Human land use alters soil microbial composition and function in a variety of systems, although few comparable studies have been done in tropical forests and tropical agricultural production areas. Logging and the expansion of oil palm agriculture are two of the most significant drivers of tropical deforestation, and the latter is most prevalent in Southeast Asia. The aim of this study was to compare soil fungal communities from three sites in Malaysia that represent three of the most dominant land-use types in the Southeast Asia tropics: a primary forest, a regenerating forest that had been selectively logged 50 years previously, and a 25-year-old oil palm plantation. Soil cores were collected from three replicate plots at each site, and fungal communities were sequenced using the Illumina platform. Extracellular enzyme assays were assessed as a proxy for soil microbial function. We found that fungal communities were distinct across all sites, although fungal composition in the regenerating forest was more similar to the primary forest than either forest community was to the oil palm site. Ectomycorrhizal fungi, which are important associates of the dominant Dipterocarpaceae tree family in this region, were compositionally distinct across forests, but were nearly absent from oil palm soils. Extracellular enzyme assays indicated that the soil ecosystem in oil palm plantations experienced altered nutrient cycling dynamics, but there were few differences between regenerating and primary forest soils. Together, these results show that logging and the replacement of primary forest with oil palm plantations alter fungal community and function, although forests regenerating from logging had more similarities with primary forests in terms of fungal composition and nutrient cycling potential. Since oil palm agriculture is currently the mostly rapidly expanding equatorial crop and logging is pervasive across tropical ecosystems, these findings may have broad applicability.

Tropical forest conversion to agriculture is a major global change process. Understanding of the ecological consequences of this conversion are limited by poor knowledge of how soil microorganisms respond. We analyzed the response of soil bacteria to conversion from primary rain forest to oil palm plantation and regenerating logged forest in Malaysia. Bacterial diversity increased by approximately 20% with conversion to oil palm because of higher pH due to liming by plantation managers. Phylogenetic clustering indicated that bacterial communities were determined by environmental filtering. Regenerating logged forests did not have significantly different soil chemistry, which did not correspond with significant differences in bacterial richness, diversity, or the relative abundances of particular taxa. However, there were significant differences in the structure of bacterial community networks between regenerating logged forests and primary forests, highlighting previously unobserved effects of these two land uses. Network analysis highlighted taxa that are potentially central to bacterial networks, but have low relative abundances, suggesting that these rare taxa could play an ecological role and therefore warrant further research.

The extensive use of synthetic fungicides in controlling plant disease generates detrimental impacts on the environment and human health. In response to this problem, an alternative method was developed, known as biological control using antagonistic microorganisms. Since investigation on fungal endophytes of Garcinia atroviridis is still unclear, it was chosen for the study. The aim of the present work was to evaluate biocontrol potential of endophytic fungi against Colletotrichum gloeosporiodes, a phytopathogen that caused anthracnose disease. A total of 92 endophytic fungi were isolated from different tissue parts of Garcinia atroviridis including leaves, petioles, branches, and fruits. Results demonstrated that, most of endophytic fungal isolates showed some inhibitory action over the growth of C. gloeosporiodes during dual culture growth. Endophyte isolate F14 showed the highest antagonistic activity against Colletotrichum gloeosporiodes with 67.38% percentage inhibition radial growth (PIRG). However, 7 out of 92 isolates showed no inhibitory effect against Colletotrichum gloeosporiodes. In conclusion, endophytic fungi isolated from G. atroviridis indicate the potential as biocontrol agents. It is hoped that the finding of isolated endophytic fungi in this study with antagonistic activity against anthracnose pathogen may be used in biocontrol programmes of plant disease in the region.

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