The Impact of Oil Palm Plantations and Pastures on Benthic Prokaryotic and Fungal Communities in Tropical Streams

The expansion of oil palm plantations and cattle grazing lands has a detrimental impact on freshwater ecosystems, causing ecological degradation and biodiversity loss in the tropics, although little is known about the effects on the aquatic microbial community. We assessed the benthic aquatic microbial community in streams in grazing lands, oil palm plantations (with and without riparian buffers) and native vegetation (rainforests) using metabarcoding to analyse prokaryotic amplicon sequence variants (ASVs) and fungal operational taxonomic units (OTUs). We observed significantly higher microbial richness in streams in rainforests than in grazing lands and oil palm plantations lacking buffers, but not in oil palm plantations with riparian buffers. Groups commonly found in faecal matter were found in streams in grazing land, streams in plantations lacking buffers showed lower abundance of wood decomposers, and both land uses had more primary producers. Prokaryote richness and diversity were associated positively with riparian buffers and negatively with temperature, light and grazing lands, while fungal richness was positively associated with the proximity of forests and the protected area. The negative effects of agriculture on stream microbial richness, diversity and community composition were partially mitigated by the conservation of riparian buffers in the oil palm plantations and probably, the proximity to forests (a source of spores). Our findings demonstrate a potential role for metabarcoding of stream benthos for monitoring impacts in agricultural lands and underlines the importance of riparian buffers in mitigating, to some extent, biodiversity loss in agriculture streams.