Evaluating the impact of oil palm agriculture and logging on soil microbial communities in South-east Asia.

Abstract

Abstract In this study, the following hypotheses were tested: (i) microbial communities would be distinct for each land-use type (primary forest, regenerating forest, and oil palm plantation); (ii) microbial communities from forest sites (primary forest and regenerating forest) would be more similar to each other than those found in the oil palm plantation site; (iii) microbial communities would be distinct at different soil horizon depths; and (iv) soil microbial biomass (SMB) would be greater in forest sites than in the oil palm plantation sites. To test these hypotheses, soil samples collected from an intact tropical rain forest, a tropical rain forest recovering from logging 50 years previously and an oil palm plantation in active production located in and around the Pasoh Forest Reserve in Peninsular Malaysia, were analysed. Total SMB estimated by summing PLFA compunds from each soil depth revealed the SMB was significantly higher in the forest sites than that in the oil palm plantation (P<0.001). Across soil depths (0-2, 2-10 and 10-20 cm), the greatest magnitude of difference in SMB across sites was observed within the 10-20 cm profile. At this depth, both forest sites had greater SMB than the oil palm plantation and between the forest sites, the regenerating forest had greater SMB than the primary forest (P<0.05). In the 0-2 cm depth, both forest sites had greater SMB than the oil palm plantation (P<0.05). Last, in the 2-10 cm depth, there was no significant difference between the primary forest and the oil palm plantation (P =0.06) but the regenerating forest had greater SMB than both the primary forest and the oil palm plantation (P<0.001). At all sites, bacterial-to-fungal ratios declined with sampling depth. Bacterial-to-fungal ratios in the oil palm plantation were significantly lower than in the forest sites and this was most notable in the lower soil horizons (P<0.01). ANOSIM of lipid composition across samples (all horizons summed for each sample) showed that the microbial community composition was distinct across all three sites (P<0.01) for all contrasts. Finally, the results that oil palm ecosystems have lower SMB and altered microbial communities compared to forest sites indicate that plantations may experience altered biogeochemical cycling compared to forest sites.