The effect of container size and aeration conditions on growth of roots and canopy of woody plants

Studies were made on the effect of container size on the growth of Ficus retusa, Pistacia lentisucus and Dodonea viscosa. The larger the container, the larger was the plant. The ratio of plant weight to unit of container-volume decreased with increasing size, whereas the ratio of plant weight to unit surface area remained more or less constant with changing size of container.Aeration of 10-liter containers using 3 methods to increase the surface area of the mixture by 60% while reducing the volume by 40%, increased growth by as much as 165%. Especially enhanced growth was achieved when the structure of the root system was not changed by aeration devices. Root growth was enhanced most in the lower section of the containers. The ratio root-weight: container-volume increased up to 340%, whereas the ratio root-weight: mix-surface area increased by only 100% at the most.These results, and others, indicate that most of the thin roots (or root activity) of woody plants grown in containers are concentrated in the periphery of the container, whereas the roots in the center serve mainly as connectors between the main and peripheral roots.It is suggested that the root system in the containers changed the ratio between the 3 soil phases by decreasing the gaseous phase, mainly in the upper part of the container, and that this phenomenon is a major contributor to the low efficiency of the container-volume usage. Correction can be best achieved by increasing the outer surface of the mixture rather than by using a better aerated mixture.     

Growth and stability of deep planted red maple and northern red oak trees and the efficacy of root collar excavations

Trees with root systems established well below grade due to deep planting or soil disturbance are common in urban landscapes, yet the long term effects of buried trunks and subsequent remediation strategies, such as root collar excavation are poorly documented. We evaluated the consequences of deep planting over a 10-year period on tree growth and stability, with and without root collar excavation, for red maple [Acer rubrum L. Red Sunset^® (‘Franksred’)] and Northern red oak (Quercus rubra L.) planted at grade or 30-cm below grade. Sleeves to prevent soil-trunk contact were installed around trunks on a subset of deep trees. Root collar excavations were made during the 6th growing season for both species and trees were grown for an additional 4 and 3 growing seasons for red maples and Northern red oaks, respectively. Within two weeks of root collar excavations, pulling tests compared the effect of treatments on stability of red maples. Deep planting generally slowed growth of red maple but had no clear effect on Northern red oak. Root collar excavation had no lasting effect on growth of either species. Approximately 55% of deep red maples and 33% of deep Northern red oaks had roots crossing and in intimate contact with buried trunks, suggesting a potential for future girdling roots. Approximately 25% of deep maples had substantial adventitious rooting. All deep Northern red oaks had new roots emerging just above the first original structural roots but none were clearly adventitious. Trunk sleeves had no effect on growth for either species. Neither deep planting nor root collar excavation resulted in a loss of tree stability compared to trees planted at grade, although failure patterns varied among treatments. Overall, the biggest long term concern for deep-planted trees is the potential for girdling root formation.     

平邑甜茶幼苗生长、根构型及吸收特性的容器调控

 以平邑甜茶[Malus hupehensis (Pamp.) Rehd.] 幼苗为材料, 研究了栽培容器形状对幼苗新梢生长、幼苗根构型特征及根系营养吸收特性的影响。结果显示, 生长在“深窄盆”中的幼苗新梢生长量最大, 主根粗, 侧根多且短, 毛细根丰富, 对钙及锌的吸收能力较强, 但根系活力及根系对磷、铁的吸收能力较弱; “等高径盆”中幼苗新梢生长量小, 根冠比接近1, 主根细短、一级侧根少且粗长, 对钾的吸收能力较强; “浅宽盆”幼苗根冠比最大, 一级侧根数量、长度和粗度居中, 二级侧根粗长, 根系活力及根系对磷、铁的吸收能力较强, 但对钾、钙及锌的吸收能力弱。     

Growth of rose roots and shoots is highly sensitive to anaerobic or hypoxic regions of container substrates

Commercial greenhouse cut rose plants commonly have shallow root systems, even in well-drained substrates. We studied rose plant responses to a wide range of soil air-filled porosity values to determine tolerance to low soil aeration. ‘Kardinal’ rose plants on ‘Natal Briar’ rootstock were grown for 11 weeks in containers holding 2.5 l of Yolo loam soil. The soil had been treated with a polyacrylamide soil conditioner to stabilize aggregates after they had been separated into three size fractions: coarse (1–2 mm), medium (0.1–1 mm), and fine (<0.1 mm). Plants were irrigated frequently to keep the soil at container capacity. Total new root growth was greatest in the medium and coarse soil fractions, which had average air-filled porosities of 7.6% and 15.9%, respectively. The fine soil fraction, which had an average air-filled porosity of 1.3%, had almost no root growth. In all soil fractions, roots were absent or scarce in regions of soil that were anaerobic or hypoxic. Highest root length densities occurred at air-filled porosity values of 12–17%, and no new roots grew at air-filled porosity values below 3%. Shoot yields were lower for plants in the substrate with low air-filled porosity, and their leaves had lower stomatal conductance, chlorophyll content, mid-day water potential, and macronutrient concentrations. Frequent irrigation that precludes aeration of the lower regions of the substrate profile will result in shallow root systems and could lead to decreased yields.     

Growth and establishment of container-grown London planetrees in response to mulch,root-ball treatment and fertilization

We conducted two experiments to evaluate the impact of cultural treatments on growth and establishment of container-grown London planetrees (Platanus × acerifolia’ Bloodgood’). In both experiments, 48 trees grown in 100 l (#25) black plastic containers were assigned at random to one of three root-ball treatments prior to planting; no treatment (Control), outer 3 cm of roots removed around entire root-ball (Shave), or outer circling roots disentangled from the root-ball (Tease). In Experiment 1, half of the trees were fertilized with 400 g of controlled release fertilizer (15-9-12; N-P₂O₅-K₂O) at planting and the remainder of the trees were not fertilized. In Experiment 2, half of the trees were mulched with an 8 cm deep × 2 m diameter ring of coarse ground pine bark at planting and the remainder of the trees were not mulched. In Experiment 1, fertilization at planting increased SPAD chlorophyll content on two of four measurement dates but did not affect cumulative height or caliper growth after two years. After two growing seasons, root-ball treatments (shaving or teasing) increased root growth outside the original root-ball compared to control trees. Both root-ball treatments also reduced circling roots. In Experiment 2, mulching at planting increased soil moisture and cumulative tree height and diameter growth. Shaving increased new root growth and both root-ball treatments improved root architecture and reduced circling roots. Overall, the study demonstrates that root-ball manipulations can stimulate new root growth and reduce circling roots. Mulch is a valuable aid to conserve soil moisture and increase tree growth. Fertilization at planting provided little benefit in this experiment, which may have been related to a high level of soil fertility at the site or nutrient loading of the trees from nursery culture prior to transplanting.     

Effect of different lifting dates and different lengths of cold storage on plant vitality of silver birch and common oak

Woody ornamental bare-root plants transplanted in urban areas frequently show poor establishment and occasionally high mortality. Tolerance to different stress factors during transplanting is dependent on plant vitality. The significance of lifting date, in combination with different lengths of time in cold storage, was investigated with 2-year old plants of silver birch (Betula pendula Roth.) and common oak (Quercus robur L.). Plants were grown on a field site in Southern Sweden and were lifted on four occasions, at intervals of 4 weeks, during autumn and early winter. After lifting, plants were stored in a cold store for 90, 135 and 180 days and then (a) xylem water potential in roots and shoots, (b) root growth potential (RGP), (c) mortality and die-back, and (d) shoot and leaf growth were assessed. Lifting bare-root plants of silver birch and common oak too early in the autumn resulted in 62% mortality in birch and 43% in oak, and 31 and 26% die-back in birch and oak, respectively. Plants lifted at a later date showed no mortality in birch and <10% in oak, and almost no die-back. Plants lifted too early in autumn showed decreased root, shoot and leaf growth, compared with those lifted later in the autumn. A longer time in cold storage had a further negative effect on plant vitality in plants lifted too early. Plants lifted later in autumn showed little or no difference in mortality or die-back, for different periods of cold storage, and showed an increase in growth with longer periods of cold storage. Birch plants lifted too early had lower water potential, both in roots and shoots, compared to plants lifted at a later date, while oak plants had the lowest water potential when lifted late. Plants lifted on the first occasion had not been exposed to temperatures below +5°C before lifting, while plants lifted 4 weeks later had been exposed for 67 h to a mean temperature below +5°C. Plants lifted on the first occasion had high mortality and more die-back, while those lifted 4 weeks later showed almost no damage at all. These observations indicate that accumulated exposure to low temperature is probably an important factor in the development of stress tolerance in bare-root plants of silver birch and common oak.     

Winter protection of container-grown nursery stock as affected by container design,hardening-off time and solar exposure

The effects of container type (round vs. square), solar exposure (100% vs. 50%) and hardening-off time (0, 3 or 6 weeks) on winter damage to Ilex crenata Thumb. ‘Hetzii’ (Hetz Japanese holly) and Buxus sempervirens L. (common boxwood) were studied. Container type and hardening-off time had significant effects on plant viability of Ilex crenata ‘Hetzii’ after exposure to freezing temperatures. Plants in square containers achieved substantially higher viability ratings than plants in round containers after freezing. Buxus sempervirens was significantly affected by hardening-off time only. Plant viability increased greatly with 3 or 6 weeks of hardening-off as compared to no hardening-off. Common boxwood plants in square containers did not achieve the same level of growth as plants in round containers during the 1980 growing-season (before freezing). Optimum growth for Buxus sempervirens occurred under full solar exposure.     

The importance of native valley oaks (Quercus lobata) as stopover habitat for migratory songbirds in urban Sacramento,California, USA

Urban development occupies over 375,000 ha (6%) of California's Central Valley, and expansion continues to displace natural and agricultural landscapes. The value of urban areas as habitat for native wildlife and the characteristics that determine its value, however, remain little studied. Many Neotropical migrant passerine bird species are declining due to changes in breeding, migratory, and wintering habitats and climatic conditions. During 2010–2013, we evaluated the importance of native valley oak (Quercus lobata) as stopover foraging habitat used by Neotropical migrant birds in urban areas of the Sacramento region in California, USA. Over 3 years, we surveyed spring and late summer-early fall migrant songbirds and measured tree canopy cover within 31 c.0.91 ha transects in Curtis Park, an older residential neighborhood. We detected 607 individuals from 20 migrant species, but four wood warblers comprised the bulk of observations: black-throated gray (Setophaga nigrescens), Wilson's (Cardellina pusilla), orange-crowned (Oreothlypis celata), and yellow warblers (Setophaga petechia). Migrant abundance was closely correlated with valley oak canopy abundance and increased linearly with oak canopy especially during fall migration. Migrants were nearly absent from areas lacking oak canopy. Migrant bird species as a group also foraged in valley oak substantially more often (74%) than would be expected based on its 15% relative canopy cover (χ²_1d.f. = 924, p < 0.0001), as did all species whose selectivity could be tested. These results are important in demonstrating previously undocumented migrant use of urban areas with remnant valley oak canopy and suggest that protecting existing valley oaks and increasing their use in future urban forestry and landscape plantings in the Central Valley could provide substantial habitat benefits for native migratory birds.     

Estimation of relative water use among ornamental landscape species

Low water use plantings may enhance water conservation in dry landscapes. However, appropriate plant selection is hindered by the dearth of information available on the water needs of different species. A direct method of classification was tested under the hypothesis that relative water use by woody landscape species growing in 3.8 l containers would be representative of the water use of the same species in the landscape. Four species of distinctly different ecological origin (Leucophyllum frutescens, Spiraea vanhouteii, Viburnum tinus, Arctostaphylos densiflora) were chosen in order to obtain a wide range of responses, and their water use was measured in plants growing in 3.8 l containers and compared to that of the same species growing in drainage lysimeters, representative of landscape conditions. Half of the plants were subjected to successive cycles of stress by withholding water after irrigation to container capacity in containers, or applying a fraction of the potential evapotranspiration in lysimeters. The good fit of the regression of average daily water use by lysimeter plants on average daily water use by container plants (R²=0.87,P<0.01) reflects the consistency of relative water use of the four species. Measurement of water use at the end of nursery production may be useful for predicting the relative water use of various species after establishment in the landscape.     

Nitrate uptake kinetics of grapevine under root restriction

To examine the effect of root restriction on the nitrate uptake and the nitrate transport system activity, 2-year old “Fenghou” grapevines (Vitis Vinifera × V. Labrasca) were planted in pots with volume 2 L and 12 L served as root restriction and the control, respectively. The pots were filled with perlite and watered with rainwater and nutrient solution. Vine growth and kinetics of nitrate uptake in vine roots were evaluated. The results showed that root restriction significantly inhibited the shoots and roots growth, enhanced the nitrate uptake rate, decreased the kinetics parameter K_m value and increased V_max value, that is to say, root restriction depressed the affinity of nitrate high-affinity transport system (HATS) and improved the nitrate uptake rates of both high (HATS) and low-affinity transport system (LATS). However, root restriction significantly decreased the amount of net nitrate uptake, which led to the low nitrate concentration in leaves and roots.     

Effect of arbuscular mycorrhizal fungal inoculation on root system architecture of trifoliate orange (Poncirus trifoliata L. Raf.) seedlings

Plant root system architecture is essential characteristics in relation to nutrient acquisition by root system from soil volume. Many environmental factors can affect the establishment of root system architecture, e.g. arbuscular mycorrhizal (AM) fungi. We inoculated the trifoliate orange (Poncirus trifoliata L. Raf.) seedlings with four AM fungal species in rhizoboxes, with non-inoculated seedlings as control. Using the WinRHIZO^® image analysis system, the root system architecture of seedlings was characterized. Results indicated that AM colonization did not affect the tap root length, the average root diameter, the basal root growth angle in spite that four AM fungal species exerted differential influence on the plant growth. Contrastingly, AM colonization significantly reduced the total root length, the root volume, the root surface area, but promoted the formation of lateral roots of high order. In addition, AM colonization induced more fine roots and less coarse roots. To our knowledge, it is the first report on the influence of AM fungi on the distribution of root diameter size classes. The mechanisms and implication of AM fungi on root system architecture is discussed.     

How good are containerized trees for urban cooling?

The capacity of urban trees in mitigating urban heat is well-known. As space is often limited, one feasible option for increasing the urban green would be containerized plants. Nevertheless, for optimizing the vitality and benefits, detailed knowledge on tree growth reactions in different types of containers is missing. We designed an experiment with two commonly planted but ecologically contrasting urban tree species Tilia cordata and Platanus x hispanica planted into the ground and in containers according to four different planting types, with or without drought stress. Along with the meteorological variables, continuous soil moisture and temperature at 25 cm depth, sap flow, as well as measurements of leaf physiological responses i.e. stomatal conductance, mid-day leaf water potential and chlorophyll content were measured three times on sunny and warm summer days during 2020 and 2021. P. hispanica showed more than double diameter increment at breast height in the ground than in containers; however, the growth trend was relatively better for T. cordata in containers. While comparing different container types and species reactions, it was clear that soil temperature within the plastic containers were significantly higher, whereas insulation is not enough to reduce either the temperature or slowing down the soil drying out. Where both the species showed lower stomatal control over atmospheric demand, P. hispanica showed leaf transpiration energy loss of around 300 W m⁻² when planted in the ground and T. cordata trees around 260 W m⁻² when planted in non-insulated containers, which are comparable to the energy loss from the street trees. Therefore, a strategy of mixed planting with faster growing species such as P. hispanica that provide stronger cooling at the initial stage in the containers to be complemented and eventually replaced with medium growing species T. cordata for relatively longer time period could be suggested.     

成龄苹果树形改造对根系生长分布的影响

以成龄红富士苹果为试材,应用壕沟法研究小冠疏层形改造成高干开心形对根系分布状况的影响。结果表明:垂直分布上,改造树总根数增加,直径小于2mm的吸收根密集分布于20～40cm土层,而对照则分布于0～20cm;改造树和对照树水平分布最高峰分别出现在距树干100～120cm和60～80cm处。改造树根干重显著高于对照,提高了13.4%。可见,小冠疏层形改造为高干开心形后,根数目、干重增加;根系向下延伸,向外扩展。     

Quantitative trait analysis of transplanting time and other root-growth-related traits in tomato

Transplanting time is determined by factors such as the field conditions, the age of the seedlings, and the size of the container, but little information is available on the effect of the genetic background on transplanting time. Here, we examined root dry weight (RDW), shoot dry weight, root/shoot ratio (RSR), time at which 50% of the germinated seedlings have expanded cotyledons (CE50), root ball formation (RBW), the length of time from the cotyledon expansion from the first to the last germinated seedling (ES) and transplanting time (TRD) in a BC₁F₆ population derived from Solanum lycopersicum and Solanum pimpinellifolium. All traits exhibited significant correlation with each other, except for RSR, which was only significantly correlated to RDW. A total of eight additive quantitative trait loci (QTLs) were detected for the five traits, i.e., RSR, RBW, CE50, ES, and TRD. One epistatic (QTL × QTL) interaction each was identified for RSR and TRD. QTLs for RSR, RBW, CE50, ES and TRD clustered near marker LEOH37 on chromosome 4. Clustering of ce50-4, rsr4, rbw4, and es4 with trd4 reflected the dependence of transplanting time on root ball formation, growth uniformity and early seedling growth, especially root growth. In addition, several QTLs in this study were mapped to regions where QTLs for days to flowering or number of leaves before the first inflorescence had been identified previously. This suggests that the roots may exert some influence on the flowering time in tomato.     

Nitrogen storage and mobilisation for spring growth in Ligustrum cultivated in container

In soilless cultures, fertiliser leaching is particularly large in spring, when fertilisation is applied during rainy periods. Therefore, a better knowledge of the N uptake periods and of the amount of N mobilised from the storage organs could improve fertilisation management during spring growth. Nitrogen allocation was studied for two consecutive years in Ligustrum ovalifolium L. These shrubs were cultivated in containers, fertilised (with or without ¹⁵N) in spring and autumn of the first year, and received either fertilisation or only tap water on the subsequent spring growth. Nitrogen assimilated in spring was preferentially allocated to the leaves whereas a large part of N assimilated in autumn was directly stored in the perennial organs, mainly in roots. During the subsequent spring period, N was mobilised from all perennial organs, with a proximity gradient, to sustain bud break and shoot growth. Nitrogen assimilated in autumn was preferentially used to sustain shoot growth, with a rate of 68% of its winter N content against 55% for N assimilated the previous spring. When plants were subjected to spring fertilisation, growth was initially sustained by N mobilisation before N assimilation resumption, but N mobilisation was 15% lower than in unfertilised plants. Overall results are discussed in terms of the improvement of the N-fertilisation efficiency relative to spring growth of ornamental shrubs cultivated in container.     

Effects of nitrogen and phosphorus on root and shoot growth of Cotoneaster divaricata Rehd. & Wils.

Root and shoot growth rates of Cotoneaster divaricata were determined using a growing system of polyvinyl chloride pipe cylinders in which longitudinal sections could be removed for periodic root observations. Plants were fertilized with nitrogen (N), phosphorus (P), and potassium (K). N, as NH₄NO₃, was applied weekly at levels of 0, 250 or 500 mg/l and P, as H₃PO₄, was incorporated in the medium at levels of 0, 5 or 50 mg/l. K, as KCl, was maintained in the medium at a 150 mg/l level by soil tests conducted weekly. Shoot growth was increased after N application. However, no difference was observed between N levels. P increased shoot growth only at the highest N level applied. Although root growth was not increased by either N or P, high N levels inhibited root growth, whereas P stimulated root growth. No correlation (r = 0.19) was observed between shoot and root growth.     

Vine growth and nitrogen metabolism of ‘Fujiminori’ grapevines in response to root restriction

Two-year-old ‘Fujiminori’ grapevines (Vitis Venifera × V. Labrasca) planted in plastic pots (10 L) were used to evaluate vine growth and nitrogen metabolism in response to root restriction. Results show that root restriction reduced shoot growth and photosynthetic rate, but promoted root growth in vines. NO₃⁻-N concentration in all plant parts, and total N concentrations in brown roots and new leaves were decreased by root restriction, and chlorophyll and carotenoid concentrations in mature leaves were also reduced. Nitrate and nitrite reductase activities in brown roots and mature leaves were significantly reduced in root-restricted vines. The results suggest that the reduction of nitrate and nitrite reductase activities caused the inhibition of nitrogen assimilation, and this might be an important reason for root restriction inhibiting shoot growth.     

Pepper (Capsicum annuum L.) root growth and its relation to shoot growth in response to nitrogen

Summary

The main objective of this work was to investigate shoot and root morphology of pepper (Capsicum annuum L.) (cvs Early Calwonder, Keystone Resistant Giant, Jupiter, Shamrock and Gator Belle) grown in sand culture at three N-levels, 56,84 and 112 mg l^?1. Shoot, root, and root components were evaluated 40, 50 and 60 days after seeding. Tap, basal and lateral root accounted for 1%, 40% and 53%, respectively, of the total root dry weight. Shoot: root ratios did not differ between cultivars. Basal root length, basal root number and first-order lateral root number increased with increasing N. Cultivars with either long lateral roots or basal roots had short basal roots or lateral roots respectively, although only small differences were observed in other root and shoot characteristics. In this greenhouse environment, shoot/root ratio was constant. Nitrogen stimulated root and shoot growth, and this effect was significantly different for the root components.     

Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Bud-grafting success in Acer platanoides ‘Crimson King‘ related to root growth

Summary

Summer bud-grafting (budding) of the red-leaved scion ‘Crimson King’ onto Acer platanoides rootstocks is unreliable. Typically, the rootstock produces copious callus from the incision in the stem, but the scion bud-chip fails to survive and complete the union. Percentage bud-take was consistently low when rootstocks were grown and budded in 2 litre containers (e.g. 33%), moderately high, but below commercially acceptable levels, when grown in a light sandy loam soil in the field (e.g. 77%), and often very high when grown in deep sand beds (e.g. 100%). The growth of larger structural roots was in the order pot < field soil < sand beds, and confining the roots of field-grown rootstocks in porous mesh bags reduced bud-take from 79 to 13% averaged over three sites. Increasing shoot growth by growing rootstocks in a polythene house did not improve bud-take, but increasing the pot size from 2.0 to 7.5 litres did so. Extensive root growth appears to be one of a number of factors determining bud-take, which was increased further by treating the scionwood and rootstocks with a mixture of Benlate and Rovral fungicides prior to budding. These results are discussed in terms of the need to maintain the bud-chip in a viable condition during the union forming process.