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OCR for page 275
METALS IN ROOTS, STEM, AND FOLIAGE OF FOREST TREES
Walter C. Shortle
USDA Forest Service
Northeastern Forest Experiment Station
Durham, NH 03824
ABSTRACT
Eight metals (Ca, K, Mg, Mn, Fe, - Zn, Cu. Mo in decreasing
molar concentrations) are considered essential for tree growth and
function. They account for less than one percent of tree mass.
They must be obtained from soils derived from the earth's crust
in which the eight most abundant metals are A1, Na, Ca, Fe, Mg,
K, Ti, Mn. To obtain the essential metals from among the
common metals requires mechanisms for selectively accumulating
some metals, while discriminating against others, by biologically
regulated energy-consuming processes. Of major concern are
forests in which soil pH is in the 3 to 4.5. range. In this range
A1 ions can be released from soil solids by inputs of strong
inorganic ions, such as sulfate and nitrate. Increased
vulnerability of large trees may be triggered as A1 ions attain
equimolar concentration with Ca ions in the absorbing fine roots.
Awareness that a fatal tree disease was developing in the spruce-fir forests of
Germany began in the mid- 1 970s with descriptions of a dieback and decline of silver fir
(Abies alba Mill.) generally referred to as ~fir-dying." Trees with dying crowns had a
marked decrease in sapwood basal area (portion of the transverse area of secondary
xylem that is functional sapwoocI) in the lower stem, and a marked increase in
"wetwood" (wound initiated infection) in the lower stem and upper secondary roots
(Bauch et al. 1979~. Firs with dying crowns and decreasing sapwood basal areas due to
the spread of wetwood had been declining in cambial activity since the 1 950s, long
before crown symptoms were observed. Dendroclimatological studies indicated that this
suppression of cambial growth was not related to weather patterns (Eckstein et al.
1983~.
By the early 1 980s, a dieback and decline syndrome was observed in Norway spruce
(Picea abies (L.) Karst), although the symptoms were not as pronounced as in silver fir
(Schutt and Cowling 1985~. Spruce accounts for 40 percent of the commercial forest in
West Germany, fir only about 2 percent. Concern now changed from "fir-dyinn" to
"forest-dying" in central Europe and in other countries including
Canada. The relationship of this sudden loss of tree health to
pollution associated with the 20tli century economy has been
scientific investigations and a matter of great public interest.
conclusions have yet been reached about the actual impact of
deposition on forests, the possibility clearly exists that forests
eastern North
the United States and
stresses created by air
the subject of many
Although no definite
air pollution and acidic
of central Europe and
America are at risk from air pollution, either by direct chronic effects
on foliage or indirect cumulative effects on fine roots in soil.
275
OCR for page 276
276
A mechanism has been proposed that links some soil related effects of acidic
deposition to suppression of cambial growth, reduction of sapwood basal area, crown
degradation, and eventual mortality (Shortle and Smith 1988~. The mechanism involves
the gradual replacement of essential metal cations, calcium and magnesium, in the
rooting zone of spruce-fir stands with aluminum, which is released into soil solution by
adding strong anions to acidic soils (pH 3 to 4.5) where spruce and fir commonly grow
(Ulrich 1983~. The molar ratio of aluminum to calcium in absorbing fine root tissue
increases and at an equImolar ratio the uptake of calcium becomes limited (Bauch and
Schroeder 1982, Stienen et al. 1984, Bauch et al. 1985a, Shortle and Stienen 1988~.
Adding calcium to decrease the ratio in soil and in fine roots restored short-term
calcium uptake in isotope studies (Schroeder, et al. 1988), partially reversed damage in
seedling studies (Stienen and Bauch 1988), and reversed the declining cambial growth of
mature trees in liming studies (Bauch et al. 1985b). The timing and dose of calcium
additions are obviously important factors in obtaining a favorable response.
Calcium is the most abundant metal in spruce, fir, and northern hardwood trees
(Young and Carpenter 1967~. The high calcium requirement for mature trees was
recognized as a major difference between trees and crop plants (Rennie 1955~. Unlike
other major essential elements (nitrogen, phosphorus, and potassium), calcium is not
recovered from older living sapwood as it is converted into a heartwood core in which
calcium will be sequestered until the wood decays (Bamber and Fukazawa 1985~.
Although the uptake of calcium and other major essential cations may vary
considerably from site to site, the amount incorporated into functional sawood appears
to remain relatively constant (Shortle and Bauch 1986~. If calcium uptake is restricted
by interference from aluminum, and the rate of incorporation is conserved, then a
prolonged suppression of cambial growth is the expected outcome. Prolonged cambial
suppression would be seen as a series of narrow growth rings. The conversion of wider
growth rings into the heartwood core at the inner sapwood boundary is no longer
balanced by the addition of new sapwood rings at the outer sapwood boundary (the
vascular cambIum), thus the sapwood basal area decreases as observed in declining
spruce and fir trees. Mature spruce and fir trees with smaller sapwood basal areas have
smaller crowns (Marchand 1984~. Large trees with small crowns and low sapwood basal
areas are more vulnerable to attack by pathogens and insects (Shigo 1 985a,b). Such trees
would also have less energy available to compensate for the adverse aluminum to
calcium ratio through additonal fine root production.
The range of soil pH values observed in the humus and underlying mineral soil in
spruce-fir stands across northern New England (Shortle and Stienen 1988) was similar to
those observed in many stands in Germany (Stienen et al. 1984~. Extracts of humus
(organic soil horizons) collected from Camels Hump, Vermont, and Mount Abraham (25
km to the south), where red spruce are dying, had a molar Al:Ca ratio of 13.0 (Taylor
et al. 1986) add 6.0 (Shortle anti Stienen 1988), respectively; those from Acadia
National Park, Maine, and Beddington (60 km to the north), where red spruce appeared
healthy, had a molar Al:Ca ratio of 1.2 and 0.S, respectively. When the humus layers
from Camels Hump and Acadia were used in an experiment with rain chemistry, mist
chemistry, and ozone, soil was the only treatment affecting both the above-ground and
below-ground biomass of red spruce seedlings (Taylor et al. 1986~. No treatment
specific symptoms of visible needle injury were observed. Experiments with spruce
seedlings under various cultural conditions in which the molar Al:Ca ratio was 1
indicated that this condition can affect the development of fine roots and shoots (Schier
1985, Stienen and Bauch 1988~.
Molar ratios of Al:Ca in spruce and fir fine root tissue were determined from
collections made from humus and mineral soil sampled across New England in 1985 and
OCR for page 277
277
1986. In brief summary, at Mount Abraham, Vermont, Al:Ca in fine root tissue taken
from the lower humus, the major rooting zone of spruce and fir, was 3.4 (spruce,
1985), 1.7 (fir, 1985), and 4.1 (spruce, 1986~. Fine root tissue in the underlying mineral
soil at Mount Abraham was 3.1 (spruce, 1986~. At Beddington, Maine, Al:Ca in fine root
tissue taken from the lower humus was 0.1 (spruce, 1985), 0.3 (fir, 1985), and 0.1
(spruce, 1986~. Fine root tissue in the underlying mineral soil at Beddington was 1.3
(spruce, 1986~. Fine root production was sparse in the mineral soil from both sites.
Values for seven additional locations between Mount Abraham and Beddington were
intermediate, but more like Beddington than Mount Abraham at this time. However, at
the Crawford Notch, New Hampshire, location where the largest spruce are dead and
dying, spruce fine root samples taken in 1987 had an Al:Ca ratio of 1.1 for humus and
3.7 for mineral soil.
Limited growth of yellow birch (Betula alleghaniensis Britton), is attributed to
aluminum in the po~zols of New England (Hoyle 1971~. The humus layer supported good
growth of younger, smaller trees, but did not compensate for the inadequacy of the
mineral subsoil to support growth of larger trees, especially in the presence of
aluminum. At high elevation sites, it appears that aluminum may now be affecting the
uptake in the lower humus, which is usually a safe place for fine root absorption.
The molar Al:Ca ratio of fine root tissue may be a useful indicator of the
influence of acidic deposition on spruce-fir forests on acid soils (pH 3 to 4.5~. Under
existing acidic conditions, forests are at risk from the continued input of strong anions
derived from emissions of sulfur and nitrogen. Above-ground tissues are highly
conserved with respect to major metal ion concentrations with stemwood being more
stable than foliage. These parts of the tree appeared to respond to changing soil
conditions by changing rates of tissue development from cambium and buds. Changes in
cambial activity, sapwood basal area, and the spread! of infection in forest trees can be
monitored by electrical measurements (Shigo and Shortle 1985~.
Sampling absorbing fine roots (0.2 mm diem X<5 mm length) in amounts sufficient to
determine molar ion ratios is not feasible on a routine basis over large geographic areas.
However, some simpler analyses applied in sequence on samples of soil from the zone of
major fine root activity may be useful as an indicator of atmospheric effects in the
forest. Presumptive tests for low acidity and high ionic strength could be made by
simple electrical measurements followed by determination of soluble or exchangeable
metal ion ratios, such as Al:Ca and Al:Mg on acidic soils, or Ca:K on less acidic soils, by
routine chemical analysis. Coupling such measurements with periodic electrical
measurements of cambial activity and internal infections could help locate areas of
progressive decline and impending mortality, or of recovery following episodes of decline
and mortality.
REFERENCES
Bamber, R.K., and K. Fukazawa. 1985. Sapwood and heartwood: A review. Forestry
Abstracts 46:567-580.
Bauch, J., P. Klein, A. Fruhwald, and H. Brill. 1979. Alteration of wood
characteristics - in Abies -alba Mill. due to "fir-dying" and considerations
concerning its origin. Eur. J. For.Pathol. 9:321-331.
OCR for page 278
278
Bauch, J., P. Rademacher, W. Berneike, J. Kroth, and W. Michaelis. 198 5a. Breite
und Elementgehalt der Jahrringe in Fichten aus Waldschadensgebieten. Pp. 943-
959 in Waldschaden-Einflussfaktoren und ihre Bewertung. Dusseldorf, FRG:
VD1 Berichte 560.
Bauch, I., and W. Schroeder. 1982. Zellularer Nachweis van Elementen in den
Feinwurzeln gesunder und erkrankter Tanne (Abies alba Mills.
Forstwissenschaftliches Centralblatt 101 :285-294.
Bauch, J., H. Stienen, B. Ulrich, and E. Matzuer. 1985b. Einfluss einer Kalkung
bzw. Dungung auf den Elementgehalt in Feinwurzeln und das Dickenwachstum
von Fichten aus Waldschadensgebieten.
43:1148-1150.
Allgemeine Forst Zeitschrift
Eckstein, D., R.W. Aniol, and J. Bauch. 1983. Dendroklimatologische
Untersuchungen zum Tannesterben. Eur. J. For. Pathol. 13:279-288.
Hoyle, M.C. 1971. Effects of the chemical environment on yellow birch root
development and top growth. Plant and Soil. 35:623-633.
Marchand, P. J. 1984. Sapwood area as an estimator of foliage biomass and
projected leaf area for Abies balsamea and Picea rubens. Can. J. For. Res.
14:85-87.
Rennie, P. J. 1955. The uptake of nutrients by mature forests growth. Plant and
Soil 7:49-95.
Schier, G. A. 1985. Response of red spruce and balsam fir seedlings to aluminum
toxicity in nutrient solutions. Can. J. For. Res. 15:29-33.
Schroeder, W.H., J. Bauch, J., and R. Endeward. 1988. Microprobe analysis of Ca
exchange and uptake in the fine roots of spruce: influence of pH and
aluminum. Trees 2~3~: (in press).
Schutt, P., and E.B. Cowling. 1985. Waldsterben, a general decline in forests in
central Europe: symptoms, development and possible causes. Plant Disease
69:548-558.
Shigo, A. L. 1985a. Compartmentalization of decay in trees. Sci. American
252:96- 103.
Shigo, A. L. l985b. Wounded forests, starving trees. J. Forestry 83~11~:668-673.
Shigo, A. L., and W.C. Shortle. 1985. Shigometry: A reference guide. USDA For.
Serv. Agric. Handb.646. 48 p.
Shortle, W. C., and I. Bauch. 1986. Wood characteristics of Abies balsamea in New
England states compared to Abies aZba from sites in Europe with decline
problems. IAWA Bull. n.s. 7:375-387.
Shortle, W.C., and K.T. Smith. 1988. Aluminum-induced, calcium deficiency
syndrome in declining spruce-fir forests Science 240:1017-1018.
OCR for page 279
279
Shortle, W.C., and H. Stienen. 1988. Role of ions in the etiology of spruce decline.
In Proc. Research Symposium, The effects of atmospheric pollution on spruce
and fir forests in the eastern United States and the Federal Republic of
Germany, October 18-23, 1987. Burlington, VT. USDA For. Serv. Gen. Tech.
Rep. NE- (in press).
Stienen, H., R. Barckhausen, H. Schaub, and J. Bauch. 1984. Mikroskopische und
rontgenenergiedispersive Untersuchungen an Feinwurzeln gesunder und
erkrankter Fichten (Picea abies (L.) Karst.) verssschiedener standarte.
Forstwissenschaftliches Centralblatt 103:262-274.
Stienen, H. and J. Bauch. 1988. Element determination in tissues of spruce and fir
seedlings from hydropanic and soil cultures simulating acidification and
deacidification. Plant and Soil 106:231-238.
Taylor, G.E., Jr., R.J. Norby, S.B. McLaughlin, A.H. Johnson, and R.S. Turner. 1986.
~~ ~ rubens Sarg.)
carOon d~ox~de assimilation and growth of red spruce (Picea
seedlings in response to ozone, precipitation chemistry and soil type. Oecologia
(Berlin) 70:163-176.
Ulrich, B. 1983. A concept of forest ecosystem stability and of acidic deposition
as a ctriving force for destabilization. Pp. 1-32 in Ulrich, B., Pankrath, J.
(eds.~. Effects of air pollution in forest ecosystems. Dordrecht, Holland: D.
Reidel Publishing Co.
Young, H.E., anc! P.M. Carpenter. 1967. Weight, nutrient element and productivity
studies of seedlings and saplings of eight tree species in natural ecosystems.
Tech.Bull. 28. Orono, ME: Maine Agric. Expt. Stn., Univ. of Maine. 39 p.
OCR for page 280
278
Bauch, J., P. Rademacher, W. Berneike, J. Kroth, and W. Michaelis. 198 5a. Breite
und Elementgehalt der Jahrringe in Fichten aus Waldschadensgebieten. Pp. 943-
959 in Waldschaden-Einflussfaktoren und ihre Bewertung. Dusseldorf, FRG:
VD1 Berichte 560.
Bauch, I., and W. Schroeder. 1982. Zellularer Nachweis van Elementen in den
Feinwurzeln gesunder und erkrankter Tanne (Abies alba Mills.
Forstwissenschaftliches Centralblatt 101 :285-294.
Bauch, J., H. Stienen, B. Ulrich, and E. Matzuer. 1985b. Einfluss einer Kalkung
bzw. Dungung auf den Elementgehalt in Feinwurzeln und das Dickenwachstum
von Fichten aus Waldschadensgebieten.
43:1148-1150.
Allgemeine Forst Zeitschrift
Eckstein, D., R.W. Aniol, and J. Bauch. 1983. Dendroklimatologische
Untersuchungen zum Tannesterben. Eur. J. For. Pathol. 13:279-288.
Hoyle, M.C. 1971. Effects of the chemical environment on yellow birch root
development and top growth. Plant and Soil. 35:623-633.
Marchand, P. J. 1984. Sapwood area as an estimator of foliage biomass and
projected leaf area for Abies balsamea and Picea rubens. Can. J. For. Res.
14:85-87.
Rennie, P. J. 1955. The uptake of nutrients by mature forests growth. Plant and
Soil 7:49-95.
Schier, G. A. 1985. Response of red spruce and balsam fir seedlings to aluminum
toxicity in nutrient solutions. Can. J. For. Res. 15:29-33.
Schroeder, W.H., J. Bauch, J., and R. Endeward. 1988. Microprobe analysis of Ca
exchange and uptake in the fine roots of spruce: influence of pH and
aluminum. Trees 2~3~: (in press).
Schutt, P., and E.B. Cowling. 1985. Waldsterben, a general decline in forests in
central Europe: symptoms, development and possible causes. Plant Disease
69:548-558.
Shigo, A. L. 1985a. Compartmentalization of decay in trees. Sci. American
252:96- 103.
Shigo, A. L. l985b. Wounded forests, starving trees. J. Forestry 83~11~:668-673.
Shigo, A. L., and W.C. Shortle. 1985. Shigometry: A reference guide. USDA For.
Serv. Agric. Handb.646. 48 p.
Shortle, W. C., and I. Bauch. 1986. Wood characteristics of Abies balsamea in New
England states compared to Abies aZba from sites in Europe with decline
problems. IAWA Bull. n.s. 7:375-387.
Shortle, W.C., and K.T. Smith. 1988. Aluminum-induced, calcium deficiency
syndrome in declining spruce-fir forests Science 240:1017-1018.
Representative terms from entire chapter:
root tissue
