Molecular, functional and structural diversity of bacteria in South African Forest soils

Abstract

Forest soils store substantial quantities of carbon and mediate vital stages of the global carbon cycle. Their capability to act as carbon sinks makes them important terrestrial biomes. Soil microbes, specifically bacteria and fungi, thrive well in these soils because of the accumulation of carbon. Soil biodiversity advances ecosystem functioning thus delivering numerous ecosystem services. A good perception of the relationship between biodiversity and ecosystem functioning and their response to environmental variation can maximize the contribution of soil microbes to ecosystem services. The impact of land use in temperate forest ecosystems on the composition of soil bacterial communities and the consequences on soil functioning was examined using high-throughput sequencing. Soil samples were collected from two sites namely the Tweefontein plantation and the Witklip plantation. Tweefontein is in Graskop while Witklip is sited at Witrivier. The Tweefontein forest plantation is made up of the Tweefontein commercial forest (TC) and the Tweefontein indigenous forest (TI) while the Witklip forest plantation consists of the Witklip commercial forest (WC) and the Witklip indigenous forest (WI). The dominating tree species in the two commercial forests is Pinus patula while Acacia xanthophloea and Celtis africana dominate the indigenous forests. Using the MicroResp™ method, we used multiple substrate-induced respiration and community-level physiological profiles to investigate the microbial activity and functional diversity of the microbial communities in these forest soils. The consequence of seasonality and spatial heterogeneity on soil bacterial community composition and functioning was also investigated. The different land use types had effect on bacterial communities and subsequently soil functioning. Spatial heterogeneity in the distribution of the microbial communities and significant relationships between the microbes and soil characteristics were observed. Moisture was seen to have notable impact on the bacterial community composition in the various land use types. Community composition and functional diversity exhibited high spatio-temporal variability. Spatial horizontal patterns at the local scale which shape microbial community structure and functioning were observed across sites. Notwithstanding the spatial differences, dominating tree species in each forest had important influences on the activity, structure and function of soil microbial communities. A link exists in the reduction of soil bacterial diversity and a declination in ecosystem functioning. An understanding of this can improve ecosystem services thus enhancing environmental sustainability and food security.