Enhanced Seedling Root Development in Eight Conifer Species Induced by Naphthalene Acetic Acid

Seedlings of eight conifer species, Pinus contorta, Pinus sylvestris,Pinus nigra, Larix kaempferi, Picea abies, Picea sitchensis,Pseudotsuga, nenziesii and Abies grandis, were treated withauxin, in pot and nursery experiments. Dilute solutions of naphthaleneacetic acid (NAA) were applied at two treatment times, justbefore and just after cotyledon expansion. Lateral root numberswere increased by up to 20 times on responsive species. Sensitivityvaried considerably, the three pine species showing a much greaterresponse than the two species of spruce. In most cases the meannumber of induced roots increased steadily with increasing auxinconcentration. Forest nursery results showed that NAA couldprovide an inexpensive method for stimulating lateral root formationnear the soil surface. Practical nursery aspects of treatmentare briefly discussed.     

Cronartium comptoniae, a Potential Threat to Pinus contorta in Britain

The North American Cronartium comptoniae Arth., with Pinus spp.and Myricaceae as alternate hosts, causes considerable economicloss of Pinus contorta in North America. Its introduction toBritain might have very serious consequences, especially inthose districts where Pinus contorta is being extensively planted,and foresters should guard against it.     

Soil Aeration Response to Draining Intensity in Basin Peat

Improvement in soil aeration was assessed following drainingto a range of intensity on a peatland afforestation projectat Flanders Moss in Central Scotland. A polarographic techniquewas used to measure oxygen diffusion rates in the rooting zoneof lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.)planted in 1965 on ploughed furrows. There were soil aerationdifferences because of draining intensity. Below the plantingturf oxygen diffusion rates rapidly decreased and tree rootingwas restricted to the surface layers. Aeration was found tobe closely correlated with depth of water in boreholes whichprovide a simple and reliable index of response to draining.Oxygen diffusion rate was a more sensitive means of assessingsoil aeration than oxidation-reduction potential at the lowoxygen concentrations encountered in the basin peat on the Moss.     

CONIFEROUS LITTER AMENDMENTS AND THE GROWTH OF SITKA SPRUCE

The growth of semi-checked Sitka spruce (Picea sitcbensis Carr.)on heathland has been stimulated to different degrees by theannual application of litter of Scots pine (Pinus sylvestrisL.), Corsican pine (P. nigra var. calabrica Schneid), Lodgepolepine (P. contorta Dougl.), Japanese larch (Larix leptolepisGord.), and Sitka spruce, at rates corresponding to normal plantationconditions, following an initial heavier rate. Foliar analysissuggests that the response is at least partially attributableto the influence of the litters on the nitrogen nutrition ofthe spruce and differences between litters appear to be largelydetermined by their total nitrogen contents. In this respect,Japanese larch, with an annual needle fall generally greaterthan that of the pines and a higher nitrogen content, offersthe best promise as a nurse species for spruce.     

Tree-induced soil compaction in forest ecosystems: myth or reality?

Trees subjected to wind loading are supposed to induce a soil deformation. However, knowledge is lacking about this phenomenon. In the present contribution, we hypothesized that soil compaction is higher in the surroundings of the lateral roots and in particular at their distal part where the amplitude of the root movements is expected to be largest. To test this hypothesis, we focused on a shallowly rooted tree, the European beech (Fagus sylvatica), in a large forest situated south of Brussels. Mean soil compaction significantly increased as one moves away from the tree, up to a distance of 5 m. Soil compaction was not evenly distributed around tree trunks, the highest values being in the north direction. Only part of these results supports the hypothesis about soil compaction due to wind-induced movements within near-surface lateral roots in beechwoods on silt loams. The need for additional research is highlighted.     

Bamboo hedgerow systems in Kerala, India: Root distribution and competition with trees for phosphorus

In a field study on bamboo (Bambusa arundinacea (Retz.) Willd.) hedgerow systems of Kerala, we tested the following three hypotheses: (1) Effective root foraging space is a function of crown spread, (2) Proximity of trees depress lateral spread of roots in mixed species systems and (3) The closer the trees are located the greater will be the subsoil root activity which in turn facilitates active absorption of nutrients from deeper layers of the soil profile. Root distribution of boundary planted bamboo and root competition with associated trees in two binary mixtures, teak (Tectona grandis)-bamboo and Malabar white pine (Vateria indica)-bamboo, were evaluated using modified logarithmic spiral trenching and ³²P soil injection techniques respectively. Excavation studies indicate that rooting intensity declined linearly with increasing lateral distance. Larger clumps manifested wider foraging zones. Eighty three per cent of the large clumps (>4.0 m dia.) extended roots beyond 8 m while only 33% of the small (<2.5 m dia.) clumps extended roots up to 8 m. Highest root counts were found in the 10–20 cm layer with nearly 30% of total roots. Although nearness of bamboo clumps depressed root activity of teak and Vateria in the surface layers of the soil profile, root activity in the deeper layers was stimulated. ³²P recovery was higher when applied at 50-cm depth than at 25-cm depth implying the safety net role of tree roots for leached down nutrients. Inter specific root competition can be regulated by planting crops 8–9 m away from the bamboo clumps and/or by canopy reduction treatments. This revised version was published online in June 2006 with corrections to the Cover Date.     

Regeneration and gene transformation systems of Robinia pseudoacacia ‘Idaho’ mediated by Agrobacterium tumefaciens

Robinia pseudoacacia ‘Idaho’ is one of several multi-purpose trees used in ornamental, soil and water conservation, fodder and nectar sources. Plant abiotic stress tolerance transformed by genes could meet the requirements for reclamation of arid or alkalid lands and vegetation restoration. For this paper, we studied the effects of auxin and cytokine on Idaho locust in vitro regeneration and the establishment of gene transformation systems for plants mediated by Agrobacterium tumefaciens. Results showed that the ratios of cytokinin and auxin were the major factors affecting adventitious bud differentiation on a MS medium; the concentration of 0.5 mg&#8226;L^–1 6-BA benefitted callus proliferation and 0.25 mg&#8226;L^–1 IBA promoted shoot rooting; however, a higher IBA concentration will inhibit rooting. The most effective antitoxin for screening transgenic Idaho locust shoots was G418 and the most sensitive concentra-tion of it was 8 mg&#8226;L^–1.     

Morphology of the Structural Root System of Sitka Spruce 2. Computer Simulation of Rooting Patterns

In a previous paper (Henderson et al. 1983), it was suggestedthat the processes of root growth and development proceed witha geometric regularity and that, as a consequence, root distributionis further extended and spatially more even than if growth wereat random. We examine this hypothesis and the relative importanceof the component growth processes through computer simulationof a model for root distribution at a fixed time. Root segments were measured on 16 year trees and statisticaldistributions fitted to the occurrence of lengths, branchingfrequencies and growth directions. These distributions comprisethe model which assumes that a root system consists of a numberof first-order roots originating at the stem, a number of second-orderroots originating on first-order ones and so on. Each root includesa number of bends and lateral branching points and terminatesin either a fork or when diameter reaches 5 mm, smaller rootsnot being included. Parameter manipulation of the fitted distributions and furthersimulation showed that some regular growth mechanisms were necessaryfor the simulation of realistic rooting patterns. In particularit was important that direction changes at bends and of newroots at forks were typically small to ensure that the systemspread outwards, away from the stem. Lateral branches neededto subtend large angles to their parents in order to exploitseparate soil regions. Other necessary rules were that first-orderroots were almost regularly distributed around the stem andfor a tendency for azimuth changes at bends to be alternatelyclockwise then anticlockwise. Simulations were also used to examine the possibility of estimatingtotal root length from a study of only part of a root system.An example of excavating one quarter of the system is consideredand the results indicate that root systems may be so variablethat no reliable estimate can be obtained.     

窄冠刺槐根系的研究

2006年10月用全挖法和分层分段挖掘法,研究了窄冠刺槐根系的分布特征、根系生物量以及不同密度林分根系空间分布特征.结果表明:窄冠刺槐个体根系水平分布在株间可达到6.6 m,在行间可达到5.0 m;主根可深达2 m以上,侧根垂直分布集中在10～40 cm土层内.窄冠刺槐根系生物量占全株生物量的16.82％,主根、侧根的生物量在根系生物量中分别占87.13％、12.87％.窄冠刺槐林分根系生物总量和根总长分别为6 160.2～10 940.55kg·hm-2和970.35～1 607.4 km·hm-2,并呈现出根系生物总量和根总长与林分密度成正相关的规律.在垂直方向上,林分根系中直径D<15 mm的根主要分布在地下0～20 cm土层内,而直径D≥15 mm的根主要分布在地下20～40 cm土层内;在水平方向上,直径D≥5 mm的根数量随距树干距离增加而减少,而直径D<1 mm的根数量则随距树干距离增大而增大,主要集中分布在距树干0.5～1.5 m范围内.     

河竹鞭根对长期淹水环境的生理响应

为揭示河竹鞭根对淹水环境的生理响应机制,以在淹水环境中能长期生存的河竹为材料,测定了人工喷灌供水(对照)、淹水6个月的河竹1年生竹鞭上的一级根、二级根的根系活力、抗氧化酶活性和膜脂过氧化、渗透调节物质含量。研究结果表明:河竹根系活力、抗氧化酶活性、MDA含量、相对电导率和可溶性蛋白含量总体上一级根明显高于二级根。长期淹水环境下,河竹一级根、二级根的根系活力、抗氧化酶活性较对照均有显著降低,相对电导率、MDA含量显著升高,水中生长根的根系活力、CAT活性显著高于土中生长根,SOD、POD活性则相反,并能通过维持总体上较高水平的根系活力、抗氧化酶活性、可溶性蛋白含量来适应长期淹水环境的胁迫,尤其是一级根和水中生长根。河竹鞭根通过抗氧化系统的平衡调节作用来适应长期淹水环境,维持生存,其中一级根对淹水环境的响应明显强于二级根,水中生长根在适应淹水环境上起到重要作用。     

NATURAL REGENERATION OF PINE AND BIRCH ON THE HEATHER MOORS OF NORTH-EAST YORKSHIRE

Both pine (Pinus sylvestris L.).and birch (Betula pubescensEhrh.) usually invade after a fire, the invasion reaching greatestforce after 3 to 5 years, then falling off rapidly probablywith the return of the heather (Calluna). Pine seedlings onlygrow vigorously if their tap-roots reach the pan, when secondaryroots are developed extensively. In birch the tap-root is notwell developed, but secondary roots spread vigorously sendingdown sinkers to penetrate the pan. Regeneration of birch ishelped by rotten stumps and roots which its mycorrhizal rootsexplore. The root forms are compared and contrasted and thefindings compared with the work of Laitakari and Erteld.     

Active root distribution pattern of <Emphasis Type="Italic">Hevea brasiliensis</Emphasis> determined by radioassay of latex serum

The active root distribution pattern of mature rubber (Hevea brasiliensis Muell. Arg.) up to a lateral distance of 250 cm from the tree and to a soil depth of 90 cm was studied in an oxisol by employing ³²P soil injection technique in Kerala, the state which accounts for 83% of rubber cultivation in India. The trees were aged 18 years and grown at a spacing of 4.9 × 4.9 m. The extent of absorption of applied ³²P by the tree from various placements was assessed by radio assay of leaf and latex serum. Latex serum registered higher counts and variability was less compared to leaf indicating the suitability of latex serum as a potential source for radio assay for ³²P studies in rubber. The results revealed that rubber is a surface feeder with 55% of the root activity confining to the top 10 cm of soil layer. Root activity declined with increasing depths and the concentration of physiologically active roots at 90 cm depth was only 6%. A more or less uniform distribution of root activity was noticed with respect to lateral distance indicating more extensive spread of lateral roots. Concentration of physiologically active roots in the surface layer suggests the possibility for competition under intercropped situation in mature plantations.     

The Effects of Wind on the Extension Growth of Pinus contorta Douglas

The effect of wind on the extension growth of young Pinus contortawas investigated using a controlled environment wind tunnel.Extension rates of leader and lateral shoots were reduced byabout 20 per cent by high wind speed. The ratio of the finallength of the laterals to that of the leaders (‘apicalcontrol’) was unaffected, as was the radial growth ofstems. Water potentials were slightly higher in plants subjectto high wind. In another experiment, rates of needle extensionwere reduced 30 per cent by wind. The experiments are discussedin relation to field observations by others and it is arguedthat wind is a potent ecological factor adversely affectingtree growth.     

Binucleate Rhizoctonia (Ceratorhiza spp.) induce adventitious root formation in hypocotyl cuttings of Pinus sylvestris L.

Adventitious rooting of Scots pine (Pinus sylvestris L.) hypocotyl cuttings was promoted by binucleate Rhizoctonia (BnR) and to a lesser extent by ectomycorrhizal fungi. Four BnR isolates (251, 266, 268 and 269) differentiated root meristems and significantly induced adventitious rooting in young derooted seedlings. Rooting rates were significantly higher in BnR treatments than in either indol-3-butyric acid (IBA) pretreatment (200 µm) or co-cultivation with the ectomycorrhizal fungi Suillus bovinus or Laccaria bicolor. In pre-IBA-treated cuttings, adventitious root numbers were higher in the treatments with isolates 251 and particularly 268, while more similar in other BnR treatments. In the 251, roots emerged from distal positions along the hypocotyl and not from the cut base as in the other three BnR isolate treatments. Loss of turgor and hypocotyl wilt was commonly detected up to the point of root initiation. Lateral roots and dichotomous short roots subsequently appeared at high frequency from primary adventitious roots. Mechanisms involved in root meristem differentiation, e.g. auxin production, wound response and oligosaccharide signals, are discussed with respect to host-fungal signalling mechanisms. These beneficial BnR and ectomycorrhizal fungi could provide promising new tools in the development of efficient clonal propagation methodology for this highly recalcitrant Pinus species.     

Vertical and horizontal water redistribution in Norway spruce (Picea abies) roots in the Moravian Upland

Hydraulic redistribution (HR) by roots of large Norway spruce (Picea abies (L.) Karst.) trees was investigated by means of sap flow measurements made with the heat field deformation method. Irrigation was applied to a limited portion of the root system to steepen gradients of water potential in the soil and thus enhance rates of HR. On completion of the sap flow measurements, and to aid in their interpretation, the structure of the root system of seven of the investigated trees was exposed to a depth of 30 cm with a supersonic air-stream (air-spade). Before irrigation, vertical redistribution of water was observed in large coarse roots and some adjacent small lateral roots. Immediately after localized irrigation, horizontal redistribution of water from watered roots to dry roots via the stem base was demonstrated. The amount of horizontal distribution depended on the position of the receiving roots relative to the watered roots and the absorbing area of the watered root. No redistribution from watered roots via dry soil to roots of neighboring trees was detected. Responses of sap flow to localized irrigation were more pronounced in small lateral roots than in large branching roots where release and uptake of water are integrated. Sap flow measurements with multi-point sensors along radii in large lateral roots demonstrated water extraction from different soil horizons. We conclude that synchronous measurements of sap flow in both small and large lateral roots are needed to study water absorption and transport in tree root systems.     

Root distribution of Pinus pinaster, P. radiata, Eucalyptus globulus and E. kochii and associated soil chemistry in agricultural land adjacent to tree lines

We quantified the extent and distribution of roots of four commonly planted tree species (Eucalyptus globulus Labill., Pinus radiata D. Don, P. pinaster Aiton and E. kochii Maiden & Blakely subsp. plenissima C.A. Gardner) in agricultural land adjacent to tree lines, and examined the effect of soil type and root pruning on root morphology. Root distribution in soil adjacent to tree lines was mapped by a trench profile method at 13 sites on the south coast of Western Australia. Soil samples were collected to determine water content and fertility. The lateral extent of tree roots ranged from 10 m for E. kochii to 44 m for P. pinaster. This equated to between 1.5 and 2.5 times tree height (H) for E. globulus and Pinus spp. to 4H for E. kochii. Root density declined logarithmically with distance from the trees and was greatest for P. pinaster and least for E. globulus (P < 0.001). The rate of decrease in root density with distance from the trees was greatest for the Pinus spp. and least for E. kochii (P < 0.05). Root density was generally greatest in the top 0.5 m of the soil profile and decreased with increasing depth. This decrease was relatively gradual in the deep sands, but abrupt in clay subsoil. Root dry mass in the sandy top soil beyond 0.5H ranged between 1.0 and 55.5 Mg km(treeline) (-1) for 6-year-old E. kochii and 50-year-old P. pinaster, respectively. Soil water content generally increased with distance from the trees (P < 0.001). There was no evidence of reduced soil fertility in the top 1.4 m of the soil profile adjacent to the trees. Two to four years after trees had been root pruned, both the lateral extent and vertical distribution of roots were similar for pruned and unpruned trees. The density of roots < 2 mm in diameter was greater for root-pruned trees than for unpruned trees (P < 0.05). We conclude that the study species can compete with agricultural crops based on the lateral extent of their roots and the occurrence of greatest root density within 0.5 m of the soil surface.     

Dynamics of symbiotic establishment between an IAA-overproducing mutant of the ectomycorrhizal fungus Hebeloma cylindrosporum and Pinus pinaster

To clarify the early steps of symbiotic establishment, we studied the dynamics of Pinus pinaster (Ait.) Sol. tap root colonization and mycorrhiza formation by an IAA-overproducing mutant of the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnesi and by the corresponding wild type strain. Differences between wild type and mutant strains were quantitative rather than qualitative and were detected two days after inoculation. Both fungal strains established a typical Hartig net when they colonized the tap roots. Consequently, colonized tap roots exhibited features of a true mycorrhiza and fungal colonization enhanced plant growth. Fungal colonization and Hartig net formation were more rapid with the mutant than with the wild type. Colonization, especially with the mutant strain, increased rhizogenesis and the production of mycorrhizas. The mutant formed a hypertrophic Hartig net in tap roots and mycorrhizal short roots and we obtained evidence that the process of short root transformation into mycorrhiza started before their emergence from the tap root. Hyphae of the Hartig net in the tap root penetrated the cortex of young lateral roots at the beginning of their elongation, after the endodermis layer broke under the pressure of the elongating lateral root. Colonization was inhibited when triiodobenzoic acid was added to the culture medium, providing circumstantial evidence that auxin is involved in mycorrhiza formation.     

Root biomass and distribution of five agroforestry tree species

Knowledge of the quantitative assessment and structural development of root systems is essential to improve and optimize productivity of agroforestry systems. Studies on root biomass recovery by sieves of different mesh sizes (2.0, 1.0, 0.5 and 0.25 mm) and root distribution for four-year-old individuals of five agroforestry tree species viz.; Acacia auriculiformis A. Cunn. ex Benth, Azadirachta indica A. Juss, Bauhinia variegata L., Bombax ceiba L. and Wendlandia exserta Roxb. were conducted at the research farm of Rajendra Agricultural University, Pusa, Bihar, India. The results indicated that the 0.5 mm sieve was adequate for recovery of the majority of roots. All the tree species exhibited a large variation in root depth and horizontal root spread four years after planting. The maximum root depth was recorded in W. exserta (2.10 m) and minimum in B. variegata (1.00 m). Horizontal root spread was 2.05 m in B. ceiba and 8.05 m in A. auriculiformis. Root spread exceeded crown cover for all species. The primary roots were more horizontal than the secondary roots. The length and diameter of the main root were highest in A. indica (108.3 cm) and B. ceiba (23.2 cm), respectively. Highest length and diameter of lateral roots were recorded in B. variegata (201.6 cm) and A. indica (1.8 cm), respectively. Total root biomass among different species accounted for 18.2–37.9% of the total tree biomass. Results of this study infer that although all the species have potential to conserve moisture and improve fertility status of the soil, A. auriculiformis is the most effective for promoting soil fertility. The deep rooted W. exserta and A. auriculiformis will be preferred for cultivation under agroforestry systems and could reduce competition for nutrients and moisture with crops by pumping from deeper layers of soil.     

Pathogenicity of Phytophthora species and Pythium undulatum isolated from Abies procera Christmas trees in Ireland

Phytophthora cryptogea, Phytophthora cinnamomi, Phytophthora cambivora, Phytophthora megasperma and Pythium undulatum were isolated from diseased Noble fir (Abies procera) seedlings and soil associated with dead Noble fir in Ireland. Seedlings of four Christmas tree species (A. procera, Picea sitchensis, Picea abies and Pinus contorta) were inoculated with these oomycetes to test their pathogenicity and the susceptibility of the various tree species. Phytophthora spp. and Pythium undulatum caused root rot on all tree species. Disease symptoms included reddish brown cambial discoloration, crown symptoms, brown foliage, dark brown roots, root rot and seedling mortality. These symptoms were similar to those observed on Noble fir in naturally infested plantations. Pythium undulatum appeared as the most virulent pathogen followed by P. cinnamomi, P. cambivora, P. megasperma and P. cryptogea. Noble fir showed to be most susceptible and lodgepole pine most tolerant while Sitka spruce and Norway spruce were intermediate.     

Effects of calcium, boron and nitrogen fertilization on the growth of teak (Tectona grandis) seedlings and chemical property of acidic soil substrate

Many teak plantations are established on acidic soils with low nutrient availability. There is also poor documentation of nutrient budgets for teak, therefore, a pot experiment with optimal hybrid regression design (Roquemore R311A) was implemented with calcium, boron and nitrogen treatments with teak seedlings (Tectona grandis L.f.) planted in acidic lateritic red soil substrate. Seedling growth, biomass production and root development, and soil pH, and exchangeable Ca and Al concentration were measured. Plant height, root collar diameter, biomass of leaves, stems and roots, root volume, taproot length, number of lateral roots of teak seedlings were significantly and positively correlated with soil exchangeable Ca, pH and Ca/Al molar ratio, and negatively correlated with exchangeable Al. All growth traits were significantly affected by calcium, nitrogen and their interaction, but B fertilizer and other interactions had insignificant effects. To effectively cultivate teak seedlings in acidic soil substrates, 1.68 g kg⁻¹ quicklime (CaO) and 0.65 g kg⁻¹ urea was suggested to be added to neutralize soil acidity, and enhance soil exchangeable Ca content and Ca/Al molar ratio. Urea should not be added without quicklime.