Impact of long-term fertilizer treatment on the microeukaryotic community structure of a rice field soil

Microeukaryotes play many different functional roles in soil ecosystems, but the environmental factors that shape their community composition are poorly understood. Here we studied the impact of chemical and organic fertilizers on the microeukaryotic soil communities of rice field plots under long-term (82 years) fertilizer management. Terminal restriction fragment polymorphism (T-RFLP) and clone library analyses of 18S rRNA genes and their transcripts obtained from soils subjected to five different fertilizer treatments showed that fertilizer management strongly influenced microeukaryotic community composition in the soils and that its impact was greater than that of water management or seasonality. Among the different chemical fertilizers, the effects of phosphorus fertilizer on community composition were more pronounced than those of either nitrogen or potassium. Soils without phosphorus fertilizer were characterized by a high relative abundance of diatoms and algivorous nematodes whereas in phosphorus-fertilized soils green algae predominated. Different rates of organic fertilizer (rice straw compost) application had distinctive effects on the DNA-based microeukaryotic community, especially its algal composition. Thus, protistan grazers were the largest group in the potentially active community from soils with a higher amount of organic fertilizer application. Our findings provide evidence that long-term fertilization shapes the microeukaryotic community composition of rice field soils. The results imply that fertilizer management of rice field soils is an important determinant of the structure and function of the microbial food web.