Small-scale modelling of root-soil interaction of trees under lateral loads

Aim (1) To understand the tree root-soil interaction under lateral and moment loading using a physical modelling technique; (2) To detect the possible factors (e.g. root architecture, water condition, and stress level) influencing a tree’s push-over behaviour; (3) To identify suitable scaling laws to use in physical modelling. Methods Two 1:20 scaled root models with different architectures (namely, deep and narrow, and shallow and wide) were reconstructed and 3D printed based on the field-surveyed root architecture data. Push-over tests were performed both in elevated-gravity (centrifuge 20-g) and normal-gravity (1-g) conditions. Results The shallow and wide model showed higher anchorage strength than the deep and narrow model. Regardless of the root architecture, the root anchorage strength measured from dry soil was higher than that from saturated soil. However, once the effective stress was the same, regardless of water conditions, the root anchorage strength would be the same. Conclusions The presence of water decreasing the soil effective stress and key lateral roots extending along the wind direction play a significant role on a tree’s push-over resistance. Centrifuge tests showed comparable results to the field pull-over measurements while 1-g model tests overestimated the root-soil interaction, which could be corrected for soil strength by using modified scaling laws.

Root architecture, rooting profiles and physiological responses of potential slope plants grown on acidic soil

Globally, there has been an increase in the frequency of landslides which is the result of slope failures. The combination of high intensity rainfall and high temperature resulted in the formation of acidic soil which is detrimental to the healthy growth of plants. Proper plant coverage on slopes is a prerequisite to mitigate and rehabilitate the soil. However, not all plant species are able to grow in marginal land. Thus, this study was undertaken to find a suitable slope plant species. We aimed to evaluate the effect of different soil pH on root profiles and growth of three different potential slope plant species namely, Melastoma malabathricum, Hibiscus rosa-sinensis and Syzygium campanulatum. M. malabathricum showed the highest tolerance to acidic soil as it recorded the highest plant height and photosynthetic rate. The root systems of M. malabathricum, H. rosa-sinensis and S. campanulatum were identified as M, VH- and R-types, respectively. The study proposed M. malabathricum which possessed dense and shallow roots to be planted at the toe or top of the slope while H. rosa-sinensis and S. campanulatum to be planted in the middle of a slope. S. campanulatum consistently recorded high root length and root length density across all three types of soil pH while M. malabathricum showed progressive increase in length as the soil pH increased. The root average diameter and root volume of M. malabathricum outperformed the other two plant species irrespective of soil pH. In terms of biomass, M. malabathricum exhibited the highest root and shoot dry weights followed by S. campanulatum. Thus, we propose M. malabathricum to be planted on slopes as a form of soil rehabilitation. The plant species displayed denser rooting, hence a stronger root anchorage that can hold the soil particles together which will be beneficial for slope stabilization.

A general review of the biomechanics of root anchorage

With few exceptions, terrestrial plants are anchored to substrates by roots that experience bending and twisting forces resulting from gravity- and wind-induced forces. Mechanical failure occurs when these forces exceed the flexural or torsional tolerance limits of stems or roots, or when roots are dislodged from their substrate. The emphasis of this review is on the general principles of anchorage, how the mechanical failure of root anchorage can be averted, and recommendations for future research.

Description of the soil and root biomass of two subtropical mangroves in Antonina and Guaratuba Bay, Paraná State, Brazil

ABSTRACT The soil of the mangroves influences the root anchorage and the nutrition processes of the plant community. This study evaluated the relationships among edaphic conditions, volume and biomass of roots, and tree structure of two mangroves in Paraná State. Five soil cores of 50 cm depth were collected from each mangrove for physicochemical analysis. Organosoil thiomorphic salic sodic predominated in Antonina Bay, while in Guaratuba Bay were observed the Gleysoil thiomorphic salic sodic and the Organosoil thiomorphic salic sodic. Fifteen root samples were collected from each mangrove area for root volume and dry mass analysis'?'. The higher values of root mass were found in Guaratuba Bay. The chemical analysis of the soil showed no correlation between biomass and root volume. The high coefficients of variation attested the high heterogeneity in the root distribution in both areas. However, in the Guaratuba Bay, root mass and volume are higher due to the textural composition of the soil and higher tree density.

Root growth and anchorage by transplanted ‘Tifgreen’ (Cynodon dactylon x C. transvaalensis) turfgrass

Field experiments quantified factors affecting root growth and anchorage by transplanted ‘Tifgreen’ (Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy) sod, a globally important warm-season C4 turfgrass. Vertical force required to detach recently transplanted sod from underlying soil was the measure of root anchoring strength. In early spring, date of sod harvest and transplantation was important to root growth and anchorage measured 30 days after transplantation. Delaying sod harvest/transplantation by about a month after the end of the winter shoot dormancy period increased root anchoring strength 200% and root dry mass 640% during the 30 days after sodding. The strong effect of early-spring sodding date on root anchorage was related to cumulative thermal time before sod harvesting. Root anchoring strength was directly proportional to the number, but not mass, of roots produced by transplanted sod. In late spring, anchoring of sod to very firm traffic-compacted clay was 87% greater than to loamy sand, measured 14 days after sodding. N-P-K fertilisation did not affect late-spring sod anchorage to loamy sand soil, measured 18 days after sodding, but did enhance shoot density and colour. Sod root penetration into a silt loam soil was unaffected by an initially dry surface layer when sufficient irrigation was used. Overall, root anchorage by transplanted Tifgreen sod was similar to, or greater than, values reported for cool-season C3 turfgrasses in similar circumstances.