Ann. For. Sci. 64 (2007) 765–772
c INRA, EDP Sciences, 2007
DOI: 10.1051/forest:2007056
Available online at:
www.afs-journal.org
Original article
Arbuscular mycorrhizal colonization of vascular plants
from the Yungas forests, Argentina
Alejandra Ba *, Marta Cb, Franco Ca
b
a
Instituto Multidisciplinario de Biología Vegetal, CONICET-UNC. C.C. 495. 5000 Córdoba, República Argentina
Instituto Spegazzini, Facultad de Ciencias Naturales y Museo, Avenida 53, N◦ 477, 1900 La Plata, República Argentina
(Received 21 November 2006; accepted 7 June 2007)
Abstract – In Argentina, the Yungas forests are among the ecosystems most affected by human activity, with loss of biodiversity. To assess the mycorrhizal status in these ecosystems, the roots of 41 native plant species belonging to 25 families were collected throughout the year from two sites of the
Yungas forests. Roots were washed and stained to study the presence of arbuscular mycorrhizas (AM). Morphological types of arbuscular mycorrhizas
(Arum and Paris-type) and colonization patterns were identified and photographed. All plants presented AM colonization. The AM colonization patterns
varied from single intracellular aseptate hyphae, coils, appresoria, to vesicles and/or arbuscules. Among the species studied, the Paris-type colonization
showed to be dominant. Results confirmed that AM hosts are predominant in the Yungas of South American forests.
Yungas / arbuscular mycorrhizal / Arum-type / Paris-type / Alnus forests
Résumé – Colonisation par les mycorhizes arbusculaires dans des plantes vasculaires des forêts des Yungas, Argentine. En Argentine, les Yungas
constituent un des écosystèmes les plus atteints par l’activité de l’homme, avec la perte de biodiversité qui en découle. Pour évaluer le statut mycorhizien
de ces écosystèmes, les racines de 41 plantes autochtones appartenant à 25 familles ont été collectées au cours de l’année dans deux sites des forêts des
Yungas. Les racines ont été lavées et teintes afin de déterminer la présence des mycorhizes arbusculaires (MA). Les types morphologiques de MA (type
Arum et Paris) et les patrons de colonisation ont été identifiés et photographiés. Toutes les plantes ont présenté une colonisation MA. Les structures
fongiques intraracinaires comprenaient des hyphes intracellulaires sans cloison, des boucles, des appressoria, des vésicules et/ou des arbuscules. Le
type de colonisation Paris est apparu comme dominant parmi les espèces étudiées. Les résultats confirment que les hôtes avec MA prédominent dans
les forêts sudaméricaines des Yungas.
Yungas / mycorhizes arbusculaires / type Arum / type Paris / bois d’Alnus
1. INTRODUCTION
The Yungas, or Tucuman-Bolivian forests [20, 49], which
belongs to the humid subtropical South American ecosystems,
have a great regional relevance due to their high diversity [15].
However, the Yungas are among the ecosystems most affected
by human activity, with the consequent loss of biodiversity. In
order to conserve biodiversity, not only is it necessary to identify areas with high diversity of species, but it is also necessary
to preserve different areas to protect genetic and environmental variation [15].
The Yungas are located between 300 and 3000 masl [20].
Three main environmental units can be recognized: The Premontane Forest (300–600 m asl), at present almost completely
transformed into an intensive agricultural area; the Montane
Forest (600–1500 m asl), where forestry and cattle raising are
practiced, and the Montane Cloud Forest (1500–3000 m asl),
which is being replaced by anthropic grasslands for cattle raising in some sectors.
The latter environmental unit, the montane cloud forest, has been divided into three plant communities, namely,
“Podocarpus parlatorei Pilg. (Podocarpaceae) forests”, “Al* Corresponding author: abecerra@efn.uncor.edu
nus acuminata Kunth (Betulaceae) forests”, and “Sambucus
peruviana Kunth (Caprifoliaceae) and Polylepis australis Bitt.
(Rosaceae) forests” [20]. These forests represent feature units
and constitute altitudinal levels where A. acuminata is a pioneer species that colonizes disturbed areas [1, 38].
Alnus acuminata is tolerant to infertile soils given its ability
to form ectomycorrhizal (ECM) [3–7], arbuscular mycorrhizal
(AM) [8] and actinorrhizal relationships with Frankia [22],
which enables it to fix atmospheric nitrogen in natural and disturbed soils [24]. At the same time A. acuminata can improve
soil fertility due to its seasonal fall of leaves [30]. The high
fertility of the soils may be the determining factor for the high
diversity of plants. These forests are mono-specific as regards
the tree stratum, with a high dominance of 95% of A. acuminata [10], whereas there are 186 species of different shrubs
and herbs that compose the understory [36, 74].
Arbuscular mycorrhizas play a crucial role in the mineral
nutrition of most plants, such the case of forest trees [66].
This symbiosis occurs across a wide range of environments,
probably because mutualism enables plants to obtain nutrients more effectively [62]. The arbuscular mycorrhizal fungi
diversity influences the composition of the plant community
[32, 39, 44, 45, 47, 48, 53, 54, 65, 78]. The presence of different
AM fungi can hence influence competitive interactions among
Article published by EDP Sciences and available at http://www.afs-journal.org or http://dx.doi.org/10.1051/forest:2007056
766
A. Becerra et al.
plant species and so influence the plant community composition [13].
The success of any ecosystem’s reforestation effort is,
therefore, likely to depend on the establishment of mycorrhizas [29, 46, 55, 69, 71]. Unfortunately, at present indigenous trees in the Yungas ecosystem are not being used for reforestation purposes. On the contrary, they are declining due
to the ever-increasing demand for timber and to the need of
agriculturally suitable land [61]. In the Yungas, an example
of an indigenous tree used for firewood, pulp, and timber, is
A. acuminata, which forms ECM and AM, P. parlatorei and
P. australis forming AM colonization ([58], Becerra personal
observation). Considering the predominance of ECM and AM
associations in this ecosystem, both mycorrhizal fungi should
receive special attention in indigenous tree seedling production and in any management/conservation program for these
montane cloud forests.
The mycorrhizal status of certain families and genera is
varied; it is important to evaluate mycorrhizas in terms of
soil characteristics and the mycorrhizal status of the dominant
species, and thus, the inoculum that prevails in any particular
habitat [2, 25, 26].
Attention has been focused on the mycorrhizas of forests in
the humid tropics [11, 12, 50, 51, 60, 72, 73, 77], but there is little information concerning the distribution and abundance of
these types of symbioses in the Yungas [3–8]. Little is known
of this endangered ecosystem and an urgent call is made for
its conservation. The aim of this study was to characterize and
describe the mycorrhizal status of native plants in the Yungas
forests of Argentina. This study will allow us to know the influence of mycorrhizal symbiosis on the forest structure and
stability, in order to improve our knowledge of mycorrhizal
biology and diversity for re-vegetation programs.
2. MATERIALS AND METHODS
2.1. Sampling sites
This study was carried out on two field sites in the Yungas, in the
NW region of Argentina (NOA), namely: 1) Quebrada del Portugués,
Tafí del Valle, (Tucumán Province), which is located at 26◦ 58’ S 65◦
45’ W, has an elevation of 2 187 m, an average precipitation between
1200-1500 mm. The soil was characterized as Lythic Ustorthent [83],
and 2) Sierra de Narváez, (Catamarca Province), located at 27◦ 43’ S
65◦ 54’ W, at an elevation of 1 820 m, which has an average precipitation of 698 mm. The soil was characterized as Typic Ustorthent [83].
Mean annual temperatures range from 5.8 to 24 ◦ C for both locations.
The vegetation is a nearly homogeneous A. acuminata forest (height
6–15 m, age 20–30 years).
2.2. Field collection and laboratory analysis
Among the land vegetation cover in the Yungas (Tab. I), 41 frequent species from a total of 25 families were selected in the two
sites during summer (March 2001), autumn (May 2002) and spring
(November 2002). Their choice was estimated on the basis of the
Braun-Blanquet [14] method, with an abundance scale of + to 5. In
herbs, grasses, and ferns, the whole root systems of five individuals
were sampled. In shrubs with deep root systems, soil samples of five
Table I. Land vegetation cover of the Alnus acuminata forest in Sierra
de Narváez (Catamarca province) and Quebrada del Portugués (Tucumán province).
Tree cover (%)
Shrubs cover (%)
Herbaceous cover (%)
Sierra de Narváez Quebrada del Portugués
80–90
80–90
< 20
15–20
90
90
individuals were carefully excavated around each selected plant to
confirm the connection between roots and shoots. The samples were
placed in plastic bags and stored at 4 ◦ C. Plant species were identified
at the Museo Botánico de Córdoba.
2.3. Analysis of root samples
Plants were carefully cleaned of soil and their root systems were
washed and fixed in FAA. The preserved roots were stained to study
the presence of AM according to the technique described by Phillips
and Hayman [67]. For each individual system, at least 50 root segments of 2 cm in length were firstly observed under a Leica M 420
stereoscopic magnifier and secondly mounted on glass slides for examination in a Kyowa 4-100X microscope. A root was considered
AM colonized when the following structures were observed: arbuscules, vesicles, hyphal coils, intraradical aseptate hyphae, and appressoria. We also determined the AM morphological type of the species
studied, to find out whether they were the Arum- or the Paris-type
[76]. The quantification of the AM root colonization was estimated
visually and characterized using five classes of mycorrhizal root colonization: Class I, 1–5%, Class II, 6–25%, Class III, 26–50%, Class
IV, 51–75%, and Class V, 76–100% [70].
3. RESULTS
Arbuscular mycorrhizal colonization was evident in all
plant roots collected (Tab. II). Forty one plant species were
analyzed, including 32 herbaceous dicotyledons, 3 shrubs,
4 pteridophytes, and 2 herbaceous monocotyledons. Arbuscular mycorrhizal fungi colonized all the plant species examined
(Tab. II). Appresoria, aseptate intra and intercellular hyphae,
vesicles, arbuscules, or hyphal coils were observed in the majority of the plant samples collected. Although the colonization pattern varied among the species, intracellular aseptate
hyphae and vesicles were the most frequent AM structures
present in the species studied (Tab. II).
Although external septate hyphae bearing clamp connections on the root surfaces were detected in two species,
namely, Urtica lilloi (Hauman) Geltman (Urticaceae) and
Selaginella sp. (Selaginellaceae), no evidence of ECM was
found, nor were the mantle or the Hartig net that are usually
present with them observed either. Root hairs were observed
in these species.
Appresoria, coils, aseptate intracellular hyphae, vesicles of
various shapes (oval, irregularly lobed, and rectangular) and
arbuscules were present in the majority of the plant roots
(Fig. 1) (Tab. II).
Arbuscular mycorrhizas in the Yungas forest
767
Table II. Mycorrhizal status of the native plant species from the Yungas forest in Sierra de Narváez (Catamarca, C) and Quebrada del Portugués
(Tucumán, T).
Family
Aspleniaceae
Asteraceae
Begoniaceae
Boraginaceae
Brassicaceae
Cyperaceae
Dryopteridaceae
Ephedraceae
Fabaceae
Juncaceae
Lamiaceae
Malvaceae
Melastomataceae
Nyctaginaceae
Oxalidaceae
Plantaginaceae
Poaceae
Polygonaceae
Pteridaceae
Rosaceae
Rubiaceae
Solanaceae
Scrophulariaceae
Selaginellaceae
Urticaceae
Species
Asplenium lorentzii Hieronymus
Bidens andicola Kunth.
Cirsium vulgare (Sari) Tenore
Gnaphalium sp.
Jungia pauciflora Fusby (C)
Jungia pauciflora Fusby (T)
Siegesbeckia serrata D.C.
Stevia yaconensis Hieron.
Tagetes minuta L.
Tagetes terniflora Kunth.
Taraxacum officinale Weber ex F. H. Wigg.
Begonia sp.
Cynoglossum sp.
Cynoglossum amabile Stapf. × J. F. Drumm.
Rorippa nasturtium-aquaticum (L.) Hayek
Eleocharis sp. R. Br.
Dryopteris paralleogramma (Kunze) Alston
Ephedra sp.
Crotalaria sp.
Juncus tenuis Willd. (C)
Juncus tenuis Willd.(T)
Leonurus sp.
Prunella vulgaris L. (C)
Prunella vulgaris L. (T)
Modiolastrum malvifolium (Gris.) K. Schum
Tibouchina paratropica (Griseb.) Copn.
Colignonia glomerata Griseb.
Oxalis sp.
Plantago sp.
Bromus catharticus Vahl.
Poa annua L.
Polygonum sp.
Adiantum cfr. lorentzii (Hieron) Diels.
Alchemilla pinnata Ruiz et Pav.
Galium hypocarpium (L.) Endl. ex Griseb.
Solanum sp.
Mimulus glabratus Kunth.
Veronica persica Poir.
Sibthorpia conspicua Diels.
Selaginella sp.
Urtica lilloi (Hauman) Geltman
LVCa
+
+
+
+
+
+
+
+
1
1
+
+
+
+
+
+
+
+
+
1
1
+
1-2
1-2
+
+
+
1-2
1
+
+
+
+
1
+
1
+
+
+
+
+
GFb
F
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
F
S
H
H
H
H
H
H
S
H
H
H
H
G
G
H
F
H
H
S
H
H
H
F
H
PCc
ap, h, ar, iv, c
ap, h, ar, ov, iv, c
ap, h, ar, ov, iv, c
ap, h, ar, ov, iv, c
ap, h, ov, c
ap, h, ov, c
ap, h, ar, ov, iv, c
ap, h, ov, c
ap, h, ar, iv, c
ap, h, ov, iv, c
ap, h, ov, c
ap, h, ar, ov, iv, c
ap, h, ar, ov, iv, c
ap, h, ov, c
ap, h, ar, iv, c
ap, h, ar, iv, c
ap, h, iv, c
ap, h, iv, c
ap, h, iv
ap, h, ar, ov, iv, c
h, ov, iv, c
ap, h, ar, ov, c
ap, h, ar, ov, iv, c
ap, h, ar, ov, iv, c
ap, h, ar, iv, c
ap, h, iv, c
ap, h, ar, ov, iv, c
ap, h, ar, iv, c
ap, h, ar, ov, iv, c
ap, h, ov, iv, c
ap, h, ar, ov, c
ap, h, ar, ov, c
ap, h, ov, c
ap, h, ar, ov, iv, c
ap, h, ar, iv, c
ap, h, ov
ap, h, ar, ov, iv, c
ap, h, ar, ov, c
ap, h, ar, ov, iv, c
ap, h, ov, c, cc, rh
ap, h, ov, c, rh
AM%d
II
V
IV
III
III
II
IV
II
V
V
I
II
V
III
I
IV
III
III
I
V
III
IV
V
V
III
IV
III
IV
V
V
III
IV
III
V
IV
I
IV
V
V
II
III
LVC: land vegetation cover (LVC); +: < 1%, 1: 1–5%, 2: 5–25%.
GF: Growth form; H: herbs, G: grass, F: ferns, S: shrub.
c
PC: Patterns of AM colonization (PC); ap: appressoria, h: intra- or intercellular aseptate hyphae, ar: arbuscules, ov: oval vesicles, iv: irregular vesicles,
c: coils, cc: septate hyphae bearing clamp connections, rh: root hairs.
d
AM%: AM colonization; Class I:1–5 %, II: 6–25%, III: 26–50%, IV: 51–75%, V: 76–100%.
a
b
768
A. Becerra et al.
Figure 1. Structures of arbuscular mycorrhizas formed on roots of native plants of the Yungas forest, Argentina. (a) Appressoria (ap): Prunella
vulgaris. (b) Appressoria and coils (ap, c): Bromus catharticus. (c) Intracellular hyphae (ih): Eleocharis sp.. (d, e) Vesicles (v): Juncus tenuis,
Jungia pauciflora. (f, g, h) Arbuscules (ar): Veronica persica, Juncus tenuis, Plantago sp. Bars a, b, c, d, f, g: 10 µm; e: 50 µm; h: 6.25 µm.
Arbuscular mycorrhizas in the Yungas forest
All the types of vegetation detailed in Table II are present
in both forest sites. Some plants were sampled in both sites,
in search of differences between AM colonization in the same
plant species. The morphological colonization of the species
Juncus tenuis varied in both sites (Tab. II). In Quebrada del
Portugués we observed appresoria, hyphae, arbuscules, vesicles, and coils, while in Sierra de Narváez we only observed
hyphae, vesicles, and coils. In the cases of Jungia pauciflora
and Prunella vulgaris, no morphological colonization differences were observed in either of the sites.
In all the species studied, the colonization was Paris-type,
since intracellular hyphae, intracellular hyphae coils, and terminal arbuscules were found. We also report the simultaneous development of separate and internally consistent infection units of Paris-type and Arum-type within the same root
system in Crotalaria sp. and Solanum sp.
Arbuscular mycorrhizal colonization varied among the
species studied (Tab. II). Four species had 1–5% of the root
colonized with AM and five had less than 25%. Only Bidens
andicola, Tagetes minuta, Tagetes terniflora, Cynoglossum
sp., Juncus tenuis, Prunella vulgaris, Plantago sp., Bromus
catharticus, Alchemila pinnata, Veronica persica, and Sibthorpia conspicua had always more than 75% of the roots colonized with AM. The colonization of Juncus tenuis and Jungia
pauciflora varied in both sites (Tab. II), with a low colonization degree in Quebrada del Portugués.
4. DISCUSSION
The mycorrhizal status of some herbs and shrubs of the
NOA is reported for the first time. Bearing in mind that
this study does not exclude the possibility of the occurrence
of other kinds of mycorrhizal associations in the species
examined, an absolute dominance of AM was observed in
these plants. These results are in agreement with Janos’ [52]
and other authors’ observations on the mycorrhizal status of
neotropical forests [12, 77].
No evidence of ECM was found in any of the plant species
studied, although in this forest Alnus acuminata has both types
of mycorrhizas (ECM and AM) [3–8]. Both mycorrhizal types
can occur, with a wide variation in degree of colonization,
throughout the litter and the soil organic and mineral horizons,
at least to a depth of 35 cm [60]. In stable forest communities, the soil and irradiance conditions may allow the persistence of an herbaceous understory of plants with AM beneath
a canopy of predominantly ectomycorrhizal trees. However,
different patterns of root distribution in the soil can provide
niche separation for both types of mycorrhizas [75].
In this study, a mycorrhizal plant was categorized by the
presence of arbuscules – generally used to designate plants
with functional AM [34, 35] – or by the presence of hyphae
and vesicles in the root samples [59, 79]. The frequent occurrence of vesicles in the species studied indicates that a large
part of the AM fungi belong to the Glominae, and diversity
in vesicle shape indicates the presence of both Glomus (oval
to ellipsoid vesicles) and Acaulospora (irregularly shaped to
rectangular vesicles) (Tab. II) [19].
769
The AM status of all herbs and, in particular, the families
Cyperaceae, Polygonaceae, Scrophulariaceae, and Juncaceae
found here, contrasts with the predominantly non-mycorrhizal
status previously recorded for these families [16,18,40,41,75].
Redhead [68] considered the Polygonaceae family as ECM,
although Tsuyuzaki et al. [82] observed a dual colonization
(ECM and MA).
In the present study, as already found in others [21, 27, 43,
81], species belonging to the same family tended to have the
same mycorrhizal behavior. However, several exceptions to
this general rule were observed. For instance, Juncus tenuis
belongs to a typically non-mycorrhizal family [75], but in this
study it was found to be mycorrhized and showed mycorrhizal
structures and colonization differences in both sites (Tab. II).
Another case was that of the predominance of AM in Taraxacum officinale (Asteraceae), Rorippa nasturtium-aquaticum
(Brassicaceae), and Eleocharis sp. (Cyperaceae), cited as nonmycorrhizal by Fontenla et al. [28]. Cases of species that contrast in their mycorrhizal status with taxonomically and phylogenetically closely related species have been pointed out in
other studies [29, 56, 57, 80].
The Paris-type colonization found through this study was
characterized by intracellular hyphae and intracellular hyphal
coils, although arbuscules were always simple and terminal,
never intercalary along the coils, as was described by Gallaud
[31]. This variation of the Paris-type mycorrhizas has also
been described by Gerdemann [33] and Bedini et al. [9]. The
Paris-type was seen to be dominant in the herbaceous understory plants of the NOA, similar results were found by Yamato
and Iwasaki [85] for herbaceous plants of the forests of the
Kansai region. These facts indicate that the Paris-type is advantageous for herbaceous understory plants that grow slowly
with low light intensity and low nutrient availability levels.
On the other hand, O’Connor et al. [64] found the Arum-type
in all of the 21 species of herbaceous AM plants that grow
with no shading in the Australian desert. It is well known that
the Arum-type is formed in most plants that usually grow in
sunlight. The spreading rate of colonization is slower in the
Paris-type than in the Arum-type. The slower colonization of
the Paris-type might be beneficial for the host plants, since it
probably keeps the energy supply to the fungi reduced and it
might be desirable for plants of slow growth in a woodland
environment [17]. Additionally, environmental factors such as
temperature, light intensity and soil moisture content may influence AM morphology, as these factors affect the growth and
morphology of roots [23, 84].
The ferns studied (Aspleniaceae, Dryopteridaceae, Pteridaceae, and Selaginellaceae) showed AM colonization. The
occurrence of AM fungi in these families agrees with the reports of Harley and Harley [40], Newman and Reddell [63],
Godoy et al. [37], and Zhao [86]. The presence of the Paristype predominates in ferns [76]. Only in one fern species
we have observed arbuscules (Tab. II). The grasses Bromus
catharticus and Poa annua showed AM colonization (Tab. II).
These results are in agreement with the observations of Harley
and Harley [40–42] and Fontenla et al. [28]. The presence of
external fungal hyphae with clamp connections on Selaginella
sp. root’s surface is probably due to free-living saprobes.
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A. Becerra et al.
Further work is required to determine and understand the role
of these fungi on Selaginella sp. roots.
This study showed a low AM colonization in the root samples of some species. Families such as Asteraceae, Brassicaceae, cited as non-mycorrhizal [28, 40, 41], showed a low
AM colonization. Regarding the extent of the AM colonization, the reported variations could be due to the different plant
species which exhibit varied ability to establish mycorrhizal
associations [75].
The results of this study showed differences with other findings cited in the literature. According to Brundrett [16], the
generalities about the mycorrhizal status of plants in one floristic region should not be indiscriminately applied to another;
taxonomic and environmental attributes of each community
may influence the mycorrhizal behavior of each plant species.
These results must be considered preliminary, since they
cover only a small proportion of the plant diversity of these
forests. Nevertheless, this is the first report ever published on
the mycorrhizal status of some of the species examined that
belong to the Cyperaceae, Polygonaceae, Scrophulariaceae,
and Juncaceae families.
Acknowledgements: This work was partially supported by funding
from PROYUNGAS (1999, 2001) and C.I.C. (2005). A. Bercera is
grateful to CONICET for the fellowship provided. M. Cabello is researcher from C.I.C.
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