栽培冬小麦“京冬 8号”试验研究结果表明 ,小麦开花后水分亏缺影响氚水 (3H2 O)在其根系和旗叶中动态、初生根和穗下节维管束特征、根系活力、叶片蒸腾速率、气孔阻力和14C同化物输出速率及比例。用植物生长延缓剂HK 6拌种和起身期叶面喷施处理 ,可增加初生根大导管和维管束鞘横截面积 ,提高根系活力 ,促进根系3H2 O的吸收和向地上部器官运输 ;增加穗下节大维管束横截面积 ,并可能促进水分向穗部运输 ;增加旗叶中气孔阻抗 ,维持适当水分蒸腾速率 ,缓解水分胁迫下叶片3H2 O的减少 ;提高单株水分利用效率 ,化学控制处理可缓解和补偿水分胁迫对小麦生理造成的不良影响 ,对小麦节水栽培和抗旱增产具有应用潜力     

山桃生根成苗关键技术研究

山桃是甘肃地区普遍应用的桃树优良砧木,具有抗寒、抗旱的特性。然而山桃通过种子繁殖的方式存在一定比例上的抗性分离现象,而且繁殖周期较长。为探索山桃组培快繁技术。对山桃组培苗的生根培养和炼苗移栽进行了试验。结果表明,以改良QL培养基为基本培养基,当IBA浓度为1.0 mg/L时,试管苗生根效果最好,根系粗壮,侧根较多,生根率达94%以上,平均根数6根以上,平均根长6.8 cm以上;添加80 mg/L PG的处理,无论是生根率、平均根数还是平均根长,较不添加80 mg/L PG的处理相比均表现不理想。将根长超过3 cm的山桃组培苗置于温室中,先遮光炼苗5～7 d,后将瓶盖打开1/2,并配制800倍多菌灵溶液少量倒入组培瓶中,4 d后可将瓶盖全部打开继续炼苗5～7 d,组培苗根系生长基本正常,炼苗成活率可达88%。     

酸性低钾土硫酸钾镁肥对花生生长及养分吸收的影响

在供钾水平较低的酸性赤砂土上,采用盆栽试验方法研究硫酸钾镁对花生生长发育及养分吸收的影响,结果表明:随硫酸钾镁用量的增加,花生经济产量与生物总量呈先增加后降低的趋势.施硫酸钾镁513mg·kg-1(土)处理(相当于每千克土施K2O 0.12 g、Mg 0.028 g、S 0.09 g),花生产量最高,经济产量与生物总量分别较对照增加20.2%和32.2%.随硫酸钾镁用量的增加,植株对钾、镁、硫各吸收量均有不同程度增加,其中对钾、硫吸收量呈逐渐升高的趋势,而对镁吸收量呈先升高后降低的趋势,植株对钾、镁吸收表现正相关.随硫酸钾镁用量的增加,花生果仁粗蛋白与粗脂肪均较对照有所提高,粗蛋白含量呈逐渐增加,而粗脂肪含量却呈逐渐下降趋势.在酸性低钾、中镁、潜在性缺硫的赤砂土上,花生施用硫酸钾镁肥,钾镁养分吸收里显著正相关,但钾硫相关性不明显.     

Effects of endogeic earthworms on soil processes and plant growth in coniferous forest soil

Summary The effects of the endogeic earthworm, Aporrectodea caliginosa tuberculata (Eisen) on decomposition processes in moist coniferous forest soil were studied in the laboratory. The pH preference of this species and its effects on microbial activity, N and P mineralization, and the growth of birch seedlings were determined in separate pot experiments. Homogenized humus from a spruce stand was shown to be too acid for A. c. tuberculata. After liming, the earthworms thrived in the humus and their biomass increased (at pH above 4.8). In later experiments in which the humus was limed, the earthworms positively influenced the biological activity in humus and also increased the rate of N mineralization. A. c. tuberculata increased the growth of birch seedlings, with increases observed in stems, leaves, and roots. Neither NH ₄ ⁺ -N fertilizer nor mechanical mixing with artificial worms affected seedling growth. No plant-growth-affecting compounds (e.g., hormone-like compounds) due to the earthworms were present in the humus. The shoot: root ratio in the birch seedlings was not affected by either the earthworms or the fertilizer. The experiments revealed the impact of earthworm activity on soil processes and plant growth.     

吉林省西部低洼易涝盐碱化耕地的分类管理技术研究

吉林省西部的盐碱涝洼耕地，多属于盐化或碱化土壤，本　文指其盐渍化及涝害程度划分为重度碱化涝洼弃耕地、中度碱化易涝耕地、轻度碱化易涝耕　地及盐碱集中分布的涝洼耕地群等４类，因地制宜地实施分类的技术管理，获得良好的效果　，增产增收，土壤肥力逐步提高．     

土壤消毒措施对土壤物理特性及黄瓜生长发育的影响

采用田间试验方法,研究了垄沟式太阳能消毒、石灰氮麦秸、垄鑫3种土壤消毒方法对日光温室土壤物理特性及黄瓜生长发育的影响。结果表明,垄沟式太阳能消毒处理对土壤物理特性未产生较大影响,处理后粗粉粒含量较对照降低9.5%,砂粒两个粒径(0.1～0.5mm、0.5～1.0mm)含量较对照分别增加39.4%、117.7%,其余组分无明显变化;石灰氮麦秸处理后黏粒含量增加163%,细粉粒两粒径(0.001～0.005mm、0.005～0.01mm)含量较对照分别增加52.1%和116.8%;施用垄鑫处理后土壤黏粒含量较对照降低65.8%,细粉粒两个粒径含量较对照分别降低33.0%、32.2%。不同处理对土壤微团聚体的形成均有一定阻碍作用,其中石灰氮麦秸处理对土壤团聚体的形成影响最大,其次是垄鑫处理,垄沟式太阳能消毒处理影响最小。3个土壤消毒处理都能提高黄瓜平均叶片数、平均株高、叶绿素含量和黄瓜产量,其中垄沟式太阳能消毒处理能显著提高黄瓜生物学指标,有良好的增产效果。     

Arylsulfatase activity in soil and soil extracts using natural and artificial substrates

The arylsulfatase activity of soil and humic arylsulfatase complexes extracted from soil were measured using the substrates p-nitrophenyl sulfate and low molecular weight (500–10000) soil ester sulfate compounds. Soil samples from the Aphorizon of a Podzol from S-amended wheat plots and a Regosol from dykeland hayfield plots were investigated. Soil arylsulfatase activity (assayed with p-nitrophenyl sulfate) in the fall was significantly higher than spring samples; however, no seasonal differences were observed when humic-arylsulfatase complexes were assayed with p-nitrophenyl sulfate. The discrepancy between arylsulfatase activity in soil and soil extracts was probably due to inhibitors which were found in soil materials. These results appear to support the theory that abiotic arylsulfatase is a relatively stable and persistent component of soil. There was a marked difference in the response by humic-arylsulfatase complexes to the artificial substrate p-nitrophenyl sulfate and natural low molecular weight soil substrates. Humic-arylsulfatase complexes hydrolysed 35–80% of added low molecular weight substrates depending on the treatment. The molecular size, concentration, and chemical composition of the low molecular weight ester sulfate compounds affected hydrolysis of the low molecular weight substrates. The response by humic-arylsulfatase complexes to the chromogenic ester sulfate, p-nitrophenyl sulfate did not reflect the ability of these complexes to hydrolyse natural soil substrates. In an experiments we examined arylsulfatase activity and soil S status in relation to the total S in plant tissue and grain from wheat plants grown in the Podzol. Tissue S was more strongly associated with soil S than the wheat grain. Hydriodic acid-S, Ca(H₂PO₄)₂-extractable sulfate, and hydrolysable ester sulfates in the high molecular weight (>10000) and low molecular weight (500–10000) fractions of soil organic matter extracts were strongly positively correlated with tissue S. Arylsulfatase activity in soil and humic-arylsulfatase extracts assayed with p-nitrophenyl sulfate were also strongly correlated with tissue S, while humic-arylsulfatase activity assayed with the low molecular weight substrate was negatively correlated with tissue S.