Allelopathic effects ofEupatorium riparium on population regulation of two species ofGalinsoga and soil microbes

Summary Allelopathic effect ofEupatorium riparium Regel, a dominant ruderal weed at higher altitudes in Meghalaya state in north-eastern India, was studied on two common sympatric annual weeds,Galinsoga ciliata (Raf.) andG. parviflora Cav. and on soil microbes. Seed germination and radicle and plumule growth of both species ofGalinsoga were suppressed by the aqueous extract and leachate ofE. riparium. Although the leaf leachate, leaf and litter extracts and litter bed caused considerable reduction in leaf area and seed and dry matter production in both species ofGalinsoga, the effect was much more pronounced onG. parviflora. The inhibitory effect was directly correlated with the concentration of the extract and leachate. The soil microbial population and growth of theGalinsoga spp. declined considerably in the experimental pots where the soil had earlier received leachate of different plant parts ofE. riparium growing in it. The presence of the partly decomposed litter ofE. riparium in the pots reduced soil microbial population and growth of the two weeds much more strongly as compared to the litter in the advanced stages of decomposition. The study also revealed that the abundance and colony growth of the two test fungiviz. Trichoderma viride andAspergillus flavus were differentially affected by the allelopathy ofE. riparium; T. viride being favoured andA. flavus inhibited.     

Effect of soil moisture and phosphate level on root hair growth of corn roots

Summary Root hairs have been shown to enhance P uptake by plants growing in low P soil. Little is known of the factors controlling root hair growth. The objective of this study was to investigate the influence of soil moisture and P level on root hair growth of corn (Zea mays L.). The effect of volumetric soil moistures of 22% (M₀), 27% (M₁), and 32% (M₂) and soil (Raub silt loam, Aquic Argiudoll) P levels of, 0.81 (P₀), 12.1 (P₁), 21.6 (P₂), 48.7 (P₃), and 203.3 (P₄) mol P L^–1 initially in the soil solution, on shoot and root growth, P uptake, and root hair growth of corn was studied in a series of pot experiments in a controlled climate chamber. Root hair growth was affected more by soil moisture than soil P. The percentage of total root length with root hairs and the density and length of root hairs on the root sections having root hairs all increased as soil moisture was reduced from M₂ to M₀. No relationship was found between root hair length and soil P. Density of root hairs, however, was found to decrease with an increase in soil P. No correlation was found between root hair growth parameters and plant P content, further suggesting P plays a secondary role to moisture in regulating root hair growth in soils. The increase in root hair growth appears to be a response by the plant to stress as yield and P uptake by corn grown at M₀ were only 0.47 to 0.82, and 0.34 to 0.74, respectively, of that measured at M₁ across the five soil P levels. The increase in root hair growth at M₀, which represents an increase of 2.76 to 4.03 in root surface area, could offset, in part, the reduced rate of root growth, which was the primary reason for reduced P uptake under limited soil moisture conditions.Journal Paper No. 10,066 Purdue Univ. Agric. Exp. Stn., W. Lafayette, IN 47907. Contribution from the Dep. of Agron. This paper was supported in part by a grant from the Tennessee Valley Authority.     

苜蓿与沙打旺苗期生长和水分利用对土壤水分变化的反应

通过室内生长箱内盆栽实验,比较了苜蓿和沙打旺苗期的根冠生长和水分利用对种土壤水分环境变化的响应和差异.结果表明,充分供水下苜蓿和沙打旺苗期生物量和蒸腾效率均最高,苜蓿均显著高于沙打旺.土壤水分减少后苜蓿苗期生物量和蒸腾效率下降幅度均大于沙打旺.从低水到阶段低水处理后土壤水分逐渐降低和降低后再复水到低水处理,苜蓿和沙打旺的生物量分别较持续低水处理显著减少47.8%和27.9%.旱后复水后苜蓿根冠比和单位根量耗水量较显著增加,蒸腾效率显著下降; 沙打旺根冠比显著下降,单位根量耗水量和蒸腾效率变化不显著.     

Species-mediated soil moisture availability and patchy establishment of Pseudotsuga menziesii in chaparral

The occurrence of mature individuals of Pseudotsuga menziesii in stands of Arctostaphylos species mark the initial stages of mixed evergreen forest invasion into chaparral in central coastal California. We planted two cohorts of P. menziesii seeds at three sites under stands of two Arctostaphylos species and Adenostoma fasciculatum in order to determine whether first-year seedling emergence and survival, particularly during the regular summer drought, underlie the spatial distribution of mature trees observed in chaparral. Regardless of the chaparral species they were planted under, P. menziesii seeds that were not protected from vertebrate predation displayed very little emergence and no survival. In contrast, emergence of P. menziesii that were protected from vertebrate predators was much higher but still did not significantly differ among the three chaparral species. However, survival of protected seedlings under Arctostaphylos glandulosa was much greater than under A. fasciculatum, with intermediate survival under Arctostaphylos montana. While mortality of protected seedlings due to insect herbivory, fungal infection, and disturbance displayed no consistent patterns, summer drought mortality appeared to drive the patterns of survival of P. menziesii under the different chaparral species. These emergence, mortality, and survival data suggest that spatial patterns of P. menziesii recruitment in chaparral are driven by first-year summer drought seedling mortality, but only in years when seeds and seedlings are released from vertebrate predation pressure. Because the first-year drought mortality and survival patterns of P. menziesii seedlings differed strongly depending on the chaparral species, we examined the additional hypothesis that these patterns are associated with differences in the availability of soil moisture under different chaparral species. Both higher survival and lower drought mortality of P. menziesii seedlings were associated with higher soil water potential under Arctostaphylos stands during the summer drought, especially in the subsurface soil. The data suggest that Arctostaphylos stands, particularly stands of A. glandulosa, ameliorate xeric summer conditions to a degree that facilitates first-year establishment of P. menziesii and strongly influences spatial distribution of mature trees. Received: 18 September 1998 / Accepted: 23 December 1998     

Effect of soil moisture stress on legume-rhizobium symbiosis in soybeans

Summary In a pot culture experiment, the influence of soil moisture stress at different physiological stages of soybean, cv. Hark, on nodulation, symbiosis and nitrogen accumulation was studied. Moisture stress reduced leghemoglobin content of root nodules and nitrogen uptake by plants. It had no effect on number of bacteroids. Stress at mid bloom and rapid pod filling stages reduced yield and seed protein content. However, these parameters were not affected by stress at nodule initiation and early flowering stages, though, flower initiation and maturity of the plant were delayed. Moisture stress at any stage did not alter nitrogen status of roots.     

不同土壤水分条件下容重对玉米生长的影响

用玉米作为实验材料。进行分根实验研究不同土壤水分条件下容重对玉米生长的影响,种子根平分在装有塿土的分隔的白铁皮桶中,土壤容重分4种处理：低容重(两边容重都为1．20g·cm^-3)、中容重(两边容重都为1．33g·cm^-3)、高容重(两边容重都为1．45g·cm^-3)和混合容重(一边为1．20g·cm^-3,另一边为1．45g·cm^-3),土壤水分控制在高基质势(-0．17MPa)和低基质势(-0．86MPa)两个水平,结果表明,当植株生长在紧实土壤或土壤基质势从-0．17MPa降到-0．86MPa时。根长、根干重和地上部干重都显著降低,并且地上部干重的降幅更大,紧实土壤使根长降低的同时还使根的直径增大,无论是容重增大还是土壤水分含量降低所引起的高土壤阻力都使叶片扩展速度降低和植株变小,生长在紧实土壤中的植株变小不仅是因为叶片扩展速度降低,同时是成熟叶片叶面积缩小的结果。然而,当植株生长在混合容重土壤中时,处在低容重土壤中的根系生长得到加强,补偿甚至超补偿高容重土壤中根系生长的不足,整个植株的生长状况与低容重土壤中生长的植株接近。     

黄土高原土壤紧实度对蚕豆生长的影响

通过盆栽试验、连续 2年的田间小区试验和农户生产试验 ,研究了土壤紧实状况对蚕豆 (Viciafa ba)生长的影响 ,讨论了当地土壤容重较高的原因 ,并提出了改进措施 .结果表明 ,随着 0～ 7cm土层土壤容重的增加 ,蚕豆植株每株的茎与根干重降低 ,根腐病 (Fusariumspp .)引起的死亡率增加 ,种子产量减少 .田间试验条件下 ,与生长于容重为 1.5 5和 1.6 4 g·cm-3 小区内的植株相比 ,生长于容重 1.84 g·cm-3 小区内的植株每株茎与根干重可分别减少 2 7.9%和 30 .8% ,植株累计死亡率增加 2 1.0 %～ 4 8.7% ,种子产量每公顷减少 19.8% .在 8户蚕豆田中进行的多点生产试验表明 ,春季土壤容重与蚕豆幼苗的根与茎干重、秋季土壤容重与种子产量均呈显著负相关     

齿瓣石斛的原生境播种及其株丛生长特性研究

兰科（Orchidaceae）植物是植物保护中的“旗舰”类群,其种子细小粉末状,缺乏萌发所需的营养物质,研究种子萌发和幼苗生长特性对于兰科植物保育、资源可持续利用和产业化等具有重要意义。本研究以附生齿瓣石斛（Dendrobium devonianum Paxt.）为对象,建立原生境播种方法,研究其生活史周期和不同附主树种齿瓣石斛株丛生长特性。结果显示,采取稀牛粪＋种子（或米汤＋种子）的原生境播种方法,齿瓣石斛种子可大量萌发生长形成幼苗;种子萌发当年生长缓慢,完成由种子到种子的生活史周期需3~5年或更长;不同附主树种的齿瓣石斛株丛生长及结果情况存在差异,4年生假鳞茎在不同附主树种上的茎节数指标为：李树 > 梨树 > 桃树 > 披针叶楠;茎粗指标为：披针叶楠 > 梨树 > 桃树 > 李树;茎长指标为：梨树 > 披针叶楠 > 李树 > 桃树;结实率指标为：梨树 > 桃树 > 李树 > 披针叶楠,其中,梨树上的齿瓣石斛株丛自然结果率达24.86%。该研究为附生石斛的原生态栽培和回归保育提供了一条新途径。     

Establishment and reproduction of Aeschynomene virginica (L.) (Fabaceae) a rare,annual, wetland species in relation to vegetation removal and water level

Aeschynomene virginica is a rare annual plant found in freshwater tidal wetlands of the eastern United States. We hypothesized that standing vegetation and water inundation were two important environmental factors in its population dynamics. To test these hypotheses, we sowed seeds into plots with undisturbed vegetation or plots with all aboveground vegetation removed in 1998 and 1999. Presence/absence of seedlings was noted and seedling survival to reproduction, final size, and seed set were measured throughout both growing seasons. Seedling establishment from germination to the first true leaf stage increased with decreasing water depth. Vegetation removal plots had greater seedling establishment, higher seedling survival, and higher seed set per plant than non-removal plots. In a greenhouse study designed to test the effects of water level on seed germination and seedling establishment, no seedlings established in submerged soils, and seed germination and seedling establishment were lower in waterlogged soil than in wet soil. Physical stress associated with deeper water likely limits the distribution of A. virginica to higher elevations, where seeds that colonize patches with low vegetative cover are more likely to produce reproductive adults that produce more seeds relative to patches with established vegetation. A. virginica appears to be a fugitive species specializing on open habitat patches in tidal wetlands. This species may be dependent on disturbances for population establishment and maintenance.     

胁迫时间与非毒性离子对重金属抑制拟南芥种子发芽及幼苗生长的影响

测定了Hg²⁺、Cd²⁺、Cu²⁺、Pb²⁺单一重金属胁迫对拟南芥种子发芽和幼苗生长的影响.结果表明,重金属对幼苗生长的毒性大于对种子发芽的毒性,以抑制种子发芽的IC₅₀为指标,4种重金属的毒性顺序为Hg²⁺＞Cd²⁺＞Pb²⁺/Cu²⁺,以幼苗生长为指标,则毒性顺序为:Cu²⁺＞Hg²⁺＞Cd²⁺/Pb²⁺,并随着胁迫时间延长,种子萌发率下降.此外,不同重金属在不同发芽时段对种子的毒性也不尽相同,Cd²⁺的毒性在种子吸水后的0～12 h大于12～24 h,而Hg²⁺毒性在12～24 h大于0～12 h,其中,种皮对减轻重金属毒性起着十分重要的作用.通过非毒性离子(Ca²⁺、Mg²⁺、K⁺、Na⁺)与重金属离子(Hg²⁺、Cd²⁺、Cu²⁺、Pb²⁺)交互作用对拟南芥种子发芽及幼苗生长效应的研究发现, mmol·L^-1的Ca²⁺、Mg²⁺、K⁺、Na⁺可以增强Hg²⁺对种子发芽的毒性,但对Cd²⁺的毒性却没有影响.对于幼苗来说,Ca²⁺、Mg²⁺、K⁺、Na⁺可以显著增强Hg²⁺的毒性,Ca²⁺可以缓解Cd²⁺的毒性,但却增加Cu²⁺的毒性,K⁺可以缓解Pb²⁺对幼苗的毒害作用.最后,本文对重金属的毒害机理进行了探讨.     

Effect of soil volume and plant density on mycorrhizal infection and growth response

Summary The effect of soil volume and plant density on mycorrhizal infection and growth response was studied with onion. There was a significant negative correlation between percentage vesicular-arbuscular mycorrhizal infection and root density. The growth response due to mycorrhiza decreased when less soil was available for the plant. The root: shoot ratio decreased with increasing plant density in both mycorrhizal and non-mycorrhizal plants. Pot size did not affect the root: shoot ratio.     

Cu、As对作物种子萌发和幼苗生长影响的研究

通过水培实验研究了Cu、As污染对作物种子萌发、幼苗生长及部分酶活性的影响。结果表明,Cu,As污染明显抑制黄豆种子萌发、幼苗生长,对作物种子萌发时的呼吸强度、酶活性有显著的抑制作用,且随着Cu、As浓度的增加,抑制作用增强,呈负相关;而POD活性则随污染物浓度的增加而增加,呈正相关。     

Effects of temperature, light, storage conditions, sowing time, and burial depth on the seed germination of Cardiocrinum cordatum var. glehnii (Liliaceae)

In this study, we conducted experiments to accumulate practical information on the propagation and establishment of a population of Cardiocrinum cordatum var. glehnii by seed sowing. C. cordatum var. glehnii seeds require approximately 19 months from seed dispersal to cotyledon emergence in the field. However, the period from seed dispersal to radicle emergence was shortened to approximately 7–8 months by the temperature transition of 25/15°C (60 days) → 15/5°C (30 days) → 0°C (120 days) → 15/5°C (i.e., 15/5°C represents alternating temperature treatment wherein the seeds were placed at 15°C for 12 h during the day and then at 5°C for 12 h during the night). More than 90% of the seeds, which were stored dry at 5°C for 12 months and sown in pots in the field, showed cotyledon emergence, whereas in seeds stored dry at 25°C, dry at room temperature, and non-dry at room temperature, cotyledon emergence was decreased by less than 1%. More than 88% of the seeds that were stored dry at 5°C and sown in the field in October 2002 immediately after collecting, November, and from April to July 2003 showed cotyledon emergence in spring 2004. However, seeds sown in August, September, and October 2003 showed cotyledon emergences of 57.6%, 0%, and 0% in spring 2004, respectively. Seeds collected in October 2002 and sown until July 2003 in the field received adequate high temperature in summer, moderate temperature in autumn, and cold temperature in winter; therefore, the percentage of cotyledon emergence was high in spring 2004. On the other hand, seeds sown in August 2003 or later could not receive enough high temperature; thus, cotyledons emerged from only a few seeds.     

Effect of moisture stress, plant population density and pathogen inoculation on charcoal stalk rot of sorghum

The effects of moisture deficit stress, plant population density and pathogen inoculation technique on charcoal stalk rot in the sorghum hybrid CSH 6 were studied in the 1980–81 and 1981–82 post-rainy seasons at three locations in India. Incidence and severity of charcoal rot caused by Macrophomina phaseolina were compared in three plant population densities, subjected to different moisture stress regimes created by withholding irrigation at various plant growth stages. Natural infections were compared to artificial inoculation with M. phaseolina. Combinations of moisture stress, plant population and inoculation treatments were compared to identify the combination most likely to develop maximum disease. Lodging, the first external symptom of charcoal rot, was significantly correlated with other disease symptoms used to measure charcoal rot, such as soft stalk, number of nodes crossed by M. phaseolina infection, root damage and plant senescence. In both seasons the highest incidence of lodging occurred when moisture stress was induced at the 'flag leaf visible in the whorl' growth stage. The greatest incidence of the disease was recorded in the highest plant population (266 700 plant ha^-) at all three locations. No significant differences were found between artificially and naturally inoculated treatments. The maximum number of lodged plants was found at a density of 266 700 plants ha^-1 when moisture stress was induced at the 'flag leaf visible in the whorl' growth stage.     

光、温度和土壤水分对坡垒种子萌发的影响

研究了温度,光照,土壤水分对坡垒（Hopea hainanensis Merr.et Chun)种子萌发和寿命的影响。结果表明坡垒种子萌发的最适温度为15－20℃种子在全黑暗条件与周期性光照条件下处理的萌发结果无明显差异。土壤含水量为20％－70％时种子能够萌发,而适宜的土壤含水量为30％－50％。在室内自然摊放第14天的发芽率为20％。18d完全丧失发芽能力。由于坡垒种子具有顽拗型种子的一些特点,该物种宜采取活体保存的方法,以就地保护为主,迁地保护为辅。     

土壤湿度水平和湿—干循环对硝酸钙盐积累土壤锰锰释放的影响

在[Ca(NO3)2]盐处理土壤中,研究了两种湿度水平（200,400g.kg^-1)和湿－干循环对土壤Mn释放的影响,结果表明,土壤水分状况影响土壤Mn的有效性,湿度大时,易还原态Mn转化为水溶态,交换态Mn;盐分对易还原态Mn的转化有一定影响,NO3-能缓冲土壤Eh的下降,有抑制易还原态Mn转化的作用,连续的湿干循环能使土壤2价Mn(水溶态Mn,交换态Mn)浓度降低,而a(NO3)2盐能增加Mn的不溶性,这在Mn含量低的土训上,最终将导致Mn的缺乏。     

温度和土壤含水量对青冈栎种子萌发的影响

运用直播法,研究应用人工气候箱控制温度和土壤含水量对野生青冈栎种子萌发和幼苗生长的影响。结果表明:在12h光照条件下,青冈栎种子在变温为10℃/15℃时,萌发率很低,仅为(12±12.29)%;变温为30℃/35℃时,萌发率达最大,为(81±13.7)%。土壤含水量为30%～40%时,萌发率为(79±15.9)%;土壤含水量为90%～100%时,萌发率为(56.67±19.36)%。青冈栎种子萌发呈现出迅速萌发和推迟萌发的特点;温度对青冈栎幼苗的苗高、叶长和叶宽影响显著,对幼苗的地径、叶片数量影响不显著。恒温下,不同梯度土壤含水量处理对幼苗的苗高、地径、叶长、宽影响不显著。     

耕作播种方式对稻茬小麦根系发育、土壤水分和硝态氮含量的影响

2016—2018年,以深旋耕播种模式为对照,研究了浅旋耕播种和免耕带旋播种模式对稻茬小麦根系发育、土壤水分和硝态氮含量的影响。结果表明: 孕穗期以前免耕带旋播种和浅旋耕播种处理耕层土壤含水量高于深旋耕播种处理,而硝态氮含量低于深旋耕播种处理。拔节和开花期根重密度和根表面积密度处理间差异不显著。2016—2017年,3种耕播方式的产量和地上部分氮吸收量无显著差异;2017—2018年,免耕带旋播种和浅旋耕播种处理的产量较深旋耕播种分别增加10.9%和10.5%,地上部分氮吸收量分别增加17.5%和12.0%。与深旋耕播种和浅旋耕播种处理相比,免耕带旋播种处理播种效率高、断垄率低。综上,免耕带旋播种处理可提高稻茬小麦的播种质量,增强土壤保墒能力,降低氮淋溶风险,促进产量和环境效益的协同提升。