Effects of lateral morphology on swimming performance in two sturgeon species

Fish express a high degree of diversity in morphology, which is closely related to behaviors such as swimming ability. The effect of morphology on swimming performance is explored using geometric morphometric analyses and classic critical swimming speed (U_crit) tests in Chinese sturgeon Acipenser sinensis and Siberian sturgeon A. baerii. It was found that A. sinensis is a stronger swimmer compared to A. baerii, with an average 25% higher U_crit (expressed in body lengths per second). In A. sinensis, the depth and length of the snout and the trailing edge length of the dorsal fin were negatively correlated with U_crit, whereas the height of the trunk anterior, the leading edge length of the dorsal fin and anal fin, and the length and width of the ventral lobe were positively related to U_crit; similar relationships between U_crit and morphological characters of the anterior trunk, dorsal fin, anal fin and caudal fin were found in A. baerii. Moreover, although the degree of upward bending of the snout of A. baerii was negatively related to U_crit, there was a positive relationship between the length of the caudal peduncle and U_crit as well as between the dorsal tail lobe and U_crit. In addition, the streamline index (SI) was calculated by comparing landmark coordinates on the trunk displayed in the relative warp, with its corresponding point on the NACA (the U.S. National Advisory Committee for Aeronautics) airfoil shape. SI showed that the body shape in RW1 of the A. baerii with more swimming capacity was more approximate to the NACA 0016 airfoil shape, but there was no such symmetry for A. sinensis, possibly due to body bending caused by stiffness.     

Quantifying the effects of root reinforcement of Persian Ironwood (Parrotia persica) on slope stability; a case study: Hillslope of Hyrcanian forests,northern Iran

Forest vegetation is known to enhance the stability of slopes by reinforcing soil and increasing its shear resistance through root system. The effects of root reinforcement depend on the morphological characteristics of the root system, the tensile strength of single roots, and the spatial distribution of the roots in soil. In the present study the results of research carried out in order to evaluate the biotechnical characteristics of the root system of Persian Ironwood (Parrotia persica), in northern Iran are presented. Profile trenching method was used to obtain root area ratio (RAR) values for uphill and downhill sides of the individual trees. For each species, single root specimens were sampled and tested for their tensile strength. It was found that root density generally decreases with depth according to an exponential law. Maximum RAR values were located within the first 0.1 m, with maximum rooting depth at about 0.65 m. RAR values ranged from 0.001% at lower depths to 1.39% near the surface, at upper 0.1 m depth. Significant differences of RAR values, rooting depth and root cohesion between uphill and downhill were observed, however, the differences were not significant for number of roots (ANCOVA). Downhill profiles had higher RAR values, rooting depth and root cohesion. In general, root tensile strength tends to decrease with diameter according to a power law, as observed by other researchers. Downhill roots were significantly stronger in tensile strength than uphill ones. Inter-species variation of tensile strength in downhill roots was also observed. The resulting data were used to evaluate the reinforcing effects in terms of increased shear strength of the soil, using Wu/Waldron Model. The root reinforcement provided by Persian Ironwood is about 46.0 kPa in the upper layers and 0.3 kPa in the deeper horizons. The results of Spearman test revealed a significant correlation between RAR and c_r and that best followed by a power law. The results presented in this paper contribute to expanding the knowledge on biotechnical characteristics of Persian Ironwood on slope reinforcement.     

Effects of root architecture, physical tree characteristics, and soil shear strength on maximum resistive bending moment for overturning Salix babylonica and Juglans ailanthifolia

Effects of root architecture, physical tree characteristics, and soil shear strength on overturning moment due to flooding were investigated using Salix babylonica and Juglans ailanthifolia, exotic and invasive plants in Japanese rivers. Tree-pulling experiments that simulated flood action were conducted, and the resulting damage was examined to assess the effects of physical tree characteristics and root architecture on the maximum resistive bending moment (M _max) for overturning. In situ soil shear strength tests were conducted to measure soil strength parameters. The effects of species differences on the M _max were examined by analyzing root architecture. S. babylonica has a heart-root system that produces a greater overturning moment due to the strong root anchorage and the large amount of substrate that must be mobilized during overturning. J. ailanthifolia has a plate-root system that produces a smaller overturning moment. However, trees with the plate-root system may withstand overturning better due to an increased root:shoot ratio. The results of the study show that the M _max of a tree for overturning had significant (P < 0.05) correlations with a tree’s physical characteristics, including height (H), trunk diameter at breast height (D _bh), D _bh², height multiplied by the second power of D _bh (trunk volume index H × D _bh²), and root–soil plate depth (R _d), and root–soil plate radius (R _r). Considering the strategy of J. ailanthifolia to increase the root:shoot ratio for anchoring in the substrate, the trunk volume index (H × D _bh²) is a better parameter than D _bh² because it indirectly involves the difference in below-ground volume and surface area. Different soil cohesion values were found at different experimental sites, and the average M _max for overturning each species decreased linearly with increasing soil cohesion.     

Drip irrigation,soil characteristics and the root distribution and root activity of olive trees

A study was carried out on the root distribution and root activity of the olive tree (Olea Europaea, L., var. manzanillo) as influenced by drip irrigation and by several soil characteristics such as texture and depth. The experiments were conducted in two plots within a drip-irrigated grove of 20-year-old trees planted at 7×7 m spacing. One soil was a sandy loam, the other a clay-loam. Both cylinder and trench methods were used to determine root distribution. Labelling with ³²P was used to determine root activity. Under dryland conditions the adult tree adapted its rooting system, following the installation of a drip system, by concentrating the roots within the wet soil zones near the drippers. The highest root densities occur in those zones, down to a 0.6 m depth, the most abundant being the <0.5 mm diameter roots. The most intensive root activity was also found in that zone. For a given irrigation system, wet soil bulbs are more extensive and therefore root distribution expands to a larger soil volume when the soil is more clayey and with a hard calcareous pan present at about 0.8 m depth which prevents deep drainage.     

Allometry, root/shoot ratio and root architecture in understory saplings of deciduous dicotyledonous trees in central Japan

Plant allometry that is related to plant architecture and biomass allocation strongly influences a plants ability to grow in shaded forest understory. Some allometric traits can change with plant size. The present study compared crown and trunk allometries, root/shoot biomass allometry, and root architecture among understory saplings (0.25--5m height, except for two trees > 5 < 7 m) of seven deciduous dicotyledonous species in central Japan. Associations of the crown and trunk allometries with several plant morphological attributes were analyzed. Branch morphology (plagiotropyvs orthotropy) and life size were correlated with sapling crown and trunk allometries. Both large leaves and orthotropic branches were associated with a narrow small crown and slender trunk. The root/shoot ratio decreased rapidly with increasing plant height for saplings shorter than about 1.5 m. Less shade-tolerant species tended to have smaller root/shoot ratios for saplings taller than 1.5 m. With an increase in plant height, the branch/trunk biomass ratio decreased for saplings with plagiotropic branches but increased for saplings with orthotropic branches. Four subcanopy species (Acer distylum, Carpinus cordata, Fraxinus lanuginosa and Acanthopanax sciadophylloides) had superficial root systems; a common understory species (Sapium japonica) had a deep tap root system; and a canopy species (Magnolia obovata) and a subcanopy species (Acer tenuifolium) had heart root systems of intermediate depth. The root depth was not related to shade tolerance. Among species of the same height, the difference in fine root length can be 30-fold.     

Midday depression of tree root respiration in relation to leaf transpiration

The root respiration rate often shows an exponential or a linear relationship with temperature under laboratory conditions. However, under intact conditions in the field, the root respiration rates of some tree species decreased around midday despite an increment of the root temperature (Bekku et al. 2009). To clarify the cause of midday depression, we examined the relationships between the intact root respiration and parameters of leaf gas exchange through the simultaneous field measurement of the gas exchange in the leaf and root of Quercus crispula and Chamaecyparis obtusa, which are canopy trees. There were no significant relationships between the root respiration rates (R _r) and the parameters of leaf gas exchange in the field. However, in C. obtusa, the relationships between R _r and the transpiration rates (E) at 1 h before the measurement of R _r were fitted by logarithmic function with a determination coefficient of 0.60–0.89. In the light-manipulation experiments using saplings, R _r had significant positive correlations with E at 20 min before the measurement of R _r, root temperature (T _r), and the photosynthesis (P _n) at 20 min before the measurement of R _r. We examined which factor, P _n or E, affects the root respiration rate through a manipulation experiment using a growth chamber regulating the ambient CO₂ concentration and relative humidity independently under constant air temperature and photosynthetic photon flux density. As a result, the root respiration rates changed corresponding to E and not P _n. These results suggest that the root respiration rate of trees changes significantly in the daytime and is affected by the leaf transpiration rate as well as the temperature.     

Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador

Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50°). Three tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m, 48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased significantly from 6.1 × 10⁻³ m² m⁻¹ at 1900 m to 3.2 × 10⁻³ m² m⁻¹ at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently. Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide anchorage in soils with low bulk density and in environments with high wind speeds.     

Small differences in root distributions allow resource niche partitioning

1. Deep roots have long been thought to allow trees to coexist with shallow‐rooted grasses. However, data demonstrating how root distributions affect water uptake and niche partitioning are uncommon.
2. We describe tree and grass root distributions using a depth‐specific tracer experiment six times over two years in a subtropical savanna, Kruger National Park, South Africa. These point‐in‐time measurements were then used in a soil water flow model to simulate continuous water uptake by depth and plant growth form (trees and grasses) across two growing seasons. This allowed estimates of the total amount of water a root distribution could absorb as well as the amount of water a root distribution could absorb in excess of the other rooting distribution (i.e., unique hydrological niche).
3. Most active tree and grass roots were in shallow soils: The mean depth of water uptake was 22 cm for trees and 17 cm for grasses. Slightly deeper rooting distributions provided trees with 5% more soil water than the grasses in a drier season, but 13% less water in a wetter season. Small differences also provided each rooting distribution (tree or grass) with unique hydrological niches of 4 to 13 mm water.
4. The effect of rooting distributions has long been inferred. By quantifying the depth and timing of water uptake, we demonstrated how even small differences in rooting distributions can provide plants with resource niches that can contribute to species coexistence. Differences in total water uptake and unique hydrological niche sizes were small in this system, but they indicated that tradeoffs in rooting strategies can be expected to contribute to tree and grass coexistence because 1) competitive advantages change over time and 2) plant growth forms always have access to a soil resource pool that is not available to the other plant growth form.

     

Influence of soil porosity on water use in<Emphasis Type="Italic"> Pinus taeda</Emphasis>

We analyzed the hydraulic constraints imposed on water uptake from soils of different porosities in loblolly pine (Pinus taeda L.) by comparing genetically related and even-aged plantations growing in loam versus sand soil. Water use was evaluated relative to the maximum transpiration rate (E _crit) allowed by the soil-leaf continuum. We expected that trees on both soils would approach E _crit during drought. Trees in sand, however, should face greater drought limitation because of steeply declining hydraulic conductivity in sand at high soil water potential (Ψ _S). Transport considerations suggest that trees in sand should have higher root to leaf area ratios (A _R:A _L), less negative leaf xylem pressure (Ψ _L), and be more vulnerable to xylem cavitation than trees in loam. The A _R:A _L was greater in sand versus loam (9.8 vs 1.7, respectively). This adjustment maintained about 86% of the water extraction potential for both soils. Trees in sand were more deeply rooted (>1.9 m) than in loam (95% of roots <0.2 m), allowing them to shift water uptake to deeper layers during drought and avoid hydraulic failure. Midday Ψ _L was constant for days of high evaporative demand, but was less negative in sand (–1.6 MPa) versus loam (–2.1 MPa). Xylem was more vulnerable to cavitation in sand versus loam trees. Roots in both soils were more vulnerable than stems, and experienced the greatest predicted loss of conductivity during drought. Trees on both soils approached E _crit during drought, but at much higher Ψ _S in sand (<–0.4 MPa) than in loam (<–1.0 MPa). Results suggest considerable phenotypic plasticity in water use traits for P. taeda which are adaptive to differences in soil porosity. Received: 28 December 1999 / Accepted: 31 March 2000     

Influences of plant spacing on root tensile strength of Schefflera arboricola and soil shear strength

Mechanical root reinforcement depends not only on root biomechanical properties but also on root biomass. Although it is known that plant spacing can affect root growth, it is not clear how it affects root tensile strength. We interpreted a set of field data to study the effects of spacing of Schefflera arboricola on root area ratio (RAR), root tensile strength and their combined effects on soil shear strength (also termed root cohesion). S. arboricola was transplanted into compacted silty sand at a spacing of 0.5 m, 0.8 m and 1.1 m. After 20 months of growth in the field, the root systems were excavated for root tensile testing and post-test trait measurements. Plant spacing affected the growth and tensile strength of roots. More closely spaced plants had higher RAR but lower root tensile strength, especially for roots 0.5–2 mm in diameter. According to the existing root breakage and fibre bundle models used in this study, which calculate root cohesion as the product of RAR and root tensile strength, the effects of plant spacing on root cohesion were minimal for most soil depths apart from 0.4- to 0.5-m depth.

     

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

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

Unusual Fine Root Distributions of Two Deciduous Tree Species in Southern France: What Consequences for Modelling of Tree Root Dynamics?

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.     

<Emphasis Type="Italic">In vitro</Emphasis> rooting of two <Emphasis Type="Italic">Eucalyptus urophylla X Eucalyptus grandis</Emphasis> mature clones

Abstract   The rooting capacity of microshoots derived from two mature Eucalyptus urophylla X Eucalyptus grandis half-sib clones kept for 3 y under intensive micropropagation was assessed in different in vitro conditions. A first set of experiments established that clone 147 microshoots rooted earlier and in greater proportions, while producing more adventitious roots overall than their homologs from clone 149. Modifying the composition of the basal 1/2-MS-derived rooting medium by 1/4-MS or Knop macronutrients, or reducing sucrose concentration to 10 g l⁻¹ did not enhance the rooting rates. However, together with the growth regulators added, they had a significant effect on the number of adventitious roots formed. With rooting rates reaching 81%, the higher rootability of clone 147 over clone 149 was further confirmed by the second set of experiments with significant effects of the various auxins tested and strong clone × auxin interactions on the proportions of rooted microshoots and on the number of adventitious roots. The best rooting scores were given by 5 μM indole-3-butyric acid (IBA) and 12.5 μM 1-naphthaleneacetic acid (NAA), whereas the microshoots exposed to 5 or 12.5 μM indole-3-acetic acid (IAA) were less responsive. Lower light intensities did not improve significantly root capacities, although differences might exist according to the genotype. Overall, root and shoot elongation was stimulated by light. At the end of the experiment, the rooted microshoots were markedly taller than the non-rooted ones, with significant influences of auxins and light intensity, and to a lesser extent, of the genotypes.     

Swimming performance and invasion potential of the round goby

European round gobies (Neogobius melanostomus) are displacing several important native North American fish species. Controlling their invasion is contingent on understanding their swimming inclination and potential. We assessed goby swimming inclination by recording activity in a 2 m flume over a ~24 h period, and swimming potential using a critical swimming (U _crit) test, as well as burst tests in still and flowing water. When given the choice to move, gobies covered as much as 14 m/h, with a slight bias towards nocturnal activity and an overall upstream preference. When confined and coerced to perform a U _crit test, they burst-and-held to achieve 35.5 ± 1.1 cm/s. Thirty minutes following U _crit, they were able to burst-and-coast in a sprint test to almost twice this speed. In still water, they exhibited startle bursts of up to 163 cm/s. We provide a swimming endurance model that indicates flow rates would need to be >125 cm/s to prevent upstream movement, and free of refuge areas in which to recover. The current study shows that the round goby is a surprisingly powerful swimmer with the capacity to continue its invasion should hydrologic control be absent.     

Trophic discrimination factor of nitrogen isotopes within amino acids in the dobsonfly Protohermes grandis (Megaloptera: Corydalidae) larvae in a controlled feeding experiment

The trophic discrimination factor (TDF) of nitrogen isotopes (¹⁵N/¹⁴N) within amino acids, between a stream‐dwelling dobsonfly larva (Protohermes grandis: Megaloptera; Corydalidae) and its diet (chironomid larvae), was determined in controlled feeding experiments. Last‐instar larvae of P. grandis were collected from the Yozawa‐gawa River, central Japan, and reared in the laboratory. After fed to satiation for 1 month, one group of larvae was each fed one living chironomid larva per day for 4 weeks, while a second group was starved for 8 weeks. The larvae were harvested at intervals and the nitrogen isotopic composition of glutamic acid (δ¹⁵N_Glu) and phenylalanine (δ¹⁵N_Phe) were determined to calculate TDF. The mean TDF of satiated and starved larvae were 7.1‰ ± 0.5‰ (n = 3) and 7.3‰ ± 0.5‰ (n = 5), respectively. Thus, the TDF for P. grandis larvae in this study was similar to that reported for other arthropods (approximately 7‰) and was independent of satiation or starvation. A previous study of wild P. grandis larvae, based on the δ¹⁵N_Glu and δ¹⁵N_Phe values, estimated its trophic position (TP) as approximately 2.0 ± 0.1 (n = 5), a low value close to that of algivores, although they are generally characterized as carnivores (usually accepted as TP ≥ 3). The TDF for P. grandis larvae suggests that their low TPs in nature were caused by incorporation of vascular plant‐derived amino acids (with a different δ¹⁵N profile from that of algae) and not by an unusually low TDF or by the effects of the satiation/starvation on amino acid metabolism.     

Root suckering patterns in Populus euphratica (Euphrates poplar, Salicaceae)

To understand the spatial structure of monospecific Tugai forests (Xinjiang Province, China) growing as gallery woods nourished by ground water, root suckering in Populus euphratica was studied by a combination of morphological and molecular analyses. Seedlings grow a deep tap root and keep this as adult trees, whereas root suckers never develop a tap root but utilize the horizontally stretching root of their parent trees. The resulting reverse “T” root architecture distinguishes reliably even adult root suckers from generatively grown trees. Due to assimilate input from the root sucker, the distal root (pointing away from the parent tree) becomes thicker soon than its proximal root, which allows determination of the direction of vegetative growth. One stand including 279 young trees germinated from seeds and 267 root suckers was mapped completely, and selected suckers were assigned to parent trees by genotyping with microsatellite DNA. Root suckers develop up to 40 m away from parent trees on horizontal “spacer” roots, usually originating not deeper than 20 cm below surface. Trees begin with root suckering between 10 and 15 years, shortly before reaching flowering age. Cutting experiments indicated reduced survival of young root suckers disconnected from the parent tree. Without a tap root and with a rooting point close to the surface, declining ground water levels should lower the fitness of root suckers even more than that of generatively grown trees.     

Maximum rooting depth of vegetation types at the global scale

The depth at which plants are able to grow roots has important implications for the whole ecosystem hydrological balance, as well as for carbon and nutrient cycling. Here we summarize what we know about the maximum rooting depth of species belonging to the major terrestrial biomes. We found 290 observations of maximum rooting depth in the literature which covered 253 woody and herbaceous species. Maximum rooting depth ranged from 0.3 m for some tundra species to 68 m for Boscia albitrunca in the central Kalahari; 194 species had roots at least 2 m deep, 50 species had roots at a depth of 5 m or more, and 22 species had roots as deep as 10 m or more. The average for the globe was 4.6±0.5 m. Maximum rooting depth by biome was 2.0±0.3 m for boreal forest. 2.1±0.2 m for cropland, 9.5±2.4 m for desert, 5.2±0.8 m for sclerophyllous shrubland and forest, 3.9±0.4 m for temperate coniferous forest, 2.9±0.2 m for temperate deciduous forest, 2.6±0.2 m for temperate grassland, 3.7±0.5 m for tropical deciduous forest, 7.3±2.8 m for tropical evergreen forest, 15.0±5.4 m for tropical grassland/savanna, and 0.5±0.1 m for tundra. Grouping all the species across biomes (except croplands) by three basic functional groups: trees, shrubs, and herbaceous plants, the maximum rooting depth was 7.0±1.2 m for trees, 5.1±0.8 m for shrubs, and 2.6±0.1 m for herbaceous plants. These data show that deep root habits are quite common in woody and herbaceous species across most of the terrestrial biomes, far deeper than the traditional view has held up to now. This finding has important implications for a better understanding of ecosystem function and its application in developing ecosystem models.     

The clonal root system of balsam poplar in upland sites of Quebec and Alberta

Balsam poplar seeds are short‐lived and require moist seedbeds soon after they are released to germinate. In addition to sexual reproduction, balsam poplar stands can regenerate clonally by root suckering. The origin of stands will in turn affect their genetic structure and root system architecture, which are poorly understood for upland forest stands. Three stands were hydraulically excavated in Quebec (moist) and Alberta (dry) to determine the origin of trees and to characterize root systems with respect to presence of parental roots and root grafts connections. Clones were identified using single‐nucleotide polymorphism (SNPs), and all stems, roots and root grafts were aged using dendrochronology techniques. All 82 excavated trees were of sucker origin, and four of the six stands contained a single clone. Parental root connections were found between 22% and 25% of excavated trees, and 53% and 48% of trees were linked with a root graft between the same or different clones, in Alberta and Quebec, respectively. Mean distance between trees connected by parental root was significantly lower than the distance between unconnected trees (0.47 ± 0.25 m vs. 3.14 ± 0.15 m and 1.55 ± 0.27 m vs. 4.25 ± 0.13 m) in Alberta and in Quebec, respectively. The excavations also revealed many dead stumps with live roots, maintained through root connections with live trees. This research highlights that balsam poplar growing in upland stands is a clonal species that can maintain relatively high genotypic diversity, with frequent root connections between trees at maturity. Maintaining an extensive root system through root connections increases the chances of a clone surviving when the above ground tree is dead and may also enhance the resilience of balsam poplar stands after disturbance.     

Phosphorus availability and rootstock affect copper-induced damage to the root ultra-structure of Citrus

The control of several citrus diseases requires continuous applications of fungicides containing copper (Cu) which favor to the accumulation of this metal in the soil. Therefore, the evaluation of how nutrient availability and rootstock interact with Cu toxicity in the citrus trees is required to maintain sustainability of fruit production in Cu-contaminated soils. Valencia orange trees on Sunki mandarin (SM) or Swingle citrumelo (SC) rootstock were grown in nutrient solutions combining adequate Cu (1.0 μmol L⁻¹), excess Cu (50.0 μmol L⁻¹), deficient phosphorus (P) (0.01 mmol L⁻¹) and sufficient P (0.5 mmol L⁻¹). The excess Cu reduced root and shoot growth, chlorophyll and relative water content in the leaves of the trees compared to those under adequate Cu supply. Furthermore, excess Cu caused severe damage to the root ultra-structure, characterized by the degeneration of the middle lamella and the presence of a thin and sinuous cell wall, as well as, starch accumulation in the plastids, disruption of the mitochondrial membranes and cellular plasmolysis. The damage caused by excess Cu in the cell wall and middle lamella on the root cells of SC was less severe than SM. Sufficient P supply improved the structure of the cell wall and middle lamella of trees subjected to excess Cu in comparison to P-deficient ones. Thus, the occurrence of more preserved cell wall and middle lamella supports the idea that sufficient P availability in the rooting medium and the use of SC rootstock might contribute to increase the ability of young citrus trees to cope with Cu toxicity.     

Induction of root and shoot formation from root meristems ofPetunia hybrida

Summary A procedure has been developed for the induction of root or shoot formation from root meristems of germinated seeds ofPetunia hybrida. Root formation was obtained on Murashige and Skoog (MS) medium supplemented with a combination of 6-benzylaminopurine (BA) (0–0.5 mg/l) and naphtaleneacetic acid (NAA) (0.05–2.0 mg/l). Induction of predominantly shoot formation was obtained on MS medium containing the following combinations of hormones (in mg/l): 0.05–0.5 NAA and 0.25–2.0 BA. Complete plant formation was obtained after rooting of the shoots on MS medium supplemented with IAA (0–2.0 mg/l) or NAA (0-0.5 mg/l).