195 
Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 
Relationship between soil and leaf metal content and Landsat MSS 
and TM acquired canopy reflectance data 
C.Banninger 
Institute for Image Processing and Computer Graphics, Research Centre Joanneum, Graz, Austria 
ABSTRACT: The presence of high concentrations of copper, lead, and zinc in the soils under 
lying a spruce tree stand is not mirrored in the metal content of the spruce needles, except 
for zinc. A much stronger correlation exists between Landsat canopy reflectance data and soil 
metal content than with spruce needle metal content. This implies that the toxic effects of 
the heavy metals on the spruce trees are centered in the root systems rather than in the fo 
liar parts of the trees. 
1 . INTRODUCTION 
Plants respond to the uptake of toxic 
amounts of heavy metals into their system by 
undergoing physiological and morphological 
changes that are detectable using spaceborne 
sensor systems. These metal-induced changes 
are commonly expemplified by a reduction in 
leaf pigment and water content and a decrease 
in plant foliar biomass or density, which, 
in turn, result in changes in the spectral 
response of the stressed plants. Although the 
relationship between soil and leaf metal con 
tent and canopy reflectance can conceptually 
appear straightforward, it is often much more 
complex and less well-defined than it ini 
tially appears. Such is the case with the 
study described in this paper, which set out 
to establish the connection between soil geo 
chemistry, leaf biogeochemistry, and changes 
in Landsat MSS and TM reflectance data from 
a coniferous tree stand growing in soils con 
taining high concentrations of copper, lead, 
and zinc. 
2. HEAVY METAL UPTAKE AND TOLERANCE IN PLANTS 
Most plant species restrict their metal 
uptake by exclusion or internal regulatory 
mechanisms operating at the plant roots-soil 
interface and within the plant's metabolic 
systems, provided that the available metal 
concentration in the soil does not exceed a 
certain critical threshold, which varies for 
each species and set of environmental site 
conditions. Above this threshold concentra 
tion, the regulatory mechanisms breakdown 
and are unable to prevent an unstricted up 
take of metals by the plant. The uptake pro 
cess operating in a plant involves the ab 
sorption of elements by the plant root sys 
tem, their translocation through the aerial 
parts of the plant, and their subsequent de 
position in the plant's leaves and woody 
parts. Heavy metals, therefore, can accumu 
late in all parts of the plant, although a 
large fraction of the absorbed metals is pre 
vented from reaching the aerial parts of a 
plant by being precipitated in the tissue 
cells of the root system. The roots of plants 
generally contain greater amounts of metals 
than the aerial parts, particularly at high 
soil metal concentrations (Hawkes and Webb, 
1962; Antonovics et al., 1971). Cannon (1960) 
reported ratio values of heavy metals in 
plant roots to aerial parts as high as 200:1. 
3. COPPER, LEAD, AND ZINC UPTAKE AND TOLER 
ANCE IN PLANTS 
Plants take up from the soil only those 
elements that are freely and readily avail 
able in water-soluble form. Element uptake 
occurs mainly in response to a plant's nutri 
tional requirements, and most plants attempt 
to control the absorption and level of con 
centration of the various elements within 
their system, regardless of the amounts in 
the soil. Plants exhibit a strong biological 
absorption for zinc, moderate for copper, and 
weak for lead (Perel'man, 1967), which mirror 
the moderate, moderately severe, and severe 
levels of toxicity, respectively, of these 
metals to plants (Hawkes and Webb, 1962; 
Bowen, 1966; Brooks, 1972). 
The uptake pattern of copper and lead 
differs markedly from that of zinc. The ab 
sorption of zinc into a plant's system is 
normally unrestrictive, which indicates that 
an internal tolerance mechanism, rather than 
an exclusion mechanism, operates in plants for 
zinc. For copper and lead, their uptake by 
plants is small compared to zinc, and is con 
trolled by an exclusion mechanism situated in 
the plant root system. Both copper and lead, 
and even zinc, are largely accumulated in the 
plant root tissues, which generally contain 
greater concentrations of the metals than the 
leaves and twigs. 
4. LANDSAT MSS AND TM SPECTRAL BANDS FOR 
STRESS DETECTION 
The Landsat MSS and TM sensor systems 
collect reflectance data in the visible to 
shortwave infrared spectral region, which 
can be used to assess the state of health of 
vegetation. Although the four sensor band- 
widths of the MSS system encompass a number 
of plant-energy relationships useful for de- 
terming the condition of a plant canopy, the 
presence of more than one important plant- 
radiation association within these bands de- 
minishes their ability to detect changes in 
the spectral properties of plants related to 
their health.