Life history and population dynamics of whitetop ( Scolochloa festucacea) shoots under different levels of flooding and nitrogen supply

Abstract

Tagged shoots of the perennial grass whitetop ( Scolochloa festucacea (Wild.) Link) were followed in a seasonally flooded prairie marsh at Delta, Manitoba, Canada, under different treatments of flooding and nitrogen (N) addition to examine how these factors influenced the timing and magnitude of shoot emergence, flowering and mortality. Deep flooding (10–20 cm of water during most of the growing season) increased the total number of shoots that emerged during early spring, the number and percentage of flowering shoots, and total biomass and net primary production compared with shallow flooding (flooded for only several days with less than 5 cm of water). Shoot emergence during July and August was high under deep flooding, but absent under shallow flooding. These new shoots produced during late summer under deep flooding accounted for 56% of the total difference in annual production of unfertilized marsh between shallow and deep flooding. Shoot mortality was low during early summer and increased during July and August at both levels of flooding. Shoot turnover was similar (19–22%) between flooding treatments in the absence of fertilization. Nitrogen increased shoot mortality under both levels of flooding, but effects were greater under shallow flooding and generally restricted to late summer. Nitrogen availability enhanced shoot growth, but did not change the basic pattern of shoot dynamics, indicating that environmental factors other than N availability were largely responsible for controlling differences in production between deep- and shallow-flooding regimes.