nitrogen mineralization in a tussock tundra soil

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The Regents of the University of Colorado, a body corporate, contracting on behalf of the University of Colorado at Boulder for the benefit of INSTAAR Nitrogen Mineralization in a Tussock Tundra Soil Author(s): G. M. Marion and P. C. Miller Source: Arctic and Alpine Research, Vol. 14, No. 4 (Nov., 1982), pp. 287-293 Published by: INSTAAR, University of Colorado Stable URL: http://www.jstor.org/stable/1550791 . Accessed: 17/06/2014 05:07 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. . INSTAAR, University of Colorado and The Regents of the University of Colorado, a body corporate, contracting on behalf of the University of Colorado at Boulder for the benefit of INSTAAR are collaborating with JSTOR to digitize, preserve and extend access to Arctic and Alpine Research. http://www.jstor.org This content downloaded from 185.2.32.152 on Tue, 17 Jun 2014 05:07:56 AM All use subject to JSTOR Terms and Conditions

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Page 1: Nitrogen Mineralization in a Tussock Tundra Soil

The Regents of the University of Colorado, a body corporate, contracting on behalfof the University of Colorado at Boulder for the benefit of INSTAAR

Nitrogen Mineralization in a Tussock Tundra SoilAuthor(s): G. M. Marion and P. C. MillerSource: Arctic and Alpine Research, Vol. 14, No. 4 (Nov., 1982), pp. 287-293Published by: INSTAAR, University of ColoradoStable URL: http://www.jstor.org/stable/1550791 .

Accessed: 17/06/2014 05:07

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

INSTAAR, University of Colorado and The Regents of the University of Colorado, a body corporate,contracting on behalf of the University of Colorado at Boulder for the benefit of INSTAAR are collaboratingwith JSTOR to digitize, preserve and extend access to Arctic and Alpine Research.

http://www.jstor.org

This content downloaded from 185.2.32.152 on Tue, 17 Jun 2014 05:07:56 AMAll use subject to JSTOR Terms and Conditions

Page 2: Nitrogen Mineralization in a Tussock Tundra Soil

Arctic and Alpine Research, Vol. 14, No. 4, 1982, pp. 287-293

NITROGEN MINERALIZATION IN A TUSSOCK TUNDRA SOIL

G. M. MARION AND P. C. MILLER* Systems Ecology Research Group, San Diego State University

San Diego, California 92182, U.S.A.

ABSTRACT

The effects of substrate quality, temperature, and moisture on nitrogen mineralization from a tussock tundra soil were examined with laboratory soil incubations utilizing both air-dried samples and field-moist intact cores. The potentially mineralizable nitrogen (PMN) was highly correlated to both total soil nitrogen (positively) and the carbon/nitrogen ratio (negatively). All soil horizons exhibited a net nitrogen mineralization even at a high carbon/nitrogen ratio of 92. It was concluded that field-moist intact soil cores provide a more reliable estimate than the air-dried samples of both PMN and the mineralization rate under standard laboratory conditions. There was no significant effect of moisture tension (0.0 to 0.4 bars) on net nitrogen mineralization. The average Qlo (temperature effect) for net nitrogen mineralization was 2.5. Based on this study and others, it was concluded that temperature through its effect on nitrogen mineralization plays an important role in controlling plant productivity in these naturally nitrogen-deficient tundra ecosystems.

INTRODUCTION

Nitrogen is the most frequently limiting nutrient for plant growth in tundra ecosystems (McCown, 1978; Ulrich and Gersper, 1978; Shaver and Chapin, 1980). Mineralization of nitrogen by microorganisms is the key process controlling nitrogen availability in tundra soils (Chapin et al., 1980; Rosswall and Granhall, 1980; Dowding et al., 1981; Van Cleve and Alexander, 1981). Despite the obvious importance of nitrogen mineraliza- tion as a key process in the functioning of tundra eco- systems, little experimental work to quantify this process has been reported in the literature. Rosswall and Gran- hall (1980) measured net nitrogen mineralization by in situ nitrogen incubations of soils from a subarctic mire; they also examined, in the laboratory, the effect of tem-

*Dr. P. C. Miller died on 26 July 1982, while this paper was in press. 0004-0851/82/040287-07$01.05 ?1982, Regents of the University of Colorado

perature, moisture, and substrate quality on nitrogen mineralization for the soils from the subarctic mire. Ross et al. (1979) measured, in the laboratory using an incu- bation technique, net nitrogen mineralization for sub- antarctic soils.

Nitrogen mineralization depends largely on four fac- tors: substrate quantity, substrate quality, soil tempera- ture, and soil moisture. Soil incubations, both in situ and in vitro, can consider these factors explicitly; as a conse- quence, soil nitrogen incubations are generally highly cor- related to plant nitrogen availability (Harmsen and van Schreven, 1955; Stanford et al., 1973a; Smith et al., 1977; Ross and Bridger, 1978; Marion et al., 1981).

The objectives of this paper are to assess the effect of soil horizon (substrate quality), temperature, and mois- ture on potentially mineralizable nitrogen (PMN) in a tussock tundra soil using a laboratory soil incubation technique.

G. M. MARION AND P. C. MILLER / 287

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Page 3: Nitrogen Mineralization in a Tussock Tundra Soil

METHODS AND MATERIALS

THE EXPERIMENTAL SITE The experimental site is located at Eagle Summit,

Alaska (65?26'N, 145?30'W; elevation 730 m) in Erio- phorum vaginatum L. tussock tundra. Vegetation includes E. vaginatum, Ledum palustre L., Vaccinium vitis-idaea L., Vaccinium uliginosum L., Carex spp., and Sphagnum spp. (Wein and Bliss, 1974; Chapin et al., 1979). The mean annual temperature is -7?C, and the mean July temperature is 12?C (Miller, P. C., unpublished data, 1981). The mean ( SE) precipitation for the June-August growing season, based on 1977, 1979, and 1980 data, is 166 (+34) mm.

THE SOIL The soil is classified as a Histic Pergelic Cryaquept

(Rieger et al., 1979). The soil is poorly drained and con- sists of a 10 to 50-cm-thick peat layer overlying a silt- clay loam (Furbush and Wiedenfeld, 1968). The site is underlain by permafrost with an average depth of thaw of 50 to 60 cm. The principal soil horizons are Oi (brown fibrous), Oe (black fibrous), Oa (black decomposed), and C (a buried mineral horizon). Because of the marked dif- ferences in soil physical and chemical properties beneath the tussock and intertussock zones (Chapin et al., 1979), separate samples of the tussock and intertussock soils were taken. The base of the brown moss layer was desig- nated as the soil surface.

E Q-

a) C:

C)

0

a)

._

-0

N

C C-

In order to evaluate the effect of sample pretreatment on laboratory nitrogen incubations, two sets of soil samples were collected. The first set of soil samples were collected from four soil pits in late July 1979. These samples were first air-dried and then composited. These samples will be referred to as the air-dry samples in the text. Mineral soil horizons were sieved to pass a 2-mm screen; particles >2 mm were designated as gravel. The organic soil horizons contained negligible gravel. The second set of soil samples were collected in late August 1980. These samples were cut in the field to fit the incu- bation chambers and were kept refrigerated at 5?C for approximately 30 d until the incubation experiments began. These soil samples will be referred to as the field- moist intact cores in the text.

Bulk density and soil horizon depths were determined by cutting cores of known volume to the permafrost table. The bulk density and soil depth means are based on 12 to 46 measurements which were taken as part of a '5N study (Marion et al., in press). The soil nitrogen and car- bon concentrations were determined, with four replicates, using samples collected with the field-most intact soil cores.

THE INCUBATIONS The incubations closely followed previously published

methods (Stanford and Smith, 1972; Marion et al., 1981).

0

0 .." -I -Jmm~~~~~~~~~~~e

-Q

a

20

Weeks FIGURE 1. The effect of sample pretreatment on nitrogen mineralization (35?C and 0.2 bar soil moisture tension) in tussock air-dried (0), tussock field-moist (0), intertussock air-dried (L), and intertussock field-moist (U) samples of the Oe soil horizon. The dashed lines are the regression lines for the air-dried samples, and the solid lines are the regression lines for the field-moist samples.

288 / ARCTIC AND ALPINE RESEARCH

ow I I 4 I I I6 1

0 2 4 6 8 10 12 14 16 18

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Page 4: Nitrogen Mineralization in a Tussock Tundra Soil

Ten grams (30 g for mineral horizons) of air-dry soil were mixed with 30 g of quartz sand (20 to 30 mesh) and placed in Falcon filter units; the original membrane filters had a tendency to clog and were replaced with Whatman GF/A glass microfibre filters. In what follows, both the air-dry and the field-moist intact cores were treated simi- larly. All soils were leached with four 25-ml solutions of 0.01 MCaC12 followed by a 25-ml leaching with nutrient solution (0.002 M CaSO4 * 2H20; 0.002 M MgSO4; 0.005 M Ca(H2PO4)2 * H20; and 0.0025 M K2SO4). These leachings were used to remove soluble plus ex- changeable nitrogen initially present in the soils and to periodically remove mineralized nitrogen. All soils were incubated, in triplicate, at 35?C and 0.2 bar soil mois- ture tension; this choice of temperature and moisture is considered optimum for nitrogen mineralization (Stan- ford et al., 1973b; Stanford and Epstein, 1974). The incu- bation times varied from 11 to 20 wk. For the 35?C incu- bations, a mathematical relationship (Eq. 1) was used to extrapolate to infinite time (Figure 1).

In order to examine the effects of temperature and moisture, the following additional incubations were con- ducted. The air-dried tussock and intertussock Oe soil samples were incubated, in duplicate, at 5, 15, and 25?C and at 0.0, 0.1, 0.2, and 0.4 bar soil moisture tension for 84 d. Also, the field-moist intact cores from the tussock and intertussock Oe zones were incubated, in triplicate, at 5, 15, and 25?C and 0.2 bar soil moisture tension for 77 d. In general at 5, 15, and 25?C, nitrogen mineraliza- tion had essentially ceased by the end of the incubations.

Soil moisture tension was initially set by vacuum extrac- tion and maintained by equilibration with salt solutions

within a closed container; these containers were opened periodically to prevent buildup of toxic CO2 concentra- tions. The incubations were carried out at constant tem- perature (+?2?C) in environmental growth chambers.

The three-parameter nitrogen mineralization equation:

Log (No - N,) = Log N, - ktb (1)

was fitted to the nitrogen mineralization data where No is potentially mineralizable nitrogen (PMN), N, is ac- cumulative nitrogen mineralized (measured), k is the rate constant, t is time, and b is the time exponent (Marion et al., 1981). In solving for N,, k, and b, an initial approx- imation was made of No; then values of k and b were cal- culated by least squares; and last, a refined estimate of No, based on the calculated k and b, was made by least squares. This successive approximation technique was necessary because allowing N,, k, and b to vary without constraint sometimes led to parameter sets which fit the data mathematically but lacked physical significance.

CHEMICAL ANALYSES The Technicon autoanalyzer was used to analyze

leachate ammonium (Technicon Industrial Method No. 154-71W 1973) and nitrate plus nitrite (Technicon Indus- trial Method No. 158-71/A 1977). Total soil nitrogen was determined with a Kjeldahl method (Isaac and Johnson, 1976). Total carbon was determined with a Leco carbon analyzer. All chemical analyses were corrected for per- cent gravel and are reported on an oven-dry basis (105?C for 24 h).

RESULTS AND DISCUSSION

BASIC SOIL PROPERTIES There was a sharp discontinuity in soil physical and

chemical properties at the organic horizon-mineral hori- zon junction (Table 1). Bulk densities were an order of magnitude greater for the mineral horizon than for the organic horizons. Carbon concentrations decreased with increasing soil depth within the organic layers; on the other hand, nitrogen concentrations increased with in- creasing soil depth within the organic layers. The resul- tant decreasing carbon/nitrogen ratio with increasing soil depth is typical of tundra soils and is a reflection of a more highly decomposed organic matter with increasing soil depth (Malmer and Nihlgard, 1980).

NITROGEN MINERALIZATION UNDER OPTIMAL CONDITIONS

Under optimal temperature (35?C) and moisture (0.2 bar soil moisture tension), all soil horizons exhibited a net nitrogen mineralization (Table 2). For the air-dried samples, PMN increased with increasing horizon depth in the organic horizons. The coefficient of determination (r2) between PMN and percent total nitrogen was 0.88 for the air-dried organic horizons. The coefficient of de- termination between PMN and carbon/nitrogen ratio was

0.99 for the air-dried organic horizons. There is a gener- ality in the soils literature that states that soils having a carbon/nitrogen ratio greater than about 20 to 30:1 should exhibit net nitrogen immobilization, while soils having carbon/nitrogen ratios less than 20 to 30:1 should exhibit net nitrogen mineralization (Dutt et al., 1972; Gersper et al., 1980). All soil horizons exhibited net nitrogen mineralization, even the surface horizon with a carbon/nitrogen ratio of 92. It is clear that PMN is negatively correlated to carbon/nitrogen ratio; but at least for these tundra soils under optimal temperature and moisture, there is no apparent carbon/nitrogen ratio above which net nitrogen mineralization does not occur. However, nitrogen mineralization at 35?C is highly arti- ficial for microbial populations adapted to cold tempera- tures. There is evidence, that will be discussed in the fol- lowing section, that under suboptimal temperatures, net nitrogen mineralization may be negligible.

The PMN for both air-dried samples and the field- moist intact cores are in relatively good agreement with the exception of the Oa horizon (Table 2). For the Oa horizons, the air-dried samples showed about four times more release of nitrogen than was the case for the field-

G. M. MARION AND P. C. MILLER / 289

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Page 5: Nitrogen Mineralization in a Tussock Tundra Soil

moist intact cores. In the field, the Oa horizon would almost always be saturated. Since air drying of the Oa horizon is a rare natural occurrence, the PMN from the field-moist intact cores probably is a more accurate re- flection of the PMN.

Although the PMN was similar, except for the Oa hori- zon, for the two sample pretreatments, the rate constants (k) were different; in all cases, the rate constants were greater for the air-dried samples indicating a more rapid release of nitrogen (Table 2). In fact, with several of the horizons, virtually all nitrogen mineralization occurred in the first two weeks (Figure 1). It is clear that air dry- ing these organic soils prior to incubation can affect both the nitrogen quantity released and the rate of nitrogen release. Because of the highly artificial drying of these naturally wet soils, the use of field-moist soil cores to esti- mate nitrogen mineralization probably gives a truer esti- mate of PMN and the potential rate of nitrogen release than the air-dried samples. Soils that naturally dry

annually (e.g., chaparral soils, Marion et al., 1981) may not be so adversely affected by air drying.

NITROGEN MINERALIZATION UNDER SUBOPTIMAL

CONDITIONS Soil temperature and moisture are seldom optimum in

the field. Utilization of the nitrogen mineralization equa- tions (Table 2) to estimate field nitrogen mineralization would require corrections for suboptimal temperature and moisture (Marion et al., 1981).

In six of eight cases for the air-dried soil samples, the amount of nitrogen released under saturated soil condi- tions (0.0 bars) exceeded the nitrogen released under un- saturated soil conditions (Figure 2); this effect was most clear at the higher temperatures (25 and 35?C). However, given the variability, few of these differences were statis- tically significant. Recent work with Florida Histosols (Terry, 1980) showed that nitrogen mineralization was not affected by soil moisture over the range from 0.1 to

TABLE 1 The basic physical and chemical properties of the tussock tundra soil (mean ? standard error)

Bulk density Carbon Nitrogen Carbon/Nitrogen (g cc-') (%o) (%Oo) ratio

0.106 0.004 0.139?0.006 0.236 + 0.010 1.11 ?0.07 0.108 + 0.006 0.220 +0.012 1.12 ?0.05

40.8 0.4 39.8 + 1.0 36.5 + 1.4 6.4+0.1

38.9?0.8 33.2?2.3

0.45 ? 0.03 0.96 +0.06 1.64+ 0.10 0.30 + 0.01 1.23 + 0.04 1.34 +0.11

92.1 ?4.9 42.1 + 2.8 22.3 + 0.5 21.2? 0.2 31.7 +0.5

24.9 +0.7 st

*These samples were not analyzed; but, they should be similar to the tussock C horizon.

TABLE 2 The tussock tundra soil nitrogen mineralization constants (35?C and 0.2 bar soil moisture tension) for the

equation, Log (No - Nt) = Log No - ktb

Soil pretreatment

Air-dried

Field-moist intact cores

Intertussock Air-dried

Field-moist intact cores

Potentially mineralizable nitrogen (No)

(ppm)

100 310 470

2.3

110 350 110

2.2

380 520

2.5 360 130

Rate constant (k)

(wk-1)

1.029 0.507 0.251 0.091

0.127 0.111 0.135 0.026

0.210 0.137 0.038 0.071 0.058

Time exponent

(b)

0.22 0.50 0.45 1.02

1.27 1.07 0.90 1.27

0.49 0.76 1.32 1.12 0.98

Coefficient of multiple

determination (R2)

0.95 0.93 0.65 0.96

0.92 0.98 0.98 0.95

0.90 0.95 0.98 0.97 1.00

290 / ARCTIC AND ALPINE RESEARCH

Soil location

Tussock

Intertussock

Horizon

Oi Oe Oa C Oe Oa C

Depth (cm)

9.8 ?0.4 14.4+0.6 12.4+0.7 19.6+ 2.7 9.7 ? 0.8

13.7 + 0.8 22.4 ?2.4

Soil location

Tussock

Horizon

Oi Oe Oa C

Oi Oe Oa C

Oe Oa C Oe Oa

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Page 6: Nitrogen Mineralization in a Tussock Tundra Soil

3.0 bars which agrees with the results of this study. Also, laboratory incubations of subarctic mire organic soils (Rosswall and Granhall, 1980) showed no significant dif- ferences in nitrogen mineralization in soils incubated between 20 and 100% of the water holding capacity in the temperature range from 5 to 20?C; at 30?C, maxi- mum nitrogen mineralization occurred at 60% of water holding capacity. The consensus is that the effect of mois- ture on nitrogen mineralization of organic soils is not great at low moisture tension.

There appears to be a much more clearly defined effect of temperature on nitrogen mineralization (Figure 2 and Table 3). For the air-dried soil samples, there is a rela- tively flat temperature dependence between 5 and 15?C, a moderate temperature effect between 15 and 25?C, and a sharp temperature effect between 25 and 35?C (Table 3). However, there was a potential source of error in the incu- bations at 15 and 25?C for the air-dried samples. These incubations were carried out in lighted growth chambers and moss growth was evident in some cases during the early incubation; this could account, in part, for the low apparent nitrogen mineralization in these soils at 15 and 25?C (Figure 2).

The field-moist intact soil cores showed an inconsistent temperature effect. There was virtually no nitrogen release from the tussock Oe horizon at 5, 15, and 25?C; but, there was a steady increase in nitrogen mineraliza- tion with temperature for the intertussock Oe horizon (Table 3). This lack of a consistent relationship between nitrogen mineralization and temperature has been shown, previously, for both mineral soils (Ross and Bridger, 1978) and organic soils (Ross et al., 1979). In the latter work, this lack of a consistent temperature effect was attributed to a variable initial mineral nitrogen content due to sample pretreatment; however, in our work soils

were initially leached to remove mineral nitrogen. In our case, the more likely explanations for the inconsistent temperature effect are high soil spatial variability with a concomitant lack of sufficient replication, moss growth which may have immobilized mineral nitrogen, and chan-

500- tussock E 400- C- 300- - 0 200-

100- I'

-. --intert

-o 500-intertussock a 400-

E300- X A 200-

100-

5 15 25 35

Temperature, ?C FIGURE 2. The effect of soil moisture tension [0.0 bars (3), 0.1 bars (OC), 0.2 bars (1), and 0.4 bars (E)] and tempera- ture on nitrogen mineralization of the Oe soil horizon in the tussock and intertussock areas for the air-dried samples (84 d incubation).

TABLE 3 The effect of temperature range and moisture on the Qlo valuesfor the Oe horizons

Soil pretreatment

Air-dried

Field-moist intact cores

Air-dried

Field-moist intact cores

Mean + standard error

Moisture tension (bars)

0.0 0.1 0.2 0.4

0.2a

0.0 0.1 0.2 0.4

0.2

Temperature range (?C) 5-15

2.3 0.6 1.5 0.5

1.0 0.8 0.5 0.6

3.4

15-25

1.7 3.8 1.5 3.7

2.1 1.4 2.6 2.7

2.4

25-35

5.1 4.2 3.8 3.5

3.0 5.8 2.8 3.9

2.9

1.2?0.3 2.4+0.3 3.9+0.3

Mean + standard error

3.0? 1.0 2.9+ 1.1 2.3 + 0.8 2.6 1.0

2.0?0.6 2.7+ 1.6 2.0?0.7 2.4 + 1.0

2.9+0.3

2.5 0.8

aThere was an insignificant release of N at 5, 15, and 25?C.

G. M. MARION AND P. C. MILLER / 291

Soil location

Tussock

Intertussock

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Page 7: Nitrogen Mineralization in a Tussock Tundra Soil

neling of the leaching solution which may not have ex- tracted all of the mineral nitrogen. The latter problem was probably more important for the field-moist intact cores.

Given the experimental uncertainties, it would seem best to assume an average Q0o of 2.5 across the entire temperature range (Table 3). This Qio is slightly higher than an average Qio of 2.3 for tussock grassland soils (Ross and Bridger, 1978), an average Q o of 2.0 for agri- cultural soils (Stanford et al., 1973b), and a range of Qio values from 1.3 to 1.9 for subarctic mire organic soils (Rosswall and Granhall, 1980). The difference between

reported Qio values are significant in the physical, if not the statistical, sense. For example, a Qio of 2.0 implies an 8-fold difference in nitrogen mineralization rates between 5 and 35?C; on the other hand, a Qio of 2.5

implies a 15.6-fold difference in nitrogen mineralization rates between 5 and 35?C. Possible explanations for the

reported differences in Qlo values include: (1) high natural soil variability, both within and between soils, (2) differ- ences in experimental techniques, and (3) with-in tech- nique error. Despite this variability, it is clear that tem- perature plays a critical role in controlling nitrogen min- eralization in these cold, wet soils; as a consequence, temperature will play an important role in controlling plant productivity in these naturally nitrogen-deficient tundra ecosystems.

ACKNOWLEDGMENTS

We would like to thank D. C. Hammond, S. Light- foot, and J. Verfaillie for assistance with the incubations and chemical analyses. The assistance of P. M. Miller, B. Sigren, and R. Watson in preparing the manuscript was appreciated. This work was funded under DOE Con- tract No. DE-A503-77EV01525.

REFERENCES CITED

Chapin, F. S., III, Miller, P. C., Billings, W. D., and Coyne, P. I., 1980: Carbon and nutrient budgets and their control in coastal tundra. In Brown, J., Miller, P. C., Tieszen, L. L., and Bunnell, F. L. (eds.), An Arctic Ecosystem. The Coastal Tundra at Barrow, Alaska. Stroudsburg, Pennsylvania: Dowden, Hutchinson & Ross, 458-482.

Chapin, F. S., III, Van Cleve, K., and Chapin, M. C., 1979: Soil temperature and nutrient cycling in the tussock growth form of Eriophorum vaginatum L. Journal of Ecology, 67: 169-189.

Dowding, P., Chapin, F. S., III, Wielgolaski, F. E., and Kil- feather, P., 1981: Nutrients in tundra ecosystems. In Bliss, L. C., Heal, O. W., and Moore, J. J. (eds.), Tundra Eco- systems: A Comparative Analysis. Cambridge: Cambridge University Press, 647-683.

Dutt, G. R., Shaffer, M. J., and Moore, W. J., 1972: Com- puter Simulation Model of Dynamic Bio-physiochemical Pro- cesses in Soils. The University of Arizona, Agricultural Experiment Station, Technical Bulletin 196.

Furbush, C. E. and Wiedenfeld, C. C., 1968: Soils of the Eagle Summit Area, Alaska. U.S. Department of Agriculture, Soil Conservation Service, Portland. 23 pp.

Gersper, P. L., Alexander, V., Barkley, S. A., Barsdate, R. J., and Flint, P. S., 1980: The soils and their nutrients. In Brown, J., Miller, P. C., Tieszen, L. L., and Bunnell, F. L. (eds.), An Arctic Ecosystem. The Coastal Tundra at Barrow, Alaska. Stroudsburg, Pennsylvania: Dowden, Hutchinson & Ross, 219-254.

Harmsen, G. W. and van Schreven, D. A., 1955: Mineraliza- tion of organic nitrogen in soil. Advances in Agronomy, 7: 299-398.

Isaac, R. A. and Johnson, W. C., 1976: Determination of total nitrogen in plant tissue using a block digester. Journal of the Association of Official Analytical Chemists, 59: 98-100.

Malmer, N. and Nihlgard, B., 1980: Supply and transport of mineral nutrients in a subarctic mire. In Sonesson, M. (ed.), Ecology of a Subarctic Mire. Ecological Bulletin 30. Stock- holm: Swedish Natural Science Research Council, 63-95.

Marion, G. M., Kummerow, J., and Miller, P. C., 1981: Pre- dicting nitrogen mineralization in chaparral soils. Soil Science Society of America Journal, 45: 956-961.

Marion, G. M., Miller, P. C., Kummerow, J., and Oechel, W. C., 1982: Competition for nitrogen in a tussock tundra ecosystem. Plant and Soil (in press).

McCown, B. H., 1978: The interactions of organic nutrients, soil nitrogen, and soil temperature and plant growth and sur- vival in the arctic environment. In Tieszen, L. L. (ed.), Vege- tation and Production Ecology of an Alaskan Arctic Tundra. New York: Springer-Verlag, 435-456.

Rieger, S., Schoephorster, D. B., and Furbush, C. E., 1979: Exploratory Soil Survey of Alaska. Washington, D.C.: U.S. Department of Agriculture, Soil Conservation Service. 213 pp.

Ross, D. J. and Bridger, B. A., 1978: Influence of tempera- ture on biochemical processes in some soils from tussock grasslands. 2. Nitrogen mineralization. New Zealand Jour- nal of Science, 21: 591-597.

Ross, D. J., Campbell, I. B., and Bridger, B. A., 1979: Bio- chemical activities of organic soils from subarctic tussock grasslands on Campbell Island. 1. Oxygen uptake and nitro- gen mineralization. New Zealand Journal of Science, 22: 161-171.

Rosswall, T. and Granhall, U., 1980: Nitrogen cycling in a sub- arctic ombrotrophic mire. In Sonesson, M. (ed.), Ecology of a Subarctic Mire. Ecological Bulletins 30. Stockholm: Swedish Natural Science Research Council, 209-234.

Shaver, G. R. and Chapin, F. S., III, 1980: Response to fertili- zation by various plant growth forms in an Alaskan tundra: Nutrient accumulation and growth. Ecology, 61: 662-675.

Smith, S. J., Young, L. B., and Miller, G. E., 1977: Evalua- tion of soil nitrogen mineralization potentials under modi- fied field conditions. Soil Science Society of America Jour- nal, 41: 74-76.

Stanford, G. and Epstein, E., 1974: Nitrogen mineraliza- tion-water relations in soils. Soil Science Society of America Proceedings, 38: 103-107.

292 / ARCTIC AND ALPINE RESEARCH

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Page 8: Nitrogen Mineralization in a Tussock Tundra Soil

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