Comparative life history characteristics of two high arctic grasses, Northwest Territories

Two grasses wiith differing adaptations were studies in an extreme, but variable, high arctic environment. Phippsia algida is a ruderal species that colonizes bare soil in mesic sites, but also occurs across a broad range of habitats. Puccinellia vaginata occurs in xeric microsites with little soil disturbance. The phenology, carbon allocation, physiological adaptations to drought, and reproductive effort were compared between these two closely related species. Leaf water potential was variable on a daily basis in both species despite high soil water potential. Of the six physical factors studied (vapor pressure deficit, soil moisture, leaf and root temperature, wind, PAR), only wind and PAR (photosynthetically active radiation) were not limiting to leaf conductance at any level measured in the field. Phippsia experienced more frequent and severe drought stress at less extreme physical conditions than Puccinellia. In general, Phippsia had higher leaf turgor and growth rates. Puccinellia generally had higher leaf conductance, lower turgor and growth rates. Drought stress and low temperatures reduced whole plant biomass of Phippsia at all ages but affected only seedlings on Puccinellia. Phippsia root biomass was lower with drought and low soil temperatures, but was high and constant throughout the study for Puccinellia. Phippsia was relatively short lived (23 yr mean, maximum 34 yr) and Puccinellia long lived (35 yr mean, maximum 74 yr). The mean age of initial reproduction was relatively late when compared to temperate species, but it occurred sooner in PHippsia (17 @+ 6 yr) than Puccinellia (26 @+ 9 yr). Phippsia had high, constant seed set under all field conditions monitored. Production of viable seeds in Puccinellia was restricted by short growing seasons, low solar radiation, and low temperatures. During stressful years, Phippsia continued high carbon allocation to reproduction, but also had high rates of plant mortality. In contrast, Puccinellia generally had low carbon allocation to reproduction, and low rates of mortality during periods of stress. Although both species tolerate stress in the sense that they persist in an extreme environment, Phippsia algida has many characteristics of a ruderal and fills this role in a high arctic ecosystem. Puccinella vaginata has most characteristics of a stress-tolerant species.