Rhizophagus clarus

WHOLE SPORES

COLOR: Hyaline to subhyaline (0/0/10/0), with yellowish spores (0/0/40/0 a 0/0/60/0)

SHAPE: Globose to subglobose.

SIZE DISTRIBUTION (lenght x width): 154-274 x 135-248 µm, mean = 204 x 193 µm (n = 100).

SUBCELLULAR STRUCTURE OF SPORES

SPORE WALL: Formed by three layers (L1, L2 and L3). L1 is not usually present in mature spores since it is an evanescent layer that tends to slough off. L2 is laminated but very brittle and usually appears fragmented if spores are heavily broken. L3 laminated with thickness varying according to the number of sublayers added during differentiation.

L1: Outer evanescent layer, hyaline (0-0-10-0), smooth, which tends to degrade and often absent in mature spores. This layer stains heavily in Melzer´s reagent turning pinkish-red (20/80/20/0); Melzer´s reaction is not always uniform and some patches reacts stronger than others, producing some darker circular areas in some spores. Thickness of L1 is 1-4 µm (mean 1,7 µm). In young spores, this layer varies in thickness within the same spore and can reach up to 4 µm.

L2: A layer consisting of several sublayers, hyaline, 4-13 µm thick (mean = 8.3 µm). Sublayers of this layer have a granular appearance and are fragile. As a result, it appears squashed if spores are crushed hard.

L3: A pigmented laminated layer, 1-5 µm thick (mean = 1.8 µm), yellow to dark yellow. This layer is formed by several sublayers that are adherent but can separate when spores are broken. Perception of spore color (more yellowish or more hyaline) is related with the thickness of this layer.

SUBTENDING HYPHA

WIDTH: 15-37.5 µm (mean = 25.5 µm).

WALL STRUCTURE: Formed by three layers continuous with the layers forming the spore wall and that are more visible near the spore base. L1 is not usually present because it tends to degrade. C2 is the main layer that form the wall of the subtending hypha. L3 is thinner in the subtending hypha compared to the spore wall.

OCCLUSION: The innermost sublayer of L3 closes the pore, although in some spores this occlusion is difficult to observe. In some spores. In some spores, it appears that there is no occlusion.

Comparison with Original Description

Color:

Description: Hyaline

RJN102A: Hyaline to subhyaline, yellowish

Shape:

Description: Globose to subglobose

RJN102A: Globose to subglobose

Size:

Description: 68-290 µm , mostly 190 µm

RJN102A: 154-274 x 135-248 µm, mean = 204 x 193 µm.

Spore Wall: L1

Description: referred as “hyaline outer mucilaginous coat (0.5-2 µm) which with age becomes verrucose or rugose with folds up to 5 µm”.

RJN102A: evanescent layer ranging of 1-4 µm thick (mean = 1.8 µm)

Spore Wall: L2

Description: referred as "outer wall, 5 to 20 µm, that do not separate readily".

RJN102A: laminated fragile layer, hyaline, ranging in thickness of 4-13 µm (mean = 8.3 µm).

Spore Wall: L3

Description: referred as "inner wall (2-9 µm)...inner wall of several (two to five) layers of 0.5-2.0 µm in width".

RJN102A: pigmented laminated layer of 1-5 µm thick (mean = 1.8 µm)

Taxonomic History

Reference: Nicolson TH, Schenck NC (1979). Endogonaceous mycorrhizal endophytes in Florida. Mycologia 71(1):178-198.

Etymology: Latin (clarus = clear, transparent) referring to the hyaline spore wall.

Type: spores from soil on the Agronomy Farm, University of Florida collected July, 1975 and maintained in pot culture on bahia grass. Type OSC, isotypes FH and FLAS.

Biogeography

Rhizophagus clarus is a cosmopolitan species detected in all biogeographical realms, in all continents (except Antarctica) and in 34 countries, occurring in tropical, subtropical, temperate, boreal regions and with two records from tundra. Rhizophagus clarus was recorded from several ecosystems like sand dunes, agroecosystems, mining degraded areas, forests, prairies, rupestrian fields, and alpine ecosystems, in biomes like Boreal Forests (Varga 2015), Deserts (Chaudhary et al. 2014), Flooded Grasslands and Savannas (Gomide et al. 2014), Mangroves (Furrazola et al. 2015), Temperate Forests (Shi et al. 2013), Temperate Grasslands (Cofré et al. 2017), Tropical Dry Broadleaf Forests (Pontes et al. 2017), Tropical Moist Broadleaf Forests (Stürmer & Siqueira 2011) and Tropical Grasslands and Savannas (Carneiro et al. 2019).

The map below shows countries (in red) where Rhizophagus clarus was detected.

References:

Carneiro MAC, Assis PCR, Paulino HB, Rocha MR, Teixeira RA, Pinto FA, Santos JV, Siqueira JO, Souza ED. 2019. Diversity of arbuscular mycorrhizal fungi and nematodes in a 14 years no-tillage chronosequence. Rhizosphere 10:100149

Chaudhary VB, O'Dell TE, Rillig MC, Johnson NC. 2014. Multiscale patterns of arbuscular mycorrhizal fungal abundance and diversity in semiarid shrublands. Fungal Ecology 12:32-43.

Cofré MN, Ferrari AE, Becerra A, Dominguez L, Wall LG, Urcelay C. 2017. Effects of cropping systems under no-till agriculture on arbuscular mycorrhizal fungi in Argentinean Pampas. Soil Use and Management, 33:364-378.

Furrazola E, Covacevich F, Torres-Arias Y, Rodríguez-Rodríguez RM, Ley-Rivas JF, Izquierdo K, Fernández-Valle R, Berbara RLL. 2015. Functionality of arbuscular mycorrhizal fungi in three plant communities in the Managed Floristic Reserve San Ubaldo-Sabanalamar, Cuba. Rev. Biol. Trop. 63:341-356.

Gomide PHO, Silva MLN, Soares CRFS, Cardoso EL, Carvalho F, Leal PL, Marques RM, Stürmer SL. 2014. Fungos micorrízicos arbusculares em diferentes fitofisionomias do Pantanal da Nhecolândia, Mato Grosso do Sul. Revista Brasileira de Ciência do Solo 38:1114-1127.

Pontes JS, Oehl F, Marinho F, Coyne D, Silva DKA, Yano-Melo AM, Maia LC. 2017. Diversity of arbuscular mycorrhizal fungi in Brazil's Caatinga and experimental agroecosystems. Biotropica DOI 10.111/btp.12436.

Shi Z, Chen Y, Hou X, Gao S, Wang F. 2013. Arbuscular mycorrhizal fungi associated with tree peony in 3 geographical locations in China. Turkish J Agr For 37:726-733.

Stürmer SL, Siqueira JO 2011. Species richness and spore abundance of arbuscular mycorrhizal fungi across distinct land uses in Western Brazilian Amazon. Mycorrhiza 21:255-267.

Varga S. 2015. Effects of arbuscular mycorrhizal fungi and maternal plant sex on seed germination and early plant establishment. American Journal of Botany 102:358-366.

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