大田期烟草根系构型参数的动态变化

采用“根箱”法研究了大田期烟草根系构型参数在时间、空间上的动态变化.结果表明, 烟草2级侧根总长度的增加明显大于1级侧根,根快速增长期分别出现在移栽后26～40和56～70 d.栽后57 d(打顶)前,烟草根系的分枝密度表现为10～20＞0～10＞20～30＞30～40 cm,此后随土层的加深呈递减趋势.在主根上,以7～21 cm范围内的分枝密度最大.打顶前,比根长随着入土深度的加深而递增;栽后90 d,比根长随土层的加深而递减.1级侧根根长密度在0～10 cm土层内的变化呈“S”型曲线,10～20、20～30和30～40 cm内表现为双峰曲线;2级侧根根长密度随生育期的进程而增加,其中0～10 cm根长密度的变化为“S”曲线,其它层次为单峰曲线.     

Transformation and mineralization of soil organic nitrogen by the humivorous larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

In common bean (Phaseolus vulgaris L.), Fusarium root rot (caused by Fusarium solani f. sp. phaseoli) disease severity is increased by environmental factors that stress the plant. The current study used reciprocal grafting techniques with the resistant cultivar FR266 and the susceptible cultivar Montcalm to determine if the genetic control of resistance is conferred by the rootstock (root genotype) or the scion (shoot genotype) and if root vigor played a role in resistance. The influence of a compacted layer on root and shoot genotype response and root rot resistance was studied. Root rot resistance was found to be controlled by the root genotype, such that on a scale of 1 to 7 (severe disease) the FR266 root had an average score of 2.3 and the Montcalm root had an average score of 4.4. However, when grafted plants were grown in the presence of a compacted layer, the FR266 root and/or shoot genotype in any graft combination with the susceptible Montcalm had reduced root rot (score = 2.4 average) than the Montcalm self graft (score = 4.5). Root mass was shown to be controlled by the root genotype in the absence of compaction such that the FR266 root was 26% larger that the Montcalm root when grafted onto a FR266 shoot or a Montcalm shoot. When a compacted layer was present the root and shoot genotype both contributed to root mass. Average root diameter was controlled by the shoot genotype, as the FR266 shoot grafted to Montcalm or FR266 roots had thicker roots (average diameter 0.455 mm) than the Montcalm shoot (average diameter 0.418 mm). This study shows evidence that root vigor in the presence of Fusarium disease pressure should be evaluated to effectively develop common bean lines resistant to Fusarium root rot across a range of environments.     

Root characteristics of representative Mediterranean plant species and their erosion-reducing potential during concentrated runoff

Gully erosion is an important soil degradation process in Mediterranean environments. Revegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass on reducing water erosion rates, whereas the role of the below-ground biomass is often neglected. In a Mediterranean context, the above-ground biomass can temporally disappear because of fire or overgrazing and when concentrated flow erosion occurs, roots can play an important role in controlling soil erosion rates. Unfortunately, information on root characteristics of Mediterranean plants, growing on semi-natural lands, and their effects on the topsoil resistance to concentrated flow erosion is lacking. Therefore, typical Mediterranean grass, herb, reed, shrub and tree root systems of plants growing in habitats that are prone to concentrated flow erosion (i.e. in ephemeral channels, abandoned fields and steep badland slopes) are examined and their erosion-reducing potential was evaluated. Root density (RD), root length density (RLD) and root diameters are measured for 26 typical Mediterranean plant species. RD values and root diameter distribution within the upper 0.10–0.90 m of the soil profile are then transformed into relative soil detachment rates using an empirical relationship in order to predict the erosion-reducing effect of root systems during concentrated runoff. Comparing the erosion-reducing potential of different plant species allows ranking them according to their effectiveness in preventing or reducing soil erosion rates by concentrated flow. RD in the 0.10 m thick topsoil ranges between 0.13 kg m⁻³ for Bromus rubens (L.) and 19.77 kg m⁻³ for Lygeum spartum (L.), whereas RLD ranges between 0.01 km m⁻³ for Nerium oleander (L.) and 120.43 km m⁻³ for Avenula bromoides ((Gouan) H. Scholz.) Relative soil detachment rates, compared to bare soils, range between 0.3 × 10^-12 and 0.7 for the 0.10 m thick topsoil. The results show that grasses such as Helictotrichon filifolium ((Lag.) Henrard), Piptatherum miliaceum ((L.) Coss.), Juncus acutus (L.), Avenula bromoides ((Gouan) H. Scholz), Lygeum spartum (L.) and Brachypodium retusum ((Pers.) Beauv.) have the highest potential to reduce soil erosion rates by concentrated flow in the 0–0.1 m topsoil. But also shrubs such as Anthyllis cytisoides (L.) and Tamarix canariensis (Willd.), having high root densities in the topsoil, can reduce erosion rates drastically. Among the species growing in channels, Juncus acutus (L.) has the highest erosion reducing potential, whereas Phragmites australis (Cav.) is the least effective. On abandoned fields, Avenula bromoides ((Gouan) H. Scholz) and Plantago albicans (L.) are the most effective species in reducing concentrated flow erosion rates, while Thymelaea hirsuta (L. (Endl.)) and Bromus rubens (L.) perform the worst. On steep badland slopes, Helictotrichon filifolium ((Lag.) Henrard) and Anthyllis cytisoides (L.) perform the best in the analysis of erosion reducing potential, while Ononis tridentata (L.) is the least effective species. These findings have implications for ecological restoration and management of erosion-prone slopes.     

Estimating root lifespan of two grasses at contrasting elevation in a salt marsh by applying vitality staining on roots from in-growth cores

Contrasting soil conditions caused by different inundation frequenciesrequire different root growth strategies along the elevational gradient ofcoastal salt marshes. The objective of this study was to examine (1) if rootlifespan was shorter in Elymus pycnanthus, a relativelyfast-growing competitive species dominating high marshes, than inSpartina anglica, a relatively slow-growingstress-tolerating species dominating low marshes, and (2) if the species withlonger lifespan had higher tissue density (g cm^–3) and lowerspecific root length (m g^–1) than the species with shorterlifespan. Root production and mortality rates were established by samplingrootsin in-growth cores, and using triphenyltetrazolium chloride (TTC) staining todistinguish vital from dead roots. Root lifespan was estimated by dividing theliving root biomass (Elymus: 36 gm^–2, Spartina: 100 gm^–2) by root production (Elymus:0.28 g day^–1 m^–2,Spartina: 0.25 g day^–1m^–2) or root mortality rates(Elymus: 0.42–0.53 g day^–1m^–2). Spartina did not exhibitsubstantial mortality. Despite the present method only yielding rough estimatesof average root lifespan, it is evident that root longevity is much shorter inElymus than in Spartina. Rootlifespanranged between 10–19 weeks for Elymus but was closeto 1 year in Spartina, indicating thatElymus replaces it's roots continuously throughout thegrowing season, whereas Spartina maintains its roots overthe growing season. Fine roots of Elymus had slightlylowertissue density (0.094) than those of Spartina (0.139),whereas coarse roots of Elymus andSpartina had similar tissue density (0.100 gcm^–3). Fine roots of Elymus andSpartina had similar specific root length (195 mg^–1). However, coarse roots ofElymus (50 m g^–1) had higherspecific root length than those of Spartina (20 mg^–1) due to having smaller root diameter(Elymus: 548 m,Spartina: 961 m). We conclude thatpresentobservations on Elymus and Spartinasupport our first hypothesis that the competitive species fromthehigh marsh had short-lived roots compared to the'stress-tolerating'species from the low marsh. However, our result provide only weak support forthe existence of a positive correlation between root longevity and tissuedensity and a negative correlation between root longevity and specific rootlength.     

The response of sorghum and sunflower to short-term waterlogging

Summary Sorghum and sunflower were waterlogged for nine days during the vegetative, floral initiation/buds-visible or anthesis stage of growth under glasshouse conditions to observe the effects on root growth and development. In addition, some plants were waterlogged at all three stages to observe any adaptations induced by waterlogging. The most marked effects occurred at the initiation/buds-visible stage where a 30% reduction in root length and a 40% reduction in root dry weight of sorghum occurred with comparable figures for sunflower being 50 and 60% respectively. Generally, sorghum roots had a higher porosity than sunflower which may contribute to its greater tolerance to waterlogging. The observed changes in root growth are discussed in relation to previously documented effects of waterlogging on growth of the two species and changes which occur in the soil environment.     

Root distribution and water uptake patterns of maize cultivars field-grown under differential irrigation

Summary Rooting and water uptake patterns were determined for three maize (Zea mays L) varieties field-grown during the 1983/84 dry season under seven irrigation levels on a sandy loam soil. Roots were mainly concentrated in the top 22 cm due to a 40 cm thick compact gravelly layer occurring from about this depth in the profile. There were significant varietal differences, distinguished by root length density (RLD) and length/weight ratio (LAR) distributions at depth and at varying soil moisture regimes. These properties were related to water extraction patterns and grain yields. Yields obtained at adequate soil moisture were 6.9 tha⁻¹ for TZESR-W (var 1), 4.2 t/ha for TZSR-W (var 2) and 3.7t ha⁻¹ for FARZ-7 (var 3). These yeilds were respectively associated with maximum RLD of 2.56, 1.88 and 1.70 cm cm⁻³ and corresponding LWR of 2.64, 1.93 and 1.62 cm mg⁻¹. Average seasonal water uptake was estimated at 4.2, 3.0 and 2.8 mm day⁻¹ for var 1, 2 and 3, respectively. Better performance of var 1 was attributed to the development of a more active and deep rooting system.     

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.     

水曲柳根系生物量、比根长和根长密度的分布格局

采用连续钻取土芯法在生长季内对东北林业大学帽儿山实验林场17年生水曲柳人工林根系取样,研究水曲柳不同直径根系现存生物量、比根长和根长密度及垂直分布状况.结果表明,水曲柳人工林根系总生物量为1 637.6 g·m^-2,其中活根生物量占85%,死根占15%.在活根生物量当中,粗根(直径5～30 mm)占的比例最高（69.95%）,其次为活细根（直径<1 mm,13.53%）,小根(1～2 mm)和中等直径的根(2～5 mm)比例较小（分别为7.21%和9.31%）.直径<1 mm活细根的比根长为32.20 m·g^-1,直径5～30 mm粗根的比根长为0.08 m·g^-1.单位面积上活根的总长度为6 602.54 m·m^-2,其中直径<1 mm的细根占92.43%,其它直径等级则不到活根总长度的8%.直径<1 mm的细根生物量与根长密度具显著线性关系（R²=0.923）,但与比根长无显著相关关系（R²=0.134）.     

Vertical distribution of fine roots in relation to soil factors in Pinus tabulaeformis Carr. forest of the Loess Plateau of China

Growth and vertical distribution of fine root closely depend on soil resource availability. Better understanding of relationships of root profile with vertical distribution of available soil resource and soil characteristics can allow ecologists to predict the fine root distribution on the scales ranging from individual plants to vegetation communities. The objective of the study was to understand the fine root mass density (FRMD), fine root length density (FRLD), fine root area density (FRAD), mean root diameter and specific root length (SRL), vertical distribution in soil profile and their relation with soil environment factors in semiarid and arid Loess Plateau of China. The vertical fine root distribution and soil bulk density, soil moisture and soil inorganic N in 0-60 cm soil profile (0–15, 15–30, 30–45 and 45–60 cm intervals) were investigated by soil coring methods in three Pinus tabulaeformis Carr. forests chosen at three locations. The fine root density parameters (FRMD, FRLD and FRAD) and SRL peaked in the most upper soil layer (0–15 cm interval) and decreased with increased soil depth. The results provided a strong support that soil water rather than soil inorganic N is a key control on fine root distribution in the Loess Plateau. With increased soil moisture, the root mass, length and SRL increased and the mean root diameter decreased. The effects of soil bulk density on the fine root parameters were consistent with those of the soil water. An unexpected result was obtained about the relationships between soil organic N and the root distributions and occurrences because of no differences among the soil depth intervals in soil inorganic N content. It might be associated with severe soil water deficit limiting soil nitrogen utilization efficiency in arid Loess Plateau.     

Root water uptake and profile soil water as affected by vertical root distribution

Water uptake by plant roots is a main process controlling water balance in field profiles and vital for agro-ecosystem management. Based on the sap flow measurements for maize plants (Zea mays L.) in a field under natural wet- and dry-soil conditions, we studied the effect of vertical root distribution on root water uptake and the resulted changes of profile soil water. The observations indicate that depth of the most densely rooted soil layer was more important than the maximum rooting depth for increasing the ability of plants to cope with the shortage of water. Occurrence of the most densely rooted layer at or below 30-cm soil depth was very conducive to maintaining plant water supply under the dry-soil conditions. In the soil layers colonized most densely by roots, daytime effective soil water saturation (S _e) always dropped dramatically due to the high-efficient local water depletion. Restriction of the rooting depth markedly increased the difference of S _e between the individual soil layers particularly under the dry-soil conditions due likely to the physical non-equilibrium of water flow between the layers. This study highlights the importance of root distribution and pattern in regulating soil water use and thereby improving endurance of plants to seasonal droughts for sustainable agricultural productivity.     

Variations of root traits in three Xizang grassland communities along a precipitation gradient北大核心CSCD

Aims Root functional traits and their variations mediate coexistence and adaptive strategy of plant species. Yet, strong environmental constraints may induce convergence of root traits among different plant species. To study the variations of root traits and clarify the diverse adaptive strategies across plant species, we sampled three alpine grasslands along a precipitation gradient in the Xizang Plateau. Methods In three grassland communities along a precipitation gradient: Nagqu, Baingoin and Nyima from east to west of Xizang Plateau, we collected 22 coexisting plant species and measured three key root traits: 1st-order root diameter, 1st-order lateral root length and root branch intensity. Important findings The main results showed that: (1) the root of plants in the alpine grassland was generally thin, and the interspecific variation was also small (22.76%); (2) the root diameter of 86% plant species was in the range from 0.073 mm to 0.094 mm. Compared with the thick-root species, thin-root species had a higher root branching intensity, but shorter lateral root length. In addition, at community-level, plants mainly increased root diameter and lateral root length, but reduced root branching intensity to adapt to the decreasing precipitation; while at species-level, the plant species exhibited diverse adaptive strategies along the precipitation gradient. © Chinese Journal of Plant Ecology.     

Using a fine root extraction device to quantify small diameter corn roots (≥0.025 mm) in field soils

The study of fine roots growing under field conditions is limited by the techniques currently available for separating these roots from soil. This study had two objectives: to measure the total root length of field grown corn (Zea mays L.) by root diameter class, and to develop an inexpensive and efficient root washing device that would effectively capture all of the roots in a field soil sample. An inexpensive Fine Root Extraction Device (FRED) was constructed from readily available materials and was successful at extracting all roots, including very fine diameter roots (0.025 mm), from field soil samples. Greater than 99.7% of marked roots introduced to the FRED were recaptured by the device. Soil samples from three depths, and on three dates, from field grown corn were placed in the FRED. We found that more than 56% of total root length occurred in roots whose diameters were smaller than 0.175 mm, and more than 35% of root length occurred in roots smaller than 0.125 mm in diameter. Corn roots of the diameters described here have not been reported in field soils prior to this study. Root researchers who fail to measure these very fine roots will significantly underestimate root length density. Widespread use of the FRED should improve our understanding of root distribution in field soils.     

落叶松人工林细根动态与土壤资源有效性关系研究

树木细根在森林生态系统C和养分循环中具有重要的作用。由于温带土壤资源有效性具有明显的季节变化, 导致细根生物量、根长密度 (Rootlengthdensity, RLD) 和比根长 (Specificrootlength, SRL) 的季节性变化。以 17年生落叶松 (Larixgmelini) 人工林为研究对象, 采用根钻法从 5月到 10月连续取样, 研究了不同土层细根 (直径≤ 2mm) 生物量、RLD和SRL的季节动态, 以及这些根系指标动态与土壤水分、温度和N有效性的关系。结果表明 :1) 落叶松细根年平均生物量 (活根 +死根 ) 为 189.1g·m-2 ·a-1, 其中 5 0 %分布在表层 (0~ 10cm), 33%分布在亚表层 (11~ 2 0cm), 17%分布在底层 (2 1~ 30cm) 。活根和死根生物量在 5~ 7月以及 9月较高, 8月和 10月较低。从春季 (5月 ) 到秋季 (10月 ), 随着活细根生物量的减少, 死细根生物量增加 ;2 ) 土壤表层 (0~ 10cm) 具有较高的RLD和SRL, 而底层 (2 1~ 30cm) 最低。春季 (5月 ) 总RLD和SRL最高, 分别为 10 6 2 1.4 5m·m-3 和 14.83m·g-1, 到秋季 (9月 ) 树木生长结束后达到最低值, 分别为 2 198.2 0m·m-3 和 3.77m·g-1;3) 细根生物量、RLD和SRL与土壤水分、温度和有效N存在不同程度的相关性。从单因子分析来看, 土壤水分和有效N对细根的影响明显大于温度, 对活根的影响大于死根。由于土壤资源有效性的季节变化, 使得C的地下分配格局发生改变。各土层细根与有效性资源之间的相关性反映了细根功能季节性差异。细根 (生物量、RLD和SRL) 的季节动态 (5 8%~ 73%的变异 ) 主要由土壤资源有效性的季节变化引起。     

Root growth and water uptake in winter wheat under deficit irrigation

Root growth is critical for crops to use soil water under water-limited conditions. A field study was conducted to investigate the effect of available soil water on root and shoot growth, and root water uptake in winter wheat (Triticum aestivum L.) under deficit irrigation in a semi-arid environment. Treatments consisted of rainfed, deficit irrigation at different developmental stages, and adequate irrigation. The rainfed plots had the lowest shoot dry weight because available soil water decreased rapidly from booting to late grain filling. For the deficit-irrigation treatments, crops that received irrigation at jointing and booting had higher shoot dry weight than those that received irrigation at anthesis and middle grain filling. Rapid root growth occurred in both rainfed and irrigated crops from floral initiation to anthesis, and maximum rooting depth occurred by booting. Root length density and dry weight decreased after anthesis. From floral initiation to booting, root length density and growth rate were higher in rainfed than in irrigated crops. However, root length density and growth rate were lower in rainfed than in irrigated crops from booting to anthesis. As a result, the difference in root length density between rainfed and irrigated treatments was small during grain filling. The root growth and water use below 1.4 m were limited by a caliche (45% CaCO₃) layer at about 1.4 m profile. The mean water uptake rate decreased as available soil water decreased. During grain filling, root water uptake was higher from the irrigated crops than from the rainfed. Irrigation from jointing to anthesis increased seasonal evapotranspiration, grain yield, harvest index and water-use efficiency based on yield (WUE), but did not affect water-use efficiency based on aboveground biomass. There was no significant difference in WUE among irrigation treatments except one-irrigation at middle grain filling. Due to a relatively deep root system in rainfed crops, the higher grain yield and WUE in irrigated crops compared to rainfed crops was not a result of rooting depth or root length density, but increased harvest index, and higher water uptake rate during grain filling.