EFFECTS OF NITROGEN FORM AND AVAILABILITY ON SEED GERMINATION AND EARLY SEEDLING GROWTH IN INVASIVE ANNUAL AND DESIRABLE PERENNIAL GRASSES

Authors: Monaco, Thomas; Mackown, Charles; Johnson, Douglas; Jones, Thomas; NORTON, JEANETTE - UTAH STATE UNIVERSITY; NORTON, JAY - UTAH STATE UNIVERSITY; Redinbaugh, Margaret

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2003
Publication Date: 11/1/2003
Citation: Monaco, T.A., Mackown, C.T., Johnson, D.A., Jones, T.A., Norton, J.M., Norton, J.B., Redinbaugh, M.G. 2003. Effects of nitrogen form and availability on seed germination and early seedling growth in invasive annual and desirable perennial grasses. Journal of Range Management. 56:646-653.

Interpretive Summary: Competition between invasive annual grasses and desirable perennial grasses may be mediated by soil nitrogen (N). Germination and hydroponic experiments were conducted to determine the specific seedling traits modified by distinct mineral forms for two invasive annual grasses and six desirable perennial grasses. Results indicate N forms do not alter germination of either group of grasses. However, root and shoot growth of invasive annuals is more hindered by low N compared to growth of the perennial grasses.

Technical Abstract: 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 early seedling development of 2 invasive annual grasses, cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae [L.] Nevski) and 6 perennial grasses, 'Goldar' bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love), 'CD II' crested wheatgrass (Agropyron cristatum [L.] Gaertner x A. desertorum [Fisch. ex Link] Schultes), Sand Hollow and Seaman's Gulch big squirreltail (Elymus multisetus [J.G. Smith] M.E. Jones), and Little Camas and Little Wood bottlebrush squirreltail (E. elymoides [Raf.] Swezey ssp. brevifolius and E. elymoides ssp. elymoides, respectively). For the soil experiment, seeds were sown in the following 5 soil treatments to evaluate cumulative germination percentage for 20 days in an incubator: 1)control = no soil additions, 2)barley straw (1 mg kg soil), 3)NH = 10 mg N kg soil; 4)NH +I (nitrification inhibitor) = 10 mg N kg soil + 37 ml nitrapyrin (29% a.i.,2-chloro-6-(trichloromethyl) pyridine), and 5)NO = 10 mg N kg soil. For the hydroponic experiment, grass seedlings were exposed to distinct forms and uniform concentrations of mineral N with the following 4 treatments in 15-L tanks to monitor root and shoot growth for 21 days: 1)control = no N added, 2)NH (1 mM),3)NO (1 mM),and 4)NH NO (0.5 mM = 1 mM N). Distinct forms of soil N or availability did not significantly alter germination in the soil experiment, although medusahead achieved 90% germination 2 days earlier than the other grasses. Lack of effect of soil N on seed germination is likely attributed to the absence of seed dormancy in the populations of grasses we evaluated. In contrast, initial root length and overall shoot growth of all grasses in the hydroponic experiment were generally greater in the NO treatment than in the NH treatment, and this N form effect was more frequently significant for the perennial grasses. Root and shoot growth of medusahead and cheatgrass seedlings generally exceeded that of all the other grasses except crested wheatgrass regardless of treatment. However, root dry mass of the invasive annual grasses decreased relatively more than the perennial grasses in response to the N-free control treatment compared to the N-addition treatments. Our results showed that specific traits associated with the initial phases of seedling establishment were modified by distinct forms of mineral N, and these responses provide insights into potential ways to manipulate succession on degraded rangelands to favor the establishment of perennial grass seedlings.