Effect of temperature associated with levels of bulk density on rice seedling emergence

Summary A laboratory study was conducted to find out the effect of temperatures on rice seedling emergence under different levels of bulk density. The temperatures ranging from 10 to 40°C in increments of 5°C were maintained constant with ±1°C accuracy. The bulk density levels were 1.3, 1.5, 1.7, and 1.9 g cm⁻³. Aluminum cylinders with top open and bottom provided with a removable 20-mesh brass screen, were used as soil containers. The moisture content in soil was always above field capacity which could be accomplished by placing the cylinders in a tray in which water level was maintained constant to 5 cm depth. Seedling emergence counts were taken till the 10th day of seeding. At the end of the experiment, observations on root and shoot elongations were recorded. Emergence was maximum at 25 and 30°C under 1.3 and 1.5 g cm⁻³, and decreased at 35, 20, and 15°C. As compared to the lower bulk densities, the reduction in emergence under 1.7 g cm⁻³ was smaller at 25 and 30°C than at 35°C. This was ascribed to greater seedling vigour at 25 and 30°C, as could be inferred from larger root and shoot elongation. The reduction in emergence at lower temperatures (20 and 15°C) might be due to delay in time of germination as well as less seedling vigour. The soil under 1.9 g cm⁻³ was sufficiently dense that the seedlings could not emerge except a few ones at 25 and 30°C.     

煤矿复垦区土壤水动力学特性对下渗过程的影响

煤矿复垦区土壤水对植物生长、溶质运移以及土壤环境的变化起着至关重要的作用。定量揭示煤矿复垦区土壤水下渗过程是亟待诠释的关键科学问题。本研究通过测定典型矿区不同深度土壤非饱和导水率、容重、总孔隙度和粒径等水动力学参数,结合染色示踪试验,刻画矿区非饱和带土壤水运移过程。染色示踪结果显示30、60 L和90 L这3种实验下渗水量条件下,水流沿X方向侧向扩散的最大距离分别为10、30 cm和35 cm,沿Y方向侧向扩散的最大距离分别为10、25 cm和30 cm。互相关函数显示随着下渗水量增大,水流扩散作用也在加强,但过多水量并没有明显增加下渗深度和扩散距离。吸力大于300 hpa时,0.01—0.05 mm土壤粒径含量和非饱和导水率呈负相关关系;吸力和非饱和导水率采用指数函数拟合效果较好(r~20.9),对拟合参数a、b和土壤容重(x)进行回归分析:a=0.0015x~2-0.00499x+0.0004,b=0.0583x~2+0.1234x-0.072。同一吸力下土壤容重大的土样非饱和导水率较小;吸力值为300 hpa是非饱和导水率的转折点;非饱和导水率和土壤容重呈现负相关关系,和总孔隙度呈现正相关关系,且二者的相关性随吸力的增加而降低。     

Response of soil properties and maize yield to simulated erosion by artificial topsoil removal

The study was aimed at identifying the soil properties responsible for maize yield decline on eroded soils and at quantifying their relationship with yield. Topsoil was artificially removed to incremental depths of 0, 5, 10, 15 and 20 cm to simulate various degrees of erosion. Maize growth and yield were monitored on the plots and soil physical and chemical properties were determined after two years (4 seasons) of cultivation. Soil pH was significantly higher on the control plot and decreased with increased depth of topsoil removal. Bulk density (BD) increased with depth of topsoil removal from a mean value of 1.38 g cm⁻³ under control to 1.55 g cm⁻³ at 20 cm depth of removal, while cone index of penetrometer resistance (CI) correspondingly increased from 1.09 g cm⁻² to 1.37 g cm⁻². Maize yield significantly decreased in the first year from 3.2 t ha⁻¹ on the control plot to 0.12 t ha⁻¹ where 20 cm of topsoil was removed and correspondingly from 1.85 to 0.09 t ha⁻¹ in the second year of cropping. Maize yield decreased exponentially with increase in depth of topsoil removal (r ²=0.99, P<0.01) with an average of 55% yield loss on the removal of just 5 cm topsoil. Soil organic carbon (SOC), BD, CI, field capacity (FC), pH and exchangeable Mg²⁺ were significantly correlated to maize yield parameters. However, factor analysis showed that the combination of SOC and exchangeable Mg²⁺ with soil physical properties (BD, FC, CI and depth of topsoil removal) explained 99% of variation in maize grain yield. The need for conservation farm practices is recommended on the soil to prevent soil degradation. Section Editor: L. Wade     

Development of Golgi Apparatus in the Root Cap Cells of Maize (Zea mays L.) as Affected by Compacted Soil

Effects of soil mechanical impedance on the development of Golgiapparatus in the root cap cells of maize were studied undercontrolled soil-water conditions Heavily compacted soil (bulkdensity = 1.50 g cm^–2) had 3.3 to 3.4 times greater mechanicalimpedance than control soil (bulk density = 1.33 g cm^–3),but their oxygen diffusion rates were not significantly differentThe number of dictyosomes and the number and area of secretoryvesicles per unit area of tangentially sub-peripheral root capcells in the heavily compacted soil increased compared to thosein the control These results suggest that secretory activityof the root cap cells is promoted by soil mechanical impedance Dictyosome, Golgi apparatus, maize, mucilage, root cap, secretory activity, secretory vesicles, soil mechanical impedance, Zea mays L     

排水对若尔盖高原泥炭地土壤有机碳储量的影响

泥炭地作为陆地上生态系统一个重要碳汇,存储了全球土壤有机碳储量的25%—43%。泥炭地排水与其他土地利用导致了大量的土壤有机碳损失。然而,有关排水对中国泥炭地土壤有机碳储量的影响研究报道较少,因此,为了获得更多可靠的泥炭地碳储量信息,以便减少它们估算的不确定性。选取了我国若尔盖高原未排水泥炭地和排水泥炭地进行土壤剖面取样,定量评价排水对泥炭地土壤有机碳储量的影响。研究表明:(1)未排水泥炭地土壤有机碳储量平均值为(923.71±107.18)t C/hm~2,为中国陆地和全球陆地土壤有机碳储量的8.1和9.4倍;而排水泥炭地土壤有机碳储量平均值为(574.01±66.86)t C/hm~2,为中国和全球陆地的5.1和5.8倍。(2)泥炭地排水后,导致表层(0—30 cm)土壤有机碳储量增加(59.11±9.31)t C/hm~2,可能源于土壤容重增加。(3)然而,完全考虑泥炭剖面深度后,排水泥炭地土壤有机碳储量较对照样地减少了349.7 t C/hm~2,这可能是由于泥炭地排水后,水位降低,加速了泥炭氧化,降低了泥炭厚度。     

Does root-sourced ABA have a role in mediating growth and stomatal responses to soil compaction in tomato (Lycopersicon esculentum)?

Isogenic wild-type (Ailsa Craig) and abscisic acid (ABA)-deficient mutant (flacca) genotypes of tomato were used to examine the role of root-sourced ABA in mediating growth and stomatal responses to compaction. Plants were grown in uniform soil columns providing low to moderate bulk densities (1.1–1.5 g cm^?3), or in a split-pot system, which allowed the roots to divide between soils of the same or differing bulk density (1.1/1.5 g cm^?3). Root and shoot growth and leaf expansion were reduced when plants were grown in compacted soil (1.5 g cm^?3) but leaf water status was not altered. However, stomatal conductance was affected, suggesting that non-hydraulic signal(s) transported in the transpiration stream were responsible for the observed effects. Xylem sap and foliar ABA concentrations increased with bulk density for 10 and 15 days after emergence (DAE), respectively, but were thereafter poorly correlated with the observed growth responses. Growth was reduced to a similar extent in both genotypes in compacted soil (1.5 g cm^?3), suggesting that ABA is not centrally involved in mediating growth in this severely limiting ‘critical’ compaction stress treatment. Growth performance in the 1.1/1.5 g cm^?3 split-pot treatment of Ailsa Craig was intermediate between the uniform 1.1 and 1.5 g cm^?3 treatments, whereas stomatal conductance was comparable to the compacted 1.5 g cm^?3 treatment. In contrast, shoot dry weight and leaf area in the split-pot treatment of flacca were similar to the 1.5 g cm^?3 treatment, but stomatal conductance was comparable to uncompacted control plants. These results suggest a role for root-sourced ABA in regulating growth and stomatal conductance during ‘sub-critical’ compaction stress, when genotypic differences in response are apparent. The observed genotypic differences are comparable to those previously reported for barley, but occurred at a much lower bulk density, reflecting the greater sensitivity of tomato to compaction. By alleviating the severe growth reductions induced when the entire root system encounters compacted soil, the split-pot approach has important applications for studies of the role of root-sourced signals in compaction-sensitive species such as tomato.     

Mechanical resistance by an ectorganic soil layer on root development of seedling Pinus sylvestris

We investigated early root development of Pinus sylvestris seedlings in relation to bulk density and natural particle layering in an ectorganic soil layer from a bracken (Pteridium aquilinum) stand. Responses in root development to two levels of bulk density (0.07 and 0.15 g/cm³) in mixed bracken substrate were compared with effects in peat of similar bulk densities, and in sand of three different bulk densities (0.37, 0.52, and 0.67 g/cm³). The effect on root growth of the natural horizontal layering of the organic particles was examined by comparing intact with mixed ectorganic bracken soil profiles of similar bulk densities (resp. 0.09 and 0.07 g/cm³).Root length growth was significantly reduced in the organic and sandy substrates of high bulk density. Root diameter was not affected by bulk density in the organic substrate, but increased with higher bulk density in sand. Preservation of horizontal layering in the intact ectorganic profile significantly reduced root length compared with mixed substrate of similar bulk density.Roots growing in high bulk density, and intact, organic substrate showed increased twisting, which resulted in a smaller depth reached by the root relative to total root length produced. In sand, root twisting did not change with increased bulk density. It is suggested that roots growing through organic substrate follow a path of least resistance. This implies that organic particle size and orientation are more important in determining root development than bulk density.This study points out that the natural layering of organic particles presents another constraint on the establishment of plant species in sites with a well-developed ectorganic soil layer. Disturbance of this layer may therefore enhance establishment of seedlings by reducing the mechanical resistance of the ectorganic soil profile to developing seedling roots.     

Seed dormancy,soil type and protective shelters influence seedling emergence at Shark Bay,Western Australia: Insight into global dryland revegetation

Seedling emergence is a major constraint on dryland revegetation success. In this study, we investigated seedling emergence of six framework shrub species as influenced by seed treatment, soil type and protective shelters using a large field trial in arid Western Australia. We observed the main effects of seed treatment and soil type to account for the majority of the variation in emergence. For species that exhibit pronounced dormancy, we found emergence of dormancy‐alleviated or treated (T) seed to be significantly greater than dormant or untreated (UT) seed, with responses varying across species (e.g. 41 times greater for Acacia ligulata Benth., and 10 times greater for Stylobasium spathulatum Desf.). For shallowly or nondormant species like Senna glutinosa (DC) Randall, UT seed emergence was slightly greater than for T seed. Compared to subsoil, topsoil was more receptive to infiltration (3.44 vs. 0.38 mm/min), and less prone to compaction (1.24 vs. 1.67 g/cm³) and crusting (0.6 vs. 1.3 kg/cm²); however, subsoil had greater moisture retention. Shelters failed to benefit soil moisture retention in either soil type, but enhanced emergence for most species. This study provides insight into how various cost‐effective treatments can be utilized to manipulate seed dormancy to optimize seedling emergence, the intrinsic value of topsoil as a superior growth medium and the benefit of novel, low‐cost shelters for enhancing seedling emergence. In arid environments, sowing T seed in combination with UT seed increases the likelihood of capitalizing on inherently variable precipitation events.     

太行山片麻岩山区造地边坡植被恢复过程中植物多样性与土壤特性的演变

为了探究太行山片麻岩山区造地后坡面植被的演变规律,以太行山片麻岩山区不同治理年限的坡面为研究对象,研究了坡面的植被状况与土壤理化性状。结果表明:随着治理年限的增加,坡面植被覆盖度、地上生物量和植物种类均显著增加,分别由第2年的18.00%、67.52 g/m~2、10种增加到了第7年的92.67%、379.91 g/m~2、19种。随治理年限的增加,坡面土壤的理化性质得到改善,土壤容重由第2年的1.40 g/cm~3降低到了第7年的1.29 g/cm~3,土壤有机质含量由第2年的4.91 g/kg增加到了第7年的7.18 g/kg;土壤总孔隙度、全氮、碱解氮、速效钾含量分别由第2年的47.15%、0.17 g/kg、16.10 mg/kg、26.58 mg/kg增加到了第6年的51.60%、0.61 g/kg、62.18 mg/kg、57.40 mg/kg,在第7年又分别降低为51.42%、0.50 g/kg、37.80 mg/kg、30.90 mg/kg。坡面植被多样性与土壤多项理化性状表现为显著相关。随着治理年限延长,造地后的坡面土壤的理化性质发生改变,土壤有效养分增多,持水能力增强,植被覆盖度与植物种类均显著增加,植物多样性稳步提高,生态环境得到有效改善。     

玛纳斯河流域扇缘带不同植被类型下土壤物理性质

对生长在玛纳斯河流域扇缘带上的柽柳、盐穗木、白刺、猪毛菜4种植被类型下的土壤物理性质进行了研究.结果表明:在水平方向上,1m剖面内柽柳土壤pH值、全盐含量、土壤容重最小,分别为8.75、0.97g/kg和1.42g/cm3;土壤有机质、含水率、总孔隙度、毛管孔隙度均最大,分别为9.04 g/kg、16.67％、45.57％和36.18％,表明柽柳能够显著降低土壤盐分,改善土壤结构.沿垂直剖面,4种植被类型在表层0-20 cm土壤盐分均达到最高,出现盐分“表聚”现象而形成“盐霜”;随着土层深度增加,含水率和土壤容重均呈显著性升高,土壤有机质、田间持水量、总孔隙度、毛管孔隙度和非毛管孔隙度均呈显著性降低(P＜0.05).相关性分析显示,土壤有机质是引起其他土壤物理性质变化的主要原因.相比空裸地,4种植被覆盖类型1 m剖面内土壤有机质、总孔隙度和毛管孔隙度均呈显著性提高,土壤容重显著性降低,有机质分别提高了162.94％、82.94％、85.59％和27.94％,总孔隙度分别提高了44.90％、20.83％、36.06％和15.80％,毛管孔隙度分别提高了58.27％、30.71％、43.48％和25.72％,土壤容重分别降低了18.86％、10.86％、17.14％和7.43％,表明干旱荒漠区盐碱土上生长的不同盐生植物能够显著改善土壤质量.     

Responses of ectomycorrhizal American elm (Ulmus americana) seedlings to salinity and soil compaction

American elm (Ulmus americana) seedlings were either non-inoculated or inoculated with Hebeloma crustuliniforme, Laccaria bicolor and a mixture of the two fungi to study the effects of ectomycorrhizal associations on seedling responses to soil compaction and salinity. The seedlings were grown in the greenhouse in pots containing non-compacted (0.4 g cm^?3 bulk density) and compacted (0.6 g cm^?3 bulk density) soil and subjected to 60 mM NaCl or 0 mM NaCl (control) treatments for 3 weeks. All three fungal inocula had similar effects on the responses of elm seedlings to soil compaction and salt treatment. In non-compacted soil, ectomycorrhizal fungi reduced plant dry weights, root hydraulic conductance, but did not affect leaf hydraulic conductance and net photosynthesis. When treated with 60 mM NaCl, ectomycorrhizal seedlings had several-fold lower leaf concentrations of Na⁺ compared with the non-inoculated plants. Soil compaction reduced Na⁺ leaf concentrations in non-ectomycorrhizal plants and decreased dry weights, gas exchange and root hydraulic conductance. However, in ectomycorrhizal plants, soil compaction had little effect on the leaf Na⁺ concentrations and on other measured growth and physiological parameters. Our results demonstrated that ECM associations could be highly beneficial to plants growing in sites with compacted soil such as urban areas.     

Physical Quality Indicators and Mechanical Behavior of Agricultural Soils of Argentina

Mollisols of Santa Fe have different tilth and load support capacity. Despite the importance of these attributes to achieve a sustainable crop production, few information is available. The objectives of this study are i) to assess soil physical indicators related to plant growth and to soil mechanical behavior; and ii) to establish relationships to estimate the impact of soil loading on the soil quality to plant growth. The study was carried out on Argiudolls and Hapludolls of Santa Fe. Soil samples were collected to determine texture, organic matter content, bulk density, water retention curve, soil resistance to penetration, least limiting water range, critical bulk density for plant growth, compression index, pre-consolidation pressure and soil compressibility. Water retention curve and soil resistance to penetration were linearly and significantly related to clay and organic matter (R² = 0.91 and R² = 0.84). The pedotransfer functions of water retention curve and soil resistance to penetration allowed the estimation of the least limiting water range and critical bulk density for plant growth. A significant nonlinear relationship was found between critical bulk density for plant growth and clay content (R² = 0.98). Compression index was significantly related to bulk density, water content, organic matter and clay plus silt content (R² = 0.77). Pre-consolidation pressure was significantly related to organic matter, clay and water content (R² = 0.77). Soil compressibility was significantly related to initial soil bulk density, clay and water content. A nonlinear and significantly pedotransfer function (R² = 0.88) was developed to predict the maximum acceptable pressure to be applied during tillage operations by introducing critical bulk density for plant growth in the compression model. The developed pedotransfer function provides a useful tool to link the mechanical behavior and tilth of the soils studied.     

Effect of berseem (T. alexandrinum L.) on the growth of maize crop on artificially compacted soil

Summary A pot experiment to evaluate the effect of growing berseem on the growth of maize on soil artificially compacted to different soil bulk densities was conducted during 1964–65 and 1965–66 at the Indian Agricultural Research Institute, New Delhi. The results obtained from the experiment showed that yield of berseem fodder was almost identical in pots with 1.5 and 1.6 g/cm³ soil bulk densities, but decreased abruptly as the bulk densities increased from 1.6 to 1.8 g/cm³. Increase in bulk density of soil from 1.6 to 1.8 g/cm³ adversely affected the growth of maize plants but growing of berseem mitigated the ill-effects of soil compaction. Maize crop grown in pots where berseem was grown, exhibited better growth of roots and shoots and thus produced more dry matter per plant than where no berseem was grown.A part of the Ph.D. Thesis submitted by the senior author, Div. of Agronomy, Indian Agricultural Research Institute, New Delhi, India.Formerly Agronomist, I.A.R.I., New Delhi, Professor of Agronomy, U.P. Agricultural University, Pantnagar, India.     

陕西榆林春玉米高产田土壤理化性状及根系分布

调查分析了陕西榆林2块19500 kg·hm^-2以上超高产春玉米田的产量构成、干物质分配和0～100 cm土层根系分布及土壤理化性状指标.结果表明：其种植密度为105000～123000株·hm^-2、成穗率97.7%～102.2%、千粒重320 g以上,果穗干物质积累量占整株干物质积累量的60.2%～65.5%.0～100 cm土壤平均容重为1.28～1.33 g·cm^-3,层间（每层20 cm）土壤容重、孔隙度和田间持水量均呈“M”型变化.玉米根系主要分布在0～60 cm,0～20 cm土层根系量占根系总量的64.8%～72.1%,20～60 cm土层根系量占根系总量的23.30%～28.17%.根系分布与土壤理化性状关系密切,0～20 cm土层玉米的根系量与土壤有机质、全氮和全磷含量呈显著正相关,20～60 cm土层根系量与土壤容重和田间持水量显著相关.因此,选择通透性和保水保肥能力良好的土壤,实行宽窄行双株密植栽培是获得玉米高产的关键.     

Wetting and drying cycles in the maize rhizosphere under controlled conditions. Mechanics of the root-adhering soil

Mechanical properties of the topsoil (sandy Podsol and silty Luvisol, FAO) adhering to maize (Zea mays L.) roots and its bulk soil counterpart were studied as a function of soil texture and final soil water suction at harvest, with three soil water suction values of approximately 30, 50 and 60 kPa. Two scales of observation were also selected: the whole soil:root system and the root-adhering soil aggregates. Three methods were used to characterize the stability of the soil:root system: mechanical shaking in air, and dispersion by low-power ultrasonication, with or without preliminary immersion of the soil:root system in water. Soil disruption kinetics, which were fitted with first-order kinetics equations, were analyzed and discussed. For example, silty soil ultrasonication kinetics, without preliminary water-immersion, could be divided into two parts: the first faster part, which was characterized by a mean rate K value of 6.8–7.2 mJ^-1, is attributed to soil slaking, whereas the second slower part, which was characterized by a mean rate K value of 1.5–1.6 mJ^-1, was attributed to the rupture of the `firmly root-adhering soil' from the roots. A clear plant effect was observed for both aggregate tensile strength and friability, with higher aggregate strength for the root-adhering silty soil (450–500 kPa) than for its bulk silty soil counterpart (410–420 kPa), and lower friability (coefficient of variation of the aggregate strength) for the root-adhering silty soil (e.g. 67% at a soil water suction value of 30 kPa) than for its bulk silty soil counterpart (e.g. 49% at asoil water suction value of 30 kPa). These effects were attributed to root exudation, which was significantly higher for the driest silty topsoil than for the wetter ones. In conclusion, the mechanical properties of the silty topsoil adhering to the maize roots are attributed to both physical and biological interactions occurring in the maize rhizosphere. This revised version was published online in June 2006 with corrections to the Cover Date.     

Edaphic constraints on seed germination and emergence of three <Emphasis Type="Italic">Acacia</Emphasis> species for dryland restoration in Saudi Arabia

In situ edaphic factors affecting seed germination and seedling emergence of three framework species of Acacia were investigated with the intent of developing fundamental and scalable restoration capacity for Arabian dryland restoration. Direct seeding represents the most efficient means to restore vegetation at the landscape scale and this study provides insight into edaphic and ecological limitations, as well as effective protocols governing the use of native seeds for restoration in hyper-arid environments. The study was conducted in extant Acacia woodland habitat on conserved land (Thumamah Nature Park) in close proximity to Riyadh, Saudi Arabia. Broad-scale direct seeding using un- and pretreated Acacia gerrardii, A. tortilis, and A. ehrenbergiana seed, and two seed burial depths were implemented across three sites with distinct soil surface characteristics. Eight weeks post-sowing, random samples for each species × seed treatment × burial depth combination were excavated, sieved, and categorized as follows: failed to germinate, germinated but died prior to emerging, or successfully emerged. We show that germination and emergence of Acacia gerrardii, A. tortilis, and A. ehrenbergiana were driven by a three-way interaction among species, site, and seed burial depth. Treating seed with the signaling compound Moddus did not have a definitive effect, positive or negative, on any of the species investigated. Acacia gerrardii was the only species that exhibited widespread emergence, though emergence was not consistent across sites or burial depths. Germination was highest in disturbed soil (up to 69% for A. gerrardii), but very few (<2%) successfully emerged; a greater proportion of germinants in sandy soil emerged (up to 44% for A. gerrardii) even though the overall germination was less. Though species-dependent, a 2-cm sowing depth was most effective in sand; while in disturbed soil, sowing depths of 1 and 2 cm were comparable; and no germination was observed in gravelly clay soil. Sandy soil exhibited rapid water infiltration (107.6 mm min^?1), and post-sowing surface crusting was a non-factor (0.44 kg cm^?2). Disturbed soil exhibited moderate water infiltration (1.46 mm min^?1) and post-sowing surface crusting was double that of sand (0.88 kg cm^?2) and restrictive on seedling emergence. Gravelly clay exhibited extremely poor water infiltration (0.12 mm min^?1), and surface crusting was severe (4.49 kg cm^?2) and an order of magnitude greater than sand. The medium-coarse sand fraction, a key driver of the observed soil surface processes, was greatest in sand (55%) and significantly less and uniform in the disturbed (22%) and gravelly clay (22%) soils. Our findings demonstrate that soil surface characteristics and associated processes can dictate ecological processes at depths as shallow as 1–2 cm, and that soil crusts that slow water infiltration and impede seedling emergence rapidly reconstitute after disturbance; both are important considerations for restoring dryland vegetation.     

The strength of seeds and their destruction by granivorous insects

The influence of seed structure and strength on their destruction by granivores is central to understanding the dynamics of granivore-plant interactions. For up to nine seed species, the effects of seed size (cm³), mass (mg), density (mg/cm³) and coat strength (MPa) on the damage inflicted by three post-dispersal granivores (Harpalus pensylvanicus, Anisodactylus sanctaecrucis, and Gryllus pennsylvanicus) were evaluated. Seed destruction rates by G. pennsylvanicus were statistically unrelated to the size and toughness of the seeds. Seed densities significantly affected their destruction by A. sanctaecrucis and H. pensylvanicus, as did seed size, mass, and strength in H. pensylvanicus under choice conditions. The carabid beetles destroyed more of the small, denser seeds with stronger seed coats. The results show that different granivores are able to distinguish the structural strength and physical density of seeds as well as seed size. The relative ability of granivores to detect these seed characteristics offers a way in which diverse communities of post-dispersal insect granivores can persist within a single habitat. The authors redefine how the strength of biological structures should be evaluated in ecological studies, using guidelines commonplace in the field of engineering. Handling Editor: Stanislav Gorb The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged     

Effect of soil compaction on barley (Hordeum vulgare L.) growth: I. Possible role for ABA as a root-sourced chemical signal

Wild-type (Steptoe) and abscisic acid (ABA)-deficient mutant(Az34) genotypes of barley were grown in compacted soil to examinethe potential role of ABA as a root-to-shoot signal. Root andshoot growth and leaf conductance were all reduced when plantswere grown in compacted soil with a bulk density of 1.7g cm^–3,relative to uncompacted control plants (1.1 g cm^–3. Theseeffects occurred in the absence of detectable changes in leafwater status or foliar abscisic acid (ABA) content. Analysisof Steptoe and Az34 xylem sap showed that the ABA concentrationwas greatly increased at 6 d after emergence (6 DAE) when seedlingswere grown in compacted soil (1.7 g cm^–3); however, ABAconcentrations were never as high in the mutant as in the wildtype. The increase in xylem sap ABA concentration observed athigh bulk density was closely correlated with reductions inleaf conductance, but not leaf area. These increases were transitory,and xylem sap ABA concentrations subsequently decreased towardsthe control level by 18 DAE in both genotypes. The ABA-deficient mutant, Az34, produced a much lower leaf areathan Steptoe at a bulk density of 1.6 g cm^–3. Examinationof epidermal characteristics indicates that this effect resultedmainly from reductions in cell expansion rather than cell division,suggesting that the higher ABA concentrations detected in xylemsap from the wild-type Steptoe may have exerted a positive rolein maintaining leaf expansion in this treatment. The possibleinvolvement of ABA as a root-to-shoot signal mediating the effectsof compaction stress is discussed. Key words: Soil compaction, bulk density, ABA, ABA-deficient mutant, leaf growth     

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     

宁夏贺兰山、六盘山典型森林类型土壤主要肥力特征

采用野外调查结合室内分析的方法,对该区域典型森林类型下土壤的主要剖面肥力特征进行了研究,并对主要理化指标进行了因子分析.结果表明:受森林凋落物的累积、分解和成土母质、气候条件的影响,贺兰山、六盘山主要森林土壤的剖面肥力具有明显差异.其中,土壤孔隙度(54.50％-72.22％,剖面均值,下同)受有机质影响显著,随土层加深逐渐减小,容重(0.72-1.21 g/cm3)、比重(2.55-2.68 g/cm3)随土层加深显著增大,且六盘山各样地比重大于贺兰山.受有机质归还作用影响,有机碳(24.03-65.37 g/kg)、全N(1.48-3.49 g/kg)、NO3--N(1.88-10.50 mg/kg)、NH4+-N(5.02-11.01 mg/kg)、全P (0.37-1.19 g/kg)、有效P(4.82-13.38 mg/kg)、速效K含量(82.03-244.62 mg/kg)均随土层加深逐渐降低;全K含量(18.92-26.14 g/kg)随土层加深逐渐增大,且六盘山各样地全K含量大于贺兰山.土壤C/N (11.74-19.88)旱现B层＞C层＞A层,且贺兰山各样地C/N大于六盘山.土壤CEC(23.94-40.30 cmol/kg)受有机质的主导作用明显,随土层加深显著减小,pH值(7.09-8.09)、ESP(0.59％-2.47％)及BSP(51.24％-80.57％)均随土层加深逐渐增大,且贺兰山各样地pH值、ESP大于六盘山.粘粒(5.46％-10.20％)、TDS (0.33-1.12 g/kg)及CaCO3(1.44-14.23 g/kg)均未出现明显积聚,且贺兰山各样地TDS、CaCO3含量大于六盘山.因子分析显示,对于该区域各样地土壤的肥力特征,可以应用有机质因子、环境因子和NO3--N因子进行综合描述.其中青海云杉、山杨混交林下土壤的有机质因子得分最高,贺兰山各样地环境因子得分显著大于六盘山,NO3--N因子得分则以小叶金露梅灌丛和华北落叶松天然林最高.