Dominant Factors of the Nature Regulating CO2 Release from Boreal Forest Land

doi:10.4236/ijg.2012.32036

Paper Menu >>

Journal Menu >>

International Journal of Geosciences, 2012, 3, 333-338

http://dx.doi.org/10.4236/ijg.2012.32036 Published Online May 2012 (http://www.SciRP.org/journal/ijg)

Dominant Factors of the Nature Regulating CO2 Release

from Boreal Forest Land

Ryunosuke Kikuchi1,2, Tamara T. Gorbacheva3

1Faculty of Science and Technology, Ryukoku University, Otsu, Japan

2CERNAS-ESAC, Polytechnic Institute of Coimbra Bencanta, Coimbra, Portugal

3Institute of the North Industrial Ecology Problems, Kola Science Center,

Murmansk, Russia

Email: [email protected]. jp

Received December 22, 2011; revised February 17, 2012; accepted March 14, 2012

ABSTRACT

Temperature is often considered as a primary factor for microbial decomposition of soil organic carbon. Boreal forests

are the large terrestrial carbon pool: if carbon stored in this region is transferred to the atmosphere as CO2 by a warm-

ing-induced acceleration of its decomposition, there will be positive feedback to global warming. It is reported that real

issue regarding the release of carbon from soils to the atmosphere is how natural factors interact to influence decom-

position of soil organic matter, so we observed mass losses (indicating decomposition rates) from litter and litterfall in a

Northern Fennoscandia forest over 3 years under natural conditions. Our field survey has demonstrated that mass losses

from most kinds of sample had moderate correlation with the temperature. Of the various samples, the canopy-gap litter

alone had a greater rate (~70%) of mass loss. It is at least necessary to make a clear distinction of monitoring sites (un-

der the canopy and in the canopy gap) when discussing the effect of climate on soil CO2 release from high-latitude for-

ests. Though temperature, soil moisture and soil properties are prioritized in the issue of soil CO2 release, our results

suggest that the fungi/bacteria rate and the wind-related mix/fragmentation are also important factors to be considered;

however, this speculation is just tentative, and more detail research is called for.

Keywords: Fragmentation; Global Warming; High-Latitude Forest; Microbial Decomposition; Wind

1. Introduction

The conversion of litter carbon (i.e. young soil carbon

above the mineral soil) to CO2 by microbial respiration is

one of the major processes controlling the terrestrial car-

bon budget [1], and most ecosystem models assume that

the temperature sensitivity of decomposition is identical

for all types of organic matter (review in [2]). Global

warming may trigger an unbalance between carbon sinks

provided by plants and carbon sources from decomposi-

tion, potentially causing an acceleration in CO2 release

from the terrestrial ecosystem. Nearly half of the carbon

stored in forested ecosystems is in boreal forests, and it is

a source of anxiety that a notable characteristic of boreal

forest soils is surface accumulations (~500 giga tons C)

of organic carbon [3]. Since high-latitude regions have

warmed faster than other parts in recent decades [4] and

these regions will be intensively subjected to a warming

climate in the future [5], the effect of warming tempera-

tures on boreal forests may result in a dramatic increase

in terrestrial carbon flux to the atmosphere.

Soil organic carbon (SOM) is mainly divided into min-

eral soil and litter (cf. [6]); as degradation of litter pro-

ceeds, SOM is transformed to organic acids and humins

which accumulate in mineral soil. According to the data

from 82 sites on five continents [7], increased tempera-

ture does not stimulate the decomposition of forest-

derived carbon in mineral soil. The dependence of mi-

crobial decomposition on temperature is only known for

young organic soil [8]. Yet another experiment suggests

that SOM decomposition is affected by soil depth and

experiment method, and the temperature sensitivity for

passive SOM does not differ from that for labile SOM

[9]. Anyway, the carbon input to the young organic soil

from biomass is easily released to the atmosphere ac-

cording to the current model- and observation-based con-

cepts [2,8,9].

Not only temperature and soil properties but also soil

moisture are also prioritized in the issue of soil CO2 re-

lease [10]; e.g. there are drying/wetting cycles in natural

conditions [11]. Nevertheless, the real issue regarding the

release of carbon from soils to the atmosphere is how

temperature, soil water content and other factors interact

to influence decomposition of soil organic matter [12].

The climate effect on microbial decomposition of soil

R. KIKUCHI, T. T. GORBACHEVA

334

carbon is generally represented by applying the variable

Q10 temperature function [13]; Q10 values of ~2 at 30˚C -

35˚C, increasing to 4 - 6 at 5˚C - 10˚C. However, it is re-

ported that, after 5 years, there is no effect of a 5˚C warm-

ing on soil CO2 efflux form boreal forests in Sweden [14].

Considering this report, we observed the decomposition

rates over 3 years in a common spruce forest of the North-

ern Fennoscandia (Figure 1(a)) in order to evaluate the

climate effect under natural conditions. The obtained re-

sults are presented in this paper.

2. Materials and Methods

Sixteen sample plots are located in a subarctic region of

the Kola Peninsula (67˚51'N 32˚47'E to 66˚50'N 30˚12'E)

(see Figure 1(a)). The monitoring site is situated in

spruce forest with green mosses and dwarf shrubs (cf.

picture in Figure 1(a)), and the O horizon in this site

contains a rich amount of carbon (430 to 650 g·kg–1) [15].

According to a previous study on the biogeochemical cy-

cle in this field [15], the annual input of biomass to the

monitored litter layer is mainly composed of Picea ob-

ovata Ldb (0.47 t·ha–1 needles, 0.47 t·ha–1 wood/branches

and below 0.01 t·ha–1 bark) and dwarf shrubs (0.34 t·ha–1

Vaccinium myrtillus L. leaves, 0.22 t·ha–1 Empetrum

hermaphroditum leaves and 0.03 t·ha–1 Vaccinium vitis-

idaea leaves).

2.1. Sampling and Observation

In our survey, litter is defined as plant materials (residues)

which have already been in contact with the soil. The

surface accumulations (O horizon) of SOM in boreal

forests are basically identified as fresh litter (L layer),

partially decomposed but recognizable Formultningss-

kiktet (F layer) and relatively homogenous humus (H

layer) [16]. We took litter samples mainly from the L la-

yer (fresh litter) under the canopy and in the canopy gap

(Figure 1(b)) in October of the 1st year; a small portion

of F layer material was inadvertently mixed in, but we

avoided the mixing of H layer and E horizon materials

with the samples.

The sampled litter contained reproductive and dead

parts of the aforementioned various plants such as Picea

obovata Ldb, Vaccinium myrtillus L., Empetrum hermap-

hroditum and Vaccinium vitis-idaea.

In our survey, litterfall (browned needles, leaves, etc.)

is defined as plant materials which are still attached to

the living plants. Avoiding yellow coloring and leachate

loss, fresh litterfalls were also picked off from tree

branches and dwarf shrubs present in the survey field in

October of the 1st year.

After each collected sample of 10 g was put in a syn-

thetic mesh bag (10 × 10 cm) with breathability, these

bags (15 replicates of a sample in each plot) were sealed

(a)

(b)

Figure 1. Study area and arrangement of field survey. (a)

Study area in boreal biogeogr aphy of European region: the

border of the boreal region is shown with a bold line, and

the distribution of spruce (Picea abies ssp. obovata) species

is shown with bold dots (redrawn from [17]); (b) Sample

collection and observation sites in the study area: in our

field survey, litter is defined as dead plant materials which

are present on the soil, and litterfall is defined as plant

materials which are still attached to the living plants. Each

sample was put in a mesh bag, and these bags were placed

under the canopy and in the canopy gaps; i.e. all the sam-

ples underwent the natural decomposition pr ocess.

to prevent additional litterfalls from entering the bags,

some of the sealed bags (n = 4 in each plot) were analy-

zed in the same month as the collection (i.e. 0 year), and

the rest were placed under the canopy and in the canopy

gaps (Figure 1(b)); that is, all the samples underwent the

natural decomposition process in the mesh bags during

the survey period.

2.2. Measurement and Interval

Mass loss (percentage of the original mass) can be used

to predict biodegradation-related carbon loss (indicating

the rate of microbial CO2 respiration), and its measure-

ment can be easily conducted by using a weight-mea-

suring scale (review in ref. [18]). The sample bags were

dried in a desiccator and then measured with respect to

the following items: weight change of the sample bag (i.e.

gross mass loss) and hydroscopic coefficient for conver-

sion of sample weight to dry-base weight. Using quite a

simple method—mass loss of the sample, we attempted

to assess the climate sensitivity of a carbon pool so as not

to isolate the decomposition of soil carbon from the local

climate (i.e. natural conditions).

R. KIKUCHI, T. T. GORBACHEVA 335

If data of total mass loss from soil incubations longer

than one year are used to assess the SOM dependence on

temperature, there is a possibility that the obtained value

may be underestimated because respiration rates at all

temperatures are close to zero at the later stage of in-

cubation [9]. Viewed in this light, we set an interval of

one year for data collection in the survey field. We ca-

rried out measurement using the samples each October

over 3 years.

(a) (b)

2.3. Data Processing

The warmth index is defined as the yearly sum of the

mean monthly temperature minus 5˚C for the months

with the mean temperature above 5˚C (cf. [19]). There is

the limitation in applying the Q10 value to the rate of

SOM decomposition—the Q10 value is not adequate

when simulating the effect of temperature on decom-

position below 5˚C [20,21]. Considering the filed con-

ditions and the Q10 temperature function (i.e. the tem-

perature-decomposition relationship), we modified the

interval of warmth index in order to adapt the index to

the cold region of our survey; that is, the yearly sum of

the daily mean temperature minus 5˚C for the days with a

mean temperature above 5˚C.

Mass loss of sample was determined as a percentage of

the original mass, and their rates (%) were compared

using statistic analysis of variance (ANOVA) with a

probability value of 0.05.

3. Results and Interpretation

CO2 production by microorganisms is measurable at

–39˚C [22], and microbial decomposition in the arctic

ecosystem is relatively independent of temperature when

moisture content is less than 20% [23]. The climate con-

ditions recorded in our field were not so severe to micro-

organisms: the annual mean temperature varied between

+0.2˚C and –1.8˚C over our field survey. During the

plant-growing season (mid-June to mid-September) at

the daily mean temperature of 14.7˚C ± 1.4˚C standard

deviation (SD), the site under the canopy was 5.2˚C ±

1.8˚C (SD) cooler than the canopy gap, the throughfall

(precipitation passing through the canopy) averaged

62.8% ± 11.9% (SD) of gross rainfall, and the soil

moisture in the monitored litter layer was 52.9% ± 2.9%

(SD) under the canopy and 60.4% ± 1.6% (SD) in the

canopy gap, respectively.

As stated in the section entitled materials ands meth-

ods, we shortened the interval of warmth index order to

adapt the index to the cold region of our survey. This

warmth index and the mass-loss rates of each sample are

plotted in Figure 2.

Mass losses from all the samples occurred (p < 0.05)

during the 1st year (warmth index of 1530˚C) at the rate

Figure 2. Variations of mass loss (n = 4 in each plot) in

sample types as a function of warmth index with monitoring

site (a) canopy gap and (b) under canopy as parameter.

Warmth index in this figure means the sum of daily mean

temperature above 5˚C: 1530˚C from October the 1st year

to September the 2nd year, 2710˚C from October the 1st

year to September the 3rd year, and 4161˚C from October

the 1st year to September the 4th year.

of about 20% except for woody litterfalls and the canopy-

gap litter (Figure 2). The early-stage (over the 1st year)

decomposition rates range from ~10% near the Arctic

Circle to ~40% in northern Germany [24]. It is consi-

dered that the measured mass losses except those for the

above-mentioned two samples are approximately inter-

mediate between the Arctic value and the northern Ger-

many value.

The climate effect on decomposition of soil carbon is

represented by a water-stress function and the variable

Q10 temperature function [25,26]. The canopy gap was

~5˚C warmer and ~7% wetter than the under-canopy

floor, so this warmer and wetter microclimate seemed to

cause a greater rate of mass loss; however, as shown in

Figure 2, no clear difference between mass loss in the

canopy gap and mass loss under the canopy was ob-

served (p ≥ 0.05) (excluding the litter samples).

4. Discussion

Of the various samples, special attention should be paid

to the woody litterfalls and the canopy-gap litter because

these samples showed their own patterns of mass loss.

4.1. Woody Litterfalls

The mass-loss rates from woody litterfalls both in the

canopy gap and under the canopy were quite small

(~10% over 3 years). This low rate can be interpreted as

follows: before any weight loss, woody debris usually

has a long lag time which is related to the substrate size;

following the lag phase, the debris begins to weather and

fragment, and mass leaching and microbial activity occur

[27]. Therefore, the decomposition of woody litterfalls

was slow, that is, its mass loss was small.

R. KIKUCHI, T. T. GORBACHEVA

336

4.2. Hypothesis for Explaining the Mass Loss of

Canopy-Gap Litter

As compared with the above-mentioned data in northern

Germany (~40%) and near the Arctic Circle (~10%) (cf.

[24]), the mass-loss rate of ~70% from the canopy-gap

litter is significantly great; by contrast, the rate of ~20%

from the litter under the canopy is rational. Can we

logically interpret the obtained results to find the reason

why only the canopy-gap litter had a very high rate of

mass loss? It must be the most important rate-regulating

factor under natural conditions.

There is a clear difference between litter and litterfalls;

litter (picked from the O horizon) has already been in

contact with the soil, but litterfalls (picked from the

plants) have not yet had such contact (refer to the section

titled materials ands methods). Therefore, the following

hypothesis is built up to interpret this specific phenol-

menon.

1) Fungi/bacteria ratio: in our survey field, the F

layer under the canopy contains great amounts of fungi―

i.e. 1.73 - 8.65 mg·g–1 fungi mycelium and 0.10 - 0.25

mg· g –1 sporidium [28]. However, these amounts clearly

decrease in the canopy-gap F layer―i.e. 0.52 mg·g–1

fungi mycelium and 0.03 mg·g–1 sporidium [28]. The

bacteria community shows a different trend: 0.01 mg·g–1

under the canopy and 0.03 mg·g–1 in the canopy gap [28].

It is suggested that the changes in specie composition of

fungi potentially influence the accumulation of recalci-

trant soil organic matter derived from lignin and lignin-

like substances [29].

It is also reported that the mean percent fungal-to-

bacterial respiratory is 84-to-16 at a 6.0 pH in North

German spruce, and the metabolic quotient qCO2 (i.e.

respiration per unit biomass) declines with increasing

fungal presence [30]. Furthermore, the effect of soil war-

ming on the fungal population is still uncertain [31,32].

Based on the microbial difference, it is possible to inter-

pret the reason why the canopy-gap litter alone had a

greater rate of mass loss as follows: mite-like small ani-

mals break down dead plant materials on the soil into

fine pieces in a process called fragmentation; litter frag-

mentation (reduction of litter size and increase of surface

area) results in the establishment of a soil bacteria popu-

lation [33]―bacteria growth is especially affected by

fragmentation size because fungi can penetrate sub-

stances more easily than bacteria. However, a high rate

of litter fragmentation by mite-like small animals is not

expected under a harsh and cold climate in high-latitude

regions.

2) Wind-related mix and fragmentation: air tempe-

ratures within the forest in the afternoon are cooler than

the temperatures in nearby cleared areas [34]. Openings

(canopy gaps) in a moderate to dense tree stand become

warm air pockets during the day, and these openings

often act as natural chimneys, leading to accelerate the

rate of local updraft [34]. This updraft gives vibration,

rotation, inversion and so on to the litter present on the

canopy-gap floor, contributing to litter fragmentation

(Figure 3).

During the updraft-related process, litter is mixed with

soil bacteria as well as fungi. The main benefit of frag-

mentation is the fast leaching of toxic phenolics asso-

ciated with fragmented litter [35]. The different contents

of phenolics support this leaching theory: the content (6.0

mM·kg–1) of phenolics in the canopy-gap litter is much

lower than that (14 mM·kg–1) in the litter under the

canopy [36]. Consequently, litter becomes more bioavai-

lable not only to fungi but also to bacteria in the canopy

gap.

5. Conclusions

Of the various samples, the canopy-gap litter alone had a

greater rate of mass loss in the monitored boreal forest.

Although temperature, soil moisture and soil properties

are currently prioritized in the issue of soil CO2 release,

the obtained results suggest that it is necessary to make a

clear distinction of monitoring sites (under the canopy

and in the canopy gap) as well as make a clear distinction

between litter and litterfall when discussing the effect of

climate on soil CO2 release from high-latitude forests.

Furthermore, it is also suggested that the type of mi-

crobial community and the wind effect are essential fac-

tors to be considered: 1) fungal mycelia are abundant in

the boreal tree area (under the canopy in particular); 2)

the bacteria community is abundant in the canopy gap

(i.e. open space); and 3) there is a possibility that the rate

of local updraft may make litter materials more bio-

available to the bacteria community (i.e. an increase in

the soil-CO2 release). However, this interpretation is only

tentative, and more detail research is called for.

Figure 3. Conceptual schematics of wind effect on litter de-

composition in a canopy gap for explaining the high mass-

loss rate from the canopy-gap litter. Openings (canopy gaps)

often act as natural chimneys and accelerate the rate of

local updraft (a current of rising air). The swaying motion

of litter in the wind facilitates the mixing of litter with soil

bacteria and fungi, the leaching of phenolics from litter

pieces, and litter fragmentation. Consequently, microbial

accessibility to litter rises.

R. KIKUCHI, T. T. GORBACHEVA 337

6. Acknowledgements

Thanks are due to Ms E. Belova (Kola Science Center)

for field assistance, to Ms S. Sverchkova (Kola Science

Center) for laboratorial assistance, to Dr J. Maxwell

(University of Bristol) for helpful advice on text structure,

and to Ms C. Lentfer for English review.

REFERENCES

[1] M. Coûteaux, P. Bottner and B. Berg, “Litter Decomposi-

tion, Climate and Litter Quality,” Tree, Vol. 10, 1995, pp.

63-66. doi:10.1016/S0169-5347(00)88978-8

[2] I. C. Burke, J. P. Kaye, S. P. Bird, S. A. Hall, R. L.

McCulley and G. L. Sommerville, “Evaluating and Test-

ing Models of Terrestrial Biogeochemistry—The Role of

Temperature in Controlling Decomposition,” In: C. Can-

ham, J. Cole and W. Lauenroth, Eds., Models in Ecosys-

tem Science, Princeton University Press, Princeton, 2003,

pp. 225-253.

[3] R. K. Dixon, S. Brown, R. A. Houghton, A. M. Solomon,

M. C. Trexler and J. Wisnieski, “Carbon Pools and Flux

of Global Forest Systems,” Science, Vol. 263, No. 514,

1994, pp. 185-190. doi:10.1126/science.263.5144.185

[4] W. L. Chapman and J. E. Walsh, “Recent Variations of

Sea Ice and Air Temperature in High Latitudes,” Bulletin

of the American Meteorological Society, Vol. 74, No. 1,

1993, pp. 33-47.

doi:10.1175/1520-0477(1993)074<0033:RVOSIA>2.0.C

O;2

[5] Intergovernmental Panel on Climate Change, “IPCC Spe-

cial Report on Land Use, Land-Use Change and Forest,”

Cambridge University Press, Cambridge, 2000.

[6] T. Ito and T. Oikawa, “A Simulation Model of the Carbon

Cycle in Land Ecosystems,” Ecological Modeling, Vol.

151, No. 2, 2002, pp.143-176.

doi:10.1016/S0304-3800(01)00473-2

[7] C. P. Giardina and M. G. Ryan, “Evidence That Decom-

position Rates of Organic Carbon in Mineral Soil Do Not

Vary with Temperature,” Nature, Vol. 404, No. 6780,

2000, pp. 858-861. doi:10.1038/35009076

[8] J. Liski, H. Ilvesniemi, A. Makela and C. J. Westman,

“CO2 Emissions from Soil in Response to Climatic

Warming Are Overestimated—The Decomposition of

Old Soil Organic Matter Is Tolerant of Temperature,”

Ambio, Vol. 28, 1999, pp. 171-174.

[9] C. Fang, P. Smith, J. B. Moncrieff and J. U. Smith,

“Similar Response of Labile and Resistant Soil Organic

Matter Pools to Change in Temperature,” Nature, Vol.

433, No. 7021, 2005, pp. 57-59.

doi:10.1038/nature03138

[10] A. D. McGuire, J. M. Melillo and L. A. Joyce, “Interac-

tions between Carbon and Nitrogen Dynamics in Esti-

mating Net Primary Productivity for Potential Vegetation

in North America,” Global Biogeochemical Cycles, Vol.

6, No. 2, 1992, pp. 101-124. doi:10.1029/92GB00219

[11] W. Borken, E. A. Davidson and K. Savage, “Drying and

Wetting Effects on Carbon Dioxide Release from Organic

Horizons,” Soil Science Society of American Journal, Vol.

67, 2003, pp. 1888-1896. doi:10.2136/sssaj2003.1888

[12] E. A. Davidson, S. E. Trumbore and R. Amundson, “Soil

Warming and Organic Carbon Content,” Nature, Vol. 408,

No. 6814, 2000, pp. 789-790. doi:10.1038/35048672

[13] J. Lloyd and J. A. Taylor, “On Temperature Dependence

of Soil Respiration,” Functional Ecology, Vol. 8, No. 3,

1994, pp. 315-323. doi:10.2307/2389824

[14] P. G. Jarvis and S. Linder, “Constraints to Growth of

Boreal Forests,” Nature, Vol. 405, No. 6789, 2000, pp.

904-905. doi:10.1038/35016154

[15] N. Lukina and V. Nikonov, “Nutrient Status of North

Taiga Forest,” Kola Science Center, Apatity, 1998.

[16] C. E. Prescott and D. G. Maynard, “Humus in Northern

Forest—Friend or Foe?” Forest Ecology and Manage-

ment, Vol. 133, No. 1-2, 2000, pp. 23-26.

doi:10.1016/S0378-1127(99)00295-9

[17] S. Conde, D. Richard and N. Liamine, “The Boreal Bio-

geographical Region,” European Environment Agency,

Copenhagen, 2002.

[18] D. Nicholas and D. Crawford, “Concepts in the Devel-

opment of New Accelerated Test Methods for Wood De-

cay,” In: B. Goodell, D. Nicholas and T. P. Schultz, Eds.,

Wood Deterioration and Preservation, ACS Symposium

Series #845, American Chemical Society, Washington

DC, 2003, pp. 288-312.

[19] S. Noshiro and P. Baas, “Latitudinal Trends in Wood

Anatomy within Species and Genera,” American Journal

of Botany, Vol. 87, No. 10, 2000, pp. 1495-1506.

doi:10.2307/2656876

[20] M. Gödde, M. D. David and M. J. Christ, “Carbon Mobi-

lization from the Forest Floor under Red Spruce in the

Northeastern USA,” Soil Biology and Biochemistry, Vol.

28, No. 9, 1996, pp. 1181-1189.

doi:10.1016/0038-0717(96)00130-7

[21] T. Kätterer, M. Reichstein and O. Andrén, “Temperature

Dependence of Organic Matter Decomposition: A Critical

Review Using Literature Data Analyzed with Different

Models,” Soils Biology and Fertility of Soils, Vol. 27,

1998, pp. 258-262. doi:10.1007/s003740050430

[22] N. S. Panikov, P. W. Flanagan, W. C. Oechel, M. A.

Mastepanov and T. R. Christensen, “Microbial Activity in

Soil Frozen to –39˚C,” Soil Biology and Biochemistry,

Vol. 38, No. 4, 2006, pp. 785-794.

doi:10.1016/j.soilbio.2005.07.004

[23] N. J. Nadelhoffer, A. E. Giblin, G. R. Shaver and A. E.

Linkins, “Microbial Process and Plant Nutrient Availabil-

ity in Arctic Soil,” In: F. S. Chapin, R. L. Fefferies, J. F.

Reynoldds and G. R. Shaver, Eds., Arctic Ecosystem in a

Changing Climat e—An Ecophysiological Pe rspective, Aca-

demic Press, San Diego, 1991, pp. 281-319.

[24] B. Berg, “Litter Decomposition and Organic Matter Turn-

over in Northern Forest Soil,” Forest Ecology and Man-

agement, Vol. 133, No. 1-3, 2000, pp. 13-22.

doi:10.1016/S0378-1127(99)00294-7

[25] J. Lloyd and J. A. Taylor, “On Temperature Dependence

of Soil Respiration,” Functional Ecology, Vol. 8, 1994,

pp. 315-323. doi:10.2307/2389824

R. KIKUCHI, T. T. GORBACHEVA

338

[26] A. D. McGuire, J. M. Melillo, L. A. Joyce, D. W. Kick-

lighter, A. L. Grace, B. Moore and C. J. Vorosmarty, “In-

teractions between Carbon and Nitrogen Dynamics in Es-

timating Net Primary Productivity for Potential Vegeta-

tion in North America,” Global Biogeochemcal Cycles,

Vol. 6, No. 2, 1992, pp. 101-124.

doi:10.1029/92GB00219

[27] P. Sollins, “Input and Decay of Coarse Woody Debris on

Coniferous Stands in Western Oregon and Washington,”

Canadian Journal of Forest Research, Vol. 12, No. 1,

1982, pp. 18-28. doi:10.1139/x82-003

[28] V. V. Nikonov, N. V. Lukina and L. M. Polyanskaya,

“Distribution of Microorganisms in the Al-Fe-Humus

Podzols of Natural and Anthropogenically-Impacted Bo-

real Spruce Forests,” Microbiology, Vol. 70, No. 3, 2001,

p. 319. doi:10.1023/A:1010459512590

[29] T. Osono and H. Takeda, “Fungal Decomposition of

Abies Needle and Betula Leaf Litter,” Mycologia, Vol. 98,

No. 2, 2006, pp. 172-179.

doi:10.3852/mycologia.98.2.172

[30] E. V. Blagodatskaya and T. H. Anderson, “Interactive

Effects of pH and Substrate Quality on the Fungal-

to-Bacterial Ratio and qCO2 of Microbial Communities in

Forest Soils,” Soil Biology and Biochemistry, Vol. 30, No.

10-11, 1998, pp. 1269-1274.

doi:10.1016/S0038-0717(98)00050-9

[31] K. E. Clemmensen, A. Michelsen, S. Jonasson and G. R.

Shaver, “Increased Ectomycorrhizal Fungal Abundance

after Long-Term Fertilization and Warming of Two Arc-

tic Tundra Ecosystems,” New Phytologist, Vol. 171, No.

2, 2006, pp. 391-404.

doi:10.1111/j.1469-8137.2006.01778.x

[32] M. N. Thormann, S. E. Bayley and R. S. Currah, “Mi-

crocosm Tests of the Effects of Temperature and Micro-

bial Species Number on the Decomposition of Sedge and

Bryophyte Litter from Southern Boreal Peatlands,” Ca-

nadian Journal of Microbiology, Vol. 50, 2004, pp. 793-

802. doi:10.1139/w04-064

[33] R. D. G. Hanlon, “Some Factors Influencing Microbial

Growth on Soil Animal Faeces II—Bacterial and Fungal

Growth on Soil Animal Faeces,” Pedobiologia, Vol. 21,

1981, pp. 264-270.

[34] M. J. Schroeder and C. C. Buck, “Fire Weather—A Guide

for Application of Meteorological Information to Forest

Fire Control Operations,” US Department of Agriculture

Forest Service, Washington DC, 1979.

[35] T. Gunnarsson, P. Sundin and A. Tunlid, “Importance of

Leaf Litter Fragmentation for Bacterial Growth,” Oikos,

Vol. 52, 1988, pp. 303-308. doi:10.2307/3565203

[36] T. Gorbacheva and R. Kikuchi, “Plant-to-Soil Pathways

in the Subarctic—Qualitative and Quantitative Changes

of Different Vegetative Fluxes,” Environmental Biotech-

nology, Vol. 2, No. 1, 2006, pp. 26-30.