Utilization of nitrate-nitrogen by Kentucky bluegrass
Kentucky bluegrass (Poa pratensis L.) is a major cool-season turfgrass, yet least efficient in utilizing soil nitrate-N. To develop a truly sustainable turf management strategy, information on nitrate absorption by the roots and metabolism within the grass is required. The present research was the first attempt to study the primary processes of nitrate metabolism by Kentucky bluegrass cultivars. An in situ solution depletion method was used to measure nitrate uptake rate (NUR) and an in vivo method was optimized to assay the activity of nitrate reductase (NRA) and nitrite reductase (NiRA).^ Under identical conditions, significant variations in NUR, metabolic nitrate pool (MNP), storage nitrate pool (SNP), NRA, N use efficiency (NUE) of shoots and roots, and the contribution of shoots and roots to total plant nitrate reduction were found among Kentucky bluegrass cultivars. Higher nitrate levels resulted in higher NUR, which greatly stimulated leaf NRA. NUE was negatively related to ambient nitrate levels, NUR and NRA, with leaf NRA having the strongest negative effect on NUE. A significant and positive correlation was found between NRA of new leaves and relative growth rate of the whole plant following mowing. Leaf NiRA was higher than NRA and exhibited no intraspecific variation. Root NRA was considerably lower than shoot NRA under identical assay conditions but was enhanced by lower oxygen tensions and an increased carbohydrate reserve. A significant positive correlation between carbohydrate content and NRA was found in Kentucky bluegrass roots. Cultivars that had a larger SNP in their roots, or had higher leaf NRA sustained by a larger leaf SNP when grown under limited nitrate levels, performed better under field conditions. Partitioning of nitrate reduction between roots and shoots was related to field performance in some cultivars.^ These results suggested that a strategy for managing turf with minimum N could be developed by reducing the stimulation of shoot nitrate metabolism and shoot growth, thereby increasing the allocation of carbohydrates to and nitrate metabolism in roots. The results also indicated that great potential exists in Kentucky bluegrass for improving its NUE through the manipulation of genes regulating these metabolic processes. ^
Biology, Plant Physiology
"Utilization of nitrate-nitrogen by Kentucky bluegrass"
Dissertations and Master's Theses (Campus Access).