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Recent evidence associates the persistence of invasive plant species with disturbance and fluctuations in distinct forms of mineral N in soils. We conducted soil and hydroponic experiments to investigate the influence of N form and availability on germination and seedling development of 2 invasive annual grasses, cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput-medusae) and 6 perennial grasses, bluebunch wheatgrass (Pseudoroegneria spicata), crested wheatgrass (Agropyron cristatum x A. desertorum), Sand Hollow and Seaman?s Gulch big squirreltail (Elymus multisetus), and Little Camas and Little Wood bottlebrush squirreltail (E. elymoides ssp. brevifolius and E. elymoides ssp. elymoides, respectively)....
We hypothesize that drought-avoidance in Gutierrezia sarothrae populations is characterized by well-developed lateral roots. Root growth and hydraulic conductance were studied in four populations of Gutierrezia sarothrae. Seedlings from a Malta, Idaho (ID) seed source had four times higher root/shoot ratio (P<0.05), but only 17% hydraulic conductance of those from Tahoka, Texas (TA) seed source. Consequently, transpiration surface area of the ID seedlings was 17% that of the TA seedlings. There was no difference in total root length between the seedlings, but hydraulic conductance per unit root length was 3.8 fold greater (P<0.05) in the TA seedlings, which was accompanied by a lower specific lateral root length...
The effect of herbivory on grassland whole-plant production is poorly understood. Herbivores can increase grassland aboveground productivity, and laboratory experiments suggest that herbivory should reduce grass root growth. However, few field studies have directly measured the response of grassland root production to herbivores. We examined the effect of native migratory ungulates on grassland primary production by comparing aboveground (NAP) and belowground (NBP) production in grazed vs. ungrazed (fenced) grassland at nine variable sites in Yellowstone National Park. NBP was determined with minirhizotrons to account for root turnover. Grazers stimulated aboveground, below-ground, and whole-grassland productivity...
A field experiment using 2 patterns of irrigation and 1 level of nitrogen fertilizer (10 g-N m-2) was conducted in order to discern water and nitrogen interactions that may control production of creosotebush, (Larrea tridentata (D.C.) Cov. The 2 patterns of irrigation simulated precipitation from small, frequent events (6 mm water added weekly) or large, infrequent events (25 mm water added monthly). Understanding the factors controlling the production of this rangeland shrub may aid in the development of strategies for its management. Vegetative growth occurred mostly during March-May (spring) and August-October (summer-fall). Fruit production occurred mainly in the spring and root growth occurred mainly in the...
Seeds from northern (Idaho) and southern (New Mexico and Texas) populations of broom snakeweed (Gutierrezia sarothrae) were germinated in a greenhouse and the seedlings grown in a soil mixture in 30-cm deep (19-1) plastic pots for 50 days. The pots were then fastened onto the top of similar pots and the seedling root systems were allowed to grow into the lower pots for 4 weeks through punctures in the bottoms of the upper pots. Soil water extraction from four different depths was measured using time domain reflectometry (TDR) 2 weeks after roots had begun to grow into the lower pots. The two New Mexico populations (Jornada and Mountainair) and a population from Plains, Texas extracted more water from deeper (greater-or-equal,...
The effects of salt stress on growth and development of cheatgrass (Bromus tectorum L.) were investigated in 2 greenhouse studies. The first study assessed developmental and physiological responses of this grass to 4 salinity levels. Salinity stunted growth through reduced leaf initiation and expansion, and reduced photosynthetic rates. Reduction of photosynthetic rates appeared to be primarily due to stomatal limitation. Salinity also reduced carbon isotope discrimination, indicating long-term effects on conductance and carbon gain. Root growth was severely inhibited by high salinity, resulting in a shift in the root to shoot allocation pattern. The second study investigated growth patterns of cheatgrass in relation...