Zhang:
Most root patterns are "distorted" (guided) by three things--available
water, oxygen, and pore diameter. Most plants have limited ability to
increase effective pore size (there are exceptions) at the root-tip, but
most root growth "strength" is by expansion of diameter, and that can be
considerable. Roots develop where conditions of growth are best (or at least
adequate), such as cracks in rocks. In other words, they are opportunists,
like all organisms.
"Extrapolation" is not science, but this is not to say that intuition is not
useful for developing hypotheses and making rough guesses for practical
purposes. Sure, there probably is some correlation between above-ground
biomass and below-ground biomass, but the only way to prove it is to
excavate. There are WAGS AND SWAGS, but both should have some foundation in
reality, even for practical purposes. I have used cores of various sizes,
but not to much useful effect. Beware of conjecture, "scientific" myths, and
old professor's tales. Demand evidence (at least in your own mind). Politely
to others, mercilessly to yourself. Be skeptical of "references." Checking
them out by replication is always useful--a practice honored more in the
breach than the observance, unfortunately. Explore new depths.
I have excavated to as much as 18 feet, but only in relatively fine alluvial
soils, and cored to as much as 20 feet. Going deeper is no doubt desirable,
but one might be able to extrapolate with reasonable confidence (maybe 95%,
maybe not--did you really mean 95% or was this only a way of expressing the
degree of confidence you are dreaming of getting?) once the pattern and
biomass variations with depth can be established with "reasonable"
certainty. In highly variable wildland soils and subsoils/formational
materials will cause root development to be highly variable.
My favorite technique is to use the biggest backhoe I can find and sever
almost half of the root system at the trunk, out at least as far as the
"drip-line." Gather data and photograph, use tritium or some other tracing
material, and/or follow roots to their ends by washing and carefully
digging. Ratios of root(let) diameter to length can sometimes provide enough
of an index from which to extrapolate. One can start washing the severed
half of the root system, and learn something about the radial patterning,
and, depending upon the species, the tree/shrub may have to be removed to
prevent toppling.
Another "procedure" I have found useful is studying "fresh" road cuts and
other construction excavation. Hair roots and tips often immediately
dessicate upon exposure, so one may have to remove some of the
recently-exposed profile to see (and quickly record) those parts of the
systems. Preserve and accession samples and develop your own reference
collection, making certain that the samples are in fact of the species being
studied and not some other plant.
I have read about tritium tracing but have never done it. I'd like to learn
more. I remember one paper that traced oak roots to a depth of 80 feet, much
deeper than the tree was tall, but you can't get biomass estimates this way
(if anyone knows how, please advise).
I look forward to hearing more about your work. At long last, someone is
trying to get to the root of the matter.
WT
Comments from kibitzers are always welcome. Be as rude as your little heart
desires--or doesn't desire. Demand evidence.
----- Original Message -----
From: "张玉" <[email protected]>
To: <[email protected]>
Sent: Friday, July 05, 2013 3:41 PM
Subject: [ECOLOG-L] Fwd: Root depth measurement
Hi all，
I want to do some measurement of the root depth of plants (including shrub,
grass and forb). Excavation of the whole plant root system is most
straightforward but hard to get permission for, especially for shrubs. Do
you guys have any idea how to measure/extrapolate root depth with minimum
impact on plants and soil?
Thank you so much!
Cheers,
Jade
(P.S.: I've found from literature two alternatives, one of which is to
sample soil cores near the gamet and measure root biomass at each depth
level then extrapolate 95% root depth, the other is to inject tracer into
certain depth of soil and see whether it can be detected in plants. Both
seem complicated and potentially destructive;b I am under the impression
that plant above ground height should be somehow correlated to root depth.
Is there any way of inferring root depth from this too?)
--
Yu Zhang (Jade)
Ph.D Student in Environment Science, Policy and Management
College of Natural Resources, University of California, Berkeley, USA
Tel: (+1) 510-3257206
Email: [email protected]
Skype: ElizaZ663
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1432 / Virus Database: 3204/5966 - Release Date: 07/05/13
