Establishment and Tending of Subalpine Forest: Research and Management.
H. Turner and W. Tranquillini, eds.
Proc. 3rd IUFR0 Workshop P 1.07-00, 1984. Eidg. Anst. forstl. Versuchswes., Ber. 270 (1985): 193-196.
RESPONSES OF PINUS SILVESTRIS TO MAGNESIUM DEFICIENCY E.-D. Schulze and M. Klippers
Lehrstuhl Pflanzenokologie der Universitat Bayreuth Postfach 3008, 8580 Bayreuth, West Germany
ABSTRACT
Magnesium-deficiency is one of the obvious features of forest decline in the mountainous areas (700 to 1000 m ele- vation) of mid-Europe. It is therefore appropriate to study the effect of Mg- deficiency per se in a habitat with re- latively little atmospheric pollution, but a natural soil Mg-deficiency. Leaves of Pinus silvestris showed an increasing starch content and severe needle ti~
chlorosis at less than 0.3 mg Mg g- needle dry weight. Net photosynthesis and respiration decreased with increased Mg-deficiency, but stomatal conductance and the stomatal response to humidity were unaffected. Hg-nutrition did not affect the conductance of water flow in the soil/leaf pathway. Lower water use efficiency and daily carbon balances changed the carbon partitioning during growth. Plants with less than 0.3 mg Mg g-1 needle dry weight did not survive.
INTRODUCTION
The forest decline in mid-Europe seems to exhibit two different syndromes:
(1) older trees lose the ability to form compression wood in the 2nd-order twigs a~d this leads to a hanging habit of those twigs in addition to loss of older needies, and (2) younger trees show bright yellow needle tips in their older needles,which is associated with very low magnesium content. Zech and Horn (1984) reported 0.13 to 0.25 mg Mg gdw-1 in chlorotic spruce needles versus 0.35 to 0.55 mg Mg gdw-1 in needles with a healthy appearance. The Mg-deficiency syndrome was observed on acid soils, mainly gra- nite and phyllite. It occured predomi- nantly at an elevation of significant forest damage (700 to 1000 m elevation) which was correlated with increased at- mospheric pollutant inputs. Since i t is unclear how air pollutants might cause Mg-deficiency and whether the response of the plants is the same with respect to air pollutants and to Mg-deficiencies, studies were undertaken in an area where natural Mg deficits occurred in the soil but where the input of air pollutants was low (450 m elevation).
MATERIAL AND METHODS
The vegetation of the northeast Ba- varian pine forest has been described by Lutz
(1959). Alluvial jurassic sands support a natural Pinus-Vaccinium-community of very low species diversity (5 angio- sperms). If the top soil and humus layer are eroded or erased (sand pits, road cuts), the new pine growth shows dis- tinct Mg-deficiency features, namely bright-yellow needle tips and green needle bases in older needles.
The experiments were carried out 10 km south of Pressath (Oberpfalz, West Germany) at 450 m elevation in a temper- ate zone climate, which had an annual precipitation of 650 to 700 mra and a precipitation maximum during the growing season. Individual plants were fertilized twice (1978 and 1980) with 50 g MgSO4 or 50 g Mg plus NPK-fertilizer.
Carbon dioxide and water vapor ex- change and plant water potentials of fertilized and unfertilized specimens with different degrees of Mg-deficiency were investigated two years following the last fertilization, ( 1981) . Gas ex- change was measured using gas exchange cuvettes (Schulze and Klippers, 1979) and water potentials were measured with a pressure chamber. Organic nitrogen was determined with micro Kjeldahl analysis
(Strauch, 1965). Mg-contents were deter- mined by atomic absorption spectrometry after combustion at 550°C, where magne- sium was exchanged for BaCl2 without buffer. Chlorophyll content was deter- mined by acetone extraction (Knudson et al., 1977). Starch content (as glucose) was determined following a digestion with a-amyloglucosidase. Further details have been presented by Klippers et al.
1984) .
RESULTS
At Mg contents below 0.3 mg g-1 needle dry weight, the proportion of the yellow tip as a percentage of the total needle length increased sharply (Fig 1). At the same time the chlorophyll content de- creased but starch levels increased.
Needle nitrogen content decreased as well, but not as distinctly as the other parameters.
Pinus silvestris Prttsath,August 1981
0.9 A 90~
6 C
7i
~ g' ~
h 0 7 70 .!:! .§_ 0.7 2.4
g
!<
a"~
~ go.s 50
lt
~ g:o.s~
2.0~~e 0 {-5 0 i;
a~ e 0.3 30 15 e 0.3 1.6 ~
i 10
!
0. ~ t .c eu 0.1 ,I!. 0.1
.
1.2~0 0 0
24 B 2.4iii 10 14 18 22
z Nitrogen content
c- i ___ (m9Ngo-N1)
°E 7g20 2.0
i
"g~ !
16 1.s E..s V::: Plontts
St V> 2 a. untre<1tedi 12
.
1.2 f.3 Mg-fertilized ◊ ♦y Mg-, N-, P-, K-fermized oa 0 0.2 0.4 0.6 0.8 1.0
Mgl•--conlent (mg 9.,wl)
Fig. 1 (left): Chlorophyll content, Chl, proportion of yellow tip as a percentage of total needle length, gL; content of or- ganic nitrogen, N; and starch content, St, as related to the Mg-content of the needles.
Fig. 1 (right): Chlorophyll content, Chl and starch content, St, as related to the content of organic nitrogen. For unfertilized, a, Mg-fertilized, 13 and Mg- and NPK fertilized plants, y.
During late summer, the non-ferti- lized tree had 0.17 mg Mg g-1 dry weight and 16.6 mg N g-1 in current-year nee- dles, the Mg-fertilized tree had 0.63 mg Mg g-1 and 19.9 mg N g-1 and the Mg- and NPK-fertilized tree had 0.90 mg Mg g-1 and 21.4 mg N g-1. These differences in the nutrient status of the needles in- fluenced photosynthetic performance. The non-fertilized tree had a lower rate of CO2 assimilation at a 350 ppm mesophyll internal CO2 concentration, and the ini- tial slope of the Co2 dependence of photosynthesis was steeper under ferti- lized conditions (Fig. 2A bottom). This indicated that the carboxylase activity decreased with Mg-deficiency. The de- creased photosynthetic capacity of Mg- de=icient needles was also clear from the light response curve (Fig. 2B). Not only did the CO2 fixation rate decrease, but so did the dark respiration rate. The de- crease in net photosynthesis was due mainly to the photosynthetically inactive needle tip. Kilppers et al. (1984) esti- mated that the CO2 fixation rate of the green needle base was of a similar order of magnitude in both fertilized and non- fertilized trees.
- - - ~
Fig. 2B: CO2 assimilation, leaf conduc- tance and mesophyll internal CO2 con- centration as related to light intensity at ambient air.
194
Pinus silvestris Pressath, August 1981 5 A
<
r: 5 B
.2 :§
'i~ 3
'iii
'"
a
u 0 10 -1
0 50 150 250 350
C02 concentration in leaf, C; (ppm) Plant
Light intensity (µmol photon m·2 s·l) 70-84 229-354 1208-1500
a. untreated (; t, 4
~ Mg-fertilized ◊ ◊ ♦
y Mg-, N-, P-, K-fertilized 0 0 El
LT= 25'C, \IJ=-10.3 :!:. 2.3 bar
Fig. 2A: CO2 assimilation as related to the mesophyll internal CO2 concentration at different light intensities and differ- ent Mg-treatments.
Pinus silvestris Pressath, August 1981 A
3 2
0
80 B
0 + - - ~ - - - . - - - , - - - , - - - ~ 500
~ C
E4oo
.l= a.
C 0.
2l-300
C 0
6'
u 200 u0 200 600 1000 1400
Light intensity (µmol photon m·2 s·1)
Plant \ll(bar)
a. untreated 6 - 6 0.7 Aw:17.2-19.2 mbar bar·1
~ Mg-fertilized ♦ -10 1.4 Needle temperature= 25 •c y Mg-, N-, P-, K-fertilizeda - 6.3 3.9 C0:306-318ppm
The significant alterations in the photosynthetic performance in Mg-defi- cient needles were not correlated with similar changes in the plant water re- lations. Stomata of Mg-deficient needles showed the same responses to dry air as fertilized needles (Fig. 3). In addition, i t was found that there was no alteration of the liquid flow resistance in the soil/plant liquid flow pathway. The Mg- deficient and non-deficient needles op- erated with the same transpiration/water potential relationship (Fig. 4).
C
Plant \j/(bar)
a. untreated A -65 !. 3.6
~ Mg-fertilized • - 3.St 3.5 y Mg-, N-, P-, K-fortilized • - 9.1 t. 1.6
Light intensity = 1296-1492 µmot photon m·2 s·' Nff.dle temperature= 20 ~ C,,:305 t4.5 ppm
o s m ■ ro u
Leaf/air vapour pressure difference- (mbar bar·I)
Fig. 3: CO2 assimilation, transpiration, leaf conductance and mesophyll internal CO2 concentration as related to the relative vapor pressure difference be- tween leaf and air.
0 =§
a,
0 0 -2
~~ -6
a, '-- -0 .0 0
~~-10 E a,
~
Pinus silvestris Pressath, Sept.1, 1981
0 0.2 0.6 1.0 1.4 1.8 Transpiration (mmol m-2 s-1)
Plant
a. untreated :,
~ Mg-fertilized ♦
y Mg~, N-, P-, K-fertilized 111
Fig. ~: Leaf water potential as related to transpiration for different Mg treat- ments.
Mg-deficiency lead to a deterioration of the water use efficiency, not because of a stomatal malfunctioning, but because of a decreased photosynthetic capacity.
Fig. 3 shows that the mesophyll internal C02
195
concentration was greater in Mg-deficient needles than fertilized needles. This was also an obvious difference in performance seen from observations of daily courses under natural climatic conditions. On a clear day, the daily water loss was similar in all treatments, but because of lower photosynthetic rates the water use efficiency (day-time photosynthesis per transpiration) increased from 0.43 in Mg-deficient needles to 1.42 in fertilized trees (Fig. 5).
g
10a Aw
.§. 6
~
,.1---../
- 0+-~-~~-~~-~~-~~-~~-~
Elr---....
o-c:::t
l G a 10 12 1.i.~
1s rn 20 22 24 CST(h)Fig. 5: Daily course of light, I, CO2 assimilation, A, transpiration, E, leaf temperature, BT, leaf/air vapor pressure deficit, 6 w, and leaf conductance for Mg deficient, a, Mg fertilized,
B,
and Mg- and NPK fertilized trees, y.Magnesium deficiency changed not only the needle photosynthetic physiol- ogy, but also the needle morphology.
Needles became shorter and thinner with decreasing magnesium content. Also the needle dry weight decreased sharply below 0.3 mg Mg g-1 needle dry weight. Further- more, the plants showed strong differ- ences in growth rate. The annual shoot length and the total tree height de- creased as a result of reduced carbon gain (Fig. 6).
Pinus silvestris
Pressoth. August 1981
0.2 0.4 06 0.8 10 Mg2•.content (mgg0;,1)
Fig. 6: Total tree height after 7 years of growth, annual shoot length, needle dry weight, needle surface area and needle length as related to the Mg con- tent of the needles.
Reduced carbon gain at high rates of water loss lead to a negative carbon balance and tree death in Mg-deficient trees (Fig. 7) .
~40 'o
] 30
·a C oi 20 :E Ol
i
10Pinus silvestris
Year
Pressath, 1975-81
0.90 0.50
Fig. 7: The change of tree height with tree age for trees differing in the Mg content of their needles.
DISCUSSION
The experiments show the strong in- fluence of carbon balance on the process of tree death under Mg-deficiency con- ditions. The reduction of carbon gain under Mg-deficiency is mainly due to a reduction in photosynthetic area at the needle bases. The Mg-deficient tree had a Mg content of 0.17 mg Mg g-1, which is 8.2 µmol g-1. This is much more than the
196
Mg requirement for chlorophyll formation in the same needle (0.3 µmol chlorophyll g-1). Klippers et al. (1984) discuss the role of Mg in transport processes and enzyme functioning. Mg deficient needles show a larger content of free lipids, steroids and organic acids. Also, sucrose formation seems to be inhibited. This leads to an increase in the needle starch content. Therefore, Mg-deficiency leadsto a whole plant carbon deficit but with a carbon surplus at the needle level. The water relations are not disturbed, prob- ably because of a predominant carbon partitioning towards root growth in Mg- deficient plants. It is hoped that these functional relationships may serve as a basis for understanding the growth of coni- fers under conditions of atmospheric pollution. These experiments are cur- rently in progress.
REFERENCES
Knudson, L.L., T.W. Tibbitts, and G.E.
Edwards. 1977. Measurement of Ozone injury by stermination of leaf chlo- rophyll concentration. Plant Physiol, 60:606-608.
Klippers, M.,
w.
Zech, E.D. Schulze, and -E. Beck. 1984. CO2-Assimilation,transpiration and growth of Pinus sylvestris L. at different Magnesium- nutrition. Forstwiss. Cbl. im Druck.
Lutz, J.L. 1950. Uber den Gesellschafts- anschluB oberpfalzischer Kiefern- standorte. Ber. d. Bayer. Bot. Ges., 28:64-124.
Schulze, E.D., and M. Klippers. 1979.
Short-term and long-term affects of olant water deficits on stomatal
~esponse to humiditv in Corylus avellana L., Planta:146:319-326.
Strauch L. 1965. Ultramikro-Methode zur Bestimmung des Stickstoffs in biologischem Material.
z.
Klin.Chem., 3:165-167.
Zech
w.,
and R. Horn. 1984. Forest de- cline phenomena. Exkursionsflihrer.Deutsch-fl.merikanische Exkursion des BMFT.
