Physiological, and Molecular Responses of Perennial Ryegrass to Low Nitrogen Stress.

Nitrogen (N) is a macronutrient that presents great impact on plant growth and development. N deficiency can cause chlorosis, loss of shoot density and decrease in growth. However, over utilization of nitrogenous fertilizers may pollute soil and water. Perennial ryegrass is a widely used cool-season forage and turf species, but growth and physiological mechanisms of this species to low N are not well understood. The objective of this study was to investigate physiological and molecular mechanisms of perennial ryegrass exposed to low N stress. One low N tolerant and one sensitive accession of perennial ryegrass were exposed to low (0.75 mM N) and high (7.5 mM N) for 20 d. Shoot fresh weight remained unchanged in the tolerant accession, but decreased in the sensitive accession. A decrease in chlorophyll content was found in both accessions under low N treatment but to a greater extent in the sensitive accession. A significant reduction in chlorophyll fluorescence was only observed in the sensitive accession. Both accessions had higher shoot nitrogen-use efficiency (SNUE) under low N compared to the high N treatment, but the tolerant accession showed the relatively higher SNUE. Analysis for expression of genes that regulate uptake or utilization of N are being conducted for further revealing the mechanisms of low N tolerance in perennial ryegrass.