Abstract/Summary

Oil palm is the fastest expanding equatorial crop, and is one of the biggest threats to carbon-rich tropical peatlands in Malaysia. Smallholder plantations cover a vast area of peatlands in Peninsular Malaysia and follow varied cropping systems. Here we analyse the impacts of specific crops and the effects of proximity to such crops, upon GHG emissions from the soil, and the soil microbial community phenotype. We found that only mature oil palm plants in 1st generation oil palm mono-cropping potentially had significant autotrophic contributions to total CO2 emissions with 33.5% increase in locations closer to mature oil palm stems. The sampling locations closer to younger oil palms and other crops did not significantly increase total CO2 emissions. CH4 emissions were significantly greater for sampling locations near plants with adventitious root system such as yam and pineapple crops. However CH4 emissions were very low in comparison to CO2 emissions, and their contribution to carbon loss was limited in these sites. Surface peat microbial community structure was unaffected by proximity to different crops within each cropping system, possibly due to a lack of influence of rhizosphere in the surface peat layers (0–5 cm). The results suggest that most of the total CO2 emissions from these agro-ecosystems contribute to C loss due to microbial decomposition of the peat soil, unlike greater autotrophic contributions to total emissions in forested peatlands reported in other studies. Hence without appropriate above-ground vegetation or hydrology conducive to peat formation, ancient carbon stored in these peatlands is gradually lost into the atmosphere via greater heterotrophic respiration under agricultural management on such peat-based ecosystems.