Impact of Chronosequence of Rubber Tree Plantations on Soil Microbial Activity

Soil microorganisms play a central role in decomposition, nutrient mineralization, and nearly all ecological processes in a soil ecosystem. A number of soil microbiological parameters, notably microbial biomass carbon and basal respiration, have been suggested as the promising indicators of soil quality. Therefore, this study aims to investigate microbial respiration as an indicator of microbial activity under different ages of rubber tree in different season. Three treatments were selected, categorized by tree age included: rubber trees 4-5 years old, 12 years old, and 22-23 years old. Soil samples were taken from a randomly selected location in each plot, at 0-10 cm, in rainy and dry season. The physical and chemical properties of the soil were also observed. The result showed that soil microbial biomass carbon, activity and MicroResp-CLPP (community level physiological profile) were influenced by rubber ages and season. The highest carbon dioxide emission, which was related to microbial activity, was found in the 4-5 years old rubber tree, during the rainy season. However, contrary results emerged during the dry season. In addition, the more aged rubber trees exhibited a higher microbial biomass carbon. The results further demonstrated that bacterial biomass and soil activity were higher than that of the fungi. In rainy season, MicroResp-CLPP showed the highest catabolic responses in young age (4-5 years old) of rubber tree followed by tapped rubber tree (12 and 22-23 years old). Contrary, the highest catabolic responses in dry season was observed in tapped rubber tree (12 and 22-23 years old). These findings suggested that microbial biomass and relative activity were directly correlated with the rubber tree age.