Abstract

The novelty and relevance of this study are associated to increase the understanding of the interactions between crop root exudates and the cycling of N and P in two soil-crop rhizosphere systems. Increased knowledge and understanding of these interactions will permit future manipulation of nutrient cycling processes in the pedosphere, and the development of novel nanotechnologies and nanofertilizer products for enhancing N and P use efficiencies (NUE, PUE) by crops. The NUE is about 30 % and PUE is < 15 %. The crop use efficiency of most micronutrients is even lower. This research project will focus on the following two topics: 1. The evaluation and controls of the soil N in crop rhizospheres and soil solutions as influenced by soil bacterial species and associated genes will be determined using molecular techniques in soil-plant ecosystems. The project will examine the dynamics of two soil nitrification genes: one encoding for the expression of nitrite oxidoreductase (nxrA) in nitrite oxidizing bacterial (NOB) populations; and the other gene encoding for the expression of ammonium monooxygenase amoA) in ammonia oxidizing bacterial (AOB) population. The dynamics of soil N immobilization will be studied and modeled using the soil bacterial gene (glnA) encoding for the expression of glutamine synthesase, which controls the microbial assimilation of ammonium (NH4+) in the rhizospheres of two agricultural crops (i.e., canola and maize) during the growing season. Quantitative real-time PCR will be used to quantify soil gene dynamics during crop growth. The ecology of root exudation and the soil nitrifying and N immobilizing bacteria, and their associated gene dynamics in response to anthropogenic alterations, such as those generated by agricultural practices, are scarcely known. The bacterial oxidation of nitrite and N immobilization processes can limit nitrification in disturbed soil systems. Understanding the interactions between the two N cycling processes is important to better understand their interactions in relation to the synchronization between soil N mineralization and crop N uptake. Development and use of a molecular tool to characterize the presence and quantification of this bacterial groups and processes in the soil are essential to make way for future advances in different crop rhizosphere ecosystems. This study will determine the temporal changes of nitrifying and N immobilizer populations in the rhizosphere of two industrial crops (i.e., canola and maize) grown in the greenhouse with Chilean and Canadian soil samples. 2. Parallel and complementary studies on soil-crop P cycling processes in crop rhizospheres will be conducted in relation to the dynamics and gene expression of BPP phytase in Bacillus sp by Quantitative real-time PCR (qPCR). Phosphorous is a essential nutrient for the plants growth, but is highly fixed in acid and basic soils conditions becoming unavailable for crops. One of the major environmental forms of organic phosphorus is phytate that can to be used by Phytases that are a group of enzymes capable of releasing inorganic phosphate from phytate. The bacterial encoding phytase are regarded as potential biofertilizer, but the current research about their determination in the soil, quantification and expression is also very scarce, although recent attempts are trying to increase our knowledge gaps in P cycling in relation to the biotic components of soils and crops. This project research is aimed to determine the bacterial presence in the soil, quantify and determinate the expression gene encoding for phytase in the rhizosphere of two selected crops in Chilean and Canadian soils, and to discover and to characterize native -propeller phytases or another bacteria encoding phytase in this soil. 1.2.- Objetivos generales y específicos. - To understand of bacterial diversity involved and dynamic of the nitrifier bacterial community (AOB/NOB) in the rhizosphere of two agricultural crops (Canola and Maize) at different key crop growth stages and agricultural management. - To detect, to quantify and to determinate the expression of genes Bacillus encoding BPP phytase in the rhizosphere of different industrial crops (Canola and Maize) at different stage and agricultural management using Quantitative real-time PCR (qPCR). - To determine the bacterial presence in the soil, quantify and determinate the expression gene encoding for phytase in the rhizosphere of Canola and Mayze in Chilean and Canadian soils, and to discover and to characterize native -propeller phytases or another bacteria encoding phytase in this soil. Specific Objectives: - To evaluate changes in NOB and AOB activity can be explained by changes in community composition and/or NOB and AOB abundance and/or changes in NOB, AOB specific activity in the canola and maize soil crops and management. - To identify the main agronomical management-induced changes among the different possible ones for NOB and AOB according to their ecological requirements. - To evaluate the change of GS and Glutaminase in the rhizosphere soil of canola and maize crops. To evaluated changes in the prevalence and expression of genes encoding other known bacterial phytases and to characterize of unknown or native b-propeller phytases in Canadian agricultural soil and their potential use as biofertilizers in agriculture.