Length Of Root System Research Articles

Nematicidal Activity of Some Biopesticide Agents and Microorganisms Against Root-Knot Nematode on Tomato Plants Under Greenhouse Conditions

A pot experiment was carried out under greenhouse conditions to study the impact of the evaluated treatments namely abamectin, azadirachtin 0.15%, azadirachtin 0.03%, Bacillus subtilis, Pseudomonas fluorescens, Paecilomyces lilacinus and oxamyl against root-knot nematode (Meloidogyne incognita) on the tomato plants cv. Super strain B. The results indicated that the most of the tested treatments obviously reduced root galls and remarkably increase tomato plant growth characters significantly and egg masses on root system, as well as, juvenile's numbers in the soil. P. lilacinus was the most effective treatment on both galls and egg masses achieving 88.23 and 76.94% reduction, respectively. While, less effective treatment was P. fluorescens achieving 57.53% galls reduction. Azadirachtin 0.03% was the least effective treatment giving 40.37% reduction of egg masses. The superior treatment that suppressed nematode populations was oxamyl recording (88.90%) followed by abamectin (78.69%) re- duction. Moreover, azadirachtin 0.15% was the least effective treatment which recorded 60.15% reduction. On the other hand, plants free nematode recorded the highest plant parameters for shoot system length, fresh shoot weight, dry shoot weight and root system length with values of 24.15, 107.53, 211.59 and 46.17% increase, respectively. Azadirachtin 0.15% was the least effective treatment on shoot system length and fresh and dry shoot weight. While, oxamyl recorded the least increase in root system length estimated by 18.47%. B. subtilis recorded the highest increase in fresh root weight followed by P. fluorescens with value of 125.75 and 86.57%, consecutively. Vise versa, P. fluorescens was the superior treatment to increase the dry root weight by 68.14% followed by B. subtilis which recorded 35.40%. The least effective treatment in improving fresh root weight was azadirachtin 0.15% which recorded 54.85% increase. Regarding to dry shoot weight P. lilacinus and azadirachtin 0.15% were the least effective treatments with values of 8.85 and 2.66% reduction, respectively.

Physiological potential of rice seeds treated with rhizobacteria or the insecticide thiamethoxam

Development of new technologies, aiming at increasing productivity in different crops, involves constant research on the effectiveness and application of these techniques in seed treatment. In this study, it was aimed at evaluating physiological potential of rice seeds treated with plant growth-promoting rhizobacteria (PGPR) (strains DFs185, DFs223, DFs306, DFs416), or with two dosages of the insecticide thiamethoxam. The variables assessed were: germination (G); first count of germination (FCG); cold test (CT); length of seedlings aerial parts (LAP), root system (LRS), and total length (TL); emergence speed index (ESI); emergence (E), at 14 days; and dry phytomass (DP). Treatments have had a positive effect on percentage of G, FCG and E. The strain DFs185 has promoted increase in percentage emergence, for five of the six lots assessed. The variables: LAP; LRS; TL; ESI; and DP have undergone low or none influence of treatments; and there has been no toxic effect of rhizobacteria or insecticide thiamethoxam. In the cold test, a negative effect of treatments has been detected. Seed treatment with rhizobacteria, as well as with thiamethoxam, improve quality of low quality rice seeds. The strain DFs185 is promising for treating rice seeds, once it stimulates seed germination and emergence.

Influência da contaminação do solo por cobre no crescimento e qualidade de mudas de açoita-cavalo (<i>Luehea divaricata</i> Mart. & Zucc.) e aroeira-vermelha (<i>Schinus therebinthifolius</i> Raddi)

A contaminação do solo por cobre tem se tornado comum em áreas de mineração e de viticultura no Rio Grande do Sul. O trabalho objetivou avaliar o efeito de doses de cobre sobre o crescimento e qualidade de mudas de açoita-cavalo e aroeira-vermelha. O delineamento foi inteiramente casualizado num fatorial (2 x 5), sendo as duas espécies florestais e cinco doses de cobre: 0, 64, 128, 192 e 256 mg kg-1 de solo, com cinco repetições. Avaliaram-se altura da planta, diâmetro do colo, peso da matéria seca radicular e da parte aérea, comprimento e área superficial específica radicular, e os índices de qualidade de mudas: relação entre altura da parte aérea e diâmetro do coleto; altura da parte aérea e peso da matéria seca da parte aérea e o Índice de Qualidade de Dickson. Os resultados revelaram que as doses testadas de cobre não alteraram a qualidade de mudas de aroeira-vermelha, enquanto que o açoita-cavalo apresentou melhor qualidade com aplicação de 64 mg kg-1 de Cu. O cobre afeta primeiramente o sistema radicular das mudas de açoita-cavalo e aroeira-vermelha. A aroeira-vermelha é mais tolerante a elevadas doses de cobre do que o açoita-cavalo.

Nível crítico de toxidez do ácido acético em culturas alternativas para solos de várzea

A deficiente drenagem natural dos solos de várzea proporciona um ambiente anaeróbico, favorecendo a formação de substâncias tóxicas, como o ácido acético, que afeta o desempenho de espécies de sequeiro nesses ecossistemas. O presente estudo foi conduzido com os objetivos de avaliar os efeitos e estabelecer os níveis críticos de toxidez do ácido acético para culturas de sequeiro alternativas para solos de várzea, como o milho, a soja e o sorgo. Os tratamentos constaram de seis doses de ácido acético, entre zero e 8mM, para milho (Embrapa BRS 1001) e sorgo (BRS 307), e quatro doses entre zero e 4mM, para soja (Embrapa BRS 133), com seis repetições, em delineamento completamente casualizado. Os indicadores avaliados foram os parâmetros morfológicos do sistema radicular (comprimento, raio, área e massa seca relativas) e concentração de N, P, K, Ca e Mg e massa seca relativa da parte aérea das plantas. O ácido acético foi tóxico para as culturas do milho, da soja e do sorgo, causando reduções no comprimento, na área e na massa seca radicular e na massa seca e na concentração de N, P, K, Ca e Mg da parte aérea. As concentrações de ácido acético responsáveis pela inibição de 50% do comprimento radicular relativo foram de 2mM para a soja e 2,7mM para o milho e o sorgo.

Zein-based Bioplastic Containers Alter Root-zone Chemistry and Growth of Geranium

Abstract Bioplastic containers made from zein, a protein from corn (Zea mays L.), have been developed but not evaluated as alternatives to conventional, petroleum-based plastics. We tested the hypothesis that biodegradation of zein containers provides nitrogen (N) that promotes growth of plants and examined whether plants grown in zein containers could be transplanted successfully without removing the container, thus eliminating the need to dispose of containers. Zein containers provided root zones of geranium (Pelargonium ×hortorum L.H. Bailey) with up to 298 and 277 mg·kg−1 of NH4+-N and NO3−-N, respectively, and unlike geraniums in conventional plastic containers, leaves of plants in zein containers remained dark green when produced without fertilization. Electrical conductivity and pH of the substrate in zein containers increased above ranges recommended for many horticultural crops, and NO2−, which can be toxic to plants, was present in the substrate. These chemical changes may have been responsible for reduced canopy height and width, surface area of selected leaves, length of root systems, and dry weight of shoots of geraniums in zein containers compared with geraniums in conventional plastic containers. In a second experiment, when geraniums were transplanted without removing zein containers, growth of roots and shoots was reduced until after six weeks, when biodegradation of containers was nearly complete, and extension of roots past the zone of the degraded container was documented approximately 12 weeks after transplanting. Geraniums can be produced and transplanted in containers made from zein, but additional research must solve problems that result from altered root-zone chemistry during production and from chemical and physical impediments that delay transplant success.

RESEARCH REGARDING THE PROPAGATION OF SOME DECIDUOUS SHRUBS USED FOR GREEN FANCES

,The research where carried out in the greenhouse experimental plots afferent to the Flower and Arboriculture Department, Faculty of Horticulture, University of Agricultural Science and Veterinary Medicine Cluj-Napoca The biological material taken into study was represented by cuttings provided by species Buxus sempervirens, Ligustrum vulgare and Ligustrum ovalifolium var. aureo-variegata. The cuttings have been collected after the green fence cuts made in the USAMV Park Cluj-Napoca. The experimental factors where: root substrate (Perlit 100%, Perlit 50% + Peat 50%), used species (Buxus sempervirens, Ligustrum vulgare, Ligustrum ovalifolium var. aureo-variegata), rooting regulator: Radistim 2. The tree factors where divided in tree repetitions. During the experiment the following observations where made: length of cuttings (cm), no. of leafs, diameter at the cutting base (mm), no. of nodes, no. of cuttings with root system, no. of roots/cutting, the length of the root (cm), the length of the root system (cm). Before root beginning at each species where made the following determinations: origin of the cuttings, length (cm), and no. of leafs, diameter at the base of cutting, no. of nodes. The main characteristics of the cuttings taken into study are in concordance with each species studied.

Crescimento inicial de mudas de turco sob diferentes tipos de recipientes e níveis de luminosidade

Currently the global concern with the ambient quality, has grown the demand of services and products in relation to the production of forest seedlings,  aiming at reclamation of degraded areas. The success of reforestation program depends on choice of the species to be planted, as well as of the quality of the produced seedlings. In this direction, the study was conducted with the objective to evaluate the effect of different recepients and levels of luminosity in the production of Parkinsonia aculeata seedlings. The used delineation was entirely randomized, the treatments of luminosity, in two levels (full sun and 75% shading) and pots (plastic bag and plastic tube) with 4 repetitions. The seeds were sown manually, distributing three per container. The used substrate was plantmax, combined with organic manure and soil, in 2:1:1 ratio. The evaluated parameters were: aerial part height, stem diameter, root length, root and aerial part dry weight. the seedlings increased growth height and length of root system under shade. In general way, the seedlings developed better when produced in the combination of plastic bags without shade.

Impact of salt stress on the features and activities of root system for three desert halophyte species in their seedling stage

Linkage between belowground and aboveground sections of ecological system is mainly depending on root system. But root system is the parts of plant that people less understand. The absorption function of root system is closely related to their morphology and activity. Moreover root system can interact with the environmental stress under the adverse situation, and adjust its system to take adaptation responses in morphology and physiology to strengthen its survival chance. This research is focused on three desert halophyte species of H. ammodendron (C.A.Mey.) Bge., S. physophora Pall., and S. nitraria Pall. under solution culture, to study the differences of their root system morphology and activity in the seedling stage under varying salt concentration conditions. The study results show that: A certain salt concentration can promote development of these three halophytes; but rather high salt concentration will restrain their growth, in particular inhibit the root system development. Under the same salt concentration condition, S. nitraria Pall. grows fast and accumulates the largest amount of biomass. Under relatively low salt concentration, the length of axial root and the total length of root system of these three halophyte species are all increased; and compared to the checking samples, S. physophora Pall. occupies the top place of root system growth, but the high salt concentration will restrain the increase of total root length; among them, the impact intensity on S. physophora Pall. is lighter than to H. ammodendron (C.A.Mey.) Bge. and S. nitraria Pall. is lighter; the salinity does not bring distinct influence on the average diameter of root system of these three plant species, but trends to reducing the size; under the solution culture conditions, the middle and lower parts of the axial root of H. ammodendron (C.A.Mey.) Bge. and S. physophora Pall. are rather equally distributed, but the central zone of S. nitraria Pall. root system is more significantly increased than the upper and lower zones; salt concentration does not bring significant impact on the root system spatial distribution of each species. The root activity of the three plants is increased along with the increase of the salt concentration. When the salt concentration is low, the root activity is not significantly increased; but when the salt concentration is high, the root activity is increased significantly. The experimental results show that the saline tolerance capacity of H. ammodendron (C.A.Mey.) Bge. is lower than the other two species, and the capacity of S. physophora Pall. ranks the top place.

Variation in xylem structure and function in roots and stems of scion–rootstock combinations of sweet cherry tree (Prunus avium L.)

To assess hydraulic architecture and limitations to water transport across scion–rootstock combinations (Prunus avium L. cultivar Van grafted on five differing size-controlling rootstocks: P. avium (vigorous) > CAB 11E > Maxma 14 > Gisela 5 > Edabriz (dwarfing)), we compared xylem anatomy, and calculated relative hydraulic conductivity (RC) and vulnerability index (VI) of roots (small, medium and large diameter) and stems. Water relations, leaf gas exchange and variations in growth were also determined. Roots exhibited larger-diameter xylem conduits (VD), greater RC and VI than stems in all Van–rootstock combinations. Moreover, there was a significantly higher vessel frequency (VF), lower VD, RC and VI in dwarfed trees, especially grafted on Gisela 5 than trees on the invigorating rootstocks, P. avium L., CAB 11E and Maxma 14. Anatomical constraints on water status imposed by the smaller VD (and/or in lower xylem thickness and root system length) of dwarfed trees imply a series of negative feedbacks, like a decrease in RC, stem water potential, leaf gas exchange and growth. On the other hand, Van grafted on CAB 11E and Maxma 14, with wide vessels and high VI, could be more susceptible to embolism, especially during periods of severe water stress, than trees on dwarfing rootstocks, which had small vessels and low VI.

Crescimento de raízes dos capins aruana e tanzânia submetidos a duas doses de nitrogênio

Foram avaliadas características do sistema radicular (pré e pós-pastejo) dos capins aruana e tanzânia submetidos a doses de nitrogênio (150 e 300 kg ha-1 de N) e pastejados por ovinos em lotação rotacionada com três a sete dias de pastejo e período de descanso variável. O delineamento experimental foi o de blocos completos casualizados (dois) com duas repetições, em esquema de parcelas subdivididas (parcelas =capins e subparcelas=doses de N) e medidas repetidas no tempo. No pré-pastejo, o capim-tanzânia, na média entre doses de N e períodos de pastejo, apresentou maior quantidade de massa seca da matéria orgânica (MSMO) (1,7 mg cm-3 de solo) que o capim-aruana (1,2 mg cm-3 de solo), além de maior comprimento de raízes (119,1 cm cm-3 de solo e 68,7 cm cm-3 de solo, respectivamente). A dose de 300 kg ha-1 de N contribuiu para maior comprimento do sistema radicular (107,1 cm cm-3 de solo) que a dose de 150 kg ha-1 de N (80,7 cm cm-3 de solo). O crescimento radicular pós-pastejo demonstrou similaridade de comportamento entre as variáveis mensuradas, de modo que o crescimento de raízes se tornou mais evidente após a segunda semana de rebrotação. Na média de capins, doses de N e idades de crescimento, no período equivalente ao outono/inverno, o crescimento de raízes (em MSMO foi de 3,9 mg 100 cm-3) aumentou para 12,9 mg 100 cm-3 no inverno, caiu para 4,7 mg 100 cm-3 na primavera e elevou novamente para 17 mg 100 cm-3 no verão. Comportamento semelhante foi observado para comprimento e superfície de raízes, coincidindo os períodos de maior crescimento com os de maior pluviosidade. A dose de 150 kg ha-1 de N promoveu maior crescimento em comprimento e superfície de raízes que a dose de 300 kg ha-1 de N nos períodos de maior pluviosidade.

Characterization of Root Systems with Respect to Morphological Traits and Nitrogen-Absorbing Ability in the New Plant Type of Tropical Rice Lines

ABSTRACT The objective of this study was to characterize the root systems of the new plant type (NPT) of tropical rice (Oryza sative (L)) lines compared with the root system of IR72, one of the elite modern varieties. Two field experiments were conducted to observe plant growth under canopy conditions in the 1997 and 1998 wet seasons. In addition, a pot experiment was conducted in the 1998 dry season to observe plant growth under isolated conditions. The root systems of the NPT lines were characterized by roots heavier than those of IR72. The larger root dry weight (DW) is attributed partly to a genetically determined high root/shoot ratio because, irrespective of growth conditions, the ratio was larger in the NPT lines than in IR72. An increase in root DW was accompanied by an increase in the length of the whole root system, including fine roots. However, despite the differences between the NPT lines and IR72 in root DW and root length, there were no significant differences in the amount of nitrogen (N) absorbed throughout the growth period. Therefore, the specific absorption rate of N per root DW (SARN, mg N g−1 root DW d−1) was lower in the NPT lines than in IR72. We concluded that, although the root systems of the NPT lines grew prolifically, they were not necessarily more efficient in terms of N absorption compared with the root system of IR72.

Root traits, nutrient uptake, multi-location grain yield and benefit–cost ratio of two lentil (Lens culinaris, Medikus.) varieties

Lentil is a protein-rich pulse, grown mainly in developing countries as a rain-fed crop in nutrient-poor soils. Hence, the importance of root traits for efficient capture of soil nutrients and water can be crucial to its economical yield. Little is known about the lentil root system and even less about its relationship to grain yield. We compared the root system of two Bangladeshi lentil varieties, Barimasur-3 (BM-3) and Barimasur-4 (BM-4), in a pot experiment and related it to their multi-location grain yield in the fields. BM-4 maintained faster root development both at an early growth stage (20 days after sowing) and at flowering (60 days) compared to BM-3. The roots of BM-4 penetrated the 25 cm depth of the soil profile after 19 ± 1 days and while those of BM-3 took 24 ± 2 days to reach the same depth. The roots of BM-4 were covered with denser (26 ± 3 mm−1) and longer (0.48 ± 0.11) root hairs than BM-3 (density 17 ± 2 mm−1, length 0.32 ± 0.09 mm). The differential presence of root hairs increased the effective length of root system of BM-4 by 12 times and that of BM-3 by five times. The lentil varieties did not differ in their ability to induce pH change and acid phosphatase activity in rhizosphere. In the pot experiment, the uptake of macro-nutrients (K, P, Ca, and Mg) as well as micro-nutrients (Fe, Mn, Zn, Cu, B and Mo) by BM-4 was significantly higher, compared to BM-3. The varieties produced the same amount of shoot biomass. At five of six agro-ecological distinct field locations in Bangladesh, BM-4 gave significantly higher (10–20%) grain yield than BM-3. Linked with the higher grain yield, the benefit-cost ratio (BCR) of BM-4 was 3.14 and that of BM-3 were 2.62, indicating that BM-4 provided better return per unit investment, compared to BM-3, supported by the better root morphology and higher nutrient uptake. This may be one of the reasons supporting the popularity and preferred adoption of BM-4 among the Bangladeshi farmers, who grow lentil mainly on nutrient-poor soils. The results indicate the benefits of selection and breeding for superior root traits for better agro-economics.

Quantitative trait loci controlling root growth and architecture in Arabidopsis thaliana confirmed by heterogeneous inbred family

Arabidopsis thaliana provides a scientifically attractive and simple model for studying root growth and architecture and, subsequently, for discovering new genes involved in the control of these characters in plants. We have used the natural variation available in Arabidopsis accessions and mapped quantitative trait loci (QTLs) for primary root length (PRL), lateral root number (LRN) and density (LRD) and for total length of the lateral root system (LRL) in the Bay-0 x Shahdara population. Total phenotypic variation was very large, and despite the importance of the environmental component we were able to map 13 QTLs and one epistatic interaction between QTLs. Our results highlight the biological relevance and genetic control of lateral root density in this material. We were also able to show that variation in the extent of the lateral root system depends mainly on the growth of the existing lateral roots rather than in a change in LRN. Factors controlling lateral root growth seemed to have no major effect on primary root growth. Moreover, Shahdara QTL alleles always increased the length of the lateral roots, which may be taken as an adaptation to its very dry natural environment in Tadjikistan. A QTL for PRL was confirmed using a type of near-isogenic line called a heterogeneous inbred family (HIF), and this QTL is a candidate for further fine-mapping and cloning.

Root Traits Play a Role in Integrated Management of Fusarium Root Rot in Snap Beans

Fusarium root rot is a major limiting factor in snap bean (Phaseolus vulgaris L.) production. The level of genetic resistance in commercial bean cultivars is minimal and disease is frequently exacerbated by environmental factors. We investigated the contribution of vigorous, adventitious roots to enhancing root rot tolerance in snap bean. Seedling root system architecture was evaluated in 17 recombinant inbred lines (RILs) from a cross of a resistant snap bean line (FR266) and a susceptible dry bean cultivar (Montcalm). The RILs varied in tolerance to Fusarium root rot. Although overall length and branching density (as measured by fractal dimension and meristem numbers) of root systems were not related to root rot resistance, the lateral root number at the root: shoot interface was positively correlated with genotype tolerance (R2 = 0.6*). Root diameter was also positively correlated with tolerance; this is consistent with the hypothesis that larger adventitious and basal roots are beneficial under disease stress. A field-based study of commercial snap bean cultivars compared raised and flat-bed systems of production, in a soil inoculated with Fusarium solani f. sp. phaseoli. Substantially greater yields (40% to 90%) were observed in raised beds. Root vigor was relatively high (root length density >0.2 cm·cm−3) and root rot scores were lower with raised than with flat-beds, in 2001, but not in 2000. Overall, this is suggestive that integrated crop management practices can improve lateral root vigor and reduce root rot severity.

Genetic variation for adventitious rooting in response to low phosphorus availability: potential utility for phosphorusacquisition from stratified soils.

We hypothesized that adventitious roots may improve crop adaptation to low-phosphorus soils by enhancing topsoil foraging. In a tropical field study, phosphorus stress stimulated adventitious rooting in two phosphorus-efficient genotypes of common bean (Phaseolus vulgaris L.) but not in two phosphorus-inefficient genotypes. Although phosphorus availability had no consistent effects on the length or biomass of whole root systems, it had differential effects on adventitious, basal, and taproots within root systems in a genotype-dependent manner, resulting in increased allocation to adventitious roots in efficient genotypes. Adventitious roots had greater length per unit biomass than other root types, especially under phosphorus stress. Adventitious roots had less construction cost than basal roots, despite having similar tissue nitrogen content. Phosphorus stress reduced lateral root density, and adventitious roots had less lateral root density than basal roots. Lateral roots formed further from the root tip in adventitious roots compared with basal roots, especially under phosphorus stress. Field results were confirmed in controlled environments in solid and liquid media. Stimulation of adventitious rooting by phosphorus stress tended to be greater in wild genotypes than in cultivated genotypes. We propose that adventitious rooting is a useful adaptation to low phosphorus availability, because adventitious roots explore topsoil horizons more efficiently than other root types.

Nutrição mineral de mudas de grápia (Apuleia leiocarpa) em ARGISSOLO VERMELHO distrófico arênico: (1) Efeito da dubaçio NPK no crescimento

A grápia (Apuleia leiocarpa Vog. Macbride) é uma espécie de grande interesse madeireiro, encontrando-se, atualmente, bastante dizimada devido â exploração extrativista, sem haver reposição através de reflorestamento. O objetivo deste trabalho foi deter,ninar os níveis de adubação nitro genada, fosfatada e potássica no crescimento de plantas jovens de grdpia. As plantas foram cultivadas em vasos contendo 3,5kg de um ARGISSOLO VERMELHO Distróflco arênico, em casa de vegeta çtlo. Foram avaliados 27 tratamentos, em esquema trifatorial completo (3x3x3), representados pela combinação de três níveis (0, 40 e 8Omg kg') de N, de P e de K na adubação. A análise do crescimento das plantas foi realizada mensalmente, através da altura da planta, di~2metro do caule e número de folhas remanescentes. Aos 140 dias após a emergência das plantas, avaliaram-se ainda o comprimento do sistema radicular, massa seca das folhas, do caule, de raízes e total da planta e a relação entre a massa seca das raízes e da parte aérea. A aduba ção fosfatada aumenta o crescimento das plantas em todos os pani metros avaliados, sendo que as maiores respostas, exceto para o comprimento do sistema radicular, ocorrem acima de 8Omg de P k5'. A aplicação de K em doses superiores a áOmg kg', influencia positivamente o comprimento do sistema radicular, ndmero de folhas, altura da planta e massa seca da folha, do caule e total da planta. Por Outro lado, não altera o didmetro do caule, massa seca da raiz e a relação entre a massa seca das raízes e da parte aérea. O efeito benéfico da adubação nitrogenada, quanto ào comprimento do sistema radicular, número de folhas, altura de planta, massa seca de folhas e total da planta, é condicionada à aplicação conjunta de K. A grdpia demonstra ser uma espécie muito exigente em P e medianamente exigente em K e N na fase inicial de crescimento, quando cultivada num ARGJSSOLO VERMELHO Distrtiflco arênico.

Linking Hydraulic Conductivity to Anatomy in Plants that Vary in Specific Root Length

In Citrus L. sp., specific root length of whole root systems has been correlated positively with root hydraulic conductivity, but there is little mechanistic understanding of the causes for this association. The hydraulic conductivity of individual roots in relation to root anatomical characteristics in seedlings of three citrus rootstocks [sour orange (SO) (Citrus aurantium L.), trifoliate orange (TO) (Poncirus trifoliate (L.) Raf.), and Swingle citrumelo (SC) (C. paradisi Macf. × P. trifoliata)] that vary widely in specific root length (SRL) was measured. Among fibrous roots, first-order and secondorder laterals were examined. Relative differences among rootstocks in the overall hydraulic conductivity (LP) and radial conductivity (LR) for individual 1-month-old and 6-month-old second- and first-order roots generally were consistent with hydraulic conductivity determined previously for entire root systems. There were no significant differences in axial conductance per unit pressure (Kh) in either first- or second-order roots among the rootstocks. This was consistent with the similarity in number and diameter of xylem vessels. One-month-old second-order roots had no suberized exodermis but varied in cortical radius. Six-month-old second-order roots of TO, however, had more nonsuberized cells (passage cells) in the exodermis than roots of SC and SO, although the cortical radius of SC and SO roots were not different. Compared to 6-month-old second-order roots, 1-month-old second-order roots had much higher LP and LR but lower Kh. Differences in overall root hydraulic conductivity among the citrus rootstocks were mainly related to structural differences in the radial pathway for water movement, suggesting that radial hydraulic conductivity was the primary determining factor of water uptake in citrus rootstocks.

Genotypic Variations in Response of Lateral Root Development to Fluctuating Soil Moisture in Rice

Developmental plasticity in lateral roots may be one of the key traits for the growth of rice plants under soil moisture fluctuations. We aimed to examine responses in seminal root system development to changing soil moisture for diverse rice cultivars. Special attention was paid to the two different types of lateral roots ; the generally long, thick L type capable of branching into higher orders, and the non-branching S type. Plants were grown in half-split polyvinyl chloride tubes fixed with transparent acrylic plate for root observation under glasshouse conditions. When plants were grown first under drought conditions, then rewatered, the seminal root system development in terms of dry weight and total length was promoted as compared with plants grown under continuously well-watered conditions in IR AT 109 and Dular, drought tolerant cultivars. Promoted production of L type lateral roots mainly contributed to the development of the longer seminal root system. Plants exposed to soil submergence before they were grown under drought conditions did not show such promoted responses in these two cultivars. However, in KDML 105, a drought tolerant cultivar, the production of especially L type laterals was substantially promoted under drought and rewatered conditions. Honenwase was characterized by the shallow root system and great reduction in root system length when soil moisture becomes limited. These facts show that genotypic variations exist in the plastic response of rice seminal root system and that the L type lateral root plays a key role in manifestation of this plasticity.

Constraints on the assembly of cliff communities at the seedling stage

Seedling establishment of woody species was examined to determine whether this stage was an important filter, removing species from the pool of potential colonists on cliff faces. Earlier studies had already explored the roles of seed rain and seed bank as regulators of community structure. In this study, newly germinated seeds of seven tree species were planted in crevices and on ledges of natural cliff faces and were censused regularly for three years. When harvested, seedling roots and shoots were measured and dry weights taken. The study was also repeated on artificial cliffs constructed of limestone blocks in order to observe rooting characteristics. On the natural cliffs, Thuja occidentalis generally survived better than Pinus strobus, Picea glauca, Larix laricina, Betula papyrifera and B. alleghaniensis. The latter two were not planted until the second year of the experiment and survived into their second year. These results were similar to those in the artificial cliff experiments. There were several root and shoot characteristics and biomass allocation patterns that were associated with Thuja. Seedlings were shorter and had extensive root systems, but their root:shoot ratios were 1:2. They were able to maximize the length of root systems, but minimized biomass allocation to the roots. Seedlings of Betula papyrifera, which are also present occasionally on cliff faces, were also short and with extensive root systems. These results suggest that seedling establishment is an important process determining community composition on cliffs of the Niagara Escarpment, but that the process is protracted over several years. Seedlings of many species are able to survive for one year; following this, however, there is a gradual decline in survivorship.

Dynamic phenotypic plasticity for root growth inPolygonum: a comparative study

Species differences in patterns of phenotypic plasticity may be an important aspect of adaptive diversity. Plasticity for functionally important root traits was studied in inbred field lineages of Polygonum persicaria and P. cespitosum (Polygonaceae). Replicate seedlings were grown in plexiglass rhizotrons under a range of constant and temporally variable moisture treatments. Plasticity was determined for final whole-plant biomass, root biomass allocation, and absolute and proportional root length. The dynamic aspect of root plasticity was examined by digitizing weekly tracings of the proportional deployment of each plant's root system to different vertical soil layers. Plants of both species expressed significant functionally adaptive phenotypic plasticity in the relative allocation, length, and vertical deployment of root systems in response to contrasting moisture conditions. Plasticity patterns in these closely related species were in general qualitatively similar, but for most traits differed in the magnitude and/or the timing of the plastic response. Dynamic changes in root deployment were more marked as well as faster in P. persicaria. Species differences in patterns of individual plasticity were generally consistent with the broader ecological distribution of P. persicaria in diverse as well as temporally variable moisture habitats.