Nutrient turnover studies in Alpine ecosystems

Oecologia (Berl.) 23, 49-62 (1976) Oecologia �9 by Springer-Verlag 1976

Nutrient Turnover Studies in Alpine Ecosystems H. Phytomass and Nutrient Relations in the Caricetum firmae

H. Rehder Institut fiir Botanik und Mikrobiologie der Technischen Universit~it, Arcisstr. 21, D-8000 Mfinchen 2, Federal Republic of Germany

Summary. 1. A plot of the Caricetum firmae in the Northern Calcareous Alps (at 2,160 m above sea level) was investigated during the growing season 1973 with regard to dry matter, nitrogen, phosphorus, and potassium content of overground and underground phytomass, including accumulated litter.

2. Compared to another habitat of the same community at 2,010 m a.s.1., the overground phytomass in the state of maximum development (ca. 250 g per m 2) and the store of nutrients (4 g N, 0.25 g P and 2.4 g K per m 2) are nealy the same, but the primary production is less (ca. 100 g as against ca. 160 g per m2).

3. The accumulation of litter in relation to the annual overground production is nearly 30: 1.

4. The content of N, P, and K in the predominant species Carex firma and Dryas octopetala ranks near the inferior limit known for terrestrial plants. The minimum values are attained in the state of maximum development (mid-August).

5. The mineralization of N amounts to about 2 g per m 2 during the growing season and thus exceeds the quantity that enters into the overground production. The maximum mineralization is found 5 to 10 cm under the soil surface. In this layer most of the fine roots are concentrated.

6. The lactate-soluble content of P and K in the soil averages ca. 0.3 or 1.5 per m 2 and decreases from the beginning to the height of the growing season by ca. 0.35 or 0.5 g per m 2 with a slight increase toward the end. In the field incubation experiments losses of P and K, interpreted as microbial incorporation, prevailed during the growing season. It was hardly possible to determine evident relations between the fluctuations of P and K in the soil and those in the phytomass.

7. The Caricetum firmae ranks between the "typical arctic tundra" and the "dwarf-shrub tundra" with regard to the obtained data on phytomass, primary production, and nutrients, except for the underground production which seems to be remarkably higher.

50 H. Rehder

Introduction

In consequence of our rather extensive investigations during the growing season (GS), 1972 (Rehder, 1976) a more intensive study of the nutrient repartition in selected alpine plant communities seemed desirable. For the GS 1973 we concentrated our efforts on the Caricetum firmae.

This low growing turf community is the characteristic type of vegetation in the alpine region of our calcareous mountains (cf. Wagner, 1970). Physiogno- mically, the predominant species, Carex firma and Dryas octopetala, reflect the extreme climatic conditions of this habitat by their evergreen, coriaceous leaves. A more detailed description was already given by Rehder in 1970 (cf. also Ellenberg, 1963). The plot investigated from 1965 to 1968 and again in 1972 appeared to be too narrow in its representative composition and already too disturbed, so that another site of the same community, more extensive but as similar as possible to the former one, had to be looked for.

We found it higher up in the "Schachen" conservation area, on the "Frauenalpe" at 2,160 m, ca. 100 m north of the plot S of 1972 on "Wettersteinkalk", at west exposure, 20 ~ inclination, with excellent homogenity (ca. 200 m z area), well accessible, but without almost any indication of cattle (sheep) grazing. The turf is scarcely 3 cm high but dense, covering 90% of the area, the rest being the interspersing calcareous rock. About 92% of the phytomass is represented by Carexfirma, 6% by Dryas and 2% by Sesleria and the other speoes of the following list:

5 Carexfirma 2 Dryas octopetala 1 Sesleria varia 1 Polygonum viviparum 1 Silene acaulis + Salix retusa + Ranunculus alpestris + Hedysarum hedysaroides + Vaccinium uliginosum + Primula auricula + Gentiana clusii

+ Bartsia alpina + Pedicularis rostrato-capitata + Euphrasia minima + Pinguicula alpina + Campanula scheuchzeri + Crepisjacquinii + Tortella tortuosa + Cetraria islandica

(+) Saxifraga aizoides (+) Saxifraga caesia

The soil is the "Alpine Pitch Rendsina" type as in the plot F (1972). But it is slightly poorer in debris and more profound, the "Pitch Moder" forming a layer of about 15 cm depth above the solid rock here as aginst only 10 cm in F. The carbon content being slightly lower than in the soil of F we find similar total amounts of N, P, and K in relation to the C content (Table 1 ; cf. Fig. l of Rehder, 1976).

Table 1. Carbon content and content of nitrogen, phosphorus, and potassium referred to carbon in the mixed soil samples of the 10.7. 1973

Soil layer C % N. 100 P. 100 K- 100

C C C

a (0 5 cm) 33.4 6.41 0.42 1.17 b (5-10 cm) 29.2 7.84 0.62 1.61 c (10-15 cm) 29.5 8.16 0.47 1.53

Nutrient Turnover Studies in Alpine Ecosystems. II 51

Methods

In general the same methods were applied as in the preceding GS (Rehder, 1976). The taking of volumetric cuts, however, was performed in a different, more detailed manner. Two sheet brass frames, one exterior of 35x35 cm side length and 5 cm height and one interior of 15x 15 cm, 15 cm high were inserted into the turf at a representative spot, cutting out a "border zone" and a "central block" by the aid of a serrated knife. The overground phytomass of the border zone was cut off and completely gathered for further separation into living and died parts in the laboratory. The soil below the cutting level including the mass of litter and other underground phytomass was cut out in three layers of 5 cm depth each, sifted (4 mm sieve), and mixed. The sieving residues were taken to the laberatory for further cleaning and for separation of at least some representative portions into litter, roots, and rhizomes (Dryas), whereas the sifted soil was used for the following analyses and for the field incubation tests.

The interior frame meanwhile was carefully pushed into 15 cm depth. In the case of debris lying in the cut line it was removed from the outside in the process of excavating the border zone. This frame with its content was also brought to the laboratory. Here, more precisely than was possible in the course of our field work with respect to the border zone, the overground phytomass was cut off at the base level of the bottommost, still green leaves. This overground portion was divided just as that of the border zone into living green and dead (yellowed) parts, made up of mainly leaves and few stalks. A separation into leaves of this year and those of the last year turned out not to be practicable throughout the GS. Below the cutting level, the central block was divided like the border zone into the soil layers a (0-5), b (5-10), c (10-15 cm), and in some cases a protruding layer d (below 15 cm). A layer of litter (0.5-1 cm thick), consisting mainly of the residues of Carex firma leaves and being nearly free of roots was separable from the surface of layer a. The remaining underground phytomass including the fine roots could be isolated from the soil material (which had to be abandoned here) more completely than from the border zone by rinsing and floating over sieves of different mesh density down to 0.3 mm (cf. Wagner, 1972). Rhizomes and roots of Dryas, being mostly well discernible, were selected. An extra separation into "litter" and "roots" from the underground phytomass of layer a was necessary and easy to perform by hand with representative portions of the total. This was possible because of the characteristic habitus of the individual plants of Carex firma (Fig. 1), which are closely joined together to from the dense turf. The bulk is formed by the dead leaves and their remains, the rosette of green leaves sitting on the top of them. A little below our cutting level, that was already defined as being the base level of the oldest green leaves, we find the axis also dead. The main portion of the roots originating from the living shoot passes as a vertical cord through the dissolved center of a column built up by the dark brown remains of the leave bases. These can easily be stripped offthe root cord by manual separation. A smaller portion of roots which spreads sideways, is also separable. In this way it was possible to estimate quite exactly from numerous

Fig. 1. Habitus of Carexfirma

1cm

of leaves ~ . . ~ ~ ! ~

green

J leaves ~ . died [eaves (yellowed)

cutting tevet

tower delimitation of the riving axis

'. roots

52

L

H. Rehder

" 1 i A B C D

- , 2 6 . 6 . , , - 1 0 . ? . . ~ , 1 6 . 8 . , ~ 4 . 1 0 . , -

Fig. 2. Repartition of phytomass components (dry substance/m 2) in Caricetum firmae on 4 dates (A-D) 1973. Narrow columns: contents of "central blocks", representing 225 cm 2 surface each. Broad columns beside them: contents of surrounding "border zones" representing 1,000 cm 2 surface each. Signs above abscissa: white = living overground parts ("green mass") o f Carex firma; black = other living herbs (mainly Dryas), grasses (mainly Sesleria), mosses and lichens; wide hachure = standing dead overground parts, mainly leaves of Carexfirma ("standing dead mass"); narrow hachure = dead undecomposed leaves and leave remains below cutting level ("deposit litter"). Signs below abscissa: shaded = roots of Carex firma and other plants without Dryas, a = 0- 5 , b=5-10 , c=10-15, d = m o r e than 15 cm soil depth; black = the obviously stronger roots and rhizomes of Dryas

samples the average ratio of litter to root dry substance in the layer a. A satisfactory separation of living and dead roots, however, was not of course attainable by this procedure.

The sampling was not spread over the GS as performed for S in 1972, but concentrated onto three times: early stage, height, and end of the GS, the dates A and B (26. 6. and 10.7., Fig. 2) representing the "early stage" together. In 1972, we comprised a maximum area of 400 cm 2


per date by the volume cuts, whereas in 1973 we obtained 900 m 2 (of 4 central blocks) and 4,000 cmz (of 4 border zones) on dates A and B, 675 and 3,000 cm 2 on date C (16. 8.), 450 and 2,000 cm 2 on date D (4.10.). In the intervals of 7 weeks between these dates (but only 5 weeks between B and C) the field incubation test was performed with the mixed soil samples from the border zones, while parallel samples were subjected to a standard incubation test in the laboratory (storage at 25 ~ C constant, the water content brought to 60% of saturation).

The methods of analysis were the same as in 1972.

Results and Discussion

l. Phytomass Relations and Repartition of Nutrients

A synopsis of the phytomass proportions in this plant community during the GS is given by Figures 2 and 3. As was found in 1972 in the Caricetumfirmae F, the high amount of "overground dead mass" in relation to the living leaves is striking and obviously a characteristic feature of this type of vegetation.

There appears to be a difference between "central blocks" and "border zones" concerning the relation of "standing dead mass" to "deposit litter". This indicates an unintentional difference

Fig. 3. Mean dry substance of phytomass components for dates (cf. Fig. 2) A/B (combined), C, and D. The more comprehensive results from "central blocks" (/) are confronted with those of "border zones" (I/). Signs as in Figure 2

A/B C D A / B C ] ' ' ' I!

D I

54 H. Rehder

of the cutting level, which in most cases was placed somewhat lower in the "border zone" in the course of the field work. Furthermore, a higher loss rate of parts of "deposit litter" was unavoidable in the procedure of coarse sieving at the site, compared to the more throrough fine sieving of the "central block" portions in the laboratory. This is the same for a larger portion of roots, especially fine roots, which could not be detained by the coarse sieving of the "border zone" material and which thus passed into the soil sample. This methodically conditioned difference in "'root mass" between "central blocks" and "border zones" is especially evident in the layers b and c. Only by the more comprehensive gathering procedure does an increase of "root mass" during the GS become noticeable.

The increase of "green mass" from the beginning (26. 6. and 10. 7.) to full development (16. 8.) by about 100 g dry substance (DS)/m 2 and also its decrease to the 4. 10. are outstanding. The difference is smaller than in the comparable plot F of 1972, where it came to 160 g/m 2.

In the overground dead phytomass, we find no significant tendency of increase or decrease during the GS.

Bringing the annual increase of "green mass" into relation with the average mass of dead leaves accumulated below the green carpet, we get a ratio of about 1 : 30. Even higher is, in consideration of the portion already decomposed, the number of years required for building up this dead component of the ecosystem.

The partition of the three main nutrients and their changes in the phytomass are shown in Figures 4-6. Again the increase in the percentage of the three elements in the green parts toward the end of the GS is obvious, following a minimum on the 16. 8., when the absolute amounts are most elevated in coincidence with the maximum of dry substance.

In the roots, as long as the samples obtained were complete enough by fine sieving, an increase in percentage of nutrients toward the end also becomes apparent. With these results, the absolute amounts in the underground phytomass at the end of the GS are also remarkably higher than in the beginning. In the case of potassium, the values are more than doubled.

In general the results concerning the percentage contents of N, P, and K in the several phytomass components are in accordance with those of the plot F from 1972. This also app l i e s - in spite of the lower p r o d u c t i o n - t o the absolute amounts of DS (ca. 250 g/m2), N (ca. 4 g/m2), P (ca. 0.25 g/m2), and K (ca. 2.4 g/m 2) in the maximal "green mass". The DS-amount of overground "dead mass", however, surpasses that of F still considerably, and consequently we find higher absolute amounts of N, P, and K in this component. In the same way, we get larger amounts in the underground phytomass, even if comparing the less completely gathered material out of the "border zones" with that of F, obtained in the same manner.

2. Mineral Nitrogen in the Soil

The actual content of mineral nitrogen (Nm) and also its accumulation, mainly appearing in the form of nitrate again, in the field and in standard incubation tests varied to a large extent as in all earlier experiments (Table 2).

There appears to be a tendency of the actual Nm-values to decrease during

Nutrient Turnover Studies in Alpine Ecosystems. II

9 N

55

N %

2

upper tower died [eoves

SesLeria Dryes and other

Corex MOSSES f i rma

a

b

N N

c

d

C. firma Dryas root~.rhizoms AIB C D A/B C D

x = no voLue existing l I 1 I [ ] I

Fig. 4. Nitrogen contents of phytomass components in percent (left and right side) and absolute amounts (central diagrams). Dates and arrangement as in Figure 3. Signs (in part different from Fig. 2) explained on left side

the GS and a decline of N-mineralization toward the middle of the GS, as was previously often observed (Rehder, 1970). The "potential N-mineralization", however, as obtained by the standard incubation, increases to extremely high values toward the end. (A field incubation was no more possible on this date.) Averagely, the field mineralization attains less than half of the "potential mineralization", though the reference period is one week longer. The duration of the GS is estimated to 15 weeks here too. For this period we get an average Nm-release of 870. ls/7= 1,864 mg or rounded 2 g Nm/m 2 as against 3.7 g in the plot F (1965-1968).

The fluctuation of N as observed in the "green mass" during the GS amounts to about 1 g/rn 2, the largest difference being nearly 1.5 g/m 2 between 16.8.

56 H. Rehder

P %

oL lllilllllllllllil[

a

b

L ~ lLx r

I

IN I L - J

Fig. 5. Phosphorus contents of phytomass components. Arrangement and signs as in Figure 4

and 4. 10. in the "central block" mean. So it is lower than the Nm supply obtained from the soil for the GS, as was already stated in the case of F. In fact there is an additioiaal N-mineralization outside the GS to be expected especially under the impact of frost (cf. Biederbeck and Capbell, 1973; Gerlach, 1973). This is indicated by the higher actual Nm-values on the 26.6. (and 10. 7.) compared to those of the 4. 10. On the other hand, the increase of N in the " root mass" by 7 g/m 2 from the beginning to the end of the GS, that has to be balanced by an equal release of N out of older root substance up to the start of the following GS, seems to be rather high. It is, however, remarkable, that the highest N-mineralization is not furnished by the superior layer with its litter store, but in 5-10 cm depth, where the portion of fine roots is elevated. We may


] nN

K

~176 I

0

a

b

e

d

I - F N

I , . .

- ~ ~ 1

Fig. 6. Potassium contents of phytomass components. Arrangement and signs as in Figure 4

deduce from these findings at least, that the participation of the " root mass" in the annual N-turnover is probably higher than that of the "green mass" in this ecosystem, since the roots decomposing every year provide more basic material for mineralization than the leaves.

3. Plant Available Phosphorus and Potassium Content in the Soil

The amounts of lactate-soluble P and K, determined from the mixed soil samples of the "border zones" in the state of natural moisture only, presented considerable variations too (Tables 3 and 4). The Plact-content is generally higher at the beginning of the GS (26.6. and 10. 7.) than later (16.8. and 4. 10,). In the field incubation test, we find a remarkable decrease after 7 weeks storage in the initial phase, explicable as microbial incorporation, whereas in the later

58 H. Rehder

Table 2. Actual content of mineral nitrogen and accumulated amounts in 0 15 cm depth of soil (mg/m2). F . I .=f ie ld incubation, difference after 7 weeks (in the case of date B converted from 5 into 7 weeks values); S.I. = s tandard incubation, difference after 6 weeks. Total mean from the three partial means

Dates Samples from border zones

0-5 cm depth Actual F.I, S.I.

5-10 cm depth Actual F.I, S.I.

10-15 cm depth Actual F.I. S.I.

Total 0 .15 cm Actual F.I. S.I.

A (26. 6.) B A + B C (16.8.) C D (4. 10.) D Total (10. 7.)

1 2 3 1 Mean 1 2 3 Mean 1 2 Mean Mean

179 148 162 197 172 92 125 203 140 88 61 75 129 429 208 348 121 277 --10 116 150 85 - - - 181 498 464 451 331 436 1 188 330 173 1,321 1,280 1,301 637

284 318 365 398 341 289 294 335 306 28l 184 232 293 616 511 641 573 585 134 202 306 214 - - - 399 913 885 598 1,011 852 497 430 799 575 1,835 1,835 1,835 1,087

131 271 222 269 223 188 190 200 193 107 122 115 177 433 268 461 399 390 157 78 333 189 - - - 290 719 617 1,342 449 782 331 396 680 469 706 646 676 642

594 737 749 864 736 569 609 738 639 476 367 422 599 1,478 987 1,450 1,093 1,252 281 396 789 488 - - - 870 2,130 1,966 2,391 1,791 2,070 829 1,014 1,809 1,217 3,862 3,761 3,812 2,366

stage a slight release of P appears, the actual Pla~<content consequently being somewhat higher on the 4. 10. again.

In the average of the GS, however, the Pla~cdecrease prevails clearly in the field incubation tests. After this we have to assume, that the main portion of P~a~t is released under winter conditions only. Just as in the case of Nm, the soil layer of 5-10 cm is averagely distinguished by the highest Placcvalues. The total mean of Pl~t (0.3 g/m 2) is still lower than that of F from 1972 (0.4 g/ m2). The fluctuation of the actual P~a~t-values in the soil, in comparison to those of dates A and B with C, comes to about 0.35 g/m 2. This difference is confronted with a temporary incorporation of P into the "green mass" of less than 0.1 g/m 2, but to a P-increase in the "root mass" of likewise 0.35 g/m 2 up to the end of the GS. Of course we should not overrate this parallelism. But it may be stated, that for the P-cycle again the "root mass" probably contributes more than the "green mass". The differences appearing in the overground "dead mass", however, are at any rate insignificant in view of the variations of DS.

In principle, we find similar relations for Kiact as for Plact, that is a tendency for a decrease in the actual values from A and B to C with a subsequent slight increase to D, and furthermore the prevailing immobilization in the incubation tests, being pronounced again mainly at the beginning of the GS. The average (1.5 g K/m 2) is near to that of F in 1972 (1.6 g). The amplitude of


Table 3. Lactate-soluble phosphorus content in 0-15 cm soil depth (rag/m2). Actual values and differences obtained after 7-week field incubation (F.I., a conversion of the 5-week interval into 7 weeks, after the date B, is omitted here since the negative values would exceed the actual values in this case)


0-5 cm depth

Actual F.I.

5-10 cm depth Actual F.I.

10-15 cm depth Actual F.I,

Total 0-15 cm Actual F.I.

A (26.6) B (10.7.)

1 2 3 1

95 107 130 75 206 --80 - 1 0 5 - 6 0

123 199 270 258 - 5 2 - 1 0 2 - 2 0 6 - 2 1 2

86 148 164 398 32 - 1 0 2 - 1 1 2 -350

304 454 564 731 186 --284 -423 - 6 2 2

A+B C (16, 8.) C

Mean 1 2 3 Mean

I02 48 43 13 35 - 1 0 70 8 26 35

213 65 77 37 60 - 1 4 3 58 15 6 26

199 58 76 18 51 -133 24 - 1 3 54 22

514 171 196 68 146 - 2 8 6 152 10 86 83

D(4. 10.) D Total

1 2 Mean Mean

102 60 81 73 - - - - 13

126 108 117 130 . . . . 59

45 42 44 98 . . . . 56

273 210 242 301 . . . . . 102

Table 4. Lactate-soluble potassium content in 0-15 cm soil depth (rag/m2). Explanations as in Table 3




10-15 cm depth a, ctual F.I.

I'otal 0-15 cm Actual F.I.

A (26.6.) B A + B C (16.8.) (10. 7.)

1 2 3 1 Mean 1 2

439 395 447 528 452 - 2 1 6 24 - 1 0 9 - 1 8 2 -121

681 597 791 925 749 - 1 8 4 - 3 0 - 2 7 0 -540 - 2 5 6

459 560 506 724 562 339 - 4 7 60 - 2 1 4 - 5 9 2 - 1 9 8 - 1 0 9

1,579 1,552 1,744 2 ,177 1,763 1,05i - 4 4 7 54 - 5 9 3 -1,314 - 5 7 5

C D (4. 10.) D

Mean 1 2 Mean

302 442 291 345 67 - 5 0 80 32

410 770 417 532 117 - 2 0 0 7 - 2 5

518 266 374 - 4 0 138 - 4

1,730 974 1,251 75 - 2 9 0 225 3

460 460 460

628 668 648

409 230 320

1,497 1,358 1,428

Total

Mean

419 - 4 5

643 - � 9

419 - . - 1 0 1

1,481 -286

fluctuation in the soil (ca. 0,5 g/m z) here again is similar to that in the "green mass" (cf. plot S in 1972!), whereas the increase in the "root mass" appears much higher. Further deductions, however, are not possible for the present.

60 H. Rehder

Table 5. Mean content (%) of nitrogen, phosphorus, and potassium in the overground organs of three prevailing species of the habitat. Also, amplitude as known for terrestrial plants in general (from diverse authors from Larcher, 1973, Table 20)

Carexfirma D~asoct~etaN ~s~r~var~. Terrestrialplants

N 1.8 2.0 2.4 1.0-5.0 P 0.10 0.14 0.13 0.1-0.8 K 1.1 0.7 1.2 0.5-5.0

4. The Nutrient Content of Carex firma, Dryas octopetala, and Sesleria varia Compared with Other Terrestrial Plants

The content of N, P, and K in the three prevailing species of this habitat (cf. Figs. 4-6) ranges near the lower limitations of the values known from terrestrial plants as a whole, shown in Table 5.

5. Phytomass, Production, and Nutrient Content of Alpine Stand Compared with Tundra Vegetation

Because of the ecologic relation between the alpine meadows and the arctic tundra it is appropriate to compare the data obtained from the Caricetum firmae with that from the tundra (Table 6).

The Caricetum firmae ranges between the two types of tundra with respect to most of the values. The high increase of DS in the underground parts, however, as obtained in our investigation, represents a considerable deviation. This discrepancy against the tundra should be clarified by further studies. Never- theless we may already state that in both types of vegetation the underground production obviously surpasses the overground production.

6. Conclusion

After this detailed investigation of a selected plant community there are several questions still left unsettled. Their solution is impeded by the difficulty of obtain- ing appreciably larger amounts of random samples under the alpine conditions within an appropriate time. Most of the widely extended stands are or have been either pastured or they are hardly accessible. Therefore it is difficult to get significant values, e.g., concerning the underground phytomass. Further studies on the relation of living and dead roots are planned, for instance by measuring the N-content of samples of both extremes and of the total mass in comparison.

Investigations on the mineralization of N, P, and K during the winter would be useful, but again are hardly practicable in the alpine region. They could be, however, replaced by model experiments in the laboratory to some extent.


Table 6. Dry substance (DS) and nutrient relations in tundra vegetation (from Rodin from Walter, 1968, p. 546) and in the Caricetum firmae (cf. the values for I in Figs. 3-6). (For overground living phytomass: maximal value. For underground phytomass: living and dead parts together, mean of the three stages, for litter: standing and deposit dead parts together, mean of the three stages)

Phytomass-DS (t/ha)

Green and other living overground parts Underground parts

Total

Litter above soil surface

Primary production DS (t/ha)


Total

N + P + K and other bioelements. For Caricetum only N + P + K (kg/ha)

Phytomass


Total

Litter

Primary production Green parts only

Typical Tundra

1.5 3.5

5.0

0.35

0.30 0.70

1.00

64.7 94.3

159.0

280.0

18.9

Caricetum firmae Dwarf Shrub Tundra

2.5 4.9 16.7 23.1

19.2 28.0

29.0 83.0

1.0 0.98 7.5 1.40

8.5 2.38

N P K Total

45 2.5 25 72.5 136.0 183 9.5 35 227.5 765.0

228 12.0 60 300.0 901.0

286 10.0 33 329 4,200

10 0.7 6 16.7 47.0

Acknowledgements. The author is obliged to the Deutsche Forschungsgemeinschaft for the financial support to this program and to the cooperators A. Schfifer, M. G6kceoglu, E. Hoerner, K. Kiihner, M. Olbrich, V. Schacht, and A. Holzmayr for their effective services.

References

Biederbeck, V.O., Capbell, C.A.: Soil microbial activity as influenced by temperature trends and fluctuations. Canad. J. Soil Sci. 53, 363-376 (1973)

Ellenberg, H. : Vegetation Mitteleuropas mit den Alpen in kausaler, dynamischer und historischer Sicht. Stuttgart: Ulmer 1963

Gerlach, A.: Methodische Untersuchungen zur Bestimmung der Stickstoffnettomineralisation. Scripta Geobotaniea, Bd. 5. G6ttingen: Goltze 1973

Larcher, W. : Okologie der Pflanzen. Stuttgart: Ulmer 1973 Rehder, H. : Zur Okologie, insbesondere Stickstoff-Versorgung subalpiner und alpiner Pflanzenge-

sellschaften im Naturschutzgebiet Schachen (Wettersteingebirge). Diss. Bot., Bd. 6. Lehre: Cramer 1970

Rehder, H.: Nutrient turnover studies in alpine ecosystems. I. Phytomass and nutrient relations in four mat communities of the Northern Calcareous Alps. Oecologia (Berl.) 22, 411~423 (1976)

62 H. Rehder

Wagner, H.: Zur Abgrenzung der subalpinen gegen die alpine Stufe. Mitt. Ostalp.-din. Ges. f. Vegetkde. 11, 225-234 (1970)

Wagner, P.: Untersuchungen fiber Biomasse und Stickstoffhaushalt eines Halbtrockenrasens. Dipl. Arb. Syst. Geobot. Inst.,Univ. G6ttingen (1972)

Walter, H. : Die Vegetation der Erde in 6kophysiologischer Betrachtung. Band II: Die gemfil3igten und arktischen Zonen. Stuttgart: Fischer 1968

Received December 4, 1975

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Nutrient turnover studies in Alpine ecosystems