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Impacts of forest conversion for bacterial soil communities in Sumatra

Changes in active bacteria communities result from rubber and oil palm cultivation

Palm oil cultivation has led to swathes of deforestation in Indonesia, resulting in great losses of biodiversity. Conversion of forest land to that of palm oil and rubber cultivation has effects far beyond the obvious loss of tree and mammal species but these are often understudied. This study by Berkelmann et al., seeks to understand the effects of this conversion at the soil level, specifically the impact on functional bacterial communities. Bacterial species make up a key component of the microbial communities which drive most soil biogeochemical cycles including nutrient cycling. These communities are therefore key in providing fertile soil for cash crop growth.

Previous studies have used DNA sampling to understand bacterial communities however this belies the fact that some microorganisms may be dormant and functionally inactive in the soil. To overcome this bias, this study has used RNA sampling so that bacterial activity can be assessed. The key hypothesis of this study was therefore that soil bacterial diversity remains unchanged between systems however functional diversity changes as a result of land-use type.

Sample sites covered two areas in SW Sumatra; the Harapan Rainforest Concession and the Bukit Duabelas. Both contained areas of secondary forest and comparable examples of land-use conversion for rubber and oil palm crops. Four land-use types were sampled from each area: Oil palm plantations (monoculture of Elaeis guineensis), rubber plantations (monoculture of Hevea brasiliensis), rubber agroforestry (trees in secondary forest without fertiliser or liming) and secondary forest.  A total of 96 soil core samples were taken from across these sites and a soil RNA isolation kit used to extract and amplify sequences. The results yielded 1,333,275 16S rRNA transcripts equating to 32,280 OTUs at species level.

The results showed that species richness was highest in oil palm, then rubber, rainforest and jungle rubber and that there was consistency in bacterial community of the same land type in different forest regions. The conversion of forest to managed land was confirmed to impact active community composition but not diversity. Abiotic drivers of bacterial community abundances were assessed and pH, calcium concentration, base saturation and carbon to nitrogen ratio were all found to be important. PH changes are a common indirect consequence of fertiliser usage and both plantation-type areas used herbicides every 6 months and applied inorganic NPK fertiliser.

At the taxonomic level there was a significant difference in community composition between the converted areas and rainforest sites. Alphaproteobacteria was significantly lower in oil palm areas whereas Acidobacteria increased. Rhizobiales decreased with increased land use intensity and higher fertiliser application from rainforest to oil palm. The metabolic and gene abundance analysis showed genes associated with nitrogen fixation, motility, competition and gene-transfer ability decreased after conversion. N-fixing bacteria were more associated with rainforest soils whereas nitrifiers and heat-resistant bacteria were associated with oil palm soils.

Conversion of forest land to that of crop production entails large changes in soil characteristics and plant diversity and this is reflected in the functional shift in active bacterial communities. These groups of microorganisms play a key role in ecosystem functioning and the loss of above-ground tropical forest biodiversity in Indonesia threatens the maintenance of this natural soil fertilisation and cycling.

Read the full paper here: Berkelmann, D., Schneider, D., Engelhaupt, M., Heinemann, M., Christel, S., Wijayanti, M., Meryandini, A. and Daniel, R., 2018. How rainforest conversion to agricultural systems in Sumatra (Indonesia) affects active soil bacterial communities. Frontiers in microbiology, 9.

To find over 80 similar papers use the search term below in the Forest Science Database:"Bacteria" AND "soil" AND ("RNA" OR "DNA") AND "plantation*"

Article details

  • Author(s)
  • Ellen Baker
  • Date
  • 23 January 2019
  • Source
  • Berkelmann, D., Schneider, D., Engelhaupt, M., Hei
  • Subject(s)
  • Environment