Seasonal Nitrogen Translocation in Big Bluestem During Drought Conditions

Abstract

This study, conducted during a severe drought in 1980, assesses the effects of burned and unburned treatments in tallgrass prairie on nitrogen content of big bluestem, Andropogon gerardii Vitman. Seasonal total nitrogen and amino-nitrogen translocations in big bluestem in the tallgrass prairie were studied on burned and unburned treatments within Konza Prairie Research Natural Area, Manhattan, Kans. Leaf total nitrogen dropped from .71% in June 1980 to .21% in November with no significant difference between treatments. Rhizome total nitrogen was significantly different between treatments with a June to November increase of .46% to .86% in unburned and .41% to .82% in burned treatments. Roots averaged 72% of rhizome total nitrogen, indicating that roots are also used as storage organs for nitrogen. Comparisons with other studies conducted in 1980 and 1971-1972 indicate that drought stress may reduce the total nitrogen content of big bluestem. In April 1980, emerging leaves on the unburned plots were significantly higher in amino acid concentration than those on the burned plots. Although leaf amino acid concentration was constant after July, the percent of total nitrogen as amino acids increased 3 to 4 fold from mid-August to October. Rhizome amino acid concentration was significantly higher on the unburned than on burned plots. The September 1980 increase in leaf amino acid concentration and percent of total nitrogen as amino acids indicates a breakdown of protein in aboveground tissue. The concurrent increase in rhizome amino acid concentration and percent of total nitrogen as amino acids supports the concept of fall translocation of nitrogen to the belowground parts which serve as storage organs.