Title : Plant-microbe synergies in mitigating nitrous oxide emissions from grazed pastures
Abstract:
Nitrous oxide (N2O) emissions from grazed pastures contribute significantly to global greenhouse gas emissions, primarily from urine and dung deposited on the land (~50-70%). Despite years of soil-focused research, the role of plant traits in influencing N2O cycling remains largely unexplored. Recent findings from AgResearch reveal that a genetically modified (GM) perennial ryegrass, engineered for higher lipid content, shows a 40-50% reduction in N2O emissions compared to control plants. This research identifies specific plant-level traits reducing N2O emissions, using the High Metabolisable Energy (HME) ryegrass as a model. The study explores morphological, biochemical, physiological, and plant-microbe interactions to understand the mechanisms behind N2O reduction. A comparison is made between HME ryegrass and high-N2O emission control plants, assessing traits such as plant dry matter production, carbon assimilation, nitrogen partitioning, and root exudates. Additionally, microbial community structures, particularly nitrifiers and denitrifiers in the rhizosphere, are examined to assess their role in N2O cycling. Traits identified from the comparison are further tested through gene editing, exudate synthesis, and grazing management approaches to assess their contribution to N2O mitigation. Initial findings show that HME ryegrass displays significant differences in plant characteristics and microbial interactions that may contribute to the observed reduction in N2O emissions, and ongoing analysis is refining these results. The research aims to provide insights into plant-mediated N2O emission mitigation and offer practical solutions for reducing greenhouse gas emissions from grazing systems. Identifying key N2O-reducing plant traits could inform the development of 'elite' environmentally friendly forage cultivars and grazing practices that promote both high productivity and low environmental impact. In the long term, these insights could contribute to more sustainable agricultural practices that address both productivity and environmental challenges in grazed systems.
