Roots - Soil Research

Argonne National Laboratory
Julie Jastrow, Project Manager

Intro - Core Collection - Aggregates - Roots - Graphs and Charts

Researchers look for the development of mycorrhizal fungi with the roots. These fungi help the plant take up nutrients.

Intact soil cores are put in buckets of water

The soil cores are manipulated by hand under water to break them apart and begin the separation of roots from soil.

Initially a rather large mass of roots is usually separated, placed in a tray of water to remove any adhering soil particles, rinsed in clear water and collected (when clean) on moist paper towels.

The remaining soil (still in the bucket) is smeared against the side of the bucket to break soil aggregates into primary particles (sand, silt, and clay) to release any fine roots from soil.

Any floating organic debris and litter is skimmed off the surface of the water and discarded.

Then the dispersed soil and water is poured through a 500 µm (micrometer sieve to catch the remaining roots.)

After the water and suspended soil particles have been poured out through the sieve, any remaining unsuspended soil is visually examined for roots. If roots are present, the process is repeated (i.e., smearing, suspension of soil and sieving) until the remaining soil free of roots.

Roots and other material collected on the sieve is washed using a spray of water from underneath the sieve to prevent clogging or pushing the collected material through the sieve.

Then the material collected on the sieve is washed into a tray for further cleaning and separation.

This remaining material is a mixture of fine roots, organic debris and litter, partially decomposed organic matter, and very small aggregates. Relatively long pieces of roots are picked out with forceps and added to the rest of the clean roots. Large debris pieces are picked out and discarded. The remaining material is poured through a sieve, collected, and placed on the wet paper towel in a separate area from the roots that are not mixed with debris.

Three examples of roots and rhizomes collected from three different soil cores are shown. The mass is roughly separated into rhizomes (underground stems and technically not roots - rhizomes do not take up water and nutrients), coarse roots (> 1mm diameter), clean fibrous roots (< 1 mm diameter) and "dirty" fibrous roots. The moist paper towels are folded over, placed in zip-lock bags and refrigerated.

Within a week the roots and rhizomes are processed in the lab. The entire mass is further (more carefully)? separated into the four categories described above. This often entails cutting fibrous roots away from coarse roots and rhizomes. A small sub-sample of the clean fibrous root is removed, weighed, placed in a special container and stained with a stain that makes it easy to view the internal mycorrhizal? fungus structures. Fresh weights of the remaining clean fibrous roots and the other three groups are taken. Each group is placed in separate paper bags to be dried.

After the roots and rhizomes have dried, dry weights are determined.

The stained sub-sample of roots is viewed under a microscope and used to determine the length of root per gram of root mass and the length of root colonized by mycorrhizal fungi. This photo shows internal fungal structures, external hyphae and spores. Lengths are determined by counting the number of times roots randomly distributed on the slide intersect the line of a grid in the ocular of the microscope.

By a whole separate procedure, external hyphae of mycorrhizal fungi can be separated from small soil samples (by dispersal, centrifugation, and filtration) collected on membrane filters and strained. Lengths per gram of soil can be determined by method similar to those used for determining root lengths.