Number Of Fine Roots Research Articles

Growth, decay, and turnover rates of fine roots of basket willows

The aim of the present study was to calculate fine-root turnover rates in stands of basket willow (Salix viminalis L.). Fine-root number was recorded in minirhizotrons in two adjacent short-rotation forest stands. Stand A was a regularly spaced plantation on clay soil. Stand B contained lysimeters, which were inserted in the soil and filled with either clay soil or washed sand. Both stands were irrigated and fertilized daily, to provide near-optimum conditions with respect to water and nutrient availability. The calculations were based on morphological studies and observations in minirhizotrons. Mean fine-root ages of growth and decay phases were calculated from third-order polynomials, and by summing up those phases and adding a short stationary phase, turnover time was obtained. Calculated fine-root turnover rates were 4.9–5.8 year–1 in the plantation and 4.8–8.1 year–1 in the lysimeters. No significant difference in turnover rates was detected between clay and sand substrates. Soil temperature had a significant effect on the decay phase, and in the calculations the data were weighted by soil temperature intervals. The importance of observing fine roots throughout the year is stressed.

Seasonal root distribution and soil surface carbon fluxes for one-year-old Pinus radiata trees growing at ambient and elevated carbon dioxide concentration.

The increase in number of fine (< 0.5 mm diameter) roots of one-year-old clonal Pinus radiata D. Don trees grown in large open-top field chambers at ambient (362 micro mol mol(-1)) or elevated (654 micro mol mol(-1)) CO(2) concentration was estimated using minirhizotron tubes placed horizontally at a depth of 0.3 m. The trees were well supplied with water and nutrients. Destructive harvesting of roots along an additional tube showed that there was a linear relationship between root number estimated from the minirhizotron and both root length density, L(v), and root carbon density, C(v), in the surrounding soil. Root distribution decreased with horizontal distance from the tree. At a depth of 0.3 m, 88% of the total C(v) was concentrated within a 0.15-m radius from tree stems in the elevated CO(2) treatment, compared with 35% for trees in the ambient CO(2) treatment. Mean C(v) along the tubes ranged up to 5 x 10(-2) micro g mm(-3) and tended to be greater for trees grown at elevated CO(2) concentration, although the differences between CO(2) treatments were not significant. Root growth started in spring and continued until late summer. There was no significant difference in seasonal rates of increase in C(v) between treatments, but roots were observed four weeks earlier in the elevated CO(2) treatment. No root turnover occurred at a depth of 0.3 m during the first year after planting. Mean values of carbon dioxide flux density at the soil surface, F, increased from 0.02 to 0.13 g m(-2) h(-1) during the year, and F was 30% greater for trees grown at elevated CO(2) concentration than at ambient CO(2). Diurnal changes in F were related to air temperature. The seasonal increase in F continued through the summer and early autumn, well after air temperature had begun to decline, suggesting that the increase was partly caused by increase in C(v) as the roots colonized the soil profile.

Role of some riparian wetland plants in reducing erosion of organic carbon and selected cations

Five riparian herbaceous plants, Leonotis nepetaefolia, Cassia tora, Ageratum conyzoides, Parthenium hysterophorus and Sida acuta, dominant on the banks of the Rihand river at Renukoot (India), were selected to assess experimentally their quantitative role in conserving organic-C, Na, K and Ca. Young seedlings from the river bank were planted on sloping experimental plots made of alluvial soil. Simulated rainfall totalling 42.5 mm was applied at 300 mm h −1 on five vegetated and one bare plots. Runoff water and eroded soil were collected from each experimental plot in artificial reservoirs and their quantities were measured. The soil conservation value of the five selected species ranged between 33 and 84% while the water conservation value varied between 19 and 50%. The overall nutrient conservation value, based on the losses in runoff water and eroded soil taken together, varied from 30 to 83% for organic-C, 19 to 78% for Na, 13 to 72% for K and 29 to 52% for Ca under different species. Loss of these four nutrients in response to 42.5 mm simulated rainfall was much higher than their input through rainfall. Loss value for the nutrients were in following order: organic-C > Ca > K > Na. The fraction of organic-C transported down the slope was higher in eroded soil (averaging 73%) and of exchangeable bases in runoff water (averaging 86% for Na, 82% for K and 90% for Ca). Flow-weighted concentrations of all the studied nutrients were consistently greater from bare stands. Number of fine roots was found to play greater role in the case of organic-C (92%; p < 0.01) and Na (70%; p < 0.05) runoff and their conservation by different plant species but canopy cover played greater role for K (58%; p < 0.08) and Ca (90%; p < 0.01).

Seasonal amount, growth and depth distribution of fine roots in an irrigated and fertilized Salix viminalis L. plantation

With the objective of examining seasonal fine-root growth in a short-rotation forest plantation of Salix viminalis L., standing crop, growth and decay dynamics and depth distribution of fine roots were investigated with the minirhizotron technique. Fine-root number was counted during two growing seasons, 1988 and 1989. Soil cores were sampled during the same period for estimation of standing crop and depth distribution of fine-root mass and fine-root length. The experimental site is situated at Uppsala, central Sweden, on former agricultural land, where the soil consists of a heavy clay. The plantation was irrigated and fertilized daily, through a computer controlled system, from late May until mid-August. The intention was to create near-optimum conditions for growth with respect to water and nutrients. Fine-root growth started in May and fine-root number increased throughout summer and early autumn. A decrease followed from September and continued during autumn, although root growth was still occurring in October. Growth and decay of fine roots, measured as positive and negative net changes in fine-root number between observations, occurred simultaneously throughout the growing seasons. Most of the fine roots were found in the upper 40–45 cm of the soil profile. A dry period in the summer of 1989 resulted in a lower fine-root number in the upper soil layers and in a deeper mean root depth, as compared to 1988. A comparison of relative depth distribution of fine-root number, obtained from minirhizotrons, and fine-root mass, achieved from soil coring, revealed a close agreement between methods. The relative depth distribution remained fairly constant during the growing seasons. The seasonal variation of fine-root number, observed in minirhizotrons, and fine-root mass and live fine-root length, measured by soil coring, showed no significant differences between the methods or between mass and length.

Effects of irrigation and coppicing on above-ground growth, physiology, and fine-root dynamics of two field-grown hybrid poplar clones

To determine the effects of irrigation and coppicing on above- and below-ground growth dynamics, a plantation of Populus X euramericana cv. 'Eugenei' and Populus tristis X Populus balsamifera cv. 'Tristis 1' was established in May 1984 on a level site in East Lansing, MI, USA. Supplemental water in the form of drip irrigation was applied to half the trees beginning the first growing season. All trees were cut down in March 1988 and the stumps allowed to coppice. Pre- and post-coppice height and diameter growth of 'Eugenei' always exceeded that of 'Tristis', and the former clone showed a positive response to irrigation, whereas the latter did not. The greater growth of 'Eugenei' was primarily due to its full use of the growing season. Post-coppice rates of photosynthesis were not affected by irrigation in either clone, but stomatal conductances were reduced in non-irrigated trees. Analysis of microvideo images taken in minirhizotron tubes buried in the soil close to the trees showed that 'Tristis' produced a greater length and number of fine roots in the top 30 cm of soil than 'Eugenei', regardless of treatment. Irrigated trees consistently produced more fine roots at 0–30 cm soil depth than non-irrigated trees only in 'Eugenei', but both clones showed greater fine-root production in non-irrigated trees at 30–100 cm. Both clones also showed substantial fine-root production in the spring immediately following coppicing, with no evidence of a shock-induced dieback of roots. The root systems of these two poplar genotypes apparently contain sufficient carbon and nitrogen reserves to fuel a spring flush of fine-root growth, even though the tops have been severed during the dormant season.

Effect of urea fertilization on ectomycorrhizae of 20-year-old Tsugaheterophylla

Granular urea (46% N) was applied at rates of 224 and 448 kg N/ha to 4 × 4 m plots within at 20-year-old stand composed almost exclusively of western hemlock (Tsugaheterophylla (Raf.) Sarg.), located in the Mount Seymour Demonstration Forest, North Vancouver, British Columbia. Changes in the abundance of 10 mycorrhizal types (Cenococcumgeophilum Fr., Lactariusscrobiculatus (Fr.) Fr., Myceliumradicisatrovirens Melin, Thelephoraterrestris Fr., three Russula morphotypes, two unidentified basidiomycetes, and a mantleless morphotype resembling E-strain) were assessed using random soil cores taken at 0, 1, 3, 6, and 11 months after fertilization. On both treated and control plots, total number of fine roots and number of basidiomycetous mycorrhizae remained constant, while C. geophilum mycorrhizae decreased slightly and those lacking mantles increased. The observed changes were independent of fertilizer levels and the shifts in pH brought about by urea hydrolysis.

Root demography of mature citrus trees: the influence of Phytophthora nicotianae

The amount of root mortality caused by root pathogens such as Phytophthora nicotianae (syn. Phytophthora parasitica) has typically been inferred from the net change in root length density in sequential soil cores. Because such measurements give information only on net changes in root populations, the actual rate of root turnover is often underestimated. We used minirhizotrons to track the fate of a large number of individual fine roots of mature field-grown citrus trees over a 6-month period. This method enabled us to examine the effect of P. nicotianae population levels on fine-root mortality. Seasonal and genotypic variation in patterns of citrus fine root mortality were associated with variation in population levels of P. nicotianae. Fine root lifespans were shorter when populations of P. nicotianae were high. Fine roots of the Phytophthora-susceptible rootstock, rough lemon (Citrus jamibhiri), had shorter median lifespans and supported larger populations of P. nicotianae than the fine roots of the more tolerant rootstock, Volkamer lemon (Citrus volkameriana). Rates of root mortality were either relatively constant for roots of all ages, or increased with age; the latter pattern was most pronounced for Volkamer lemon roots. Differences in the age-dependence of root mortality may, therefore, play a role in genotypic differences in tolerance of Phytophthora root rot by these two rootstocks. H Lambers Section editor

Reduction of Oak Chlorosis with Wood Chip Mulch Treatments

Wood chip mulch and ammonium sulfate treatments around urban white oaks (Quercus alba) were associated with favorable changes in soil properties. Bulk density and pH were lower, and moisture content was higher under the mulch. Fine root development and number of mycorrhizal roots were also increased. Foliar manganese increased and phosphorous decreased. These changes were associated with a reduction of interveinal chlorosis.

Root Distribution of a Plantation‐Grown Red Pine in an Outwash Soil

Root distribution and mass of a single dominant sample tree (17 m high, 20 cm diameter) in a 39—year—old Pinus resinosa Ait. plantation supported by a deep, stratified, outwash sandy soil were related to soil horizonation characteristics and aboveground tree components (foilage, branches, bolebark, and bolewood). All roots were excavated by hand in the A_p and B horizons and by 0.3—m depths in the C strata, were separated into five size classes, cleaned, dried, and weighed. Root—depth penetration terminated in a great number of fine roots in a thick, very fine sandy—silty stratum below the coarser textured solum at 2.7 m. Lateral root distribution was extremely variable; the maximum radial extent was approximately 9 m from the stump. Total root weight was approximately twice the total needle weight.

THE STRUCTURE OF MYCORRHIZAL ROOTS OF FAGUS SYLVATICA

The root system of Fagus sylvatica has been described by Biisgen (I905) as intensive because of the relatively large number of fine roots per unit volume. It has been carefully investigated by Harley (I937, I939a, I940) in natural forests and under experimental conditions, and he showed that the form of the system in mature trees varies with the depth of the soil and degree of humus incorporation, as does the degree of dominance in the tap-roots of young plants. In non-mycorrhizal root systems of Fagus there is a considerable difference in size between the 'long' and 'short' roots. The long roots comprise the main laterals and have indefinite growth; the short roots provide most of the surface area of the system and have a restricted life. The life of the short roots is probably brief, and crops of them are produced once or twice a year at the periods of maximum root growth in the spring and autumn. It has long been known that some plants show some degree of heterorhizy associated with the nutritional and anchoring functions of roots, and it has been suggested that there are anatomical differences between feeding roots and other roots (Tschirch, I905). This is not so in Fagus. There are anatomical differences between thick and thin roots (Clowes, I950), and it is suggested that Tschirch's data refer to these, since feeding roots are generally, though not invariably, thinner than the others. Thus Fagus root systems differ conspicuously from those of Pinus, which shows inherent morphological differences between long and short roots (Preston, I943; Hatch, I937; Hatch & Doak,