Root sampling methods

Overview

Interest in root sampling was first stimulated on an ecological scale in 1960 by an ecologist testing soil water availability to plants(Gardener). Methods have been developed since that are able to produce both rough estimations and almost exact representations of root biomass. Rhizodeposition is a key factor in Plant establishment and these sampling methods become useful when gathering information on plant nutrient allocation and development. Root systems are highly variable in growth, so results from any root sampling method can be challenging to interpret.(Johnson) It’s been estimated that in order to have a 90% confidence interval using any technique 40 or more samples must be taken, which is unfeasible for the majority of research purposes. (Taylor)

Root Length Equation

[1]

Where R = total length of the root, N = # of intersections between the root and straight lines, A = area of the sampled rectangle, and H = total length of the straight lines. The line intersect method (including the root length equation) was created by E.I. Newman after he recognized that absorption of nutrients and water from the soil depends on root length and surface area rather than overall biomass. (Newman) Newman used various mathematical and ecological equations to derive this one specifically for complicated root systems so direct counting and measurement under a microscope can be avoided. Through this calculation, ecologists were able to precisely measure the root lengths contained in a system in one third of the time it took prior.(Tennant) It holds importance as it was one of the first offering a quicker, more accurate approach to counting roots and fine root hairs.

Uses for Root Sampling

Root samples are useful for many agricultural, ecological, and educational purposes. Depending on the situation and ecosystem different methods may be preferred over others. Generally, root data is collected to analyze the overall health and development of a tree or plant.

With the increasing occurrence of habitat restoration projects and wildlife rehabilitation, root sampling is a vital management step to see the extent to which introduced plants have assimilated into new territory. Plant establishment will be checked at constant intervals after a site is designed, until the restoration efforts can be confirmed as successful. These experimental techniques allow the Rhizosphere of the modified ecosystems to be checked, and aid in detecting potential Ectomycorrhizal Fungi and Arbuscular Mycorrhizal Fungi connections.(Barnett)

Destructive Sampling Methods

The Harvest Method

The harvesting method is performed by extracting an undisturbed, vertical sample of ground soil and keeping it preserved in situ to examine the characteristics of the different soil layers. First, the size of the desired sample must be determined and the auger to retract the soil must be chosen. These auger devices come in small, hand-held sizes or larger sizes which are mechanical and sometimes mounted on trucks.(Barnett)

The soil is either kept intact and preserved as a monolith or the roots in the sample are rinsed free of the soil particulates. Monoliths are created by cutting the cylindrical soil core in half and transferring one of the profiles to a solid surface, like ply board, using an acrylic bonding agent for mounting. (Haddad)(Kiniry) The other half not used for display purposes is used for lab sampling or classification purposes. Monoliths can be kept for decades if done correctly. When root samples are desired, a lot of water and patience is required. Roots are generally pre-soaked to minimize water usage, and in some cases dispersing chemicals are applied. (Barnett) Separated root samples can be stored up to 10 weeks, so it gives ample time for those studying the systems.

Despite this being considered a destructive sampling technique, it minimizes site disturbance while allowing a lot of valuable information to be gathered.(Haddad)

Non-destructive Sampling Methods

Rhizotrons

Rhizotrons are underground walkways with glass walls on other one, or both sides that expose the soil and living Rhizosphere surrounding the structure. These structures are special because they allow scientists to go inside and study the root systems that are still living and developing. Individual roots are easy to keep track of and measure which is great for succession and development research. A big limitation to this type of research is that large rhizotrons can be very costly to construct and operate.(Taylor)

Sources

Gardener, W. R. “DYNAMIC ASPECTS OF WATER AVAILABILITY TO PLANTS.” SOIL SCIENCE, vol. 89, no. 2, Feb. 1960, pp. 63–73., journals.lww.com/soilsci/Citation/1960/02000/DYNAMIC_ASPECTS_OF_WATER_AVAILABILITY_TO_PLANTS.1.aspx.

Johnson, Jane M.F., Morgan, Jack. “Sampling Protocols.” Plant Sampling Guidelines. IN Sampling Protocols, Ch. 2. R.F. Follett, editor. 2010, pp. 2-10. www.ars.usda.gov/research/GRACEnet

Newman, E. I. “A Method of Estimating the Total Length of Root in a Sample.” Journal of Applied Ecology, vol. 3, no. 1, 1966, pp. 139–145. JSTOR, www.jstor.org/stable/2401670.

Taylor, H. M., et al. “Applications and Limitations of Rhizotrons and Minirhizotrons for Root Studies.” Plant and Soil, vol. 129, no. 1, 1990, p. 29.

Taylor, H.M. 1986. Methods of studying root systems in the field. Hortscience 21:952-956.

Tennant, D. “A Test of a Modified Line Intersect Method of Estimating Root Length.” Journal of Ecology, vol. 63, no. 3, 1975, pp. 995–1001. JSTOR, www.jstor.org/stable/2258617.

United States, Congress, Kiniry, Lauren N., and Conrad L. Neitsch. “Monolith Collection and Preparation For Soils without Restrictive Layers*.” Monolith Collection and Preparation For Soils without Restrictive Layers*, 1994.

Vanderford, C. F. "The soils of Tennessee. Univ. Tennessee Agr. Experiment Station." Bulletin 10.3 (1897): 1-139.