Mycorrhizal Responses To Biochar In Soil – Concepts And Mechanisms

  • Thread starter jumpincactus
  • Start date
  • Tagged users None
jumpincactus

jumpincactus

Premium Member
Supporter
11,609
438
Daniel D. Warnock & Johannes Lehmann &
Thomas W. Kuyper & Matthias C. Rillig

Received: 19 April 2007 /Accepted: 9 August 2007 / Published online: 19 September 2007
# Springer Science + Business Media B.V. 2007

Responsible Editor: Hans Lambers.
D. D. Warnock : M. C. Rillig
Microbial Ecology Program,
Division of Biological Sciences, University of Montana,
Missoula, MT 59812, USA
J. Lehmann
Department of Crop and Soil Sciences, Cornell University,
Ithaca, NY 14853, USA
T. W. Kuyper
Department of Soil Quality, Wageningen University,
P.O. Box 47, 6700 AA Wageningen, The Netherlands
M. C. Rillig (*)
Institut für Biologie, Freie Universität Berlin,
Altensteinstr. 6, 14195 Berlin, Germany
e-mail: [email protected]-berlin.de

Link for graphs and tables: http://www.css.cornell.edu/faculty/lehmann/publ/PlantSoil 300, 9-20, 2007, Warnock.pdf

Abstract
Experiments suggest that biomass-derived
black carbon (biochar) affects microbial populations
and soil biogeochemistry. Both biochar and mycorrhizal
associations, ubiquitous symbioses in terrestrial
ecosystems, are potentially important in various
ecosystem services provided by soils, contributing to
sustainable plant production, ecosystem restoration,
and soil carbon sequestration and hence mitigation of
global climate change. As both biochar and mycorrhizal
associations are subject to management, understanding
and exploiting interactions between them
could be advantageous. Here we focus on biochar
effects on mycorrhizal associations. After reviewing
the experimental evidence for such effects, we critically
examine hypotheses pertaining to four mechanisms by
which biochar could influence mycorrhizal abundance
and/or functioning. These mechanisms are (in decreasing
order of currently available evidence supporting
them): (a) alteration of soil physico-chemical properties;
(b) indirect effects on mycorrhizae through effects
on other soil microbes; (c) plant–fungus signaling
interference and detoxification of allelochemicals on
biochar; and (d) provision of refugia from fungal
grazers. We provide a roadmap for research aimed at
testing these mechanistic hypotheses.

Keywords Biochar. Arbuscular mycorrhiza .
Ectomycorrhiza . Carbon storage . Restoration .
Terra preta

Introduction
Pioneering studies, conducted primarily in Japan,
where biochar application to soil has a long tradition
(Ishii and Kadoya 1994), provided evidence that
biochar can have positive effects on the abundance
of mycorrhizal fungi (Table 1). Soil micro-organisms,
especially arbuscular mycorrhizal fungi (AMF), in
addition to ectomycorrhizal fungi (ECM) and ericoid
mycorrhizal fungi (ERM), have well-recognized roles
in terrestrial ecosystems (Zhu and Miller 2003; Rillig
2004; Read et al. 2004; Rillig and Mummey 2006).
Mycorrhizal fungi are frequently included in management,
since they are widely used as soil inoculum
additives (Schwartz et al. 2006). With both biochar
additions and mycorrhizal abundance subject to
management practices, there clearly are opportunities
for exploiting a potential synergism that could
positively affect soil quality.
While data on biochar effects on mycorrhiza are
accumulating, there are several important gaps in our
knowledge on these interactions. The most important
gap concerns the mechanisms by which biochar might
affect the abundance and functioning of mycorrhizal
fungi. Therefore, the goals of this paper are to first
evaluate the evidence of biochar effects on mycorrhizal
associations thus far, and then to propose
mechanisms for these biochar effects on mycorrhizae
(primarily using examples of arbuscular mycorrhiza
and ectomycorrhiza). In doing so, we also point out
future research priorities (Fig. 1). To clarify the
nomenclature used throughout this discussion we first
provide a brief overview of biochar properties.
Biochar definition and properties
Biochar is a term reserved for the plant biomassderived
materials contained within the black carbon
(BC) continuum. This definition includes chars and
charcoal, and excludes fossil fuel products or geogenic
carbon (Lehmann et al. 2006). Materials
forming the BC continuum are produced by partially
combusting (charring) carbonaceous source materials,
e.g. plant tissues (Schmidt and Noack 2000; Preston
and Schmidt 2006; Knicker 2007), and have both
natural as well as anthropogenic sources. Restricting
the oxygen supply during combustion can prevent
complete combustion (e.g., carbon volatilization and
ash production) of the source materials. When plant
tissues are used as raw materials for biochar production,
heat produced during combustion volatilizes a
significant portion of the hydrogen and oxygen, along
with some of the carbon contained within the plant’s
tissues (Antal and Gronli 2003; Preston and Schmidt
2006). The remaining carbonaceous materials contain
many poly-aromatic (cyclic) hydrocarbons, some of
which may contain functional groups with oxygen or
hydrogen (Schmidt and Noack 2000; Preston and
Schmidt 2006). Depending on the temperatures
reached during combustion and the species identity
of the source material, a biochar’s chemical and
physical properties may vary (Keech et al. 2005;
Gundale and DeLuca 2006). For example, coniferous
biochars generated at lower temperatures, e.g. 350°C,
can contain larger amounts of available nutrients,
while having a smaller sorptive capacity for cations
than biochars generated at higher temperatures, e.g.
800°C (Gundale and DeLuca 2006). Furthermore,
plant species with many large diameter cells in their
stem tissues can lead to greater quantities of macropores
in biochar particles. Larger numbers of macropores
can for example enhance the ability of biochar
to adsorb larger molecules such as phenolic compounds
(Keech et al. 2005).
Because of its macromolecular structure dominated
by aromatic C, biochar is more recalcitrant to
microbial decomposition than uncharred organic
matter (Baldock and Smernik, 2002). Biochar is
believed to have long mean residence times in soil,
ranging from 1,000 to 10,000 years, with 5,000 years
being a common estimate (Skjemstad et al. 1998;
Swift 2001; Krull et al. 2003). However, its recalcitrance
and physical nature represent significant
obstacles to the quantification of long-term stability
(Lehmann 2007).

Evidence for biochar effects on mycorrhizal fungi
From the experiments summarized in Table 1, it
appears that the addition of biochar materials to soil
often results in significant responses by both plants
and mycorrhizal fungi.
Tryon (1948), Matsubara et al. (2002), DeLuca et
al. (2006), and Gundale and DeLuca (2006) demonstrated
that biochar additions can change soil nutrient
availability by affecting soil physico-chemical properties.
Increases in soil nutrient availability may result
in enhanced host plant performance and elevated
tissue nutrient concentrations in addition to higher
colonization rates of the host plant roots by AMF
(Ishii and Kadoya 1994). Lastly, experiments by
Matsubara et al. (2002) suggested that biochar can
also increase the ability of AMF to assist their host in
resisting infection by plant pathogens.
In three of the six ECM studies and the single
ERM study represented in Table 1, experiments
demonstrated the effects of adding biochar in growth
media on both the ability of the ECM and ERM fungi
to colonize the host plant seedlings, and the overall
effects on seedling growth. Additionally, the experiment
conducted by Herrmann et al. (2004) showed
that activated carbon (AC), which may in many cases
have similar properties as biochar, affected the timing
of host plant colonization by ECMF, which occurred
4 weeks earlier in the AC treatment than in the
control. The other ECM related experiments evaluated
the effects of biochar presence on host tree colonization
rates (Harvey et al. 1976; Mori and Marjenah
1994). In these two cases, the presence of biochar
corresponded with significant increases in plant root
colonization by ECM. Observations made by Harvey
et al. (1978, 1979) also support these results.
In contrast to those experiments in Table 1 showing
positive effects of biochar or AC additions on
abundance of mycorrhizal fungi, a few studies
observed negative effects. In these cases, it appears
that the negative effects of the biochar or AC additions
on AMF were largely due to nutrient effects. For
example, Gaur and Adholeya (2000) found that the
biochar media limited the amount of P taken up by
host plants, compared to rates from plants grown in
river sand or clay-brick granules, suggesting that P
was less available. Additionally, Wallstedt et al. (2002)
reported decreases in both bio-available organic
carbon and nitrogen in their ectomycorrhizal system.
An important consideration pertains to the study
design of the experiments reported in Table 1. The
first issue deals with the soils used in the experiments,
e.g. river sand or OM-rich field soil; the other issue
concerns the materials added to these soils as controls,
e.g. organic matter vs biochar. Are soil biota,
including mycorrhizal fungi, responding to an experimental
addition of biochar simply because carbon is
being added or are they responding to biochar’s
unique properties? In at least two cases where data
from field soils were presented, it appears that
mycorrhizal fungi responded more positively to
biochar additions than to additions of other types of
organic material added as control (Harvey et al. 1976;
Ishii and Kadoya 1994). The experiment by Matsubara
et al. (2002) showed that a fresh organic amendment
had fairly similar effects as biochar in increasing AMFmediated
host plant resistance against Fusarium and
Plant Soil (2007) 300:9–20 13that the asparagus plants reached similar mycorrhizal
colonization levels with both additions. But the 9-week
gap between inoculation with AMF and with Fusarium
makes this aspect of the experiment somewhat difficult
to evaluate. However, it is still possible that these
positive responses shown by mycorrhizal fungi are
determined in part by the amount of carbon in the
material being added to the soil, with the expectation
that the biochar is more carbon-rich than the organic
matter. We may not be able to answer this question
satisfactorily until experiments control for C amendment
effects in the biochar treatment(s) and/or take into
account the relative addition of C to soils.
Work on terra preta de índio (TP) soil, the fertile
Amazonian Dark Earths, has served as a major
inspiration for the use of biochar as a promising soil
additive promoting crop growth and carbon storage
(Glaser et al. 2002; Glaser and Woods 2004;
Lehmann et al. 2006; Glaser 2007). However, no
published data are available on the impact of TP soils
on mycorrhizal functioning. For that reason, the
studies discussed above refer to short-term experiments
and not to the historical, pre-Columbian
Amazonian soils. TP soils are not only much richer
in biochar than the surrounding soils, but also in nonpyrogenic
carbon and nutrients, especially phosphorus
and calcium; therefore it is likely that TP effects
on mycorrhizal functioning could be beyond those of
biochar addition alone.
Mechanisms
At least four mechanisms could explain how biochar
can lead to altered total abundance and/or activity of
mycorrhizal fungi in soils and plant roots: (1) Biochar
additions to soil result in altered levels of nutrient
availability and/or other alterations in soil physicochemical
parameters that have effects on both plants
and mycorrhizal fungi. (2) Additions of biochar to
soils result in alterations with effects that are
beneficial or detrimental to other soil microbes, for
instance mycorrhization helper bacteria (MHB) or
phosphate solubilizing bacteria (PBS). (3) Biochar in
soils alters plant–mycorrhizal fungi signaling processes
or detoxifies allelochemicals leading to altered root
colonization by mycorrhizal fungi. (4) Biochar serves
as a refuge from hyphal grazers. Since a primary goal
of this discussion is identifying mechanisms explaining
the effects of biochar on mycorrhizae, with the
intention of guiding attempts for developing methods
to exploit them as soil management tools, and because
many of the biochar effects included in Table 1 appear
positive, we primarily present arguments explaining why
biochar generally appears beneficial to mycorrhizae.
However, as discussed previously, biochar applications
do not always benefit mycorrhizal fungi (see
Table 1). In these situations, one could argue that
biochar, via any of our proposed mechanisms, reduces
formation of mycorrhiza, e.g. by decreasing nutrient
availability or creating unfavourable nutrient ratios in
soils (Wallstedt et al. 2002). This negative effect
could be especially prominent in cases where the
biochar has a very high C/N ratio and a portion of the
biochar is decomposable, leading to N-immobilization.
Under such conditions, biochar could also
negatively affect plant growth, e.g. as seen in Gaur
and Adholeya (2000). Given the above possibilities
for negative responses by both plants and mycorrhizal
fungi to biochar amendments, and plants to mycorrhizal
fungi (Johnson 1993), it cannot be assumed that
biochar amendments will always result in a net
benefit to plant productivity even though few such
cases have been reported so far.
A conceptual overview of the mechanisms and
hypothesized pathways discussed in the following
sections is provided in Fig. 1, emphasizing the
hierarchical nature of contributing factors. In the
following discussion it should be kept in mind that
(a) mechanisms are not mutually exclusive but likely
several contribute to the outcome, perhaps even with
opposite effects; (b) there is little information available
on which mechanism is likely the most important
in any given environmental situation; and finally that
(c) many mechanisms are hypothetical with most
support for mechanism 1 at this time (we are
presenting mechanisms below in decreasing amount
of evidence). This figure therefore also serves as a
roadmap for future research.
Mechanism 1: Biochar changes soil nutrient
availability
Modifications of nutrient availability would clearly be
a mechanism of primary importance for mycorrhizal
fungal abundance. For example, nutrient additions
might alleviate growth limitations of the fungi
14 Plant Soil (2007) 300:9–20themselves in nutrient-poor soils (Treseder and Allen
2002). Additionally, altering the balance of nutrients
can exert strong control over fungal root colonization,
as for example known for shifts in soil N/P ratios for
AMF (Miller et al. 2002).
Biochar addition can result in elevated quantities of
bio-available nutrients such as N, P and metal ions, in
the affected soils (Tryon 1948; Lehmann et al. 2003;
Gundale and DeLuca 2006; DeLuca et al. 2006), but
has also been shown to lead to decreases particularly
of N availability (Lehmann et al. 2003). These
changes in soil nutrient availabilities, may be
explained by some of the following observations.
Additions of biochar to soil alters important soil
chemical and physical (see below) properties such as
pH (has caused both increases and decreases), and
typically increase soil cation exchange capacity
(CEC), and can lead to greater water holding capacity
(WHC), while generally decreasing bulk density
(Tryon 1948). Increases in soil pH towards neutral
values (Lucas and Davis 1961), in addition to
increased CEC (Glaser et al. 2002), may result in
increases in bio-available P and base cations in
biochar influenced soils. Additionally, Lehmann et
al. (2003), Topoliantz et al. (2005), Gundale and
DeLuca (2006) and Yamato et al. (2006) showed that
biochar itself contained small amounts of nutrients
that would be available to both soil biota (including
mycorrhizal fungi) and plant roots. Lastly, DeLuca et
al. (2006) showed that biochar from forest wildfire
stimulated gross and net nitrification rates, most likely
mediated by biochar adsorbing inhibitory phenols.
This mechanism is likely specific to soils with
ectomycorrhizal trees and/or ericaceous shrubs with
an abundance of phenolic compounds, whereas in
agricultural soils biochar may in the short term reduce
ammonification and nitrification by a reduction either
in N availability due to immobilization during initial
decomposition of the N-poor biochar (Lehmann et al.
2006) or by a reduction in C cycling.
Some of the experiments conducted to evaluate
the effects of biochar upon mycorrhizae (Table 1)
lend support to mechanism 1. These experiments
show that additions of biochar materials generally
result in the alteration of soil physico-chemical
properties that may lead to increases in soil nutrient
availability (measurements taken from both soil
samples and plant tissues) and/or increases in root
colonization by mycorrhizal fungi (Ishii and Kadoya
1994; Matsubara et al. 2002; Yamato et al. 2006). In a
greenhouse experiment by Matsubara et al. (2002),
the soil pH of treatments receiving biochar increased
from 5.4 to 6.2 (10% biochar by volume) and 6.3
(30% biochar by volume). According to Lucas and
Davis (1961), these pH values fall within the pH
range (5.5 to 7.0) where plant nutrients are near their
maximum availability in agricultural soils. Many of
these alterations in soil characteristics probably occur
at a micro-scale (Gundale and DeLuca 2006), and thus
may only affect hyphae that are in the immediate
vicinity of biochar particles.
Mechanism 2: Biochar alters the activity of other
micro-organisms that have effects on mycorrhizae
Mycorrhization Helper Bacteria (MHB; Garbaye 1994)
are capable, under specific conditions, of secreting
metabolites, e.g. flavonoids (AMF) and furans (ECM),
that facilitate the growth of fungal hyphae and the
subsequent colonization of plant roots by ECM
(Founoune et al. 2002; Duponnois and Plenchette
2003; Aspray et al. 2006; Riedlinger et al. 2006) and
AM fungi (Duponnois and Plenchette 2003; Hildebrandt
et al. 2002, 2006). Hildebrandt et al. (2002, 2006) have
demonstrated that certain compounds (including raffinose
and other unidentified metabolites) produced by
strains of Paenibacillus can directly enhance the
growth of AMF extraradical mycelium. Additionally,
Kothamasi et al. (2006) demonstrated that other species
of bacteria, such as Pseudomonas aeruginosa, can
solubilize important plant nutrients, especially phosphate,
making them part of a group of bacteria called
phosphate solubilizing bacteria (PSB). These mineralized
nutrients are then accessible to mycorrhizal fungi
and eventually to the host plant. Furthermore, Xie et al.
(1995) and Cohn et al. (1998) state that Rhizobium sp.
and Bradyrhizobium sp. can produce compounds that
induce flavonoid production in nearby plants (legumes)
that may ultimately increase root colonization of plant
roots by AM fungi.
Biochar may serve as a source of reduced carbon
compounds (either the biochar particle itself, or organic
molecules adsorbed to the particle’s matrix), and/or
nutrients, and as a refuge (see mechanism 4) for any
biochar colonizing soil bacteria, including MHB and
PSBs (Pietikäinen et al. 2000; Samonin and Elikova
2004). Increased populations of PSB and/or MHB
might then indirectly benefit mycorrhizal fungi (Fig. 1).
Plant Soil (2007) 300:9–20 15Mechanism 3: Biochar alters the signaling dynamics
between plants and mycorrhizal fungi or detoxifies
allelochemicals
The rhizosphere is a zone of intense signaling
between microbes, including mycorrhizal fungi, and
plant roots (Bais et al. 2004; Harrison 2005; Bais et
al. 2006; Paszkowski 2006). For example, experiments
conducted using both field soils and in vitro cultures
show that compounds (e.g. CO2, flavonoids, sesquiterpenes
and strigolactones) secreted by plant roots lead to
both increased colonization of plant roots by AMF
(Bécard and Piché 1989; Nair et al. 1991; Xie et al.
1995) and increased spore germination and AMF hyphal
branching (Gianinazzi-Pearson et al. 1989; Akiyama et
al. 2005). Additions of biochar could alter the exchange
of signals in several ways, as shown in Fig. 1; however,
we emphasize that most of the pertinent evidence stems
from sterile in vitro culture studies with uncertain
relevance to conditions in the soil.
Angelini et al. (2003) demonstrated that some
flavonoid signaling compounds could be either
inhibitory or stimulatory to specific groups of soil
biota as a function of pH. As discussed under
mechanism 1, biochar additions usually increase soil
pH. Hence, it is possible that these pH changes alone
can lead to stimulatory effects, causing increases in
fungal abundance.
Sorptive properties of biochar (e.g. for hydrophobic
substances), particularly higher temperature (e.g.,
800°C) biochar, could also cause signaling interference
in the rhizosphere: biochar could serve as signal
reservoirs or as a sink, both for signaling compounds
and for inhibitory compounds (allelochemicals). Recently,
Akiyama et al. (2005) demonstrated that AC
was capable of adsorbing AMF signaling (strigolactones)
compounds from a hydroponic solution that
were subsequently desorbable with acetone. Once
desorbed, these compounds retained their activity and
stimulate hyphal branching and growth of Gigaspora
margarita. Biochar particles could adsorb signal
molecules not immediately intercepted by AMF
hyphae or spores, or consumed by other soil biota.
Later on, these stored signal molecules could be
desorbed by soil water reaching the biochar particles.
After being re-dissolved into soil water, they would
again be available to stimulate mycorrhizal colonization
of plant roots. By functioning in this manner,
biochar particles would be serving as secondary
sources of signal molecules, acting concomitantly
with MHB and plant roots.
However, biochar’s capacity to adsorb signaling
compounds and add as a sink could also decrease the
ability of mycorrhizal fungi to colonize plant roots. If
biochar permanently rather than temporarily removes
signal molecules from soils, this signal sorption
activity results in a net decrease in the number of
signal molecules reaching mycorrhizal hyphae and
spores. As a result, hyphal growth and spore germination,
and ultimately fungal abundance, could actually
decrease because of biochar activity.
In addition to chemical signals, biochar may also
adsorb compounds toxic to mycorrhizal fungi. For
example, Wallstedt et al. (2002) showed that the
addition of an AC slurry to an experimental soil
resulted in a decreased amount of water-soluble
phenols. Herrmann et al. (2004) and Vaario et al.
(1999) related their results of stimulated ECM fungus
colonization of roots in the presence of AC to toxin
sorption.
Mechanism 4: Biochar serves as a refuge
for colonizing fungi and bacteria
This mechanism is purely physical in nature, and
therefore could function in a similar fashion for ECM,
ERM, AMF and bacteria. Hyphae and bacteria that
colonize biochar particles (or other porous materials)
may be protected from soil predators (Saito 1990;
Pietikäinen et al. 2000; Ezawa et al. 2002), which
includes mites, collembola and larger (>16 μm in
diameter) protozoans and nematodes. The documented
physical parameters of the biochar particles
themselves make this mechanism plausible. The
average sizes of soil bacteria and fungal hyphae range
from 1 to 4 μm and 2 to 64 μm, respectively, with
many fungal hypha being smaller than 16 μm in
diameter (Swift et al. 1979). Additionally, the average
body-size of a soil protist is between 8 to 100 μm,
while the average body size of soil micro-arthropods
ranges from 100 μm to 2 mm (Swift et al. 1979). In
contrast, the pore diameters in a biochar particle can
often be smaller than 16 μm in diameter (Kawamoto
et al. 2005; Glaser 2007; Hockaday et al. 2007).
Based on the differences in the body sizes across
these different organisms, it is clearly possible that
many of the pores within a biochar particle are large
enough to accommodate soil microorganisms, includ-
16 Plant Soil (2007) 300:9–20ing most bacteria and many fungi, to the exclusion of
their larger predators. Thus, the biochar would be
acting as a refuge for MHB, PSB and mycorrhizal
fungi. Supporting evidence for this hypothesis comes
from Saito (1990), Gaur and Adholeya (2000) and
Ezawa et al. (2002) who all showed that AMF readily
colonize porous materials and were capable of heavily
colonizing biochar particles in the soil. Lastly,
Pietikäinen et al. (2000) and Samonin and Elikova
(2004) showed that bacteria readily colonized biochar
particles; these may include MHB and/or PSB.
An important factor controlling pore size distribution
is the charring temperature with higher temperatures
yielding finer pores. Another major factor in determining
the degree to which biochar may serve as a refuge is the
anatomical structure of the biological tissues pyrolyzed
to yield the biochar. Considering the effects that cell
diameter alone can have on the sorptive capability of a
given biochar material (Keech et al. 2005; Gundale and
DeLuca 2006), it stands to reason that the cell types
contained within the original plant tissues (e.g.,
tracheids, vessel elements or sieve cells) determine the
pore sizes of the biochar. Not only the charring
conditions and source material, but also subsequent
interactions of biochar with soil can change porosity
and pore sizes. For example, adsorption of organic
matter to biochar surfaces can decrease porosity by
blocking pores (Kwon and Pignatello 2005).
While it seems clear that mycorrhizal fungi can use
biochar as a habitat, the quantitative importance to the
extraradical mycelium is not evident. This will highly
depend on the biochar properties and the biochar
addition rates. Nevertheless, the finer parts of the
mycelium, generally the absorptive hyphae, are more
vulnerable to fungal grazers (Klironomos and Kendrick
1996), and it is primarily these architectural elements
that could be effectively protected within biochar
particles. It would depend, then, on the extent to which
these ‘protected’ fine hyphae make a substantial
contribution towards nutrient uptake compared to the
relatively ‘unprotected’ hyphae in the mineral and
organic soil, whether this hypothesized mechanism is
quantitatively important.
Conclusions and research recommendations
Experimental results (Table 1) point to exciting
possibilities regarding biochar and its possible synergy
with arbuscular, ericoid, and ectomycorrhizal
symbioses. We have synthesized available data into
several potential mechanisms of biochar effects on
mycorrhizae (Fig. 1). This should serve as a springboard
for testing the occurrence and relative importance
of these factors/mechanisms in the soil. Based
on this discussion we derive the following research
recommendations:
(a) Methods reporting. In many cases it is helpful to
know as much detail about the experimental
biochar application as possible. This should include:
source material, production temperature,
application rate, application method, and what
material was used in the control application to
account for C addition effects (and the amounts of
available nutrients for both). This would facilitate
comparisons among studies and help distinguish
among the different mechanistic pathways; frequently
these pieces of information are incomplete.
(b) Management implications. None of the studies to
date have examined the management context of
biochar application on AMF, and this would also be
an important research need, since application
practices could have overriding effects on soil biota.
(c) Fungal communities. Studies to date have focused
on quantifying potential responses in fungal abundance
measures, primarily root colonization and
spore numbers (see Table 1). However, mycorrhizal
fungi occur as species assemblages in ecosystems
and in roots of individual plants (Johnson et
al. 1992; Husband et al. 2002; Vandenkoornhuyse
et al. 2003; Mummey et al. 2005). The species
composition of a mycorrhizal fungal assemblage
can be important to mycorrhizal functioning (e.g.,
van der Heijden et al. 1998). Data on this
important aspect of the response of mycorrhizal
fungi to biochar are not yet available, but represent
an important priority for future studies. Here, we
limited our discussion to mechanisms affecting
abundance; however, many of the arguments
presented could also be applied to explain potential
shifts in mycorrhizal fungal species composition,
because fungal life history strategies and
responsiveness to changing soil environments vary
between fungal taxa (e.g., Hart and Reader 2002;
Escudero and Mendoza 2005; Drew et al. 2006).
(d) Negative effects. There is a potential for negative
effects on mycorrhizal fungi, as discussed above;
Plant Soil (2007) 300:9–20 17it is therefore clearly also a research priority to
define the environmental circumstances (e.g., soil
nutrient content, plants species) and biochar
parameters (e.g., quality and application rate) that
lead to such effects. It is possible that negative or
neutral effects have been under-reported.
Increasing atmospheric concentrations of carbon
dioxide have prompted the search for avenues of
long-term sequestration of carbon, particularly in the
soil (Lal 2004; Schiermeier 2006). Work on terra
preta de índio soil has inspired the use of biochar as a
promising soil additive promoting carbon storage
(Day et al. 2005; Lehmann et al. 2006; Marris 2006;
Glaser 2007). Biochar can add value to non-harvested
agricultural products (Major et al. 2005; Topoliantz et
al. 2005), and can promote plant growth (Lehmann et
al. 2003; Oguntunde et al. 2004). Lehmann et al.
(2006) estimated that a total of 9.5 billion tons of
carbon could potentially be stored in soils by the year
2100 using a wide variety of biochar application
programs. Once equipped with a better understanding
of this potential synergism and the mechanisms that
drive it, we could utilize biochar/mycorrhizae interactions
for sequestration of carbon in soils to
contribute to climate change mitigation. This interaction
could also be harnessed for the restoration of
disturbed ecosystems, the reclamation of sites contaminated
by industrial pollution and mine wastes,
increasing fertilizer use efficiencies (with all associated
economic and environmental benefits) and the
development of methods for attaining increased crop
yields from sustainable agricultural activities.

References
Akiyama K, Matsuzaki K-I, Hayashi H (2005) Plant sesquiterpenes
induce hyphal branching in arbuscular mycorrhizal
fungi. Nature 435:824–827
Angelini J, Castro S, Fabra A (2003) Alterations in root
colonization and nodC gene induction in the peanutrhizobia
interaction under acidic conditions. Plant Physiol
Biochem 41:289–294
Antal MJ Jr, Grønli M (2003) The art, science, and technology of
charcoal production. Indust Engin Chem Res 42:1619–1640
Aspray TJ, Eirian Jones E, Whipps JM, Bending GD (2006)
Importance of mycorrhization helper bacteria cell density
and metabolite localization for the Pinus sylvestris–
Lactarius rufus symbiosis. FEMS Microbiol Ecol 56:25–33
Bais HP, Park SW, Weir TL, Callaway RM, Vivanco JM (2004)
How plants communicate using the underground information
superhighway. Trends Plant Sci 9:26–32
Bais HP, Weir TL, Perry LG, Gilroy S, Vivanco JM (2006) The
role of root exudates in rhizosphere interactions with plants
and other organisms. Annu Rev Plant Biol 57:233–266
Baldock JA, Smernik RJ (2002) Chemical composition and
bioavailability of thermally altered Pinus resinosa (Red
pine) wood. Organic Geochem 33:1093–1109
Bécard G, Piché Y (1989) Fungal growth stimulation by CO2
and root exudates in vesicular–arbuscular mycorrhizal
symbiosis. Appl Environ Microb 55:2320–2325
Cohn J, Bradley D, Stacey G (1998) Legume nodule organogenesis.
Trends Plant Sci 3:105–110
Day D, Evans RJ, Lee JW, Reicosky D (2005) Economical
CO2, SOx, and NOx capture from fossil-fuel utilization
with combined renewable hydrogen production and largescale
carbon sequestration. Energy 30:2558–2579
DeLuca TH, MacKenzie MD, Gundale MJ, Holben WE (2006)
Wildfire-produced charcoal directly influences nitrogen
cycling in ponderosa pine forests. Soil Sci Soc Am J 70:
448–453
Drew EA, Murray RS, Smith SE (2006) Functional diversity of
external hyphae of AM fungi: ability to colonize new
hosts is influenced by fungal species, distance and soil
conditions. Appl Soil Ecol 32:350–365
Duclos JL, Fortin JA (1983) Effect of glucose and active
charcoal on in-vitro synthesis of ericoid mycorrhiza with
Vaccinium spp. New Phytol 94:95–102
Duponnois R, Plenchette C (2003) A mycorrhiza helper
bacterium enhances ectomycorrhizal and endomycorrhizal
symbiosis of Australian Acacia species. Mycorrhiza 13:
85–91
Escudero V, Mendoza RE (2005) Seasonal variation of
arbuscular mycorrhizal fungi in temperate grasslands
along a wide hydrologic gradient. Mycorrhiza 15:291–299
Ezawa T, Yamamoto K, Yoshida S (2002) Enhancement of the
effectiveness of indigenous arbuscular mycorrhizal fungi by
inorganic soil amendments. Soil Sci Plant Nutr 48:897–900
Founoune H, Duponnois R, Bâ AM, Sall S, Branget I, Lorquin
J, Neyra M, Chotte JL (2002) Mycorrhiza Helper Bacteria
stimulate ectomycorrhizal symbiosis of Acacia holosericea
with Pisolithus. New Phytol 153:81–89
Garbaye J (1994) Helper bacteria: a new dimension to the
mycorrhizal symbiosis. New Phytol 128:197–210
Gaur A, Adholeya A (2000) Effects of the particle size of soilless
substrates upon AM fungus inoculum production.
Mycorrhiza 10:43–48
Gianinazzi-Pearson V, Branzanti B, Gianinazzi S (1989) In
vitro enhancement of spore germination and early hyphal
growth of a vesicular–arbuscular mycorrhizal fungus by
host root exudates and plant flavonoids. Symbiosis 7:
243–255
Glaser B (2007) Prehistorically modified soils of central
Amazonia: a model for sustainable agriculture in the
twenty-first century. Phil Trans R Soc B 362:187–196
Glaser B, Lehmann J, Zech W (2002) Ameliorating physical
and chemical properties of highly weathered soils in
the tropics with charcoal – a review. Biol Fert Soils 35:
219–230
Glaser B, Woods W (2004) Towards an understanding of
amazon dark earths. In: B Glaser, W Woods (eds)Amazon
dark earths: explorations in space and time. Springer,
Berlin, pp 1–8
18 Plant Soil (2007) 300:9–20Gundale MJ, DeLuca TH (2006) Temperature and source
material influence ecological attributes of Ponderosa pine
and Douglas-fir charcoal. For Ecol Manag 231:86–93
Harrison MJ (2005) Signaling in the arbuscular mycorrhizal
symbiosis. Annu Rev Microbiol 59:19–42
Hart MM, Reader RJ (2002) Taxonomic basis for variation in
the colonization strategy of arbuscular mycorrhizal fungi.
New Phytol 135:335–344
Harvey AE, Jurgensen MF, Larsen MJ (1976) Comparative
distribution of ectomycorrhizae in a mature Douglas-fir/
Larch forest soil in western Montana. Forest Sci 22:350–358
Harvey AE, Jurgensen MF, Larsen MJ (1978) Seasonal
distribution in a mature Douglas-fir/Larch forest soil in
western Montana. Forest Sci 22:203–208
Harvey AE, Larsen MF, Jurgensen MF (1979) Comparative
distribution of ectomycorrhizae in soils of three western
Montana forest habitat types. Forest Sci 25:350–358
Herrmann S, Oelmuller R, Buscot F (2004) Manipulation of the
onset of ectomycorrhiza formation by indole-3-acetic acid,
activated charcoal or relative humidity in the association
between oak micro-cuttings and Piloderma croceum:
influence on plant development and photosynthesis. J
Plant Physiol 161:509–517
Hildebrandt U, Janetta, K, Bothe H (2002) Towards growth of
arbuscular mycorrhizal fungi independent of a plant host.
Appl Environ Microb 68:1919–1924
Hildebrandt U, Ouziad F, Marner F-J, Bothe H (2006) The
bacterium Paenibacillus validus stimulates growth of the
arbuscular mycorrhizal fungus Glomus intraradices up to
the formation of fertile spores. FEMS Microbiol Lett 254:
258–267
Hockaday WC, Grannas AM, Kim S, Hatcher PG (2007) The
transformation and mobility of charcoal in a fire-impacted
watershed. Geochim Cosmochim Ac 71:3432–3445
Husband R, Herre EA, Turner SL, Gallery R, Young JPW
(2002) Molecular diversity of arbuscular mycorrhizal
fungi and patterns of host association over time and space
in a tropical forest. Mol Ecol 11:2669–2678
Ishii T, Kadoya K (1994) Effects of charcoal as a soil
conditioner on citrus growth and vesicular–arbuscular mycorrhizal
development. J Jpn Soc Hortic Sci 63:529–535
Johnson NC, Tilman D, Wedin D (1992) Plant and soil controls
on mycorrhizal fungal communities. Ecology 73:2034–2042
Johnson NC (1993) Can fertilization of soil select less
mutualistic mycorrhizae?. Ecol Appl 3:749–757
Kawamoto K, Ishimaru K, Imamura Y (2005) Reactivity of
wood charcoal with ozone. Wood Sci 51:66–72
Keech O, Carcaillet C, Nilsson MC (2005) Adsorption of
allelopathic compounds by wood-derived charcoal: the
role of wood porosity. Plant Soil 272:291–300
Klironomos JN, Kendrick WB (1996) Palatability of microfungi
to soil arthropods in relation to the functioning of
arbuscular mycorrhizae. Biol Fert Soils 21:43–52
Knicker H (2007) How does fire affect the nature and stability
of soil organic nitrogen and carbon? A review. Biogeochemistry
85:91–118
Kothamasi D, Kothamasi S, Bhattacharyya A, Kuhad RC, Babu
CR (2006) Arbuscular mycorrhizae and phosphate solubilising
bacteria of the rhizosphere of the mangrove
ecosystem of Great Nicobar island, India. Biol Fert Soils
42:358–361
Krull ES, Skjemstad JO, Graetz D, Grice K, Dunning W, Cook
G, Parr JF (2003) 13C-depleted charcoal from C4 grasses
and the role of occluded carbon in phytoliths. Org
Geochem 34:1337–1352
Kwon S, Pignatello JJ (2005) Effect of natural organic
substances on the surface and adsorptive properties of
environmental black carbon (char): pseudo pore blockage
by model lipid components and its implications for N2-
probed surface properties of natural sorbents. Env Sci
Technol 39:7932–7939
Lal R (2004) Soil carbon sequestration to mitigate climate
change. Geoderma 123:1–22
Lehmann J (2007) Bio-energy in the black. Frontiers in
Ecology and the Environment 5:381–387
Lehmann J, Da Silva JP Jr, Steiner C, Nehls T, Zech W, Glaser
B (2003) Nutrient availability and leaching in an archaeological
Anthrosol and a Ferralsol of the Central Amazon
basin: fertilizer, manure and charcoal amendments. Plant
Soil 249:343–357
Lehmann J, Gaunt J, Rondon M (2006) Biochar sequestration
in terrestrial ecosystems – a review. Mitig Adapt Strat
Global Change 11:403–427
Lucas RE, Davis JF (1961) Relationships between pH values of
organic soils and availabilities of 12 plant nutrients. Soil
Sci 92:177–182
Major J, Steiner C, Ditommaso A, Falcão NP, Lehmann J
(2005) Weed composition and cover after three years of
soil fertility management in the central Brazilian Amazon:
compost, fertilizer, manure and charcoal applications.
Weed Biol Manag 5:69–76
Marris E (2006) Black is the new green. Nature 442:624–626
Matsubara Y-I, Hasegawa N, Fukui H (2002) Incidence of
Fusarium root rot in asparagus seedlings infected with
arbuscular mycorrhizal fungus as affected by several soil
amendments. J Jpn Soc Hortic Sci 71:370–374
Miller RM, Miller SP, Jastrow JD, Rivetta CB (2002)
Mycorrhizal mediated feedbacks influence net carbon gain
and nutrient uptake in Andropogon gerardii. New Phytol
155:149–162
Mori S, Marjenah (1994) Effect of charcoaled rice husks on the
growth of Dipterocarpaceae seedlings in East Kalimantan
with special reference to ectomycorrhiza formation. J Jap
Forestry Soc 76:462–464
Mummey DL, Rillig MC, Holben WE (2005) Neighboring
plant influences on arbuscular mycorrhizal fungal community
composition as assessed by T-RFLP analysis. Plant
Soil 271:83–90
Nair MG, Safir GR, Siqueira JO (1991) Isolation and
identification of vesicular–arbuscular mycorrhiza-stimulatory
compounds from clover (Trifolium repens) roots.
Appl Environ Microb 57:434–439
Oguntunde PG, Fosu M, Ajayi AE, Van De Giesen ND (2004)
Effects of charcoal production on maize yield, chemical
properties and texture of soil. Biol Fert Soils 39:295–299
Pan MJ, Van Staden J (1998) The use of charcoal in in-vitro
culture – A review. Plant Growth Regul 26:155–163
Paszkowski U (2006) A journey through signaling in arbuscular
mycorrhizal symbioses. New Phytol 172:35–46
Pietikäinen J, Kiikkilä O, Fritze H (2000) Charcoal as a habitat
for microbes and its effect on the microbial community of
the underlying humus. Oikos 89:231–242
Plant Soil (2007) 300:9–20 19Preston CM, Schmidt MWI (2006) Black (pyrogenic) carbon:
A synthesis of current knowledge and uncertainties with
special consideration of boreal regions. Biogeosciences
3:397–420
Read DJ, Leake JR, Perez-Moreno J (2004) Mycorrhizal fungi
as drivers of ecosystem processes in heathland and boreal
forest biomes. Can J Bot 82:1243–1263
Riedlinger J, Schrey SD, Tarkka MT, Hampp R, Kapur M,
Fiedler H-P (2006) Auxofuran, a novel metabolite that
stimulates the growth of fly agaric, is produced by the
mycorrhiza helper bacterium Streptomyces strain AcH
505. Appl Environ Microb 72:3550–3557
Rillig MC (2004) Arbuscular mycorrhizae and terrestrial
ecosystem processes. Ecol Lett 7:740–754
Rillig MC, Mummey DL (2006) Mycorrhizas and soil
structure. New Phytol 171:41–53
Rondon M, Lehmann J, Ramírez J, Hurtado MP (2007)
Biological nitrogen fixation by common beans (Phaseolus
vulgaris L.) increases with biochar additions. Biol Fert
Soils 43:699–708
Saito M (1990) Charcoal as a micro habitat for VA mycorrhizal
fungi, and its practical application. Agric Ecosyst Environ
29:341–344
Samonin VV, Elikova EE (2004) A study of the adsorption of
bacterial cells on porous materials. Microbiology 73:810–816
Schiermeier Q (2006) Putting the carbon back. Nature
442:620–623
Schmidt MWI, Noack AG (2000) Black carbon in soils and
sediments: Analysis, distribution, implications and current
challenges. Global Biogeochem Cy 14:777–793
Schwartz MW, Hoeksema JD, Gehring CA, Johnson NC,
Klironomos JN, Abbott LK, Pringle A (2006) The promise
and the potential consequences of the global transport of
mycorrhizal fungal inoculum. Ecol Lett 9:501–515
Skjemstad JO, Janik LJ, Taylor JA (1998) Non-living soil
organic matter: What do we know about it? Aust. J Exp
Agr 38:667–680
Swift RS (2001) Sequestration of carbon by soil. Soil Sci
166:858–871
Swift MJ, Heal OW, Anderson JW (1979) Decomposition in
terrestrial ecosystems. University of California Press, Berkeley
Topoliantz S, Ponge J-F, Ballof S (2005) Manioc peel and
charcoal: a potential organic amendment for sustainable
soil fertility in the tropics. Biol Fert Soils 41:15–21
Treseder KK, Allen MF (2002) Direct nitrogen and phosphorus
limitation of arbuscular mycorrhizal fungi: a model and
field test. New Phytol 155:507–515
Tryon EH (1948) Effect of charcoal on certain physical,
chemical, and biological properties of forest soils. Ecol
Monogr 18:81–115
Vaario LM, Tanaka M, Ide Y, Gill WM, Suzuki K (1999) In
vitro ectomycorrhiza formation between Abies firma and
Pisolithus tinctorius. Mycorrhiza 9:177–183
Vandenkoornhuyse P, Ridgway KP, Watson IJ, Fitter AH,
Young JPW (2003) Co-existing grass species have
distinctive arbuscular mycorrhizal communities. Mol Ecol
12:3085–3095
Van der Heijden MG, Klironomos JN, Ursic M, Moutoglis P,
Streitwolf-Engel R, Boller T, Wiemken A, Sanders IR (1998)
Mycorrhizal fungal diversity determines plant biodiversity,
ecosystem variability and productivity. Nature 396:69–72
Wallstedt A, Coughlan A, Munson AD, Nilsson MC, Margolis
HA (2002) Mechanisms of interaction between Kalmia
angustifolia cover and Picea mariana seedlings. Can J For
Res 32:2022–2031
Xie Z-P, Staehelin C, Vierheilig H, Wiemken A, Jabbouri S,
Broughton WJ, Vogeli-Lange R, Boller T (1995) Rhizobial
nodulation factors stimulate mycorrhizal colonization
of nodulating and nonnodulating soybeans. Plant Physiol
108:1519–1525
Yamato M, Okimori Y, Wibowo IF, Anshiori S, Ogawa M
(2006) Effects of the application of charred bark of Acacia
mangium on the yield of maize, cowpea and peanut, and
soil chemical properties in South Sumatra, Indonesia. Soil
Sci Plant Nutr 52:489–495
Zhu YG, Miller RM (2003) Carbon cycling by arbuscular
mycorrhizal fungi in soil–plant systems. Trends Plant Sci
8:407–409
 
Top Bottom