Limited Soil Volume Research Articles

Effect of pile spacing on the thermal performance of thermo-active pile groups

Effect of pile spacing on the thermal performance of thermo-active pile groups

Nutrient interactions and salinity effects on plant uptake of phosphorus from waste-based fertilisers

Many organically managed farms in Europe have low levels of soil phosphorus (P). Arable farms that rely strongly on biological nitrogen fixation (BNF) have been shown to have rather low outputs and a tendency to deplete soil P and potassium (K) compared with arable farms that have a lower reliance on BNF and higher external inputs. Therefore, research focusing on providing a balanced input of nitrogen (N), P, K and sulphur (S) from alternative sources is of interest to organically managed farms in Europe. The aim of this study was to quantify P availability from different organic wastes applied alone or in combination to improve the mixtures’ N:P:K:S ratio. P availability was measured by P uptake and recovery in ryegrass grown in pots. The isotope dilution approach was used in which a non-labelled fertiliser is added to a soil that has been pre-incubated and equilibrated with labelled 33P. The P recovery of the different organic wastes varied significantly (10–20 %). Manure and anaerobically digested manure mixed with ash from straw had the lowest P recovery. All the organic waste treatments had higher plant growth and P uptake compared with the negative control, but none of them reached the values observed after application of mineral P. Mixing digested manure with ash increased soil pH at the end of the experiment, which may explain the lower P availability. The highest P recovery was found in digested products, either manure alone or mixed with municipal waste or the industrial waste product Fertigro®. However, the mixture of digested manure and Fertigro® led to lower dry matter production, whereas Fertigro® used alone resulted in high leaf P concentrations but depressed shoot and root growth, presumably due to salinity effects and a decrease in soil pH. Anaerobic digestion increased the availability of P, which may be explained by the lower immobilisation potential of the remaining organic matter in the digestate. This study highlights the potential challenges when attempting to improve the N:P:K:S ratios of waste-based fertilisers through mixing due to material interactions. However, such effects are likely to be overexpressed in pot trials that have a limited soil volume. Field trials are therefore needed to quantify such effects in practice.

An evaluation of corn production within a Wetlaculture™ system at Buckeye Lake, Ohio

Harmful algal blooms (HABs) are increasing in frequency and severity worldwide due to nonpoint source nutrient pollution, mainly a product of agricultural runoff. This issue is compounded by the steady, global loss of wetlands and their water quality services. Wetlaculture, an integrated system of wetlands and agriculture, has been proposed as a solution to HABs in which farmland located on former wetlands is flipped to serve as a nutrient-sequestering treatment wetland for a period of years, then flipped back to farmland which consumes the stored nutrients for crop production without the need for fertilizers. A wetlaculture mesocosm experiment was initiated at Buckeye Lake, Ohio in 2016, where all of the site's mesocosms had been functioning as treatment wetlands fed with water from an adjacent, nutrient-impaired stream prior to the 2020 season. This study serves as both a continuation of the treatment wetland experiment, and a first attempt at the cultivation of an agricultural crop in wetlaculture mesocosms. Eight of the twenty-eight mesocosms were drained and planted with corn (Zea mays), while the remaining twenty continued to function as treatment wetlands. Inflow and outflow concentrations of five nutrient species were monitored in the wetland mesocosms, while suitability for corn was evaluated via preplant soil tests and ultimate grain yield, which was compared to that of a nearby commercial farm. End-of-season soil analyses from both the corn and wetland mesocosms were taken to determine the impact of these disparate management regimes on total soil N, P, K, and C. Results indicate that the treatment wetlands continued to improve water quality and that the mesocosms planted with corn produced a grain crop without fertilization. Mesocosm yields (58 ± 9.5 bu./ac) fell significantly below those of the reference farm (160 ± 15.3 bu./ac)(p = 0.004). Some of that difference may be due to the frequent herbivory that occurred during this study, in addition to the limited soil volume in the 0.285 m3 mesocosm tubs versus the open agricultural field.

Irrigation and fertigation effects on phosphorus and potassium nutrition of wine grapes

The optimal rate of irrigation of the three wine grapes Sauvignon blanc, Merlot, and Cabernet Sauvignon, grown in a semi-arid environment in Israel, was investigated during 1992 - 1998, The drip irrigation I ate was gradually raised after bud break up to a level of either 0.3, 0.4 or 0.5 Pan A coefficient, and then these coefficients vi ere maintained throughout the rest of the growing season. In an additional experiment the effects of secondary purified recycled effluent and fresh water irrigation was compared in Merlot and Cabernet Sauvignon, irrigated by surface and sub-surface drippers. The nutritional status of the vineyard was followed by leaf petiole and leaf blade analyses carried out at flowering and at harvest. Leaf petiole and blade analyses indicated that the nitrogen status of the vines was adequate. The tissue potassium level in the young vineyard was luxurious (ca, 2-3 % in petiole at harvest), reflecting an abundant supply of It by the soil, while the tissue concentration of P was at a deficient level (ca, 0.1 % and less in blades at harvest). Potassium levels declined as the vines matured, probably as a result of K depletion from the limited soil volume explored by the root system under drip irrigation. Low rates of annual phosphate fertigation (5.6-13.7 kg ha -1 P) raised tissue-P proportionally to the rate of fertigation, Irrigation according to a Pan A coefficient of 0.3, as compared to coefficients of 0.4 and 0.5, significantly reduced tissue-K levels. Irrigation with recycled water (high in NPK) raised tissue-P significantly, The relative depletion of K and P in leaf petioles and blades, from flowering to harvest, was found to be a good indicator of the nutritional status of these two elements. At flowering petiole-P was polynomially and linearly correlated with petiole- and blade-P at harvest, respectively, under a wide range of P nutritional intensities. Leaf blades at flowering and harvest had higher priority for P under low intensity of P nutrition. Suboptimal P nutrition could be diagnosed best by petiole-P concentration at harvest. The inflection petiole concentration associated with optimum P nutrition was 0.413 % P at flowering, which corresponded to 0.133 % P in petiole and blade at harvest time.

Urban forest resilience through tree selection—Variation in drought tolerance in Acer

It is widely recognized that trees contribute a range of ecosystem services in urban environments. However, the magnitude of their contribution is closely related to their physiological condition and capacity to persist within our towns and cities. Root loss during transplanting, limited soil volume, disruption to soil hydrological processes and impermeable surfaces result in water deficits being major physiological stress limiting the performance of urban trees. The leaf water potential at turgor loss (ΨP0) provides a robust measure of drought tolerance since a more negative ΨP0 allows the leaf to maintain physiological function over a wider range of leaf water potentials and, by implication, soil matric potentials (Ψsoil). In this study, ΨP0 was calculated for 27 maple (Acer) genotypes based on a known linear relationship between the osmotic potential at full turgor (Ψπ100) and ΨP0. In spring, ΨP0 varied between −1.4MPa in Acer carpinifolium and −2.7 in both Acer rubrum ‘Northwood’ and Acer x freemanii ‘Autumn Blaze’. During summer, Acer spicatum had the highest ΨP0 at −1.6MPa and Acer monspessulanum had the lowest ΨP0 at −4.3MPa. Significant differences in ΨP0 were found between cultivars of A. rubrum and Acer saccharum. A highly significant relationship was found between seasonal osmotic adjustment and summer ΨP0 suggesting that osmotic adjustment is a driving force for summer ΨP0 in Acer leaves. These data confirm the wide range of tolerance to water deficits in Acer and give important insight into the potential of species to tolerate periods of low water availability by providing quantitative data not previously available. The technique shows great promise as a screening tool for the drought tolerance of new and traditional plant material. This data will be highly relevant for those selecting trees for urban sites as well as for nurseries seeking to evaluate genotypes for production purposes.

The effect of permeable pavements with an underlying base layer on the growth and nutrient status of urban trees

Trees in urban areas increase the liveability of towns and cities but street tree growth can be constrained by the limited soil volume available for root growth and by reduced water and nutrient availability under impervious urban surfaces. An approach to improve the growth and health of street trees is the installation of permeable pavements. This study assessed whether permeable pavements with varying depths (0, 100 or 300mm) of an underlying base layer affected soil moisture, soil temperature, tree growth and leaf nutrient status when broad-leaf paperbark (Melaleuca quinquenervia) trees were planted in two soil types, sand and clay.Permeable pavements increased moisture levels in drier sandy soil but decreased moisture levels in wetter clay soil after rainfall, with the stabilising effect of the permeable pavement on moisture levels being related to the depth of the underlying base layer. Permeable pavements and their base layers also had moderating effects on soil temperature. Permeable pavement with a deep drainage layer (300mm) increased trunk diameter growth by 55%, although growth was only increased when trees were planted in clay. Permeable pavements with a shallower drainage layer (0 or 100mm) did not affect tree growth compared with trees in control asphalt pavements. However, permeable pavements without a drainage layer reduced tree height growth in clay soil by 37 to 38% compared with pavements with a 100mm or 300mm drainage layer. In contrast, permeable pavements without a drainage layer increased trunk diameter growth in sandy soil by 65% compared with permeable pavement with a 100mm drainage layer. Leaf nutrient concentrations were often unaffected by pavement design but differences in growth between treatments were associated with differences in the concentrations of some nutrients including K, Mg and S. This study demonstrated that inclusion of underlying base layers is important for tree growth when permeable pavements are installed on poorly-draining soils. Inclusion of a base layer may not be optimal for tree growth when permeable pavements are installed over freely-draining soils.

Methodology for obtaining prediction models of the root depth of lettuce for its application in irrigation automation

Irrigation scheduling and automation are usually conducted using models that are based on the measurement of the soil water content. In this sense, water balance has established itself as a good indicator of the growth and development of crops and is currently used in several automatic programming systems, primarily in intensive farming and microirrigation systems. This method analyses the gains and losses of water in a limited volume of soil to determine the water availability for crops and the soil water status. A parameter of great importance for the application of this method is the root depth, which limits the soil volume to be considered in the water balance. In most cases, the actual evolution of this parameter during crop development is not considered, using instead fixed tabulated values or values that have been proposed in the literature. However, during some periods of crop development, the soil profile that is considered for the water balance does not correspond to the profile that is actually explored by the root system, resulting in a mismatch in the water balance. A good relationship between the root depth and the percentage of ground cover in lettuce has been observed, the latter of which is associated with crop development and the evapotranspirative demand. Therefore, this paper presents a methodology for obtaining prediction models of the root depth of the ‘Little Gem’ lettuce crop from the percentage of ground cover. The implementation of this prediction model in an automated irrigation management system will permit the optimisation of water resources due to the adjustment of the water content to the actual volume that is explored by the roots.

Impacts of Aerated Compost Tea on Containerized Acer saccharum and Quercus macrocarpa Saplings and Soil Properties in Sand, Uncompacted Loam, and Compacted Loam Soils

Aerated compost teas (ACTs) are applied to soils with the intent of improving microbial properties and nutrient availability and stimulating plant growth. Anecdotal accounts of ACT for these purposes far outnumber controlled, replicated, and peer-viewed experiments that have examined the impacts of ACT on soil properties and plant growth responses. This research assessed the impacts of four rates of ACT compared with water on containerized Acer saccharum and Quercus macrocarpa saplings growing in loam, compacted loam, and sandy soils. No significant differences were found comparing water with ACT applied at rates of 2, 4, and 40 kL ACT/ha for any of the six tree responses and 21 soil responses. Microbial biomass nitrogen (N) and potassium (K) increased, and available N decreased, in soils treated with ACT at 400 kL·ha−1 compared with water. Shoot, root, total biomass, and the root/shoot ratio were significantly greater for Quercus macrocarpa trees growing in compact loam with the 400 kL ACT/ha treatment compared with water, but significant differences were not detected for this application rate compared with water in the other soil types and in no instances with Acer saccharum saplings. These results provide some support for claims of ACT being able to increase soil microbial biomass and K, but provide minimal support for ACT being able to increase tree growth across multiple species in a variety of soil types. An application rate of 400 kL ACT/ha may be attainable for trees in containers with limited soil volumes, but this application rate is likely cost-prohibitive, and not practical, in the landscape. At this application rate, ≈1000 L of ACT would be required to treat a typical, and relatively small, critical root zone of 25 m2.

Growth and transpiration of maize and winter wheat in response to water deficits in pots and plots

Pots used for experiments conducted on plants grown in them create rooting environments that are affected by limited soil volume, which can affect various physiological processes, including transpiration, and plant growth. However, the applicability of results from pot experiments to the field has received limited attention. The objective of this study was to compare the growth and transpiration of maize (Zea mays L.) and winter wheat (Triticum aestivum L.) when grown in pots and field plots under various constant water deficits. The experiments were conducted under similar environmental conditions for both pots and plots. Transpirational responses at both transient (RTTr) and daily (RDTr) time scales to a decreasing fraction of available soil water (FASW) were analyzed. For a comparable FASW, there was a significant reduction in shoot dry weight and total transpiration for plants in pots compared to those in plots. A parabolic relationship between shoot dry weight and total transpiration existed and was not influenced by soil volume or crop type. The plot experiment data for both crops was consistent with pot data for the response of RDTr and RTTr to changes in FASW, which was represented by a linear-plateau function. However, the threshold values were significantly different for the two time scales. The threshold values and slopes of the linear-plateau function for maize and wheat were not significantly different in the response of RTTr to FASW, but were significantly different in the response of RDTr to FASW. Therefore, the transpirational responses of the selected maize and winter wheat hybrids to soil drought were different at the daily and transient time scales.

Habitat Studies Identifying Potential Trees for Urban Paved Environments: A Case Study from Qinling Mt., China

Trees in urban paved environments are highly exposed to heat, low air humidity, periods of critical water stress, high soil lime content and soil pH, limited soil volume, pollutants, and de-icing salts. Combined with the challenges of climate change and the threat of disease and pest infestations, this has led to considerable and persistent arguments for using a more varied range of trees, including stress-tolerant species, at urban paved sites. Extensive fieldwork was carried out in the Qinling Mountains, China, in a search for tree species suitable for urban paved sites in northern parts of central Europe and in adjoining milder parts of northern Europe (CNE-region), where tree species are exposed to seasonally dry and harsh conditions. The study identified habitats in the Qinling Mountain range that are similar to those at sites in paved environments, and analyzed the growth and performance of different tree species in these habitats. A total of 25 tree species representing 21 genera were found, of which 14 species were identified as specialist colonizers of warm, dry south-facing slopes where site conditions are similar to those in paved environments of the CNE-region.

Soil Compaction Effects on the Establishment of Three Tropical Tree Species

Tree seedlings planted in containers along sidewalks in urban environments show restricted growth and development over time. This is the result of limited soil volume and soil compaction that hampers nutrient availability and water movement. Using tree species commonly used in urban forestry in Puerto Rico, this study was conducted to determine their growth response when planted in compacted soils. Seedlings of three ornamental tropical tree species, trumpet bush [Tecoma stans (L.) Juss. ex Kunth], bottle brush [Callistemon citrinus (Curtis) Skeels], and pink trumpet (Tabebuia rosea dc.) were transplanted into pots of sandy clay loam or clay soils at three levels of compaction: control (no compaction), 1.2 g/cm3 and 1.4 g/cm3 bulk density, respectively. Plant height, shoot diameter, leaf number and color, foliar area, and root, shoot, and leaf dry weights were measured on two plants every two months for six months. All species exhibited better growth in sandy clay loam at 1.2 g/cm3; after six months, all species showed a reduced root-shoot ratio. When planted in clay at 1.4 g/cm3, all trumpet bush seedlings died within two months. No leaf color differences were observed between species at different compaction levels. Bottle brush showed less growth suppression by increasing compaction level in both soils.

Soil steaming to reduce intrarow weed seedling emergence

SummarySteaming the soil prior to crop establishment can be a very effective method of preventing weed seedling emergence on raised beds of vegetable crops. However, current mobile steaming technology for outdoor vegetables is characterized by an extremely high energy consumption and a low work rate. This has led to the concept of band‐steaming, where only a limited soil volume is steamed corresponding to the intrarow area of a row‐grown vegetable crop. Weeds growing in the intrarow area are difficult to remove by traditional non‐chemical means, usually involving substantial input of manual labour in organic cropping. This paper presents the initial results from laboratory studies with steaming a limited soil volume simulating a band. The investigations describe the relationship between maximum soil temperature achieved from soil steaming for different periods and effects seen on subsequent weed seedling emergence. The relationships obtained were generally sigmoid and could appropriately be described by a common dose–response function. Seedling emergence from natural weed species was reduced by 90% when the maximum soil temperature reached 61°C, and a further 10°C rise in temperature gave 99% reduction. Added and non‐imbibed seeds of Lolium perenne and Brassica napus generally required higher temperatures to achieve the same control level as the natural weeds in the soil samples.

Limited reinforced space in segmental retaining walls

Current design of geosynthetic reinforced segmental retaining walls considers an a priori limitless length for reinforcement installation. Such length is typically 0.5–0.7 times the height of the wall. However, often there are constraints on such space; e.g., bedrock formation located at a small distance behind the facing. The objective of this note is to introduce a procedure for assessing the required long-term strength of the reinforcement while considering its limited length. Predictions by a conventional slope stability analysis were first checked against a continuum-mechanics based numerical analysis. Upon obtaining good agreement, a design chart was developed. The chart enables the determination of the reduction in the lateral earth pressure coefficient due to the constrained space. The revised earth pressure coefficient can be used with current analytical methods to account for the limited space. The results appear to be valid for conventional walls retaining a limited volume of soil. Comparison with limited experimental results for unreinforced backfill shows reasonably good agreement.

Zn fertilization improves water use efficiency, grain yield and seed Zn content in chickpea

In a number of the major chickpea-growing areas in the world, rainfed crops of chickpeas are often grown on soils with low available zinc (Zn). Consequently, chickpea crops can be challenged by soil water deficits and Zn deficiency coincidentally during the growing season. The interaction between these stresses was examined in two glasshouse experiments using genotypes differing in Zn efficiency. Water stress was imposed during podding. Increasing the level of Zn resulted in large and significant increases in vegetative growth up to podding. Applying Zn increased grain yields when the plants were well watered, but not under water stress, except for the Zn-efficient and drought-resistant genotype ICC-4958. Harvest indices were generally reduced as the supply of Zn and water increased. Applying Zn increased water use and water use efficiency of chickpea. Yields were reduced by water stress, largely due to fewer pods set per plant. Losses from water stress were greatest at the highest level of Zn, which was attributed to the limited soil volume afforded by the pots and the rapid development of stress in the larger plants grown at adequate levels of Zn. However, at each level of Zn, the loss in yield from water stress tended to be less in a Zn-efficient genotype. The major factor determining the distribution of Zn in the plant was the supply of Zn, while differences due to water stress and genotype were relatively small. Two-thirds of the Zn present in the plant at maturity was accumulated after the start of podding and this was little affected by water stress. The proportion of Zn in the roots of Zn-deficient plants was less than that in Zn-adequate plants. As the Zn supply increased, Zn accumulation was higher in leaves than in the stem and reproductive parts, due to combined effect of both higher Zn concentration and higher dry matter. At maturity, senesced leaves and pod walls had relatively lower concentrations of Zn compared to leaves and pods at the start of podding in all Zn treatments. In contrast, the Zn content in the stem either increased or remained unchanged. At maturity, Zn accumulation in plant organs generally increased with increasing Zn supply, but the largest proportion of Zn was found in the seeds, which is a beneficial nutritional trait for human nutrition.

Growth response of Ficus benjamina to limited soil volume and soil dilution in a skeletal soil container study

The interactive effects of rooting volume and nutrient availability in a skeletal soil medium designed to meet street tree and pavement needs were observed in a containerized experiment. Benjamin fig ( Ficus benjamina L.) was grown in a stone-soil blended skeletal soil material (CU-Soil™) and compared to a loam soil. The same topsoil used as the soil component in the skeletal soil material was used as the sole component in the comparison soil-only treatment. Plants grown in the skeletal soil material had reduced leaf tissue N content and depressed growth compared with plants grown in non-diluted soil. No other mineral deficiencies were found. Leaf number, chlorophyll concentration, shoot weight, and root characteristics were all affected. Reduced growth from soil dilution could be offset by the provision of an enlarged rooting volume for root development. Large containers of skeletal soil were observed to have smaller root systems compared to equivalent net volumes of loam soil at the first two harvest dates of the study. By the end of the study, the large containers of skeletal soil were observed to have developed larger root systems compared to equivalent net volumes of loam soil; resulting in comparable leaf N levels and total plant dry matter. Plants in skeletal soil had lower shoot: root ratios at the end of the study. Investing resources to further root growth in times of nutrient shortages is a probable plant reaction as evidenced by differences in specific root length between treatments. The study allowed a method for directly partitioning the containerization effect by having equivalent amounts of soil over two volumes.

Measurement and modeling of the transpiration of a temperate red maple container nursery

This study was designed to estimate transpiration in a container nursery under both irrigated and water stressed conditions using a biologically based canopy model. The model, MAESTRA, was parameterized with a suite of physiological measurements and an explicit response function for soil moisture deficit was incorporated. The model was validated against transpiration measurements monitored by the stem heat balance method in both irrigated and non-irrigated plots. Distinct disconnects between estimated and measured values were found at high soil moisture deficits. The data justify the incorporation of a soil moisture component to simulate transpiration of plants with root zones in limited soil volumes. The agreement between measured and modelled canopy transpiration separated at a soil moisture deficit of 0.85 or greater, however, estimates of daily transpiration simulated by the model were in agreement with sap-flow measurements when water was not limiting. The data indicate that cuticular conductance at soil moisture deficits ≤0.85 may explain the separation in model estimates and actual plant water loss.

Stem water relations and net CO 2 uptake for a hemiepiphytic cactus during short-term drought

Hylocereus undatus is widely distributed naturally and is currently cultivated in 19 countries for fruit. Because of its relatively thin stems, H. undatus was hypothesized to respond to drought more rapidly than other cacti. Stem water potential, water content and thickness were monitored during drought to provide easily measured parameters to be correlated with net CO 2 uptake ability, allowing the development of irrigation schedules to optimize water-use efficiency. H. undatus exhibited Crassulacean acid metabolism, as maximal stomatal opening and net CO 2 uptake occurred at night. Although the soil water potential decreased to −4.2 MPa during 12 days without watering, the stem water status parameters remained near their values under wet conditions ( Ψ stem of −0.67 MPa, water content of 90.8%, thickness of 4.48 mm). The drought was accompanied by a 63% decrease in the maximal water vapor conductance and a 57% decrease in the maximal net CO 2 uptake rate, but when the roots were excised for plants under wet conditions, neither parameter decreased appreciably over a comparable time period. Injection of 100 μM abscisic acid into attached stems and placing cut ends of detached stems in such a solution substantially reduced gas exchange 1 day later; at 2 days after injecting the hormone, the maximal water vapor conductance was similar to the minimal daytime values under wet conditions and the net CO 2 uptake rate was inhibited by 97%. Abscisic acid produced in the roots apparently leads to stomatal closure for this hemiepiphyte—whose roots can occur in very limited soil volumes—as soon as the water supply starts to deplete rather than after a large fraction of its stem water is transpired.

Allelopathy in black walnut ( Juglans nigra L.) alley cropping. I. Spatio-temporal variation in soil juglone in a black walnut–corn ( Zea mays L.) alley cropping system in the midwestern USA

A study was conducted to quantify the spatial and temporal variation in soil juglone (5-hydroxy-1,4-naphthoquinone) in a 10-year-old black walnut (Juglans nigra L.)–corn (Zea mays L.) alley cropping system. Two treatments (‘root barrier’ and ‘no barrier’) were applied to determine if soil juglone in the alley can be minimized by preventing black walnut root growth into the alley. Although no significant seasonal variation in soil juglone existed, a distinct spatial pattern was observed. Juglone concentration decreased as much as 80% as the distance increased to 4.25 m from the tree row. Installation of polyethylene root barriers minimized juglone concentration to trace levels in the alley. However, this treatment increased juglone levels within the tree row as compared to the ‘no barrier’ treatment, probably as a result of increased rooting density within a limited volume of soil.

Interactive effects of ozone and soil volume on Plantago major

summary Plantago major L. ssp. major usually grows on trampled paths, tracks and gateways, and its root system is often restricted by compaction or by a limited volume of soil. In this heterogeneous environment, individuals close to each other will experience variable degrees of root restriction. As some populations of P. major have been demonstrated to be sensitive to ozone, the aim of this study was to investigate the effect of root restriction on the response of P. major to ozone.It was hypothesized that root restriction should reduce the effects of ozone. If this is true it would have implications for evolution of ozone resistance. A single population of P. major was grown in controlled‐environment chambers and exposed to either charcoal/Purafil‐filtered air or to ozone (70 nl O3 l−1for 7 h d−1). Plants were grown in pots of four different volumes: 0.175 1; 0.3651; 2.2801; and 5.8301. Four harvests were performed, at 21, 37, 51 and 91 d from germination. At the final harvest, the total nitrogen content of leaf tissue was analysed and compared with that of plants collected from the field. Stomatal conductance (gs) and net carbon assimilation (A) rate were also recorded during development.Plants grown in the smallest pots exhibited severely impaired growth, lower gs and lower A than non‐restricted plants. Root growth was less impaired than shoot growth. However, only plants in the smallest pots resembled those found in the field, which implies that realistic assessment of ozone effects on this species should involve a degree of root restriction. Appearance and leaf nitrogen content of leaves suggested that root restriction may have caused nitrogen deficiency. Contrary to the initial hypothesis, exposure to ozone reduced the growth of plants in all sizes of pot. Stomatal conductance was consistently lower in plants exposed to O3, but there was no effect of ozone on A.

Changes in Root Hydraulic Conductivity for Two Tropical Epiphytic Cacti as Soil Moisture Varies

The tropical epiphytic cacti Epiphyllum phyllanthus and Rhipsalis baccifera experience extreme variations in soil moisture due to limited soil volumes and episodic rainfalls. To examine possible root rectification, whereby water uptake from a wet soil occurs readily but water loss to a dry soil is minimal, responses of root hydraulic conductivity (Lp) to soil drying and rewetting were investigated along with the underlying anatomical changes. After 30 d of soil drying, Lp decreased 50%–70% for roots of both species, primarily because increased suberization of the periderm reduced radial conductivity. Sheaths composed of soil particles, root hairs, and mucilage covered young roots and helped reduce root desiccation. Axial (xylem) conductance increased during drying due to vessel differentiation and maturation, and drought-induced embolism was relatively low. Within 4 d of rewetting, Lp for roots of both species attained predrought values; radial conductivity increased for young roots due to the growth of new branch roots initiated during drying and for older roots due to the development of radial breaks in the periderm. The decreases in Lp during drought reduced plant water loss to a dry soil, and yet maximal water uptake and transpiration occurred within a few days of rewetting, helping these epiphytes to take advantage of episodic rainfalls in a moist tropical forest.