Research in many fields of plant ecology could be helped by quicker and more satisfactory methods of determining the amount of root in a volume of soil. Most quantitative studies of roots have used weight as the means of assessing the amount of root; but it is generally accepted that the capacity to take up water and salts is usually more closely related to the surface area or total length of the root system than to its weight. Interest in root length has been stimulated by papers by Gardner (1960, 1964) and Cowan (1965) dealing with water uptake from soil, in which length of root per unit volume of soil is an important parameter. The main difficulties indetermining root length arise from the great lengths which can occur in even small volumes of soil. Some root densities which have been reported for plants growing outdoors are: 364-3434 m of root per litre of soil under grass swards (data of Pavlychenko quoted by Troughton 1957), 66-548 m/l under Graminae (Dittmer 1938), up to 21 m/l under coffee trees (Nutman 1934), up to 18 m/l under sugar-cane (Evans 1938). Thus, even if it is practicable to use soil samples as small as 041 1., direct measurement of the roots may take a long time. Indirect methods have been used: for instance, measuring root diameters and then determining root volume (Evans 1938); or measuring the length of a small portion of the root sample, then weighing this portion and the remainder. However, these methods are often inaccurate because of variations in the ratios volume: length and weight: length. This paper describes a new method of estimating the total length of root in a sample, the line intersection method. I believe that it will in many circumstances prove more satisfactory than any existing method.

A method of estimating the total length of root in a sample

Global biogeochemical models have improved dramatically in the last decade in their representation of the biosphere. Although leaf area data are an important input to such models and are readily available globally, global root distributions for modeling water and nutrient uptake and carbon cycling have not been available. This analysis provides global distributions for fine root biomass, length, and surface area with depth in the soil, and global estimates of nutrient pools in fine roots. Calculated root surface area is almost always greater than leaf area, more than an order of magnitude so in grasslands. The average C:N:P ratio in living fine roots is 450:11:1, and global fine root carbon is more than 5% of all carbon contained in the atmosphere. Assuming conservatively that fine roots turn over once per year, they represent 33% of global annual net primary productivity.

https://www.pnas.org/content/pnas/94/14/7362.full.pdf

A global budget for fine root biomass, surface area, and nutrient contents

http://directory.umm.ac.id/Data%20Elmu/jurnal/P/PlantScience/Plant%20Science_BioMedNet/061-080/062.pdf

Phytoremediation of toxic elemental and organic pollutants.

Publisher Summary This chapter discusses the ecological implications of mycorrhizal associations in natural ecosystems and the role of soil or environmental factors, mycorrhizal fungus characteristics or host plant properties. Mycorrhizal associations are regulated by features of the host plant and mycorrhizal fungus, as well as by soil conditions and environmental factors. Factors which can influence the occurrence and effectiveness of mycorrhizal associations include (1) root properties (2) edaphic or climatic factors (3) soil organisms, (4) soil disturbance, and (5) host-fungus compatibility. Several other complex ecological topics also discussed in the chapter include (1) mycorrhizal phenology , (2) factors responsible for varying degrees of mycorrhizal dependency in host plants, (3) the role of mycorrhizal hyphae in soil (4) nutrient competition involving mycorrhizal and non-mycorrhizal plants, and (5) mycorrhizal interactions involving pollution and other stresses, the rhizosphere, soil properties and allelopathy. Finally, the chapter also discusses the population ecology of mycorrhizal fungi and the influence of their associations on plant population ecology.

Mycorrhizas in Natural Ecosystems

Summary
Although plants devote a large proportion of their resources to roots, we have a poor understanding of the constraints under which root systems function. Roots are much less variable morphologically than leaves and it is likely that root systems rather than individual roots are the focus of natural selection. In other words, architecture is more important than morphology. Existing classifications of root systems, based on the developmental model, have failed to provide much insight into their functioning and an alternative, topological model is outlined, in which the link is the basic unit of classification. Other components of the architecture of root systems, including link lengths, branching angles and diameters, are considered and the ecological implications of variation in each is discussed.

Simulation models of transport and space exploration are discussed and it is shown that resource cost, transport efficiency and exploration efficiency cannot be simultaneously minimized and that optimum form may vary with the mobility of the resource. In general, a ‘herringbone’ structure seems to be the most efficient at exploration of space but the least transport-efficient and the most expensive.

An architectural approach to the comparative ecology of plant root systems

AS AN element of the plant cover, grasses are efficient as soil binders and occupy a particularly prominent place in erosion studies. Their compact fibrous root systems develop mainly in the upper soil levels which gives them a very advantageous position in soil binding. Fortunately their economic importance as field and forage crops makes their cultivation porfitable from an agricultural standpoint as well as from one of soil conservation. The investigations by Weaver and his associates (1926) have given a general picture of the subterranean parts of many plants. Reports of these investigations deal more particularly with the horizontal and vertical distribution of root systems. A recent paper by Pavylechenko (1937) is one of the first attempting a quantitative survey of the roots of a mature plant. In this study, dealing with competition between weed and crop plants, Pavylechenko reports the total root length of several individual field grasses -namely, wild oats, 54.3 miles; Marquis wheat, 44.2 miles; and Prolific spring rye, 49.1 miles. These figures were based upon measurements of single plants grown widely separated. The survey of the root systems of these plants did not include all roots. Pavylechenko states there were "further subdivisions" which were neither counted nor measured. Had these, the quaternary roots, been included, the total figures would certainly have been much higher, probably doubling his reported totals. In general the work on root hairs has been carried on by a group of investigators whose interests have been mainly in growth responses as influenced by external factors, and apparently none of them has made a count of root hairs for an entire well-developed plant. This paper gives the figures for the root and root hair systems of a single cereal plant, Secale cereale L. Of several grasses studied in a preliminary waynamely, Andropogon furcatus Muhl., Sorgastrum nutans (L.) Nash., Poa pratensis L., and Triticum sativum L.-winter rye was selected because it has been used successfully in retarding erosion and also because of its importance as a grain and forage crop. Studies in progress deal similarly with several other grasses. The seedling of winter rye produces a whorl of four primary roots. These function for a number of weeks but disappear later as numerous permanent adventitious roots grow out from the base of the stem area and become the main roots of the plant. Branches from these are the more numerous secondary roots which in turn give rise to the tertiary

Howard J. Dittmer

Papers

A quantitative study of the roots and root hairs of a winter rye plant (secale cereale)

A quantitative study of the subterranean members of three field grasses

A comparative study of the subterranean members of three field grasses