Effect of rice variety and fertilizer type on the active microbial community structure in tropical paddy fields in Sri Lanka
Abstract Tropical rice fields are a special class of wetlands, which are vital for world food production. Microbial communities that drive biogeochemical processes and nutrient availability for rice growth rely on rhizodeposited C as a source of energy. The current study revealed information on the structure of the active microbial community in tropical paddy fields in Sri Lanka by employing in situ Phospholipid Fatty Acids based Stable Isotope Probing (PLFA SIP) with 13 CO 2 pulse labeling. The study was conducted in selected rice fields cultivated long term with two rice varieties (traditional, KH vs. improved, BG) in combination with two types of fertilizers (inorganic, ING vs. organic, ORG) Multivariate analysis on relative 13 C concentration 13 CC r of the 0 10 cm soil layer revealed that the active microbial community structure varied significantly between rice varieties and fertilizers, whereas the effect of variety x fertilizer was significant as well (p 13 C. Factorial ANOVA on 13 CC r revealed significant effects of variety, type of fertilizer and variety x fertilizer type on active C uptake by actinomycetes. Rice variety significantly influenced the active fungal and Gram negative bacterial groups, while none of the factors affected Gram positive bacteria. Active Gram negative bacteria were higher with BG variety, whereas fungi and actinomycetes were higher with KH variety in both inorganic and organic fertilizer applied fields. Gram negative and Gram positive bacteria were the most active functional groups in the paddy soil microbial community, whereas actinomycetes only relied to a minor extent on rhizodeposit C to meet their energy requirement. It is concluded that rice microbial communities differ significantly as a function of cultivation practices, potentially showing a large impact on ecosystem processes such as greenhouse gas emissions and plant nutrient availability.