High abundance of non-mycorrhizal plant species in severely phosphorus-impoverished Brazilian campos rupestres
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Background and aims
We sought to describe the species and functional composition of Brazilian campos rupestres plant communities on severely nutrient-impoverished white sands, to test hypotheses relating plant communities and physiological adaptations to infertile soils. Based on recently-published information on a south-western Australian dune chronosequence, we hypothesised that campos rupestres plant communities would similarly contain a relatively large proportion of non-mycorrhizal species, because of the phosphorus-(P) impoverished nature of the soils. We also sought to test the hypothesis that many of these non-mycorrhizal species have high leaf manganese (Mn) concentrations as a consequence of carboxylate exudation to mobilise soil P.
We conducted flora surveys and quantified mycorrhizal status and foliar Mn concentrations in field sites with strongly-weathered sandy soils. Rhizosphere carboxylates were collected from glasshouse-grown plants to assess a potential correlation of carboxylates and leaf Mn concentrations.
Soils were depleted of all major plant nutrients. Non-mycorrhizal plants were abundant in most field sites (mean relative cover = 48%). Vellozia species were dominant aboveground; belowground, roots were colonised more by dark septate endophytic fungi than by mycorrhizal fungi. From the field sites, foliar Mn concentrations in non-mycorrhizal species increased with decreasing soil P concentrations, but only when soil Mn concentrations were above a minimum threshold (exchangeable [Mn] above detection limit). Across all species, however, there was no relationship of foliar Mn concentrations with soil P concentrations.
Our hypothesis that white-sand campos rupestres communities contain a relatively large proportion of non-mycorrhizal plants was supported. Comparison with similar ecosystems in south-western Australia suggests that plant communities on severely P-impoverished sandy soils, despite differing evolutionary histories and little overlap in plant families, follow convergent evolutionary paths towards increasing abundance of non-mycorrhizal species.
KeywordsCarboxylates Leaf manganese concentrations Mycorrhizas Non-mycorrhizal plants Sandy soils Vellozia
GZ was supported by a scholarship from the Paul Hasluck Bequest administered by the Kwongan Foundation and was the recipient of an Endeavour Research Award provided by Austraining International. GZ also acknowledges the Plant Ecology Program at Unicamp, for financial support for the field work. HL acknowledges support from a CNPq grant, CAPES PVE 88887.108541/2015-00. We thank the Minas Gerais State Park authority for permission to conduct research in the state parks under their administration. UPLC laboratory analyses were done by Alexandra Sarawaya. Sara Adrian, Paulo Mazzafera and Sandra Maria Carmello-Guerreiro, provided laboratory assistance and facilities for the mycorrhizal analysis of roots; Sara Adrian kindly analysed the roots of Vellozia stenocarpa. Livia Echternacht, Graça Wanderley, Juliana dos Santos, Renato de Mello-Silva, Taciana Barbosa Calvacanti, João Martins do Carmo, Edson Dias da Silva, Suzana Costa, Angela Martins and Gustavo Shimizu provided valuable assistance in species identification, and many people from Unicamp assisted with field work. Topographic data for Fig. 1 are based on data services provided by the OpenTopography Facility with support from the National Science Foundation under NSF Award Numbers 1226353 & 1225810.
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