Developing methods to evaluate phenotypic variability in Biological Nitrification Inhibition (BNI) capacity of Brachiaria grasses

摘要

A spart of the nitrogen (N) cycle in the soil, nitrification is an oxidation process mediated by microorganisms that transform the relatively immobile ammonium (NH_4~+ ) to the water soluble nitrate (NO_3~-), enabling the production of nitrous oxide (N_2O), a potent greenhouse gas) by denitrifica-tion as a by-product (Canfield et al. 2010). Researchers at CIAT-Colombia in collaboration with JIRCAS-Japan, reported that Brachiaria humidicola forage grasses have the ability to inhibit the nitrification process by exuding chemi-cal compounds from its roots to the soil. A major hydro-phobic compound was discovered and named brachial-actone (Subbarao et al. 2009). This capacity of Brachiaria grasses is known as biological nitrification inhibition (BNI)and it could contribute to better N use efficiency in crop-livestock systems by improving recovery of applied N while reducing N~-O_3 leaching and N_2O emission. The current methodologies for quantifying the BNI trait need farther improvement to facilitate high throughput evalua-tion to quantify genotypic differences.In this paper, we aim to develop new (or improve the existing) phenotyping methods for this trait. Preliminary results were obtained using three different methods to quantify BNI: (1) a mass spectrometry method to quantify brachialactone; (2) a static chamber method to quantify N_2O emission from soils under greenhouse conditions; and (3) an improved molecular method to quantify microbial populations by Real-Time PCR. Using these three methods we expect to score a bi-parental hybrid population (n= 134)of two B. humidicola accessions differing in their BNI ca-pacity CIAT26146 (medium to low BNI) x CIAT16888 l(high BNI), in an attempt to identify QTLs associated with the BNI trait.