Effect of water stress mediated through agar on <Emphasis Type="Italic">in vitro</Emphasis> growth of potato

With the objective to develop a practical method of screening potato for drought tolerance, shoot and root growth in plantlets raised in vitro (from nodal cuttings drawn from in vivo as well as in vitro grown plantlets) were studied in three genotypes with known root mass production under field conditions. Different levels of water stress were induced using five concentrations of agar in MS (Murashige and Skoog in Physiol Plant 15:473–497, 1962) medium. Water potential of various media ranged from −0.70 MPa to −0.98 MPa. Water stress in culture adversely affected plantlet growth, and the responses varied with genotype and explant source. Genotype IWA-1 was less affected than Konafubuki and Norin-1. In the experiment with explants from in vivo grown plants, the time to rooting was considerably delayed in Konafubuki and Norin-1 by an increase in agar concentration, but no such effect was observed in IWA-1. In all media, the mean number of roots and root length was greater in IWA-1 than Konafubuki and Norin-1, and the latter two genotypes were at par. At 10 gl⁻¹ agar, IWA-1 had taller plantlets, heavier foliage dry weight, root volume, as well as root dry weight than Konafubuki and Norin-1, whereas the latter two genotypes were at par for all these characteristics. This pattern was similar to the reported pattern of these genotypes for root dry weight under field conditions. However, such similarity in the in vitro and field behavior of the tested genotypes was not observed when nodal cuttings drawn from in vitro plantlets were used as explants. It is concluded that in vitro screening of potato under specific and limited water stress conditions by raising plantlets from nodal cuttings drawn from in vivo grown plants may provide a system for effectively differentiating the genotypes for their expected root mass production under field conditions.     

Influence of Pratylenchus penetrans on Plant Growth and Water Relations in Potato

Plants of potato (Solanum tuberosum) cultivars Katahdin and Superior were inoculated with 0, 1,500, or 15,000 Pratylenchus penetrans. Transpiration, measured in the greenhouse with a porometer after 56 days of growth, was not significantly different among nematode inoculum levels or between cultivars. The rate of xylem exudation from decapitated root systems of Katahdin plants inoculated with 1,500 or 15,000 P. penetrans and Superior plants inoculated with 15,000 P. penetrans was lower than from noninoculated plants. Root weight of Katahdin and Superior was not affected by P. penetrans inoculum level. Transpiration of plants inoculated with 0, 500, 5,000 or 50,000 P. penetrans was recorded weekly from 14 to 56 days after planting. No consistent effects of nematode inoculum density on transpiration rate were observed. Root hydraulic conductivity was lower in Katahdin plants inoculated with 266 P. penetrans per plant and in Chippewa with 5,081 per plant than in noninoculated plants. Nematodes reduced leaf area of Superior, Chippewa, and Katahdin and root dry weight of Chippewa but had no effect on growth of Hudson, Onaway, or Russet Burbank plants. Assessing nematode effects on root hydraulic conductivity may provide a measure of the tolerance of potato cultivars to nematodes.     

The Wageningen Rhizolab — a facility to study soil-root-shoot-atmosphere interactions in crops

Roots in the Wageningen Rhizolab are observed using two methods: (i) non-destructively, using horizontal, glass minirhizotrons at intervals of 14 days between observations; (ii) with destructive sampling using augers on three dates in the season. This paper reports changes with depth and time in root numbers per unit interface area of the minirhizotron tube (number of intersections) of four crop species (wheat, Brussels sprouts, leek and potato). The number of root intersections of Brussels sprouts, wheat and potato declined with depth at any time, whereas leek showed a different pattern because maximum root growth was observed at a depth of 10–20 cm. Root density generally decreased in the following order: Brussels sprouts, wheat, potato and leek. Plots of root length densities, L_rv(cm. cm^-3), obtained by auger sampling, versus the number of intersections showed considerable variation in slope with species, time in the season and year, implying that a single, universal equation to convert minirhizotron observations into volumetric root densities does not exist. Causes of variation in the slopes are discussed. It is concluded that limited auger sampling combined with minirhizotron observations yield adequate quantitative estimates of relevant root properties.     

Growth and nitrogen fixation inAlnus glutinosa (L.) Gaertn. under carbon dioxide enrichment of the root atmosphere

The effects of aeration of the N-free rooting medium with elevated CO₂ on (a) acetylene reduction by perlite-grown plants and (b) N₂-fixation and long-term growth of nutrient solution-grown plants were determined for nodulatedAlnus glutinosa (L.) Gaertn. In the former experiments, roots of intact plants were incubated in acetylene in air in darkened glass jars for 3 hr, followed by a further 3 hr incubation period in air enriched with CO₂ (0–5%). During incubation, the CO₂ content of the jars increased by 0.17% per hour due to respiration of the root system, so that the CO₂ content at 3 hr was 0.5%. Additional enrichment of the rooting medium gas-phase with CO₂ equivalent to 1.1% and 1.75% CO₂ of the gas volume significantly increased nitrogenase activity (ethylene production) by 55% and 50% respectively, while enrichment with greater than 2.5% CO₂ decreased activity. In contrast, ethylene production by control plants, where CO₂ was not added to the assay jars, decreased by 8% over the assay period. In long-term growth experiments, nodulated roots of intactAlnus glutinosa plants were sealed into jars containing N-free nutrient solution (pH 6.3) and aerated with air, or air containing elevated levels of CO₂ (1.5% and 5%). Comparison of the appearance of CO₂-treated with air treated plants suggested that 1.5% CO₂ stimulated plant growth. However, at harvest after 5 or 6 weeks variability between plants masked the significance of differences in plant dry weight. A significant increase of 33% in total nitrogen of plants aerated with 1.5% CO₂, compared with air-treated plants, was demonstrated, broadly in line with the short-term increase in acetylene reducing activity observed following incubations with similar CO₂ concentrations. Shoot dry weight was not affected significantly by long-term exposure to 5% CO₂, the main effect on growth being a 20% reduction in dry weight of the root system, possibly through inhibition of root system respiration. However, in contrast to the inhibitory effects of high CO₂ on acetylene reduction there was no significant effect on the amounts of N₂ fixed.     

Root development and heavy metal phytoextraction efficiency: comparison of different plant species in the field

Heavy metal phytoextraction is a soil remediation technique which implies the optimal use of plants to remove contamination from soil. Plants must thus be tolerant to heavy metals, adapted to soil and climate characteristics and able to take up large amounts of heavy metals. Their roots must also fit the spatial distribution of pollution. Their different root systems allow plants to adapt to their environment and be more or less efficient in element uptake. To assess the impact of the root system on phytoextraction efficiency in the field, we have studied the uptake and root systems (root length and root size) of various high biomass plants (Brassica juncea, Nicotiana tabacum, Zea mays and Salix viminalis) and one hyperaccumulator (Thlaspi caerulescens) grown in a Zn, Cu and Cd contaminated soil and compared them with total heavy metal distribution in the soil. Changes from year to year have been studied for an annual (Zea mays) and a perennial plant (Salix viminalis) to assess the impact of the climate on root systems and the evolution of efficiency with time and growth. In spite of a small biomass, T. caerulescens was the most efficient plant for Cd and Zn removal because of very high concentrations in the shoots. The second most efficient were plants combining high metal concentrations and high biomass (willows for Cd and Zn and tobacco for Cu and Cd). A large cumulative root density/aboveground biomass ratio (L_A/B), together with a relative larger proportion of fine roots compared to other plants seemed to be additional favourable characteristics for increased heavy metal uptake by T. caerulescens. In general, for all plants correlations were found between L _A/B and heavy metal concentrations in shoots (r=0.758^***, r=0.594^***, r=0.798^*** (P<0.001) for Cd, Cu and Zn concentrations resp.). Differences between years were significant because of variations in climatic conditions for annual plants or because of growth for perennial plants. The plants exhibited also different root distributions along the soil profile: T. caerulescens had a shallow root system and was thus best suited for shallow contamination (0.2 m) whereas maize and willows were the most efficient in colonising the soil at depth and thus more applicable for deep contamination (0.7 m). In the field situation, no plant was able to fit the contamination properly due to heterogeneity in soil contamination. This points out to the importance and the difficulty of choosing plant species according to depth and heterogeneity of localisation of the pollution.     

Nitrogen nutrition,photosynthesis and carbon allocation in ectomycorrhizal pine

Summary Studies examined net photosynthesis (Pn) and dry matter production of mycorrhizal and nonmycorrhizalPinus taeda at 6 intervals over a 10-month period. Pn rates of mycorrhizal plants were consistently greater than nonmycorrhizal plants, and at 10 months were 2.1-fold greater. Partitioning of current photosynthate was examined by pulse-labelling with¹⁴CO₂ at each of the six time intervals. Mycorrhizal plants assimilated more¹⁴CO₂, allocated a greater percentage of assimilated¹⁴C to the root systems, and lost a greater percentage of¹⁴C by root respiration than did nonmycorrhizal plants. At 10 months, the quantity of¹⁴CO₂ respired by roots per unit root weight was 3.6-fold greater by mycorrhizal than nonmycorrhizal plants. Although the stimulation of photosynthesis and translocation of current photosynthate to the root system by mycorrhiza formation was consistent with the source-sink concept of sink demand, foliar N and P concentrations were also greater in mycorrhizal plants.Further studies examined Pn and dry matter production ofPinus contorta in response to various combinations of N fertilization (3, 62, 248 ppm), irradiance and mycorrhizal fungi inoculation. At 16 weeks of age, 6 weeks following inoculation with eitherPisolithus tinctorius orSuillus granulatus, Pn rates and biomass were significantly greater in mycorrhizal than nonmycorrhizal plants. Mycorrhizal plants had significantly greater foliar %P, but not %N, than did nonmycorrhizal plants. Fertilization with 62 ppm N resulted in greater mycorrhiza formation than either 3 or 248 ppm. Increased irradiance resulted in increased mycorrhiza formation.     

Root morphological and proteomic responses to growth restriction in maize plants supplied with sufficient N

The primary objective of this study was to better understand how root morphological alteration stimulates N uptake in maize plants after root growth restriction, by investigating the changes in length and number of lateral roots, ¹⁵NO₃⁻ influx, the expression level of the low-affinity Nitrate transporter ZmNrt1.1, and proteomic composition of primary roots. Maize seedlings were hydroponically cultured with three different types of root systems: an intact root system, embryonic roots only, or primary roots only. In spite of sufficient N supply, root growth restriction stimulated compensatory growth of remaining roots, as indicated by the increased lateral root number and root density. On the other hand, there was no significant difference in ¹⁵NO₃⁻ influx between control and primary root plants; neither in ZmNrt1.1 expression levels in primary roots of different treatments. Our data suggested that increased N uptake by maize seedlings experiencing root growth restriction is attributed to root morphological adaptation, rather than explained by the variation in N uptake activity. Eight proteins were differentially accumulated in embryonic and primary root plants compared to control plants. These differentially accumulated proteins were closely related to signal transduction and increased root growth.     

Denitrification in the top soil of managed grasslands in The Netherlands in relation to soil type and fertilizer level

The objective of this investigation was to determine how free-air carbon dioxide enrichment (FACE) of cotton (Gossypium hirsulam L.) affects root distribution in a natural soil environment. For two years cotton was grown on a Trix clay loam under two atmospheric CO₂ concentrations (370 and 550 μmol mol⁻¹) and two water treatments [wet, 100% of evapotranspiration (ET) replaced and dry, 75% (1990) and 67% (1991) of ET replaced] at Maricopa, AZ. At early vegetative and mid-reproductive growth, 90 cm soil cores were taken at 0,0.25, and 0.5 m perpendicular to row center; root variables were ascertained at three 30 cm depth increments. The effect of water stress alone or its interaction with CO₂ on measured variables during both samplings were rare and showed no consistent pattern. There was a significant CO₂ × position interaction for root length density at the vegetative stage (both years) and reproductive stage (1990 only); the positive effects of extra CO₂ were more evident at interrow positions (0.25 and 0.5 m). A CO₂ × depth × position interaction at the vegetative phase (1990) indicated that FACE increased root dry weight densities for the top soil depth increment at all positions and at the middle increment at the 0.5 m position. Similar trends were seen at the reproductive sampling for this measure as well as for root length density at both sample dates in 1990. In 1991, a CO₂ × depth interaction was noted at both periods; CO₂ enhancement of root densities (i.e., both length and dry weight) were observed within the upper and middle depths. Although variable in response, increases for root lineal density under high CO₂ were also seen. In general, results also revealed that the ambient CO₂ treatment had a higher proportion of its root system growing closer to the row center, both on a root length and dry wight basis. On the other hand, the FACE treatment had proportionately more of its roots allocated away from row center (root length basis only). Results from this field experiment clearly suggest that increased atmospheric CO₂ concentration will alter root distribution patterns in cotton.     

TL-DNA from Agrobacterium rhizogenes plasmid pRi1855 reduces the osmotic pressure in transformed plants grown in vitro

Growth, water content, osmotic pressure and solute content were examined for normal potato (Solanum tuberosum L. cv. Desiree) and a derivative (line D9X8a), which was genetically transformed with T_L-DNA from Agrobacterium rhizogenes. Plants were grown (i) in vitro, (ii) in a growth chamber and (iii) in the field. In vitro, the transformed potato plants produced more biomass than the untransformed plants, partly because they had a higher water content. Potassium concentration and osmotic pressure were lower in cell sap extracted from the transformed potato shoots. In some cases the difference was as much as 50%. These differences were less clear, absent or reversed in plants from a growth chamber or from the field. In the field, however, transformed potato senesced early. It is suggested that a cellular basis for these observations may be changes induced by Ri T_L-DNA expression products in plant membrane properties.Abbreviations Ri root inducing - Ti tumour inducing - T-DNA transferred DNA     

Relationship between Root Growth of Potato,Root Diffusate Production,and Hatching of Globodera rostochiensis

Hatching response of Globodera rostochiensis in potato root diffusate (PRD) collected by soaking individual potato, Solanum tuberosum, root systems in water for 2 hours was used to assess the relationship between root growth and PRD production. Resistant potato cultivars Hudson and Rosa were used as test plants. Maximum hatch occurred in PRD collected 3 weeks after plant emergence (AE) in the greenhouse, and declined after this time. Hatch was positively correlated with increased root weight only during the first 3 weeks AE. Hudson PRD was consistently more active than Rosa PRD in stimulating hatch, except when adjusted for root weight. Although the results indicated that cells at the root tip produced a more active PRD than cells located elsewhere, PRD appeared to be produced along the entire root. Differences in time length of the vegetative growth phase, extent of root growth, and volume of roots, rather than the production of a more active PRD per se, may explain why Hudson is more effective than Rosa in reducing G. rostochiensis population densities in soil.     

The role of GA,IAA and BAP in the regulation of <Emphasis Type="Italic">in vitro</Emphasis> shoot growth and microtuberization in potato

The effect of auxin, GA and BAP on potato shoot growth and tuberization was investigated under in vitro condition. The shoot length of potato explants increased with the increasing of concentrations (0.5 – 10 mg dm⁻³) of IAA treatment especially with the addition of GA₃ (0.5 mg dm⁻³), but was inhibited by BAP (5 mg dm⁻³). The root number and root fresh weight of potato explants increased with the increasing of IAA levels either in the presence of GA₃ (treatment IAA+GA) or not (IAA alone). However, no root was observed in the treatment IAA+BAP, instead there were brown swollen calli formed around the basal cut surface of the explants. The addition of GA₃ remarkably increased the fresh weight and diameter of calli. Microtubers were formed in the treatments of IAA+BAP and IAA + GA + BAP but not observed in the treatments of IAA alone or IAA + GA. IAA of higher concentrations (2.5 – 10 mg dm⁻³) was helpful to form sessile tubers. With the increasing of IAA levels, the fresh weight and diameter of microtubers increased progressively. At 10 mg/L IAA, the fresh weight and diameter of microtubers in the treatment of IAA + GA + BAP were 409.6 % and 184.4 % of that in the treatment of IAA + BAP respectively, indicating the interaction effect of GA and IAA in potato microtuberization.     

Stimulation of in vitro root and shoot growth of potato by increasing sucrose concentration in the presence of fluridone,an inhibitor of abscisic acid synthesis

Fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, strongly stimulated rooting of nodal stem segments of potato (Solanum tuberosum L.) cultivar Arran Banner cultured in darkness on tuberisation medium. Inclusion of 10^-6 M ABA in the culture medium prevented this rooting response, indicating that root proliferation in the presence of fluridone could be due to inhibition of ABA synthesis. The rooting response to fluridone (increased total root number and root fresh weight) was obtained only at high sucrose concentrations (0.175 and 0.234 M) and was demonstrated with two potato cultivars and two culture media; one which favoured tuberisation and one which did not. Shoot numbers were also increased, but to a lesser extent than root numbers, and total fresh weight of plant material per culture was greatly increased by inclusion of both fluridone (10^-6 or 10^-5 M) and 0.234 M sucrose in the culture medium. The role of sucrose was not simply osmotic because when the osmolarity of fluridone medium was increased using mixtures of mannitol and sucrose, no root proliferation occurred unless sucrose predominated in the mixture.     

A reliable and efficient protocol for inducing genetically transformed roots in medicinal plant Nepeta pogonosperma

Nepeta pogonosperma is an important medicinal plant with anti-inflammatory effects. An efficient and reliable transformation system for this plant was developed through optimization of several factors which affected the rate of Agrobacterium rhizogenes mediated transformation. Five bacterial strains, A4, ATCC15834, LBA9402, MSU440 and A13, two explant types, leaves and stems, and several co-cultivation media were examined. The maximum rate of hairy root induction was obtained from stem explants using MSU440 and ATCC15834 bacterial strains. A drastic increase in the frequency of transformation (91 %) was observed when MS medium lacking NH₄NO₃, KH₂PO₄, KNO₃ and CaCl₂. Hairy root lines were confirmed by polymerase chain reaction (PCR) using primers of the rolB gene. According to Southern blot analysis, one T-DNA copy was inserted into each of the hairy root lines. In the present study, transgenic hairy roots have been obtained trough genetic transformation by A. rhizogenes harbouring two plasmids, the Ri plasmid and pBI121 binary vector harbouring gus reporter gene. Expression of the gus gene in transgenic hairy root was confirmed by histochemical GUS assay.     

Devising an <Emphasis Type="Italic">in vitro</Emphasis> nodulation system for two actinorhizal plants: <Emphasis Type="Italic">Allocasuarina verticillata</Emphasis> (Lam.) L. Johnson and <Emphasis Type="Italic">Casuarina glauca</Emphasis> sieb. ex spreng (Casuarinaceae)

Summary The purpose of this study was to establish an efficient in vitro nodulation device for producing actinorhizal root nodules on Allocasuarina verticillata and Casuarina glauca. Seeds from the two species were germinated aseptically and seedlings with at least two photosynthetic branchlets and a 3–5 cm long root system were transferred into Petri dishes containing a biphasic (solid/liquid) medium. To assess the nodulation capacity, four different culture media were tested. As soon as the root system developed and spread adequately on the surface of the medium, plants were deprived of nitrogen for at least 1 wk and inoculated with the Frankia strain. The time course nodulation for A. verticillata showed that the basal Hoagland medium supplemented with CaCO₃ and KNO₃ was most efficient, with 83% of plantlets forming nodules, while the medium supplemented with CaCO₃ reached 100% nodulation for C. glauca. This procedure can provide a valuable tool for the study of early events of actinorhizal nodulation and spatio-temporal expression of symbiotic genes in transgenic Casuarinaceae.     

Competition in tree row agroforestry systems. 1. Distribution and dynamics of fine root length and biomass

Complementarity in the distribution of tree and crop root systems is important to minimise competition for resources whilst maximising resource use in agroforestry systems. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare the distribution and dynamics of root length and biomass of a 3-year-old Grevillea robusta A. Cunn. ex R. Br. (grevillea) tree row and a 3-year-old Senna spectabilis DC. (senna) hedgerow grown with Zea mays L. (maize). Tree roots were sampled to a 300 cm depth and 525 cm distance from the tree rows, both before and after maize cropping. Maize roots were sampled at two distances from the tree rows (75–150 cm and 450–525 cm) to a maximum depth of 180 cm, at three developmental stages. The mean root length density (L_rv) of the trees in the upper 15 cm was 0.55 cm cm⁻³ for grevillea and 1.44 cm cm⁻³ for senna, at the start of the cropping season. The L_rv of senna decreased at every depth during the cropping season, whereas the L_rv of grevillea only decreased in the crop rooting zone. The fine root length of the trees decreased by about 35% for grevillea and 65% for senna, because of maize competition, manual weeding, seasonal senescence or pruning regime (senna). At anthesis, the L_rv of maize in the upper 15 cm was between 0.8 and 1.5 cm cm⁻³. Maize root length decreased with greater proximity to the tree rows, potentially reducing its ability to compete for soil resources. However, the specific root length (m g⁻¹) of maize was about twice that of the trees, so may have had a competitive uptake advantage even when tree root length was greater. Differences in maize fine root length and biomass suggest that competition for soil resources and hence fine root length may have been more important for maize grown with senna than grevillea. This revised version was published online in June 2006 with corrections to the Cover Date.     

Localization by restriction fragment length polymorphism mapping in potato of a major dominant gene conferring resistance to the potato cyst nematode Globodera rostochiensis

Summary A major dominant locus conferring resistance against several pathotypes of the root cyst nematode Globodera rostochiensis was mapped on the linkage map of potato using restriction fragment length polymorphism (RFLP) markers. The assessment of resistance versus susceptibility of the plants in the experimental population considered was based on an in vivo (pot) and an in vitro (petri dish) test. By linkage to nine RFLP markers the resistance locus Gro1 was assigned to the potato linkage group IX which is homologous to the tomato linkage group 7. Deviations from the additivity of recombination frequencies between Gro1 and its neighbouring markers in the pot test led to the detection of a few phenotypic misclassifications of small plants with poor root systems that limited the observation of cysts on susceptible roots. Pooled data from both tests provided better estimates of recombination frequencies in the linkage interval defined by the markers flanking the resistance locus.     

Genetic transformation of <Emphasis Type="Italic">Gentiana macrophylla</Emphasis> with <Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis>: growth and production of secoiridoid glucoside gentiopicroside in transformed hairy root cultures

Hairy root cultures of Gentiana macrophylla were established by infecting the different explants four Agrobacterium rhizogenes strains namely A₄GUS, R1000, LBA 9402 and ATCC11325, and hairy root lines were established with A. rhizogenes strain R1000 in 1/2 MS + B₅ medium. Initially, 42 independent hairy root clones were maintained and seven clones belongs to different category were evaluated for growth, morphology, integration and expression of Ri T-DNA genes, and alkaloid contents in dry root samples. On the basis of total root elongation, lateral root density and biomass accumulation on solid media, hairy root clones were separated into three categories. PCR and Southern hybridization analysis revealed both left and right T-DNA integration in the root clones and RT-PCR analysis confirmed the expression of hairy root inducible gene. GUS assay was also performed to confirm the integration of left T-DNA. The accumulation of considerable amounts of the root-specific secoiridoid glucosides gentiopicroside was observed in GM1 ( and ) and the GM2 ( and DNA) type clones in considerably higher amount whether as two but callus-type clones (GM3) accumulated much less or only very negligible amounts of gentiopicroside. Out of four media composition the 1/2 MS + B₅ vitamin media was found most suitable. We found that initial establishment of root cultures largely depends on root:media ratio. Maximum growth rate was recorded in 1:50 root:media ratio. The maximum biomass in terms of fresh weight (33-fold) was achieved in 1/2 MS + B₅ media composition after 35 days in comparison to sixfold increase in control. The biomass increase was most abundant maximum from 15 to 30 days. Influence of A. rhizogenes strains and Ri plasmid of hairy root induction, the possible role of the T_L-DNA and T_R-DNA genes on growth pattern of hairy root, initial root inoculum:media ratio and effect of media composition is discussed.     

色季拉山急尖长苞冷杉叶片及细根性状随海拔的变异特征

叶片和细根是植物对环境变化响应的主要功能器官,在气候变化趋势下,研究其随环境梯度的变化,对理解植物对环境的适应策略具有重要意义。本文是在色季拉山急尖长苞冷杉分布区,按海拔梯度(3800、3900、4000、4100、4200、4300、4400m)选择7个典型样地,在样地内对其叶片基本特征、叶绿素含量、比叶重和细根特征(0—60cm)等参数进行了测量。结果表明:(1)随海拔梯度升高,急尖长苞冷杉叶片叶面积减小、叶片厚度增加、叶绿素含量逐渐降低、比叶重显著增大。3900m处急尖长苞冷杉的叶片形态特征表现最好,叶片长度、宽度和面积均显著优于其他海拔,海拔4200m叶片厚度达到最大值,叶片面积、叶绿素含量随海拔升高呈下降趋势,但在4200m处出现第二峰值。(2)随海拔梯度增加,细根各性状与海拔表现出非线性关系,其中细根生物量和细根体积在3900m和4200m处出现两次峰值,3900m处细根生物量达到最大值,4200m处细根体积达到最大值,4400m处细根生物量和细根体积均显著少于其他海拔。细根根长密度在海拔3900、4200、4300m较高,三者之间差异不显著,但显著高于其余海拔,4400m海拔细根根长密度最小。细根表面积在3900m海拔处达到最大值,显著高于其他海拔,4200和4300m次之,3800、4000和4400m海拔下细根表面积相对较小。4400m处细根比根长达到最大值。各海拔上细根均主要分布在0—20cm土层。随土层厚度增加,各海拔细根生物量和根系体积在0—60cm土层范围内均逐渐减小;细根根长密度、表面积在20—40cm和40—60cm显著提高;同一海拔细根比根长随土层深度增加呈明显的增加趋势。各海拔40—60cm土层细根比根长显著高于20—40和0—20cm土层。(3)综合叶片及细根特征,海拔3900m为急尖长苞冷杉的最适宜生长区域;随海拔升高,环境因子逐渐恶劣,环境胁迫加剧,急尖长苞冷杉最终形成在4400m处为其分布上限的海拔梯度格局。     

Analysis of Root Growth by Impedance Spectroscopy (EIS)

Electrical impedance spectroscopy (EIS) is investigated as a non-destructive method for monitoring root growth of tomato. This paper aims to (i) review the basic principles of EIS applied to the characterisation of the different parts of the soil–root–stem-electrode continuum, (ii) experiment the validity of the relationship between root weight and root capacitance taking into account the influence of the soil and plant electrodes position, (iii) describe an EIS analysis of the root growth of tomato plants. All experiments were carried out in 50 dm³ containers either in hydroponics at 930 μS for the test of root fresh or dry weight and root capacitance relationships, or in a potting mix (oxisol) for electrode placement tests and EIS estimation of root growth. Electrical measurements of the soil–root–stem-electrode continuum were done with a two-electrode measuring system using unpolarisable Ag–AgCl electrodes. A ‘root cutting’ and a ‘progressively immersed root system’ experiments were carried out in order to validate the relationship between root capacitance and root mass at 1 kHz. The effects of soil electrode and plant electrode placement were also tested, pointing out the sensitivity of the method to the insertion height of the “plant electrode” into the stem. For the root growth experiment, Impedance Spectra (IS) measurements were made just before harvesting the roots for dry weight and length determination. Measurements were made 14, 22, 26 and 39 days after planting, until flowering. The IS of the soil–root–stem-electrode continuum was modelled by a lumped electric circuit consisting of a series resistor R ₀ for the soil and of four parallel resistance (R _i )-capacitance (C _i ) circuits for the other components of the circuit. The model had nine parameters whose values were estimated by Complex Nonlinear Least Squares curve fitting. A stepwise ascendant regression was used to identify the electrical parameters that better correlated with root dry mass or length increment: C ₃ and C ₄ were well correlated with root dry mass with a r ² of 0.975, whereas root length was explained by the combination of 1/R ₃, C ₃, 1/R ₂ and 1/R ₁ with a r ² of 0.986. This work may be considered as a new methodological contribution to the understanding of root electrical properties in the non-destructive diagnosis of root systems.