A first record of biological soil crusts in the Cape Floristic Region

Denise M Mager,Cang Hui

doi:10.4102/sajs.v108i7/8.1013

Abstract

To date, the biological soil crusts (BSCs) of southern Africa are thought to be dominated mainly by cyanobacteria, with the exception of the lichen fields of the Namib Desert. Because soil microorganisms can physically modify, maintain or create habitat for other organisms – including soil biota and plants – they have been considered ecosystem engineers. Therefore, the presence of BSCs may be a good indicator of ecosystem resilience. Although BSCs are found throughout the world, recent work has suggested that the absence of BSCs in the fynbos of South Africa may be as a result of the inherent acidity of soils. We surveyed one area within the fynbos biome for the presence of BSCs and determined the relative cover of vegetation and different crust types. We found a widespread presence (up to 80% of surface soil) of BSC communities in fynbos soils. We conclude that soil acidity may not be a constraining factor in the development of BSCs in fynbos soils and that previous reports on the absence of BSCs in fynbos soils may have been based on insufficient field observations. We encourage future studies in this region in order to determine the currently unexplored spatial distribution of soil microbial communities and the taxonomic composition of microorganisms in fynbos soils.

Highlights

Biological soil crusts (BSCs) are formed by an association of soil mineral particles and microorganisms which live in the top few millimetres of the soil.[1]
Soil pH is important for the establishment and diversity of microorganisms.[27]
Büdel et al.[16] suggested that the absence of BSC formation, in particular of filamentous cyanobacteria, in the Fynbos Biome can be attributed to the low soil pH

Summary

Introduction

Biological soil crusts (BSCs) are formed by an association of soil mineral particles and microorganisms which live in the top few millimetres of the soil.[1] The presence, distribution and characteristics of BSCs are controlled by the interactions between climate, geology, vegetation and the disturbance impact of livestock and game.[2,3] BSC formation is often initiated by filamentous cyanobacteria, such as Microcoleus spp., during episodic events of available moisture with the subsequent entrapment of mineral particles by a matrix of extracellular polysaccharides.[4] If undisturbed, the development of an appropriate substrate by filamentous cyanobacteria may lead to the establishment of fungal, lichen and moss populations, characterised by a slower growth rate.[5] Crust organisms have low moisture requirements and tolerate a wide range of temperatures, which enables them to exist even when moisture deficit limits vascular plant growth.[6] Once crust organisms have colonised gaps, the characteristics of the crust is influenced by edaphic factors such as soil texture and topography.[7]

Methods

Results

Conclusion