Impact of mineral N and P and manure on Arbuscular Mycorrhizal fungi, other soil microorganisms and on soil functionality in different agroecosystems
Microorganisms and their interactions in soil play a critical role in nutrient transformations and cycling, and in sustaining soil productivity. Arbuscular mycorrhizal fungi (AMF) are a keystone group of fungi influencing nutrient cycling. In turn, the activity and composition of microorganisms in soil are influenced by management practices such as the choice of crop species and fertilization. Long-term effects of cropping, manuring and mineral fertilization on the soil-plant system were defined in three selected agro-ecosystems of Canada. A greenhouse experiment was also conducted to define the involvement of AMF in organic residue decomposition and nitrogen (N) mineralization. In the greenhouse experiment, pasteurized soil was inoculated or not with a strain of Glomus claroideum, G. clarum or G. intraradices. 15N-labelled organic residue in a nylon mesh was buried in the soil. The fate of residue-N was determined after 24 weeks. Arbuscular mycorrhizal fungal species enhanced mineralization of organic residue to different degrees. The highest recovery of mineralized N by plants (25%) occurred when inoculated with G. clarum. The AMF enhanced N-mineralization differentially leading to differential plant growth stimulation, differences in the C-to-N ratio of the decomposing organic residue, and in soil microbial community structure. In a field trial conducted on a Brown Chernozemic soil at the Semiarid Prairies Agricultural Research Centre in Swift Current, SK, eight years of phosphorus (P) (0, 20 and 40 kg P2O5 ha-1) application to alfalfa monoculture and alfalfa-Russian wildrye (RWR) dual culture modified the soil microbial community structure. Low levels of phosphorus (0 and 20 kg P2O5 ha-1) fertilization in alfalfa-RWR dual culture increased the abundance of fungivorous nematodes and grazing of AMF hyphae thus increasing the carbon drain from plants and ultimately reducing plant biomass. In a sub-humid region of Saskatchewan on a a Black Chernozem soil, mineral N (0, 20 or 40 kg N ha-1) was applied for 10 years to pea grown continuously or in rotation with wheat. Lower yields in continuous-pea were associated with reduced abundance of beneficial Gram positive bacteria and AMF, and an increase in uptake of plant available Fe to toxic levels. These differences in soil properties were related to root rot which increased with years in continuous-pea. The soil environment in the continuous-pea rotation further led to lower organic carbon inputs, and to reduced soil microbial biomass and soil enzyme activity indicating a negative impact on nutrient cycling. In the south coastal region of Agassiz, British Columbia, dairy manure slurry (DMS) and ammonium nitrate (AN) had been applied on a Regosol at the same annual rate of mineral N (50 or 100 kg mineral N ha-1) for nine years to perennial tall fescue, followed by one year of stand renovation through reseeding without fertilization. The multi-year application of DMS improved soil organic C, soil organic N, light fraction of organic matter, microbial biomass and enzyme activity as compared to mineral fertilization but the DMS-related increase in soil yield potential was lost in the process of stand rejuvenation. Dairy manure slurry application based on the crop N requirement also increased soil phosphate indicating increased environmental hazard. In conclusion, long-term use of DMS in multi-cut tall fescue can increase soil quality parameters but can also increase the risk of eutrophication of water bodies. Overall, data showed that higher levels of soil nutrients can select for certain bacteria while AMF and other bacteria are more abundant under low soil fertility. On the other hand, different soil microbial groups were associated with different soil enzyme activities. From this study, I succeded in proving my hypothesis that practice of fertilization and choice of crop influence soil microbial community structure which further affect soil functioning.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorHamel, Chantal; Germida, Jim
CommitteeKnight, Diane; Walley, Fran; Schoenau, Jeff; Vujanovic, Vladimir; Charest, Christiane
Copyright DateSeptember 2009
Arbuscular mycorrhizal fungi