Soil microbial communities associated with two commercially important plant species indigenous to the fynbos region of South Africa : cyclopia spp. (honeybush) and Aspalathus linearis (rooibos)

Postma, Anneke (2016-12)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The Cape Floristic Region (CFR) is characterized by nutrient poor soils which forged close symbiotic ties between plants and soil microorganisms for nutrient acquisition. Aspalathus linearis and Cyclopia spp. are two commercially important plant species endemic to the CFR in South Africa. These species are used to produce herbal teas known as rooibos and honeybush tea, respectively. Despite the important role soil microorganisms play in this environment, very few studies have been done to investigate the diversity and structure of the communities associated with these economically important plants. Furthermore, it is unclear what the effect of agricultural practices will be on these communities. Studies done on other agricultural systems, showed that the soil microbiome is greatly influenced by agricultural activities such as soil tillage, application of pesticides as well as monocropping systems. These activities often lead to the loss of soil productivity and biodiversity. We, therefore, hypothesised that the microbial communities associated with A. linearis and Cyclopia spp. plants will also be influenced by the respective agricultural activities. The overall aim of this study was to characterise and compare microbial communities associated with natural and commercially grown A. linearis and Cyclopia spp. plants. Furthermore, we aimed to investigated the effect different abiotic and physico-chemical factors may have on microbial communities in this unique region. Sampling was done on two occasions to include the dry, warm summer and the cold, wet winter seasons. A total of 29 bulk soil and 54 rhizosphere soil samples were collected during this study. The abiotic and physico-chemical properties of the soil samples were determined which included soil resistance, pH, total soil carbon, Na+, K+, nitrate and ammonia. Bacterial and fungal communities were characterised using next generation sequencing technology on the Ion Torrent (PGM) platform. For the bacteria, variable V4-V5 region of the 16S rRNA gene were amplified and sequenced. Fungal analysis used the internal transcribed spacer (ITS) region of the 18S rRNA gene. Bioinformatic and statistical analyses were performed using the software packages MOTHUR, PIPITS and R. No statistically significant differences were detected between bacterial communities from natural and commercial sites for both A. linearis and Cyclopia spp. plants. The plant-driven selection of rhizosphere microbiome for these two fynbos plants appeared to be very strong and was not significantly influenced by agricultural activities. However, significant differences in bacterial communities were observed between samples collected during the different seasons. These seasonal changes support the contention that microbial taxa adapt and resist environmental changes differently. Furthermore, the overall taxonomic classification indicated that all soils were dominated by the bacterial orders Acidobacteriales and Actinomycetales. Both these groups are known to be dominant soil colonizing bacteria and are able to grow under low nutrient conditions, characteristic to the fynbos region. Additionally, the most dominant fungal phyla detected in samples included the Ascomycota and Basidiomycota. Cyclopia spp. samples were mostly dominated by the orders Agaricales, Chaetothyriales and Mortierellales, whereas A. linearis samples were dominated by the orders Chaetothyriales, Eurotiales and Helotiales. The β-diversity analysis showed that the Cyclopia spp. samples tended to cluster into commercial and natural groups. This might be due to the differences measured in soil pH between these two groups. Overall, little evidence was found to support our hypothesis. Bacterial communities from natural and commercial soil of both plant species were very similar and fungal communities associated with natural and commercially grown A. linearis plants also did not reveal any significant difference. However, fungal communities associated with natural and commercially grown Cyclopia spp. plants appeared to differ. In short, this study improved our knowledge on the biodiversity of soil microorganisms associated with two commercially important fynbos plant species and elucidated on factors that affected the microbial community structures.

AFRIKAANSE OPSOMMING: Die Kaap Floristiese gebied word gekenmerk deur nutriënt arme grond wat die dryfveer is vir talle simbiotiese interaksies tussen fynbos plante en grond mikrobes. Twee kommersieël belangrike fynbos plante in die Kaap Floristiese gebied sluit in Aspalathus linearis en Cyclopia spp. Hierdie plante word gebruik vir die produksie van die welbekende rooibos en heuningbos kruie tees. Ten spyte van die belangrike rol wat grond mikroörganismes in hierdie omgewing speel, is daar nog relatief min studies gedoen om die diversiteit en struktuur van die mikrobiese gemeenskappe te beskryf. Dit is verder onduidelik wat die effek van landbou praktyke op die mikrobiese gemeenskappe is. Studies wat op ander landbou sisteme gedoen is, het bewys dat die grond mikrobes sterk beïnvloed word deur aktiwiteite soos grond bewerking, toediening van plaagdoders en monokultuur. Daar is bevind dat hierdie aktiwiteite grond produktiwiteit en die diversiteit van mikrobiese gemeenskappe verlaag. Gevolglik was die hipotese van hierdie studie dat die mikrobiese gemeenskappe wat met die grond van A. linearis en Cyclopia spp. plante geassosieer word, deur landbou aktiwiteite beϊnvloed kan word. Die algehele doel van hierdie studie was om mikrobiese gemeenskappe wat geassosieër word met die grond van natuurlike en komersieël geplante A. linearis en Cyclopia spp. te beskryf en te vergelyk. Die effek wat verskillende abiotiese en fisies-chemiese faktore op hierdie gemeenskappe het, is ook ondersoek. Grondmonsters is op twee verskillende tye van die jaar versamel om beide, die droë warm somer en koue, nat winter seisoene in te sluit. ‘n Totaal van 29 omliggende en 54 wortelsfeer grond monsters is deur die loop van hierdie studie versamel. Verskillende abiotiese en fisies-chemiese faktore is bepaal en sluit in elektriese geleidings weerstand, pH, totale koolstof, Na+, K+, nitraat en ammoniak. Die samestelling van bakteriële en swam gemeenskappe is beskryf deur gebruik te maak van hoë omset volgordebepaling. Vir bakterieë is die veranderlike gebied V4-V5 van die 16S rRNA geen geamplifiseer. Swam analises het gebruik gemaak van die interne getranskribeerde spasie (ITS) gebied van die 18S rRNA geen. Bioinformatiese en statistiese analises is gedoen deur gebruik te maak van die sagteware pakkette MOTHUR, PIPITS en R. Geen statistiese beduidende verskille tussen bakteriële gemeenskappe wat geassosieer is met natuurlike en kommersieël geplante A. linearis en Cyclopia spp. is waargeneem nie. Die afleiding wat ons hieruit gemaak het is dat die plant gedrewe seleksie van die wortelsfeer grond mikrobioom vir beide plant spesies baie sterk is en dat landbou aktiwiteit geen beduidende invloed op die gemeenskappe gehad het nie. Daar is wel verskille in die bakteriële gemeenskappe tussen die seisoene waargeneem. Hierdie seisoenale verandering in mikrobiese gemeenskappe ondersteun die feit dat mikrobiese taksa verskillend reageer en aanpas by verandering in omgewingstoestande. Verder het die taksonomiese klassifikasie van die bakterieë gewys dat die ordes Acidobacteriales en Actinomycetales grond monsters gedomineer het. Hierdie twee groepe is bekend daarvoor om verskeie grond omgewings te koloniseer, veral lae nutriënt omgewings wat kenmerkend is van die fynbos gebied. Die mees dominante swam filums wat waargeneem is in al die grond monsters sluit in die Ascomycota en Basidiomycota. Die Cyclopia spp. plant grondmonsters is gedomineer deur die orders Agaricales, Chaetothyriales en Mortierellales en A. linearis plante deur die orders Chaetothyriales, Eurotiales en Helotiales. Die β-diversiteit analises van Cyclopia spp. monsters was geneig om kommersiële en natuurlike monsters saam te groepeer. Dit is heel waarskynlik as gevolg van die verskille tussen grond pH tussen hierdie twee groepe. In geheel was daar min bewyse gevind wat die hipotese van hierdie studie ondersteun. Bakteriële gemeenskappe wat geassosieer is met beide natruurlike en kommersiële grond monsters was soortgelyk vir beide plant spesies, asook swam gemeenskappe wat geassosieer is met A. linearis plante. Daar is wel verskille waargeneem in swam gemeenskappe tussen natuurlike en kommersieël geplante Cyclopia spp. Kortom, hierdie studie verbeter ons kennis rakende die biodiversiteit van mikroorganismes wat geassosieër word met twee belangrike komersiële fynbos plante. Verder brei hierdie studie meer uit oor moontlike faktore wat mikrobiese gemeenskappe in fynbos grond kan beϊnvloed.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100379
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