Journal of Plant Nutrition, 30: 1841–1853, 2007

Copyright © Taylor & Francis Group, LLC

ISSN: 0190-4167 print / 1532-4087 online

DOI: 10.1080/01904160701628999

Nitrogen Fixation, Soil Nitrogen Availability,and Biomass in Pure and Mixed Plantations

of Alder and Pine in Central Korea

Yowhan Son,1 Yoon Young Lee,2 Chon Young Lee,2 and Myong Jong Yi3

1Division of Environmental Science and Ecological Engineering, Korea University,Seoul , Korea

2Forest Research Institute, Seoul, Korea3Division of Forest Resources, Kangwon National University, Chunchon, Korea

ABSTRACT

Rates of nitrogen (N) fixation, soil N availability, and aboveground biomass were mea-sured in 27-year-old pure and mixed Alnus hirsuta and Pinus koraiensis plantations incentral Korea. Nodule biomass and N fixation were 179.3 kg ha−1 and 46.6 kg ha−1yr−1

for the pure A. hirsuta plantation (PA) and 95.2 kg ha−1 and 41.1 kg ha−1yr−1 for themixed A. hirsuta + P. koraiensis plantation (MAP), respectively. A. hirsuta seemed toprovide more than two thirds of annual N requirement for P. koraiensis. Rates of acety-lene reduction were significantly related to soil temperature (R2 = 0.51, P < 0.001), butnot to soil moisture content. Total inorganic N [ammonium (NH+

4 )plus nitrate (NO−3 )]

availability measured using ion exchange bags were significantly higher under PA (27.91µg-N bag−1) and MAP (31.34 µg-N bag−1) than under the pure P. koraiensis plantation(PP) (14.31 µg-N bag−1). Especially soils under the influence of A. hirsuta showedat least 2 fold increase in resin total inorganic N concentrations. Total abovegroundbiomass (Mg ha−1) was 147.3 for PA, 145.8 for MAP, and 174.8 for PP, respectively,and was not significantly different among plantations. A. hirsuta significantly increasedsoil N availability; however, the influence of N fixation on aboveground biomass wasnot significant for the study plantations.

Keywords: aboveground biomass, A. hirsuta, nitrogen availability, nitrogen fixation,P. koraiensis

Received 4 May 2006; accepted 16 March 2007.Address correspondence to Yowhan Son, Division of Environmental Science and Eco-

logical Engineering, Korea University, Seoul 136-701, Korea. E-mail: yson@korea.ac.kr

1841

1842 Y. Son et al.

INTRODUCTION

The potential of nitrogen (N) fixation for increasing production in forest ecosys-tems has been widely studied for the past and the topic was examined throughoutthe world. Numerous studies have investigated N fixation for pure Alnus spp.forests, and relatively few studies focused on the rates and influences of N fix-ation for mixed stands of Alnus spp. with coniferous or deciduous tree species(Binkley, 1992; Binkley et al., 1994). Although N fixing woody species such asRobinia pseudoacacia L. and Alnus spp. have been extensively planted through-out Korea, very few studies examined the effects of these N fixing species onsoil fertility, nutrient cycling, and growth of other target tree species (Chae andKim, 1977; Mun et al., 1977; Lee and Son, 2005). One of the most successfulN fixing species, Alnus hirsuta Rupr., which is indigenous to northeast Asia,shows rapid growth rates in central Korea. Pinus koraiensis Sieb. et Zucc., whichoccurs naturally and also was artificially planted in Korea, is considered as oneof the most important tree species in the region because of economic value of itsseed and fine quality wood. Intensive silvicultural practices including fertiliza-tion to meet nutrient requirements seemed to be necessary to increase growthfor the species (Yi, 1998; Son et al., 2001). Based on previous studies on themixture of N fixing tree species with commercially valuable conifers (Bink-ley, 1983; Hart et al., 1997), including A. hirsuta in P. koraiensis, seems to bepromising in increasing soil N availability and biomass of both tree species.It was hypothesized that A. hirsuta would greatly increase soil N availabilityand biomass accumulation of a P. koraiensis plantation. The objectives of thepresent study were to assess the effects of N fixing A. hirsuta on soil N fixationand to examine N availability and growth of P. koraiensis and A. hirsuta in pureand mixed plantations of central Korea.

MATERIALS AND METHODS

Study Site

The study site was located on a northern slope of Yeonyeob Mountain in centralKorea (37◦ 47′ N, 127◦ 48′ E). The average annual temperature and precipi-tation are 10.9◦C and 1266 mm, respectively, with about 70% of the annualprecipitation falling between June and August. Detailed information on soilcharacteristics was presented in Lee and Son (2005). The site was logged in1976 and planted with A. hirsuta and P. koraiensis seedlings that were grownfor 2 years in a nursery. Three plantations were selected for the study: pureA. hirsuta plantation (PA), mixed A. hirsuta + P. koraiensis plantation (MAP)and pure P. koraiensis plantation (PP). Some saplings of P. koraiensis invadedPA (Table 1). Three plots each measuring 10 m × 10 m were located withineach plantation. Within each plot, all P. koraiensis and A. hirsuta trees were

Nitrogen Fixation in Pure and Mixed Alnus Hirsuta Plantations 1843

Table 1Description of the three study plantations. Means and one standard error. Pure A. hir-suta plantation (PA), mixed A. hirsuta + P. koraiensis plantation (MAP), and pure P.koraiensis plantation (PP)

PA MAP PP

Altitude (m) 525 530 510Slope (◦) 22 15–18 25Density (no. ha−1)

A. hirsuta 1960 1130 —P. koraiensis 370 1130 1030

Height (m)A. hirsuta 12.5 (0.3) 13.4 (0.4) —P. koraiensis 8.8 (0.5) 9.9 (0.4) 13.5 (0.2)

DBH (cm)A. hirsuta 10.9 (0.4) 11.1 (0.6) —P. koraiensis 11.7 (1.2) 12.4 (0.7) 18.9(0.8)

tagged and measured for diameter at breast height and height in June, 2003.Allometric regression equations from Chae and Kim (1977) for A. hirsuta andfrom Son et al. (2001) for P. koraiensis were used to estimate abovegroundbiomass.

Nitrogen Fixation

Nitrogen fixation was measured using the acetylene reduction technique (Bink-ley et al., 1994; Hurd et al., 2001; Lee and Son, 2005; Yamanaka et al., 2005).A single transect was located across each plot, and 30 cm × 30 cm × 30 cmsoil pits were excavated every 2 m along the transect (Lee and Son, 2005). Allnodulated roots were sampled from soil pits and nodule biomass was measuredon April 2, May 17, July 6, August 14, and September 28, 2003. Measurementsof acetylene reduction were repeated approximately every 45 d from April 2through December 16, 2003. Acetylene reduction was determined at each sam-pling time by incubating 10 to 30 nodulated root segments in glass bottles for1 hour in 10% acetylene (Knowles, 1987; Weaver and Frederick, 1987; Riceand Olsen, 1993). After incubation gas sample was collected and analyzedfor ethylene and acetylene with a gas chromatograph (Hewlett Packard Model6890). Nitrogen fixation was calculated by multiplying nodule biomass by theaverage rate of acetylene reduction, assuming a ratio of 3 moles of acetyleneper mole of N fixed (Hardy et al., 1973). During the measurement of acetylenereduction, soil temperature and moisture were measured adjacent soil pits. Soil

1844 Y. Son et al.

temperature was measured with a soil temperature probe (PP Systems, Inc.,UK) at 10 cm soil depth, and soil moisture was measured gravimetrically.

Nitrogen Availability

In December 2002, ion exchange resin bags were placed in the field to measureammonium (NH+

4 ) and nitrate (NO−3 ) from the soil solution. Five resin bags

were placed 5cm below the surface of the mineral soil, every 2 m along a singletransect across each plot. The resin bags were prepared by adding 14 mL ofcation resins (Sybron IONAC C-251, H+ Sybron International, Milwaukee,Wisconsin) and 14 mL of anion resins (Sybron IONAC ASB-1P OH−) intoseparate nylon stockings (Garcia-Montiel and Binkley, 1998). Resin bags wereretrieved and replaced approximately every 45 d except for winter (December19–April, April 3–May 17, May 18–July 6, July 7–August 14, August 15–September 28, and September 29–November 18). Retrieved resin bags wereextracted by shaking for 1 hour with 100 mL of 2 M potassium chloride (KCl).Extracts were settled for 24 h and filtered. Concentrations of NH+

4 and NO−3 in

the extracts were determined using a Lachat flow-injection autoanalyzer (LachatInstruments, Milwaukee, Wisconsin).

Statistical Analysis

Statistical analyses were performed using SAS 6.03 software (SAS, 1988).Analysis of variance was used to test mean differences in nodule biomass, Nfixation, N availability, and tree biomass among the three plantations. Alsoregression analysis was used to quantify the relationship between acetylenereduction and soil temperature, soil moisture content and N availability. Resultswere considered significant for P < 0.05.

RESULTS AND DISCUSSION

Nitrogen Fixation

Nodule biomass (kg ha−1) for PA and MAP during the growing season was193.3 and 96.3 for 4 April, 188.1 and 90.4 for 17 May, 181.4 and 96.7 for6 July, 160.8 and 84.5 for 14 August, and 173.0 and 108.4 for 28 September2003, respectively (Figure 1). This nodule biomass did not significantly differamong the five sampling times for both plantations, with overall averages of179.3 kg ha−1 for PA and 95.2 kg ha−1 for MAP. These values were within therange of 30-450 kg ha−1 reported for Alnus spp. by Binkley (1981), Sharma andAmbasht (1984), and Binkley et al. (1992). However, the average nodule mass

Nitrogen Fixation in Pure and Mixed Alnus Hirsuta Plantations 1845

Figure 1. Nodule biomass for the pure A. hirsuta (PA) and mixed A. hirsuta + P.koraiensis (MAP) plantations in central Korea. Bars represent one standard error of themean.

for the pure A. hirsuta plantation from this study (179.3 kg ha−1) was lower than220 kg ha−1 for the pure 38-year-old A. hirsuta plantation located on southernaspect (Lee and Son, 2005). Differences in stand age (38 vs. 27-year old), standdensity (700 vs. 2300 trees per ha), and aspect (north vs. south facing slope)might influence nodule biomass. Nodule biomass was 2-fold higher beneathPA than beneath MAP, and the stand density of A. hirsuta (1960 trees per hafor the pure plantation vs. 1130 trees per ha for the mixed plantation) appearedto influence the difference.

Soil temperature showed a clear seasonal trend; it increased from April,peaked in August, and decreased thereafter throughout the winter for the threeplantations (Figure 2a). However, there were no significant differences in soiltemperature among the plantations. Mean soil temperature (◦C, one standarderror) during the study period was 10.7 ± 2.52 for PA, 10.3 ± 2.52 for MAP,and 9.5 + 2.80 for PP, respectively. Soil moisture varied between 4% and34% during the growing season. In general, soil moisture was low in the earlygrowing season, increased after July and remained high during the rest of theseason (Figure 2b). Mean soil moisture (%, one standard error) for PA, MAP,and PP was 22.7 ± 4.1, 21.2 ± 4.0, and 19.5 ± 3.9, respectively, and was notsignificantly different among the plantations. Acetylene reduction increasedfrom early spring, remained high until late summer, and rapidly decreasedfrom late fall (Figure 2c). These seasonal changes were similar to those in soil

1846 Y. Son et al.

Figure 2. Seasonal soil temperature (a), soil moisture content (b), and acetylene reduc-tion rate (c) for the pure A. hirsuta (PA), mixed A. hirsuta + P. koraiensis (MAP), andpure P. koraiensis (PP) plantations in central Korea.

Nitrogen Fixation in Pure and Mixed Alnus Hirsuta Plantations 1847

Table 2Mean nodule biomass (kg ha−1), acetylene reduction rate (µ mol g−1

hr−1) and estimated annual N fixation (kg ha−1yr−1) for the three studyplantations

PA MAP PP

Nodule biomass 179.3 95.2 —Acetylene reduction rate 3.77 6.27 —Annual N fixation 46.6 41.1 —

temperature. However, there was relatively high variability in acetylene reduc-tion in August and September especially for MAP. Similar seasonal patterns insoil temperature and acetylene reduction were observed for a pure A. hirsutaplantation by Lee and Son (2005). Mean acetylene reduction rate (µ mol g−1

hr−1) during the study period was significantly higher under MAP (6.27) thanunder PA (3.77). These values were slightly lower than other reported values of5-10 µ mol g−1hr−1 for Alnus spp. (summarized by Binkley et al., 1992). In ageneral way, N fixation is favored by full sunlight, adequate soil moisture andnutrient, and warm temperatures (Binkley et al., 1994). Under the similar soilmoisture and temperature conditions in this study, stand density of A. hirsutaand soil N availability (see below) might influence the differences in acetylenereduction rates (Binkley et al., 1994).

Multiplying acetylene reduction rates by nodule biomass for each planta-tion yielded N estimates of 46.6 kg ha−1yr−1 for PA and 41.1 kg ha−1yr−1 forMAP (Table 2). Despite differences in nodule mass and acetylene reductionrates between the two plantations, estimates of annual N fixation rates werenot significantly different. These values were within the ranges reported forpure Alnus spp. (37–150 kg ha−1yr−1; Lee and Son, 2005) and mixed Alnusspp. with conifers (20–130 kg ha−1yr−1; Binkley, 1992). Considering annual Nrequirements of 120 kg N ha−1 yr−1 for A. hirsuta (Mun et al., 1977) and 60 kgN ha−1 yr−1 for P. koraiensis (Lee et al., 1987), estimates of N inputs throughN fixation would be substantial and especially might be more than two thirds ofannual N requirement for P. koraiensis. It appeared that continued inputs of Nvia symbiotic N-fixation by A. hirsuta in the mixed plantation could lead to theelimination of N-limitation to forest ecosystem production (Hart et al., 1997).

Nitrogen Fixation and Environmental Factors

There was no statistically significant correlation between acetylene reductionand soil moisture (Figure 3a). However, it seemed that the influence of soilmoisture on acetylene reduction varied depending on soil moisture contents.

1848 Y. Son et al.

Figure 3. Relationship between acetylene reduction rate and soil moisture content (a)and soil temperature (b) for the pure A. hirsuta and the mixed A. hirsuta + P. koraiensisplantations. Each point represents the mean of three plots for each measuring time.

Nitrogen Fixation in Pure and Mixed Alnus Hirsuta Plantations 1849

Relatively high soil moisture contents (>30%) increased acetylene reductionwhile low soil moisture contents (<10%) decreased acetylene reduction. Thesame phenomenon was reported by Lee and Son (2005). Binkley et al. (1994)also concluded that seasonal dynamics in soil moisture content likely affected Nfixation activity. More studies would be needed to clarify the relationship. On theother hand, acetylene reduction exponentially increased with soil temperature(R2 = 0.51, P < 0.001; Figure 3b). The role of soil temperature in influencing Nfixation was supported from numerous studies by seasonal patterns of acetylenereduction activity (Tripp et al., 1979; Binkley, 1981; Bormann and Gordon,1984; Binkley et al., 1994; Lee and Son, 2005).

Nitrogen Availability

Resin NH+4 , NO−

3 , and total inorganic N concentrations for the six incubationperiods were presented in Table 3. Resin NH+

4 and NO−3 concentrations (µg-N

bag−1) ranged from 0.19 and 1.26 for December 19—April 2 to 0.72 and 9.69for August 18—September 28, with a clear seasonal trend of increases duringthe early growing season, peaks during the mid growing season, and decreasesfrom the late growing season (data not shown). The resin bags revealed a strongpattern of species effect on N availability; resin NH+

4 , NO−3 , and total inorganic

N concentrations were significantly higher under PA (3.08, 24.83 and 27.91µg-N bag−1) and MAP (2.88, 28.46, and 31.34 µg-N bag−1) than under PP(2.40, 11.91, and 14.31 µg-N bag−1). Especially soils under the influence ofA. hirsuta showed at least 2 fold increase in resin NO−

3 and total inorganic Nconcentrations. Previous studies also reported significant increases in soil Navailability under N fixing tree species such as Alnus or Albizia spp. (Binkleyet al., 1984; Garcia-Montiel and Binkley, 1998; Rhoades et al., 2001). However,

Table 3Means (and standard error) for ion exchange resin NH+

4 and NO−3 (mg-N bag−1, standard

errors) measured from November 19, 2003 through November 18, 2004 and abovegroundbiomass (Mg ha−1) for the three study plantations. Same letters indicate that means donot differ among plantations at a 0.05 significance level

PA MAP PP

N availabilityNH+

4 3.08 (0.17)a 2.88 (0.15)a 2.40 (0.19)bNO−

3 24.83 (1.57)a 28.46 (1.13)a 11.91 (1.08)bTotal 27.91 (1.50)a 31.34 (1.25)a 14.31 (1.25)b

Aboveground biomassA. hirsuta 108.7 (6.6)a 70.6 (1.0)b —P. koraiensis 38.6 (8.6)b 75.2 (9.5)b 174.8 (18.6)aTotal 147.3 (9.7)a 145.8 (9.6)a 174.8 (18.6)a

1850 Y. Son et al.

there were no significant differences in resin NH+4 , NO−

3 and total inorganicN concentrations between PA and MAP. The proportion of resin NO−

3 in totalinorganic N was 89% for PA, 91% for MAP, and 83% for PP, respectively. Thesehigh nitrification ratios were similar to those for other deciduous and coniferousforests measured in the region (Son and Lee, 1997; Son et al., 1999).

In general, it is known that high levels of soil N availability lead to low Nfixation for leguminous plants. However, the evidence was not clear for Alnusspp.; some studies reported N fixation decreased as N availability increasedwhereas other studies concluded the opposite (Binkley et al., 1994; Tobitaet al., 2005). In this study, total annual N fixation was higher under PA withslightly higher total resin N availability compared to MAP plantation althoughthese differences were not statistically significant (Table 3).

Aboveground Biomass

Total aboveground biomass (Mg ha−1) was 147.3 for PA, 145.8 for MAP, and174.8 for PP, respectively (Table 3). In general, total aboveground biomass forthe three plantations was higher than the values reported for pure Alnus spp.(45 Mg ha−1 for 20-year-old A. sibirica Fischer, Chae and Kim, 1977) and pureP. koraiensis (95 Mg ha−1 for 34-year-old P. koraiensis, Yi, 1998) stands in theregion. In PP, estimated total aboveground biomass was 15 percent greater thatin PA and MAP, but the difference was not significant. In MAP, P. koraiensisshowed slightly higher biomass than A. hirsuta with the same proportion in standdensity, however, the difference was not significant. Previous studies reportedthat aboveground biomass was higher in P. koraiensis than in A. hirsuta withthe similar stand age and density (Chae and Kim, 1977; Yi, 1998). Therefore,it appeared that A. hirsuta had no impact on total aboveground biomass. No A.hirsuta invaded PP because of low light intensity while P. koraiensis invadedPA with shade tolerant characteristics. Photosynthetically active radiation (µmol m2s−1) measured using a Decagon Sunfleck Ceptometer (Model SF-80) inAugust 14, 2003 was 89.0 for PA, 100.1 for MAP, and 20.0 for PP, respectively(Lee, Y., unpublished data). Binkley (1992) reviewed literatures and concludedthat biomass accumulation was much higher in mixed N fixing stands on infertilesites while biomass accumulation was greater in single-species stands of non-N-fixers on fertile sites. Soil N availability for the three study sites was highcompared to those from other forests in the region (Son and Kim, 2000; Sonand Lee, 2001). This study demonstrated a potential for A. hirsuta incorporatinginto P. koraiensis to increase soil N availability. However, we speculated that theinfluence of A. hirsuta did not affect P. koraiensis aboveground biomass on thisrelatively fertile site. Major questions still to be answered were site-specificresponse of P. koraiensis with A. hirsuta, and whole-rotation interactions ofboth species (Heilman and Stettler, 1985). Further studies would be neededto conclude the effects of A. hirsuta on soil N availability and biomass of P.koraiensis under different soil fertility conditions.

Nitrogen Fixation in Pure and Mixed Alnus Hirsuta Plantations 1851

ACKNOWLEDGMENT

Funding for this study was provided by Korea University.

REFERENCES

Binkley, D. 1981. Nodule biomass and acetylene reduction rates of red alderand Sitka alder on Vancouver Island, B.C. Canadian Journal of ForestResearch 11:281–286.

Binkley, D. 1983. Ecosystem production in Douglas-fir plantations: Interactionof red alder and site fertility. Forest Ecology and Management 5:215–227.

Binkley, D. 1992. Mixtures of nitrogen-fixing and non-nitrogen-fixing treespecies. In The ecology of mixed-species stands of trees, eds. M.G.R. Can-nell, D.C. Malcolm, and P.A. Robertson, pp. 99–123. Blackwell ScientificPublications.

Binkley, D., J. D. Lousier, and K. Cromack. 1984. Ecosystem effects of Sitkaalder in a Douglas-fir plantation. Forest Science 30:26–35.

Binkley, D. P. Sollins, R. Bell, D. Sachs, and D. Myrold. 1992. Biogeochemistryof adjacent conifer and alder/conifer stands. Ecology 73:2022–2033.

Binkley, D., K. Cromack, and D. D. Baker. 1994. Nitrogen fixation by red alder:Biology, rates, and controls. In The biology and management of red alder,eds. D.E. Hibbs, D.S. DeBell, and R.F. Tarrant, 57–72. Corvallis, Oregon:Oregon State University Press.

Bormann, B. T., and J. C. Gordon. 1984. Stand density effects in young redalder plantations: Productivity, photosynthate partitioning, and nitrogenfixation. Ecology 65:394–402.

Chae, M. I., and J. H. Kim. 1977. Comparisons of biomass, productivity andproductive structure between Korean alder and oak stands. Korean Journalof Ecology 1:57–66.

Garcia-Montiel, D. C., and D. Binkley. 1998. Effects of Eucalyptus salignaand Albizia falcataria on soil processes and nitrogen supply in Hawaii.Oecologia 113:547–556.

Hardy, R. W. F., R. C. Burns, and R. D. Holsten. 1973. Application of theacetylene-ethylene assay for measurement of nitrogen fixation. Soil Biologyand Biochemistry 5:47–81.

Hart, S. C., D. Binkley, and D. A. Perry. 1997. Influence of red alder on soilnitrogen transformations in two conifer forests of contrasting productivity.Soil Biology and Biochemistry 29:1111–1123.

Heilman, P., and R. F. Stettler. 1985. Mixed, short-rotation culture of red alderand black cottonwood: growth, coppicing, nitrogen fixation, and allelopa-thy. Forest Science 31:607–616.

Hurd, T. M., D. J. Raynal, and C. R. Schwintzer. 2001. Symbiotic N2 fixation ofAlnus incana ssp. rugosa in shrub wetlands of the Adirondack Mountains,New York, USA. Oecologia 126:94–103.

1852 Y. Son et al.

Lee, Y. Y., and Y. Son. 2005. Diurnal and seasonal patterns of nitrogen fixationin an Alnus hirsuta plantation of central Korea. Journal of Plant Biology48:332–337.

Lee, D. K., K. J. Lee, J. H. Shin, and K. H. Lee. 1987. Biomass production andnutrient cycling of forest ecosystems in central region of Korea. Journalof Korea Forest Energy 7:15–32. (in Korean with English abstract).

Mun, H. T., J. M. Kim, and J. H. Kim. 1977. Distributions and cycling ofnitrogen, phosphorus and potassium in Korean alder and oak stands. KoreanJournal of Biology 20:109–118.

Knowles, R. 1987. Free-living dinitrogen-fixing bacteria. In Methods of soilanalysis. Part 2. Chemical and microbiological properties, 2nd ed. eds, A.L. Page, R. H. Miller, and D. R. Keeney, 1072–1092, Madison, Wisconsin:Soil Science Society of America.

Rhoades, C., H. Oskarsson, D. Binkley, and B. Stottlemyer. 2001. Alder (Alnuscrispa) effects on soils in ecosystems of the Agashashok River valley,northwest Alaska. Ecoscience 8:89–95.

Rice, W. A., and R. E. Olsen. 1993. Root nodule bacteria and nitrogen fixation.In Soil sampling and methods of analysis. ed, M.R. Carter, 303–317, BocaRaton, Florida: Lewis Publishers.

SAS. 1988. SAS/STAT user’s guide. 6.03ed. SAS Inst. Cary, NC.Sharma, E., and R. S. Ambasht. 1984. Seasonal variation in nitrogen fixation

by different ages of root nodules of Alnus nephalensis plantations, in theEastern Himalayas. Journal of Applied Ecology 21:265–270.

Son, Y., and I. K. Lee. 1997. Soil nitrogen mineralization in adjacent stands oflarch, pine, and oak in central Korea. Annals of Forest Science 54:1–8.

Son, Y., and H. S. Kim. 2000. Soil nitrogen availability in a thinned Larixleptolepis plantation using ion exchange resin bags. Korean Journal ofEnvironmental Agriculture 19:188–190. (in Korean with English abstract)

Son, Y., and S. H. Lee. 2001. Relationship between land-use change and soilcarbon and nitrogen. Journal of Korean Forestry Society 90:242–248. (inKorean with English abstract)

Son, Y., W. K. Lee, S. E. Lee, and S. R. Ryu. 1999. Effects of thinning on soilnitrogen mineralization in a Japanese larch plantation. Communications inSoil Science and Plant Analysis 30:2539–2550.

Son, Y., J. W. Hwang, Z. S. Kim, W. K. Lee, and J. S. Kim. 2001. Allometry andbiomass of Korean pine (Pinus koraiensis) in central Korea. BioresourceTechnology 78:251–255.

Tobita, H., M. Kitao, T. Koike, and Y. Maruyama. 2005. Effects of elevatedCO2 and nitrogen availability of Alnus hirsuta Turcz. Phyton 45:125–131.

Tripp, L. N., D. F. Bezdicek, and P. E. Heilman. 1979. Seasonal and diurnalpatterns and rates of nitrogen fixation by young red alder. Forest Science25:371–380.

Weaver, R. W., and L. R. Frederick. 1987. Rhizobium. In Methods of soil anal-ysis. Part 2. Chemical and microbiological properties. 2nd ed. eds, A. L.

Nitrogen Fixation in Pure and Mixed Alnus Hirsuta Plantations 1853

Page, R. H. Miller, and D. R. Keeney, 1043–1070, Madison, Wisconsin:Soil Science Society of America.

Yamanaka, T., A. Akama, C. Y. Li, and H. Okabe. 2005. Growth, nitrogenfixation and mineral acquisition of Alnus sieboldiana after inoculationof Frankia together with Gigaspora margarita and Pseudomonas putida.Journal of Forest Research 10:21–26.

Yi, M. J. 1998. Changes in aboveground biomass and nutrient accumulationof the Korean pine (Pinus koraiensis) plantation by stand age at KangwonProvince. Journal of Korean Forestry Society 87:276–285. (in Korean withEnglish abstract)