First-order Roots Research Articles

Changes in the risk of fine‐root mortality with age: a case study in peach, Prunus persica (Rosaceae)

Previous studies suggest that younger roots are more vulnerable to mortality than older roots. We analyzed minirhizotron data using a mixed-age, proportional hazards regression approach to determine whether the risk of mortality (or "hazard") was higher for younger roots than for older roots in a West Virginia peach orchard. While root age apparently had a strong effect on the hazard when considered alone, this effect was largely due to different rates of mortality among roots of different orders, diameters, and depths. Roots with dependent laterals (higher order roots) had a lower hazard than first-order roots in 1996 and 1997. Greater root diameter was also associated with a decreased hazard in both 1996 and 1997. In both years, there was a significant decrease in the hazard with depth. When considered alone, age appeared to be a strong predictor of risk: a 1-d increase in initial root age was associated with a 1.26-2.62% decrease in the hazard. However, when diameter, order, and depth were incorporated into the model, the effect of root age disappeared or was greatly reduced. Baseline hazard function plots revealed that the timing of high-risk periods was generally related to seasonal factors rather than individual root age.

Diversity of the Pythium community infecting roots of the annual legume Kummerowia stipulacea

A combination of glasshouse and field surveys was conducted to characterize the diversity of root-colonizing Pythium spp. on Kummerowia stipulacea in one small (ca. 10 m 2) restored prairie site, using naturally produced K. stipulacea plants or soil and seeds from the same site. In aggregate, 633 K. stipulacea root systems were completely extracted and examined, yielding 489 Pythium isolates. Of these, 381 isolates (78%) were identified to 15 Pythium species, only three of which were previously associated with K. stipulacea. The observed species richness was greater than that previously reported at spatial scales of 10–100 m 2. In contrast to the total species richness, a maximum of three Pythium species was recovered from any single root system. Jaccard's similarity coefficient ( S J=0.33) indicated low similarity between the portions of the complete community detected in the glasshouse vs. the field surveys; 13 and 7 species were recovered in glasshouse and field surveys, respectively. The most common species recovered in both field and glasshouse surveys were Pythium dissotocum and Pythium irregulare. Pythium diclinum was also commonly recovered in the glasshouse surveys. These results strongly suggest the importance of environmental factors for detection of resident root-infecting Pythium species. Morphometric root classification was used to characterize the architectural root order from which each Pythium isolate was derived. P. irregulare was isolated more frequently from higher-order root segments (i.e. those which do not terminate in an apical meristem) than were either P. dissotocum or P. diclinum in glasshouse surveys, though all three species were also common in first-order roots. Two glasshouse infection experiments supported the null hypothesis that when P. dissotocum and P. irregulare are present at the same inoculum concentrations, infection by each is independent of the other. Further, infection by each species alone significantly shifted root system branching ratio ( R b) from a dichotomous branching pattern towards a simpler, monopodial pattern, whereas infection resulting from comparable concentrations of inoculum of both species together did not significantly affect R b. The low isolation frequency of P. dissotocum and P. irregulare from apparently healthy K. stipulacea root systems at the conclusion of glasshouse infection experiments, despite the significant alteration of R b by each Pythium species, emphasizes the ephemeral nature of both Pythium infections and infected roots.

Linking Hydraulic Conductivity to Anatomy in Plants that Vary in Specific Root Length

In Citrus L. sp., specific root length of whole root systems has been correlated positively with root hydraulic conductivity, but there is little mechanistic understanding of the causes for this association. The hydraulic conductivity of individual roots in relation to root anatomical characteristics in seedlings of three citrus rootstocks [sour orange (SO) (Citrus aurantium L.), trifoliate orange (TO) (Poncirus trifoliate (L.) Raf.), and Swingle citrumelo (SC) (C. paradisi Macf. × P. trifoliata)] that vary widely in specific root length (SRL) was measured. Among fibrous roots, first-order and secondorder laterals were examined. Relative differences among rootstocks in the overall hydraulic conductivity (LP) and radial conductivity (LR) for individual 1-month-old and 6-month-old second- and first-order roots generally were consistent with hydraulic conductivity determined previously for entire root systems. There were no significant differences in axial conductance per unit pressure (Kh) in either first- or second-order roots among the rootstocks. This was consistent with the similarity in number and diameter of xylem vessels. One-month-old second-order roots had no suberized exodermis but varied in cortical radius. Six-month-old second-order roots of TO, however, had more nonsuberized cells (passage cells) in the exodermis than roots of SC and SO, although the cortical radius of SC and SO roots were not different. Compared to 6-month-old second-order roots, 1-month-old second-order roots had much higher LP and LR but lower Kh. Differences in overall root hydraulic conductivity among the citrus rootstocks were mainly related to structural differences in the radial pathway for water movement, suggesting that radial hydraulic conductivity was the primary determining factor of water uptake in citrus rootstocks.

Anatomical characteristics of roots of citrus rootstocks that vary in specific root length.

Among citrus rootstocks, higher specific root length (SRL, root length/d. wt) has been linked to several specific morphological and physiological traits, including smaller average root diameter, higher root hydraulic conductivity and higher rates of root proliferation. In this study, thickness of the outer tangential exodermal (hypodermal) wall and its suberin layer, number of passage cells, presence of epidermis, and stelar anatomy were examined and related to variation in root diameter of field roots of known maximum age. We also compared root morphology and anatomy of young roots in the field with those of potted rootstock seedlings in the glasshouse. Fibrous roots were measured separately from pioneer (framework) roots. Among the fibrous roots, only the first-order (root links having a root tip) and second-order (root links bearing first-order roots) laterals were examined. Among first-order field roots, larger root diameter was caused by larger rather than more numerous cells in the cortex. Root diameter of first-order roots was positively correlated with both number of passage cells in the exodermis and thickness of the secondary walls of the exodermis in both field and potted plants. Exodermal walls were about 80% thicker in field- than pot-grown roots. In the field, in more than 50% of the first-order roots examined less than 30% of the root surface was still covered by epidermis, with few differences among rootstocks. In contrast, in roots of 19-wk-old glasshouse plants generally 70-100% of the epidermis was still intact. There was no evidence of secondary xylem development in second-order fibrous roots in the field; in seedling, pot-grown rootsystems, 75-97% of second-order roots had formed secondary xylem despite their small diameter (<0.8 mm). It is argued that there can be suites of physiological, morphological and anatomical traits in roots that co-vary with specific root length. Investigations of how root morphology and anatomy are linked to root function, moreover, need to recognize trait variability and the potentially important differences between field- and pot- grown (seedling) roots.

Tomato mosaic virus infection of red spruce on Whiteface Mountain, New York: prevalence and potential impact

Tomato mosaic tobamovirus (ToMV) was detected by enzyme-linked immunosorbent assay in the roots of red spruce (Picearubens Sarg.) on Whiteface Mountain, New York. Both virus incidence and concentration in the roots of red spruce vary by site and were greater in trees with little to moderate crown dieback than in trees with severe dieback. There was no significant association between virus incidence or concentration in the roots of red spruce and elevation on Whiteface Mountain. Multiple regression analysis of virus concentration in the roots, as the dependent variable, was performed against nine selected crown and root variables. In the final regression model, the number of live second-order nonwoody roots per length of first-order nonwoody root and length of the live crown were positively and negatively correlated, respectively, with virus concentration in the roots. These results suggest a complex epidemiology and a potentially significant impact of ToMV infection on the growth of red spruce on Whiteface Mountain.

Influence of controlled water supply on shoot and root development of young peach trees.

Three controlled water supply treatments were applied to 1-year-old peach trees grown in root observation boxes. The treatments were: I(0), growth medium maintained at 50% field capacity; I(1), water supplied when daily net tree stem diameter change was negative or zero for 1 day; I(3) as for I(1) except that water was applied after net daily stem diameter change was negative or zero for 3 consecutive days. Trees in treatment I(0) had the greatest mean daily first-order shoot growth rates, and trees in treatment I(3) had the lowest shoot growth rates. Because leaf production rate (apparent plastochron) of first-order shoots was unaffected by treatment, differences in shoot length were due to differences in internode extension and not to the number of internodes. Trees in treatment I(0) had a greater number of second-order shoot axes than trees in treatment I(1) or I(3). Furthermore, an increase in the rate of growth of the first-order shoot axis was associated with an increased tendency for branching (i.e., the development of sylleptic second-order shoots). Increased leaf length was also associated with more frequent watering. Trees in treatment I(0) had the greatest root lengths and dry weights, and this was attributed to a greater number of first-and second-order (lateral) root axes compared with trees in the I(1) and I(3) treatments. The extension rate and apical diameter of first-order roots were reduced by the I(3) treatment. The density of second-order roots along primary root axes was not affected by any of the treatments.

First-order root development from cuttings of Populus trichocarpa x P. deltoides hybrids

We studied first-order root development of field-grown plants of 44 F(1) Populus trichocarpa x P. deltoides hybrids as well as 15 clones of P. trichocarpa (T) and 20 clones of P. deltoides (D) during their first growing season. The cuttings were planted in the field on May 11-12, 1988 and destructively sampled in July, August and September. By September 12, hybrids had an average of 50 first-order roots per cutting (range = 32 to 85) with an average of 25% dead roots (range = 10 to 51%). The longest roots of hybrids averaged 107 cm (range = 58 to 182 cm) and originated at the base of the cutting. Roots originating at the side of the cutting averaged 54 cm in length (range = 12 to 96 cm). For most aboveground and root parameters measured, the values for hybrids exceeded those for both parent species clones. For all clones, aboveground weights were positively correlated with weights of collected roots (R(2) = 0.66 to 0.86). In contrast, aboveground weights were negatively (but poorly) correlated with root/shoot ratios (R(2) = 0.08 to 0.21). Roots differed allometrically depending on their location on the cutting. Total weight of roots originating along the sides of the cutting was not correlated with aboveground weight (R(2) = 0.001 to 0.27), whereas total weight of roots originating at the base of the cutting was correlated with aboveground weight (R(2) = 0.52 to 0.80). Basal roots dominated the first-order root systems of most clones in terms of maximum length and total mass, but not in total numbers of roots.

Invasion of Bassendean Dune Banksia Woodland by Phytophthora cinnamomi

The rate and mechanism of the spread of Phytophthora cinnamomi in Banksia woodland of the Bassendean Dune system north of Perth, Western Australia was studied. Aerial photographs were used to measure the spread of disease in fronts longer than 5 km over 35 years. Fronts in upper slope positions moved downhill and uphill at 1.01 and 1.13 m year-1, respectively, while fronts in low-lying positions moved downgrade and upgrade (with and against the direction of water table flow) at 1.30 and 1.20 m year-1, respectively. Fronts in low-lying areas spread significantly faster than those on upper slopes. Excavations to 2 m depth of the root systems of 21 dying plants of Banksia attenuata R.Br., an overstorey co-dominant, revealed that 28% (3.9 roots/tree) of all first-order roots were infected. Assessment of the proportion of roots infected revealed a significant (P &lt; 0.01) departure from uniform distribution of disease down the profile in both upper slope and drained flat sites. In 14 trees on dune slopes, 6-40 m above the aquifer, infection rate was higher than expected in roots lying at 21-40 cm depth, but lower than expected in roots below 1 m. Seventy three percent of infected roots lay in the top 40 cm of soil. In seven trees on a drained flat, 2-3 m above the aquifer, infection rate was high in the 21-60 cm horizon and also in roots below 1 m. Even though Phytophthora cinnamomi was active in the vicinity of the water table in trees on drained flats, the slow, steady spread of the disease in all landscape positions suggested that the primary mode of fungal invasion was through roots of susceptible vegetation. No evidence was found of accelerated spread of disease caused by the dispersal of zoospores.

Normalized minimum norm digital filter structure: a basic building block for processing real and complex sequences

If a is a pole of a given transfer function, the complex first-order transfer function square root (1- mod a mod /sup 2/)/(z-a) represents a basic building block in various favorable realizations. The realization of this basic building block and its properties are investigated. It is shown that the structure is automatically scaled (normalized) and that it is a minimum norm structure (MNS) possessing low-sensitivity and low-noise properties. The structure is referred to as the normalized MNS. An elegant noise analysis of this structure is also given. As a direct application of the normalized MNS, a simple method is given to derive efficient structures for second-order filters. A particular second-order structure is suggested for very-low-sensitivity realization of classical filters. >

Development of the Root System of Young Peach Trees (Prunus persia L. Batsch): A Morphometrical Analysis

The development of the root system of young peach (Prunus persica L. Batsch) seedling is inferred from the description of root system excavated at nine dates over a 6-week experiment. Both growth and branching processes are studied.The length of the apical unbranched zone and the mean branch density are used to characterize branching processes. The branching order is an important source of variation for growth rate, growth duration and length of the apical unbranched zone. A gradient for those characteristics is found for first-order roots along the basal 40 mm of the taproots. Mean branch density is more constant. Variations in growth and branching processes are related. Fast growing roots tend to have a longer apical unbranched zone and, to a lesser extent a higher mean branch density. The consequences of those patterns of variation on the modelling of the development of root systems are discussed.

Anatomy of Dianthoveus cremnophilus (Cyclanthaceae)

Dianthoveus is a monotypic genus of the Cyclanthaceae and in this paper the anatomy of D. cremnophilus is described, including that of the lamina, petiole, peduncle, rhizome and first-order root. The lamina within interridge areas is hypostomatic and the mesophyll between boundary layers exhibits either two main regions according to sizes of intercellular spaces, or three main regions according to wall thickness of ordinary parenchyma cells. Expansion tissue occurs opposite adaxial and abaxial ridges of the lamina and where the median costa and noncostal portions of lamina are joined together. The petiole exhibits three main zones of ground tissue and the median costa has two to three zones. Certain veins of the petiole compose a conspicuous V in cross section. The peduncle has four main zones of ground tissue, including pith. This organ contains simple vascular bundles (commonly, collateral bundles) and bipolar compound vascular bundles. The rhizome has a conspicuous periderm, cortex (including endodermis), and central cylinder. Diverse forms of vascular bundles occur within the central cylinder, e.g., collateral, amphivasal, compound-tetrapolar, and compound-multipolar. In the first-order root the cortex exhibits various regions, including exodermis and endodermis, and the stele contains peripheral and nonperipheral fascicles, each type of fascicle of either xylem or phloem. Styloid sacs and raphide sacs occur in all and some organs studied, respectively, and in the rhizome and interridge areas of the lamina the styloid sacs are randomly oriented and abundant. Mucilage canals occur in the peduncle and petiole. These anatomical data are used to compare Dianthoveus with other cyclanthaceous genera, particularly Evodianthus.

Use of morphometric analysis for characterization of tobacco root growth in relation to infection byPhytophthora parasitica var.nicotianae

Development of tobacco root systems was characterized under controlled environmental conditions by use of morphometric root analysis. According to the classification scheme of this system, roots terminating in apical meristems are defined as first-order roots. Elements of second-order roots begin where two first-order roots merge, and so forth. Growth of root systems was similar for susceptible and resistant tobacco cultivars in nonautoclaved and autoclaved soils. During 15 days of growth subsequent to transplanting of 2-week-old plants, relative multiplication and extension rates of first-order and second-order roots were constant. Apparent unit extension rates of first-order and second-order root elements increased through 15 days of root system growth. Classification of tobacco root systems by the morphometric scheme provided a useful means of partitioning susceptibility of tissues to infection byPhytophthora parasitica var.nicotianae. Zoospores applied at the tips of first-order roots were most successful in causing infections; 73.3% of the roots inoculated with 16 zoospores per root tip became infected. Percentages of infections after inoculation of first-order root tissues 2 cm behind root tips or after inoculation of second-order roots were 10 and 4.3%, respectively.

Development of microbial communities associated with tobacco root systems

Comparisons were made between patterns of microbial community development associated with tobacco root systems in nonautoclaved and autoclaved soils. Patterns of root system colonization by fluorescent Pseudomonas spp, actinomycetes and other bacteria did not differ between the two soils. Fungal community diversity, measured in terms of number and densities of taxa present, was greater in association with rhizospheres and root surfaces of tobacco grown in nonautoclaved soil than in autoclaved soil. Diversity within the rhizosphere and at root surfaces increased more slowly over time in autoclaved soil than in nonautoclaved soil. At all sampling dates fungal colonization of surfaces of first-order roots was more extensive in nonautoclaved soil than in autoclaved soil. As measured by Lloyd's index of mean crowding, average densities of hyphae in colonized regions of root surfaces were greater in nonautoclaved soil than in autoclaved soil at 7 and 28 days of plant growth. Colonized regions along root surfaces were more patchy or aggregated within autoclaved soil than in nonautoclaved soil as determined from values of Lloyd's index of patchiness. Measurements describing root surface colonization remained fairly constant over time because samples at each date were taken from tissues of similar physiological age.

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

In a previous paper (Henderson et al . 1983), it was suggested that the processes of root growth and development proceed with a geometric regularity and that, as a consequence, root distribution is further extended and spatially more even than if growth were at random. We examine this hypothesis and the relative importance of the component growth processes through computer simulation of a model for root distribution at a fixed time. Root segments were measured on 16 year trees and statistical distributions fitted to the occurrence of lengths, branching frequencies and growth directions. These distributions comprise the model which assumes that a root system consists of a number of first-order roots originating at the stem, a number of second-order roots originating on first-order ones and so on. Each root includes a number of bends and lateral branching points and terminates in either a fork or when diameter reaches 5 mm, smaller roots not being included. Parameter manipulation of the fitted distributions and further simulation showed that some regular growth mechanisms were necessary for the simulation of realistic rooting patterns. In particular it was important that direction changes at bends and of new roots at forks were typically small to ensure that the system spread outwards, away from the stem. Lateral branches needed to subtend large angles to their parents in order to exploit separate soil regions. Other necessary rules were that first-order roots were almost regularly distributed around the stem and for a tendency for azimuth changes at bends to be alternately clockwise then anticlockwise. Simulations were also used to examine the possibility of estimating total root length from a study of only part of a root system. An example of excavating one quarter of the system is considered and the results indicate that root systems may be so variable that no reliable estimate can be obtained.

Morphometric analysis of root systems: application of the technique and influence of soil fertility on root system development in two herbaceous species.

Abstract. A method for describing root systems based on geomorphological techniques developed for river systems is described. Root systems, in common with other natural branching structures (rivers, bronchioles, trees), appear to obey Morton's Law of Branching: there is a constant ratio, the bifurcation or branching ratio, Rb, between the number of branches of a given order, Nu, and that of the next order. Nu+1, In experiments where Poa annua, and Rumex cripus, were grown at two levels of fertility, the first-order roots (the youngest members in this system) were generally unresponsive to fertility, and differences in the root systems were largely the result of changes in the second-order roots, those formed at the junction of two first-order roots. These differences were reflected in the branching ratio, Rb Although it is possible to explain these results by a stochastic model of branch development, the Rb values for roots are higher than for other natural branching structures, and higher than the random model predicts. It is possible that a model based on optimum exploration of space may be more appropriate and provide a key to the factors governing root branching patterns.

Asymptotic properties of linear multivariable continuous-time tracking systems incorporating high-gain error-actuated controllers

In this paper, the asymptotic properties of tracking systems incorporating linear multivariable plants which are amenable to high-gain error-actuated control (Porter and Bradshaw 1979) are characterized in terms of the eigenstructure of the closed-loop plant matrices. It is shown that the closed-loop eigenstructure is such that the tracking behaviour of systems incorporating high-gain error-actuated controllers designed in accordance with the synthesis technique of Porter and Bradshaw (1979) is increasingly dominated by the modes associated with the first-order infinito characteristic roots as the gain is increased and that increasingly ‘ tight ’ control is therefore achieved. These theoretical results are illustrated in the case of a closed-loop system incorporating a third-order plant and a high-gain error-actuated controller by the presentation of the computed closed-loop eigenstructure and of the results of computer simulation studies.