Estimated abundance and diversity of heterotrophic protists in South African biocrusts

Kenneth Dumack,Michael Bonkowsk,Bettina Weber,Robert Koller

doi:10.17159/sajs.2016/20150302

Abstract

Biological soil crusts (biocrusts) occur widely in the uppermost millimeters of the soil in arid and semi-arid systems. Worldwide they cover large terrestrial areas and play a major role in the global terrestrial carbon and nitrogen cycles. However, knowledge of the microbial decomposer foodwebs within biocrusts is particularly scarce. Heterotrophic protists in soil are predominantly bacterivores, and because of their high biomass compared with other soil fauna and fast turnover rates, protists are considered an important factor for soil nutrient cycling and energy fluxes. Thus, knowledge of their biodiversity, abundance and functional roles is important to understand soil ecosystem functions. We investigated the diversity and abundance of heterotrophic soil protists in different types of biocrusts from the Succulent Karoo, South Africa. With an overall diversity of 23 distinct morphotypes, soil protist biodiversity was shown to be high. The most abundant groups were Spumella-like chrysomonads, gliding bodonids, glissomonads and heteroloboseans. Protist abundance was highly variable among samples. The abundance and diversity did not differ significantly among different types of biocrusts, indicating that microscale differences, but not macroscopic soil crust builders (e.g. cyanobacteria, lichens and bryophytes), have a major impact on the protist community.

Highlights

Biocrusts form one subgroup within cryptogamic covers, with the latter comprising cryptogamic communities on rock and epiphytically on plants. These cryptogamic covers have been estimated to account for 7% of the net primary production fulfilled by plants, and fix about 49 Tg N per year, corresponding to about half the maximum value estimated for the total terrestrial biological nitrogen fixation.[11]
Besides determination of the diversity and abundance of amoeboid and flagellated protists, we evaluated whether they are affected by the identity of the major primary producers in primary producers in biocrusts that are dominated by cyanobacteria, chlorolichens and bryophytes
These values were more than 10 times higher than protist abundances reported from biocrusts of the Colorado Plateau and the Chihuahua Desert in the Western USA13, and up to more than 3 to 30 times higher than Bamforth[37] reported for arid desert soils and litters of northern Arizona

Summary

Introduction

Biological soil crusts (biocrusts) are microscopic ecosystems. They comprise primary producers such as cyanobacteria, algae, lichens, and bryophytes together with decomposers such as fungi, bacteria and archaea. Biocrusts grow within the uppermost millimeters of the soil in arid and semiarid regions throughout the world,[1] where they fulfil several highly relevant ecosystem services. Biocrusts cover over 10% of the terrestrial surface area, influencing global nutrient cycling and climate processes.[9,10] Biocrusts form one subgroup within cryptogamic covers, with the latter comprising cryptogamic communities on rock and epiphytically on plants These cryptogamic covers have been estimated to account for 7% of the net primary production fulfilled by plants, and fix about 49 Tg N per year, corresponding to about half the maximum value estimated for the total terrestrial biological nitrogen fixation.[11]

Methods

Results

Discussion

Conclusion