Nitrogen addition regulates allometric growth by changing the distribution patterns of endogenous hormones in different organs of Pinus tabuliformis

Background: The mechanisms by which nitrogen (N) affects the allometric growth of plant organs by influencing the distribution of different hormones in plant organs remain unclear. Therefore, this study aimed to examine the effect of soil N levels on soil properties, the hormonal activities and growth parameters of Pinus tabuliformis Carr. Methods: Seedlings of P. tabuliformis were subjected to 0, 3, 6, 12 g of N m-2 year-1. Growth parameter and hormone activity data (trans-zeatin riboside (ZR), gibberellin (GA1+3), indole acetic acid (IAA), abscisic acid (ABA)) in leaf, stem, total root, coarse root (diameters >2 mm), fine root (1-2 mm) and finest root (0-1 mm) biomass were measured and analysed. Results: The results showed that N addition increased the growth of the leaves; stems; total roots; and coarse, fine, and finest roots of the seedlings, but decreased the ratio of underground to aboveground growth. Additionally, N addition increased the ZR content in stems, while decreasing the ABA content in leaves and whole roots and the GA1+3 content in whole roots, but IAA content was not significantly influenced by N addition. Furthermore, the hormones examined significantly influenced the growth of the leaves, stems, roots, and the coarse, fine, and finest roots. Conclusions: N addition affected the trans-zeatin riboside, gibberellin, indole acetic acid, and abscisic acid content in the various organs examined, which influenced the growth of the seedlings. Our research will provide an important reference for forestland governance and forest systems management under global atmospheric N deposition.

Nutrient concentrations of roots vary with diameter, depth, and site in New Hampshire northern hardwoods

Roots are important to ecosystem nutrient pools and fluxes, but they are difficult to sample for tissue analysis, especially at depth. We analyzed patterns of nutrient concentrations in live roots up to 20 mm in diameter collected from quantitative soil pits in six northern hardwood sites at the Bartlett Experimental Forest, New Hampshire, USA. Root concentrations of nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg) were higher in the forest floor than in the mineral soil, by 23%–61% in fine roots (0–1 mm and 1–2 mm in diameter). Using only samples collected from the O horizon to characterize roots throughout the profile resulted in an average error across all elements of 16% in estimates of root nutrient contents. Within the mineral soil, there was little difference in root nutrient concentrations with depth. There were significant patterns with root diameter: N and Mg concentrations were highest in the finest roots, while Ca concentrations peaked in the 2–5 mm diameter class. One site (C8) differed from the others in having lower N but higher P, Ca, Mg, and potassium (K) concentrations in roots. In summary, analyzing roots by site and diameter class is more important to accurate nutrient accounting than is analyzing roots from depth in the mineral soil, but roots in the forest floor and the mineral soil differ dramatically for some elements.

Root length and distribution in the mineral soil of a mixed deciduous forest (experimental forest Aelmoeseneie)

Root length and root mass were studied in two different forest stands: an oak-beech and an ash stand, both in the 'Aelmoeseneie' experimental forest at Gontrode, Belgium. In the oak-beech stand, the length of the finest roots < 1 mm) was significantly higher than the length of the other diameter classes (1-2 and 2-5 mm) in the upper 60 cm of the mineral soil. Because of large variances, this significance could not be found in the ash forest. In this ash forest type, the length of the finest roots in the upper mineral soil layer (0-15 cm) was higher than all the other lengths, both considering the vertical root length distribution within the ash plot, and comparing the ash plot to the oak-beech stand. For the root mass, only the amount of roots with a diameter between 2 and 5 mm in the upper mineral soil layer of the ash plot was significantly higher than the others. SpecifiC root length (m root/g D.M.) is calculated for both the oak-beech and the ash plot. These values can be used to convert biomass data into root length data, which gives a better indication of the water uptake capacity of the forest stand.

Principles of crop modelling and simulation: III. modeling of root growth and other belowground processes, limitations of the models, and the future of modeling in agriculture

The first models of temporal variation of root systems appeared over 20 years ago. The complex architectural geometry of root systems; the wide range in size and diameter and the rapid growth and decomposition of finest roots; the different physiological activity of roots of different ages; the complex microbial processes occurring at the root-soil interface; the symbiotic relationships in the rhizosphere; the variable soil environment (physical, chemical and biological) in which roots develop are the challenges of quantifying the root growth. The models are not simple mechanisms to archive information in order to produce forecasts. Modeling represents a better way of synthesizing knowledge about different components of a system, summarizing data, and transferring research results to users.

Measuring Root Surface Area and Mean Root Diameter of Peach Seedlings by Digital Image Analysis

Using area profile integration software and an image processing system, we reliably estimated total root surface area of intact each [Prunus persica (L.) Batsch.] seedlings by 1) producing high-quality monochromatic video images under preset and constant conditions; 2) determining a threshold gray intensity value that differentiates the finest roots on the image; 3) producing a binary image where all pixels with gray values above the threshold are black; 4) determining the proportion of black pixels on the 480× 512-pixel matrix; and 5) multiplying this two-dimensional root surface value by π to estimate total root surface area. Normalized intensity (an average intensity weighted according to the proportion of the binary image in each gray scale class) was calculated using software that superimposed the video image on the binary image and was used to estimate mean root diameter. Evidence of reliability and examples of the use of both estimates are provided.

The structure of Eucalypt roots

The two eucalypt species Eucalyptus obliqua and E. st johnii differ in their susceptibility to Phytophthora cinnamomi, which infects their roots. A comparative study of the anatomy of the root systems of 12-week-old intermediate seedlings was made, the material used ranging in size from the finest roots to first order laterals. The root anatomy of the two species was similar but the species could be distinguished by differences in cortex persistence and in the rate of polyphenol accumulation. However, it was recognized that such differences were dependent on the age and growth rates of the roots sampled and could not be correlated with the differing susceptibilities of the two eucalypt species to Phytophthora cinnamomi. The walls of the exodermis and endodermis in both species are suberized and the ultrastructure of these walls was examined. Broad bands of suberized lamellae completely lined the exodermal cells in the zone of differentiation. In mature root zones the external radial walls of the epidermis were thickened and contained polyphenols. The roots which had commenced secondary thickening developed a specialized periderm, a polyderm, which consisted of alternating layers of suberized and non-suberized cells.