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1.
Unusual Fine Root Distributions of Two Deciduous Tree Species in Southern France: What Consequences for Modelling of Tree Root Dynamics? 总被引:3,自引:0,他引:3
The spatial distribution of fine roots of two deciduous tree species was investigated in contrasting growing conditions in
southern France. Hybrid walnut trees (Juglans regia×nigra cv. NG23) and hybrid poplars (Populus euramericana cv. I214) were both cultivated with or without annual winter intercrops for 10 years on deep alluvial soils. Soil samples
for measuring the fine root distribution of both trees and crops were obtained by soil coring down to 3-m depth at several
distances and orientations from the tree trunk. The distribution of live fine roots from walnut and poplar trees was patchy
and sometimes unexpected. In the tree-only stands, fine root profiles followed the expected pattern, as fine root density
decreased with increasing depth and distance from the tree trunk. However, many fine root profiles under intercropped trees
were uniform with depth, and some inverse profiles were observed. These distributions may result from a high degree of plasticity
of tree root systems to sense and adapt to fluctuating and heterogeneous soil conditions. The distortion of the tree root
system was more pronounced for the walnut trees that only partially explored the soil volume: in the tree-only stand, the
walnut rooting pattern was very superficial, but in the intercropped stand walnut trees developed a deep and dense fine root
network below the crop rooting zone. The larger poplars explored the whole available soil volume, but the intercrop significantly
displaced the root density from the topsoil to layers below 1 m depth. Most tree root growth models assume a decreasing fine
root density with depth and distance from the tree stem. These models would not predict correctly tree–tree and tree–understorey
competition for water and nutrients in 3D heterogeneous soil conditions that prevail under low-density tree stands. To account
for the integrated response of tree root systems to such transient gradients in soils, we need a dynamic model that would
allow for both genotypic plasticity and transient environmental local soil conditions. 相似文献
2.
Fine root architecture, morphology, and biomass of different branch orders of two Chinese temperate tree species 总被引:8,自引:0,他引:8
We have limited understanding of architecture and morphology of fine root systems in large woody trees. This study investigated architecture, morphology, and biomass of different fine root branch orders of two temperate tree species from Northeastern China—Larix gmelinii Rupr and Fraxinus mandshurica Rupr —by sampling up to five fine root branch orders three times during the 2003 growing season from two soil depths (i.e., 0–10 and.10–20 cm). Branching ratio (R
b) differed with the level of branching: R
b values from the fifth to the second order of branching were approximately three in both species, but markedly higher for the first two orders of branching, reaching a value of 10.4 for L. gmelinii and 18.6 for F. mandshurica. Fine root diameter, length, SRL and root length density not only had systematic changes with root order, but also varied significantly with season and soil depth. Total biomass per order did not change systematically with branch order. Compared to the second, third and/or fourth order, the first order roots exhibited higher biomass throughout the growing season and soil depths, a pattern related to consistently higher R
b values for the first two orders of branching than the other levels of branching. Moreover, the differences in architecture and morphology across order, season, and soil depth between the two species were consistent with the morphological disparity between gymnosperms and angiosperms reported previously. The results of this study suggest that root architecture and morphology, especially those of the first order roots, should be important for understanding the complexity and multi-functionality of tree fine roots with respect to root nutrient and water uptake, and fine root dynamics in forest ecosystems. 相似文献
3.
Natural root grafting has been observed in more than 150 tree species where up to 90 % of trees could be interconnected within a stand. Intraspecific root grafting was previously found in Pinus banksiana stands, ranging from 21 to 71 % of trees grafted with one another. It is not known why root grafting is frequent in some species and not in others, or why not all roots that cross form root grafts. We investigated genetic diversity of grafted and non-grafted trees to determine if there was a relationship between genetic distance and the probability of forming natural root grafts. Seven plots were hydraulically excavated in four natural forest stands and three plantations of P. banksiana in the western boreal forest of Quebec, Canada. At pairs scale, we studied the effect of geographic and genetic distances on root grafting occurrence. At stand level, we analysed the effect of tree density, soil type, stand type and mean pairwise relatedness on the mean number of grafts per tree and on the percentage of grafted trees per plot. At pairs scale, our analysis revealed that root grafting presence was influenced by spatial distance between trees and less importantly, by genetic distance between individuals. At stand level, root grafting frequency was correlated with stand type (greater in naturally regenerated stands), but not with genetic diversity between individuals. In conclusion, root grafting appears to be principally linked to tree proximity and slightly to genetic proximity between individuals. 相似文献
4.
A Dehesa is a structurally complex agro-silvo-pastoral system where at least two strata of vegetation, trees and herbaceous
plants coexist. We studied the root distribution of trees (Quercus ilex L.) and herbaceous plants, in order to evaluate tree and crops competition and complementarity in Dehesas of Central Western
Spain. 72 soil cores of 10 cm diameter (one to two metre deep) were taken out around 13 trees. Seven trees were intercropped
with Avena sativa L. and six trees were in a grazed pasture dominated by native grasses. Soil coring was performed at four distances from the
tree trunks, from 2.5 (beneath canopy) till 20 m (out of the canopy). Root length density (RLD) of herbaceous plants and trees
was measured using the soil core-break method. Additionally, we mapped tree roots in 51 profiles of 7 recently opened road
cuts, located between 4 and 26 m of distance from the nearest tree. The depth of the road cuts varied between 2.5 and 5.5 m.
Herbaceous plant roots were located mostly in the upper 30 cm, above a clayey, dense soil layer. RLD of herbaceous plants
decreased exponentially with depth until 100 cm depth. Holm-oak showed a much lower RLD than herbs (on average, 2.4 versus 23.7 km m−3, respectively, in the first 10 cm of the soil depth). Tree RLD was surprisingly almost uniform with depth and distance to
trees. We estimated a 5.2 m maximum depth and a 33 m maximum horizontal extension for tree roots. The huge surface of soil
explored by tree roots (even 7 times the projection of the canopy) could allow trees to meet their water needs during the
dry Mediterranean summers. The limited vertical overlap of the two root profiles suggests that competition for soil resources
between trees and the herbaceous understorey in the Dehesa is probably not as strong as usually assumed. 相似文献
5.
A. Singh M. S. Negi V. K. Moses B. Venkateswarlu P. S. Srivastava M. Lakshmikumaran 《In vitro cellular & developmental biology. Plant》2002,38(5):519-524
Summary The importance of neem (Azadirachta indica A. Juss.) as a medicinal tree species has been acknowledged worldwide. Superior trees with desired traits such as high azadirachtin
content have been identified and micropropagated. Somaclonal variants that may arise in vitro, however, pose limitations to large-scale micropropagation. It is, therefore, imperative to establish genetic uniformity
of such plantlets by ensuring strict quality checks at various stages of in vitro culture. This is the first study that evaluates the applicability of amplified fragment length polymorphism (AFLP) markers
in establishing clonal fidelity of tissue culture(TC)-raised neem plants. Seven AFLP primer combinations generated a total
of 334 amplified fragments across the mother plant, TC progenies, and other neem accessions that were included as controls.
Two hundred and thirty-nine amplified fragments were monomorphic across the mother tree and its TC progenies. No extra band
was detected in the TC plantlets that was absent in the mother tree, indicating that the TC plantlets regenerated through
nodal explants are indeed true-to-type. Ninety-five AFLP fragments were detected in the controls, which allowed their discrimination
from the elite mother tree and its TC progenies. Similarity matrix based on Jaccard's coefficient revealed that the pair-wise
value between the mother tree and its TC plantlets was ‘1’, indicating perfect similarity. Phenetic dendrogram based on UPGMA
(unweighted pair group method of arithmetic averages) analysis further confirmed the true-to-type nature of TC progenies,
since a tie was observed between the mother tree and its TC plantlets. On the contrary, the control neem accessions were distinct
from the mother and its TC progenies. AFLP markers proved to be an ideal tool for routine analysis and certification of genetic
fidelity of micropropagated plants prior to commercialization, especially in tree species because of their long generation
time. 相似文献
6.
With the completion of the poplar tree genome database, Populus species have become one of the most useful model systems for the study of woody plant biology. Populus tremuloides (quaking aspen) is the most wide-spread tree species in North America, and its rapid growth generates the most abundant wood-based
biomass out of any other plant species. To study such beneficial traits, there is a need for easier and more efficient transformation
procedures that will allow the study of large numbers of tree genes. We have developed transformation procedures that are
suitable for high-throughput format transformations using either Agrobacterium tumefaciens to produce transformed trees or Agrobacterium rhizogenes to generate hairy roots. Our method uses Agrobacterium inoculated aspen seedling hypocotyls followed by direct thidiazuron (TDZ)-mediated shoot regeneration on selective media.
Transformation was verified through β-glucuronidase (GUS) reporter gene expression in all tree tissues, PCR amplification
of appropriate vector products from isolated genomic DNA, and northern hybridization of incorporated and expressed transgenes.
The hairy root protocol follows the same inoculation procedures and was tested using GUS reporter gene integration and antibiotic
selection. The benefit of these procedures is that they are simple and efficient, requiring no maintenance of starting materials
and allowing fully formed transgenic trees (or hairy roots) to be generated in only 3–4 months, rather than the 6–12 months
required by more traditional methods. Likewise, the fact that the protocols are amenable to high-throughput formats makes
them better suited for large-scale functional genomics studies in poplars. 相似文献
7.
Competition in tree row agroforestry systems. 1. Distribution and dynamics of fine root length and biomass 总被引:4,自引:0,他引:4
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 (Lrv) 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 Lrv of senna decreased at every depth during the cropping season, whereas the Lrv 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 Lrv 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. 相似文献
8.
Root deformation in plantations of container-grown Scots pine trees: effects on root growth,tree stability and stem straightness 总被引:4,自引:0,他引:4
Root system deformation was studied in 23 Scots pine (Pinus sylvestris L.) stands in central Sweden. The study comprised both
plantations created with container-grown plants (Paperpot) and natural stands including young (7–9 year old) and older (19–24
year old) trees. Trees were measured with regards to distribution of roots, root deformation, stability, stem straightness
and wood properties in stumps. Root distribution was most uniform for naturally regenerated trees. Older trees generally showed
a better root distribution than young trees. The young planted trees displayed a high frequency of severely spiralled root
systems, while only a few of the older trees had spiralled root systems. No severe root deformations were observed on naturally
regenerated trees. Naturally regenerated trees were more stable than those which had been planted. Differences in bending
moment, when trees were pulled to an angle of 10°, were considerable between young planted and naturally regenerated trees,
but less pronounced for the older trees. Young planted trees had the highest frequency of severely crooked stem bases, while
naturally regenerated trees had the straightest mode of growth. Tensile strength in peripheral wood samples of the stumps
was substantially lower for planted than for naturally regenerated trees. Strain values to breakage of wood samples, taken
from the root collar and the central- and peripheral part of the stump were lower for planted trees. The conclusions from
this study are that root distribution, tree stability and stem straightness of planted Paperpot-grown trees will improve after
a certain time and approach the state of naturally regenerated trees. As trees grow older, early established crooked stem
bases will be compensated by radial growth and the tree will appear straighter. Inside the stem, however, problems may still
remain with abnormal fibre direction and compression wood together with inferior root strength due to fibre disturbances as
a result of spiralled roots.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
Partitioning of soil phosphorus among arbuscular and ectomycorrhizal trees in tropical and subtropical forests
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Xubing Liu David F. R. P. Burslem Joe D. Taylor Andy F. S. Taylor Eyen Khoo Noreen Majalap‐Lee Thorunn Helgason David Johnson 《Ecology letters》2018,21(5):713-723
Partitioning of soil phosphorus (P) pools has been proposed as a key mechanism maintaining plant diversity, but experimental support is lacking. Here, we provided different chemical forms of P to 15 tree species with contrasting root symbiotic relationships to investigate plant P acquisition in both tropical and subtropical forests. Both ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) trees responded positively to addition of inorganic P, but strikingly, ECM trees acquired more P from a complex organic form (phytic acid). Most ECM tree species and all AM tree species also showed some capacity to take up simple organic P (monophosphate). Mycorrhizal colonisation was negatively correlated with soil extractable P concentration, suggesting that mycorrhizal fungi may regulate organic P acquisition among tree species. Our results support the hypothesis that ECM and AM plants partition soil P sources, which may play an ecologically important role in promoting species coexistence in tropical and subtropical forests. 相似文献
10.
Roots,soil water and crop yield: tree crop interactions in a semi-arid agroforestry system in Kenya 总被引:4,自引:0,他引:4
Odhiambo H.O. Ong C.K. Deans J.D. Wilson J. Khan A.A.H. Sprent J.I. 《Plant and Soil》2001,235(2):221-233
Variations in soil water, crop yield and fine roots of 3–4 year-old Grevillea robusta Cunn. and Gliricidia sepium (Jacq.) Walp. growing in association with maize (Zea mays L.) were examined in semiarid Kenya during the long rains of 1996 and 1997. Even although tree roots penetrated more deeply than maize roots, maximum root length densities for both tree species and maize occurred in the top 200 mm of the soil profile where soil moisture was frequently recharged by rains. Populations of roots in plots containing trees were dominated by tree roots at the beginning of the growing season but because tree roots died and maize root length increased during the cropping season, amounts of tree and maize roots were similar at the end of the season. Thus, there was evidence of temporal separation of root activity between species, but there was no spatial separation of the rooting zones of the trees and crops within that part of the soil profile occupied by crop roots. Tree root length density declined with increasing distances from rows of trees and with depth in the soil profile. Although Grevillea trees were largest, plots containing G. sepium trees always contained more tree roots than plots containing G. robusta trees and Gliricidia was more competitive with maize than Grevillea. Overall, Gliricidia reduced crop yield by about 50% and Grevillea by about 40% relative to crop yield in control plots lacking trees and reductions of crop yield were greatest close to trees. There was less soil moisture in plots containing trees than in control plots. Such difference between control plots and plots containing trees were maximal at the end of the dry season and there was always less soil moisture close to trees than elsewhere in the plots. Plots containing Gliricidia trees contained less soil water than plots containing Grevillea trees. 相似文献
11.
The rainforest of French Guiana is still largely unaffected by human activity. Various pristine sites like the Paracou Research
Station are devoted to study this tropical ecosystem. We used culture-independent techniques, like polymerase chain reaction-temperature
gradient gel electrophoresis, and construction of clone libraries of partial 16S rRNA and nifH genes, to analyze the composition of the bacterial community in the rhizosphere of mature trees of Eperua falcata and Dicorynia guianensis, both species within the Caesalpiniaceae family. E. falcata is one of the more abundant pioneer tree species in this ecosystem and so far, no root nodules have ever been found. However,
its nitrogen-fixing status is regarded as “uncertain”, whereas D. guianensis is clearly considered a non-nitrogen-fixing plant. The rhizospheres of these mature trees contain specific bacterial communities,
including several currently found uncultured microorganisms. In these communities, there are putative nitrogen-fixing bacteria
specifically associated to each tree: D. guianensis harbors several Rhizobium spp. and E. falcata members of the genera Burkholderia and Bradyrhizobium. In addition, nifH sequences in the rhizosphere of the latter tree were very diverse. Retrieved sequences were related to bacteria belonging
to the α-, β-, and γ-Proteobacteria in the E. falcata rhizoplane, whereas only two sequences related to γ-Proteobacteria were found in D. guianensis. Differences in the bacterial communities and the abundance and diversity of nifH sequences in E. falcata rhizosphere suggest that this tree could obtain nitrogen through a nonnodulating bacterial interaction. 相似文献
12.
Referee: Dr. Dean A. Martens, USDAARS Southwest Watershed, Research Center, 200 E. Allen Road, Tucson, AZ 85719 Phytoremediation is the use of plants to remove, contain, or render harmless environmental pollutants. In recent years, much attention has been focused on the improvement of such technologies for this purpose. In this review, we introduce selenium phytoremediation and describe the attempts made to enhance it through genetic engineering. Initial efforts have taken advantage of the knowledge of the enzymatic pathways for selenium assimilation and volatilization, especially by overexpressing genes of rate-limiting enzymes in plants. Another possible approach is to introduce additional metabolic pathways from selenium hyperaccumulators or organisms other than plants that can help detoxify selenium compounds. In this way the capacity of plants to take up, accumulate, and volatilize compounds can be increased beyond that of any naturally occurring plant species. Here we report on the progress that has been made in overexpressing potentially important enzymes involved in the selenium/sulfur pathways and discuss possible future directions in the enhancement of phytoremediation through genetic engineering. 相似文献
13.
Forest die-back and impaired tree vitality have frequently been ascribed to Al-toxicity and Al-induced nutritional disorders
due to increased acidification of forest soils. Therefore, in this experiment effects of Al were studied on growth and nutrient
uptake with seedlings of five different forest tree species. During growth in culture solutions with and without Al all five
species proved to be very Al-tolerant, despite high accumulation of Al in roots. In the coniferous evergreens Douglas-fir
and Scots pine shoot as well as root Al concentrations were significantly higher than in the deciduous broad-leaved species
oak and birch. Larch showed intermediate Al levels.
In none of the five species did Al reduce nutrient concentrations or the Ca/Al ratio to values below the critical level. Besides
differences in Al accumulation, coniferous and broad-leaved species also differed with respect to uptake and assimilation
of nitrogen. Due to extra NH
4
+
uptake, oak and birch showed a much higher N uptake and higher NH
4
+
preference than the coniferous species. Especially with oak this high NH
4
+
preference in combination with a low specific root surface area resulted in a high root proton efflux density. In comparison
to both broad-leaved trees and Scots pine the NO
3
−
reduction capacity of larch and Douglas-fir was extremely low. This may have important consequences for both species if grown
in NO
3
−
-rich soils. 相似文献
14.
Transgene integration and inheritance have been investigated in a number of crop plants and few tree species. Transgene integration is predominantly a random process, whether mediated by Agrobacterium or particle bombardment. Depending on the genomic position of the integrated transgene and structure of the integration site as well as copy number of the transgene in the genome, its expression may be stable or variable. Therefore, integration patterns would affect the mode of transgene inheritance in plants, regardless of the method of gene transfer. So far, both Mendelian and non-Mendelian inheritance of transgenes has been reported across several generations (T1–T3) of crop plants. In few tree species (apple, poplar, plum, and American chestnut), mostly Mendelian inheritance of the transgenes has been observed in the T1 or BC1 generations. However, detailed studies in the transgenic papaya trees showed Mendelian segregation of the transgene in the T1 generation but non-Mendelian inheritance in the T2 generation. Variation in transgene inheritance was also detected in transgenic apple and plum trees. Long generation cycles in many economically important tree species preclude investigation of inheritance of transgenes in the tree progeny. Production of early flowering trees, either by genetic modification or by environmental modulation, would facilitate the study of transgene inheritance across generations of transgenic trees. In order to overcome problems of randomness of transgene integration, targeted transgene insertions by homologous or site-specific recombination or by designer recombinases or nucleases offer prospects for stable integration of transgenes in predetermined locations in the plant genome. And perhaps, that might provide a platform for stable expression and Mendelian inheritance of transgenes in plants. 相似文献
15.
Ian K. Dawson Peter M. Hollingsworth Jeff J. Doyle Steve Kresovich John C. Weber Carmen Sotelo Montes Terrence D. Pennington R. Toby Pennington 《Conservation Genetics》2008,9(2):361-372
Hundreds of native tree species are currently found in extensive agroforestry ecosystems in the Peruvian Amazon, forming an
important reservoir of biodiversity. To further promote conservation, farmers are encouraged to supplement intra-specific
genetic diversity in these populations with seed collected from local forests. For some tree species, however, this approach
may be inappropriate, as stands of these taxa already found on-farm may not be of local origin. Despite this issue being of
importance for conservation, little information is available on the history of cultivated trees in the region, a situation
that we here rectify for the important fruit tree Inga edulis. Based on nuclear SSR and chloroplast DHPLC analyses of closely geographically matched natural and planted stands at five
sites, it appears that cultivated material of I. edulis is primarily of non-local origin, indicating that conservation based on new wide-scale infusions from local wild stands into
farms may be inappropriate in the region. Although nuclear and chloroplast diversity were both lower in planted stands, values
were still relatively high (∼80 and 70% of natural stands, respectively), indicating that when farmers plant trees, good collection
practice of seed from already cultivated I. edulis should be an effective means for ensuring long-term conservation on farms. 相似文献
16.
“Hairy root” systems, obtained by transforming plant tissues with the “natural genetic engineer” Agrobacterium rhizogenes, have been known for more than three decades. To date, hairy root cultures have been obtained from more than 100 plant species,
including several endangered medicinal plants, affording opportunities to produce important phytochemicals and proteins in
eco-friendly conditions. Diverse strategies can be applied to improve the yields of desired metabolites and to produce recombinant
proteins. Furthermore, recent advances in bioreactor design and construction allow hairy root-based technologies to be scaled
up while maintaining their biosynthetic potential. This review highlights recent progress in the field and outlines future
prospects for exploiting the potential utility of hairy root cultures as “chemical factories” for producing bioactive substances. 相似文献
17.
Invasive Plants can Inhibit Native Tree Seedlings: Testing Potential Allelopathic Mechanisms 总被引:3,自引:0,他引:3
The mechanisms by which invasive species affect native communities are not well resolved. For example, invasive plants may
influence other species through competition, altered ecosystem processes, or other pathways. We investigated one potential
mechanism by which invasive plants may harm native species, allelopathy. Specifically, we explored whether native tree species
respond differently to potential allelopathic effects of two invasive plant species. We assessed the separate effects of Lolium arundinaceam (tall fescue) and Elaeagnus umbellata (autumn olive) on three common successional tree species: Acer saccharinum (silver maple), Populus deltoides (eastern cottonwood), and Platanus occidentalis (sycamore). Tall fescue and autumn olive are widely planted and highly invasive or persistent throughout North America where
they often grow in forest edges, old fields, and other sites colonized by pioneering tree species. In an exploratory greenhouse
experiment, we applied aqueous extracts derived from soil, leaf litter, or live leaves to native trees. We compared these
treatments to a sterile water control and also to minced leaves leached in water, a common, but potentially less realistic
method of testing for allelopathy. For all tree species, minced leaves from tall fescue reduced the probability that seedlings
emerged, and minced leaves of autumn olive reduced the number of days to emergence. During other demographic stages, the three
native tree species diverged in their responses to the invasive plants. Platanus occidentalis exhibited the widest range of responses, with reduced root biomass due to minced tissue from both invasive species, reduced
days to emergence and marginally reduced survival from minced tall fescue, and reduced leaf biomass from tall fescue leaf
litter. Populus deltoides appeared insensitive to most extracts, although survival was marginally increased with application of minced or fresh leaf
extracts from autumn olive. In addition, minced tall fescue shortened the time to seedling emergence for Acer saccharinum, potentially a positive effect. Overall, results suggest that allelopathy may be one mechanism underlying the negative impacts
of tall fescue and autumn olive on other plant species, but that effects can depend strongly upon the source of allelochemicals
and the tree species examined. 相似文献
18.
The contribution of mycorrhizal associations to maintaining tree diversity patterns in tropical rain forests is poorly known.
Many tropical monodominant trees form ectomycorrhizal (EM) associations, and there is evidence that the EM mutualism contributes
to the maintenance of monodominance. It is assumed that most other tropical tree species form arbuscular mycorrhizal (AM)
associations, and while many mycorrhizal surveys have been done, the mycorrhizal status of numerous tropical tree taxa remains
undocumented. In this study, we tested the assumption that most tropical trees form AM associations by sampling root vouchers
from tree and liana species in monodominant Dicymbe corymbosa forest and an adjacent mixed rain forest in Guyana. Roots were assessed for the presence/absence of AM and EM structures.
Of the 142 species of trees and lianas surveyed, three tree species (the monodominant D. corymbosa, the grove-forming D. altsonii, and the non-dominant Aldina insignis) were EM, 137 were exclusively AM, and two were non-mycorrhizal. Both EM and AM structures were observed in D. corymbosa and D. altsonii. These results provide empirical data supporting the assumption that most tropical trees form AM associations for this region
in the Guiana Shield and provide the first report of dual EM/AM colonization in Dicymbe species. Dual colonization of the Dicymbe species should be further explored to determine if this ability contributes to the establishment and maintenance of site
dominance.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
Scott J. Meiners 《Biological invasions》2007,9(7):849-855
Invasion of habitats by exotic shrubs is often associated with a decrease in the abundance of native species, particularly
trees. This is typically interpreted as evidence for direct resource competition between the invader and native species. However,
this may also reflect indirect impacts of the exotic shrubs through harboring high densities of seed predators––known as apparent
competition. Here I present data from separate seed predation experiments conducted with two shrub species exotic to North
America; Rosa multiflora, an invader of abandoned agricultural land, and Lonicera maackii, an invader of disturbed or secondary forest habitats. Both experiments showed significantly greater risks of seed predation
for tree seeds located under shrub canopies when compared to open microhabitats within the same site. These results indicate
the potential importance of indirect impacts of exotic species invasions on native biota in addition to the direct impacts
that are typically the focus of research. 相似文献
20.
Transgenic hairy roots. recent trends and applications 总被引:23,自引:0,他引:23
Agrobacterium rhizogenes causes hairy root disease in plants. The neoplastic roots produced by A. rhizogenes infection is characterized by high growth rate and genetic stability. These genetically transformed root cultures can produce higher levels of secondary metabolites or amounts comparable to that of intact plants. Hairy root cultures offer promise for production of valuable secondary metabolites in many plants. The main constraint for commercial exploitation of hairy root cultures is their scaling up, as there is a need for developing a specially designed bioreactor that permits the growth of interconnected tissues unevenly distributed throughout the vessel. Rheological characteristics of heterogeneous system should also be taken into consideration during mass scale culturing of hairy roots. Development of bioreactor models for hairy root cultures is still a recent phenomenon. It is also necessary to develop computer-aided models for different parameters such as oxygen consumption and excretion of product to the medium. Further, transformed roots are able to regenerate genetically stable plants as transgenics or clones. This property of rapid growth and high plantlet regeneration frequency allows clonal propagation of elite plants. In addition, the altered phenotype of hairy root regenerants (hairy root syndrome) is useful in plant breeding programs with plants of ornamental interest. In vitro transformation and regeneration from hairy roots facilitates application of biotechnology to tree species. The ability to manipulate trees at a cellular and molecular level shows great potential for clonal propagation and genetic improvement. Transgenic root system offers tremendous potential for introducing additional genes along with the Ri T-DNA genes for alteration of metabolic pathways and production of useful metabolites or compounds of interest. This article discusses various applications and perspectives of hairy root cultures and the recent progress achieved with respect to transformation of plants using A. rhizogenes. 相似文献